All praise is for ALLAH for his gracious & grants upon us.

We wish to express our sincere gratitude to the person who stands besides us with his great competence, vision and direction to present our thoughts and visions in this book, to him we dedicate this book ...

To our teacher Dr.Hamed El Shenawy.

We cannot forget to thank Head of Communication and Electronic Engineering Department Prof.Dr.Abd El Wahab Fayz for his contiguous encouragement for us to improve our skills and become innovators.

Abstract Recently WiMAX technology has gained growing interest due to its applications and advantages.

WiMAX is fast emerging as a last-mile problem solution and broadband access technology. WIMAX stands for Worldwide Interoperability for Microwave Access based on IEEE 802.16 standard. As an air Interface for Fixed Broadband Wireless Access (FBWA) in metropolitan area networks (MANs) and for Mobile Broadband Wireless Access (MBWA) Systems thus allowing technology to be embedded in handheld devices and portable devices such as laptops. The interoperability and the standard compliance of the equipments from different vendors are assured.

The key elements for coverage prediction including calculation of link budget taken into account the particularities of the WIMAX technology and different scenario were considered. The operation scenarios are specified based on real world conditions considering the regulatory rules for radio frequency spectrum utilization for licensed and licensed exempted bands and using appropriate propagation model to calculate the cell radius. Several coverage prediction models have been analyzed such as free space model, COST231 Okumara Hata model, COST231 Walfish Ikegami model and Stanford university interim (SUI) model but in our project we will focus on free space model as line of sight (LOS) and Stanford university interim (SUI) model was adopted because it provides acceptable accuracy for NLOS scenario and frequency up to 6 GHz. Finally the system performance is evaluated in terms of the maximum transmission data rate.

The influence of the key system parameters on coverage and performance are studied such as: Effect of type of CPE.

Effect of type of BTS.

The effect of different channel bandwidth

licensed and license exempted frequency bands

The impact of type of adaptive modulation and coding rate

The effect of BTS height.

The effect of the BTS & transmission power and using subchannelization scheme in WiMAX technology.

Comparison among different model.

Effect o CPE height.

II

Also the effects of the key system parameters on performance are investigated as follows: Effect of modulation type and code rate.

Effect of cyclic prefix rate.

Effect of nominal channel bandwidth and operating frequency.

Effect of subchannelization.

This project is organized as follows: Chapter one: describes the basis of WiMAX technology its standards, different network topologies, system architecture, system specifications and the major aspects of the technology. In this project only traditional cellular architecture point to multipoint (PMP) configuration is studied.

Chapter two: presents the basis of OFDM.

Chapter three: shows the key different between mobile WiMAX and other broadband technologies.

Chapter four: explains how the coverage of mobile WiMAX is done.

Chapter five: discusses the different parameters which affects in mobile WiMAX coverage and its numerical results.

Chapter six: discusses the different parameters which affects in mobile WiMAX performance and its numerical results.

Chapter seven: presents a uniform solution of Network planning of WIMAX cellular structured system.

Chapter eight: contains a hardware implementation of RF Field strength meter.

Chapter nine: discusses the functions which convert fixed WiMAX into mobile WiMAX.

Chapter ten: includes the conclusions and suggestion for future research.

III

Table of contents Chapter 1: Overview of WiMAX technology 1.1 Introduction ....................................................................................................................................... 1 - 1

1.2 WiMAX ............................................................................................................................................... 1 - 1

1.2.1 What is WiMAX? ......................................................................................................................... 1 - 1

1.2.2 WiMAX Standard ......................................................................................................................... 1 - 2

1.2.3 What is a Standard? .................................................................................................................... 1 - 3

1.2.4 Benefits of standardized WiMAX ................................................................................................ 1 - 3

1.2.5 General features of IEEE 802.16 ................................................................................................. 1 - 3

1.2.6 General features of IEEE 802.16a ............................................................................................... 1 - 4

1.2.7 General features of IEEE 802.16b ............................................................................................... 1 - 4

1.2.8 General features of IEEE 802.16c ................................................................................................ 1 - 5

1.2.9 General features of IEEE 802.16d-2004 Fixed WiMAX ............................................................... 1 - 5

1.2.10 General features of IEEE 802.16e Mobile WiMAX .................................................................... 1 - 5

1.3 WiMAX Spectrum Availability ............................................................................................................ 1 - 6

1.3.1 Licensed Band ............................................................................................................................. 1 - 6

1.3.2 Unlicensed Band ......................................................................................................................... 1 - 7

1.4 WiMAX Network Architecture ........................................................................................................... 1 - 7

1.4.1 WiMAX Network Reference Model (NRM) ................................................................................. 1 - 8

1.5 WIMAX Topologies ........................................................................................................................... 1 - 11

1.5.1 Point-to-point (P2P) .................................................................................................................. 1 - 11

1.5.2 Point-to-Multipoint (PMP) ........................................................................................................ 1 - 12

1.5.3 Mesh Topology .......................................................................................................................... 1 - 12

1.6 Line of sight (LOS) or Non-line of sight (NLOS) ................................................................................ 1 - 13

1.7 WiMAX Antennas ............................................................................................................................. 1 - 14

1.7.1 Omni directional antenna ......................................................................................................... 1 - 14

1.7.2 Sector antennas ........................................................................................................................ 1 - 15

1.7.3 Panel antennas .......................................................................................................................... 1 - 16

1.8 Subscriber Stations .......................................................................................................................... 1 - 16

1.8.1 Mobile CPE ................................................................................................................................ 1 - 16

IV

1.8.2 Portable CPE .............................................................................................................................. 1 - 17

1.9 WiMAX Technical specifications ...................................................................................................... 1 - 17

1.10 WiMAX Advantages ....................................................................................................................... 1 - 20

1.11 WiMAX Applications ...................................................................................................................... 1 - 22

1.11.1 Private Networks ..................................................................................................................... 1 - 22

1.11.2 Cellular Backhaul ..................................................................................................................... 1 - 22

1.11.3 Wireless Service Provider Backhaul ........................................................................................ 1 - 23

1.11.4 Banking Networks ................................................................................................................... 1 - 24

1.11.5 Education Networks ................................................................................................................ 1 - 25

1.11.6 Public Safety ............................................................................................................................ 1 - 26

1.11.7 Offshore Communications ...................................................................................................... 1 - 27

1.11.8 Campus Connectivity .............................................................................................................. 1 - 28

1.11.9 Temporary Construction Communications ............................................................................. 1 - 29

1.11.10 Theme Parks .......................................................................................................................... 1 - 30

1.11.11 Public Networks .................................................................................................................... 1 - 31

1.11.12 Wireless Service Provider Access Network ........................................................................... 1 - 31

1.11.13 Rural Connectivity ................................................................................................................. 1 - 32

1.12 Conclusion ...................................................................................................................................... 1 - 33

Chapter 2: Overview of OFDM 2.1 Introduction ....................................................................................................................................... 2 - 1

2.1.1 History of OFDM ......................................................................................................................... 2 - 1

2.1.2 What is OFDM? ........................................................................................................................... 2 - 2

2.1.3 Advantages and Disadvantages .................................................................................................. 2 - 3

2.1.4 Comparison among different multiplexing techniques .............................................................. 2 - 4

2.1.4.1 OFDM versus FDM ............................................................................................................... 2 - 4

2.1.4.2 OFDM versus TDM ............................................................................................................... 2 - 5

2.1.4.3 OFDM versus CDMA ............................................................................................................. 2 - 6

2.1.5 Applications ................................................................................................................................. 2 - 7

2.2 Basics of OFDM .................................................................................................................................. 2 - 8

2.2.1 Orthogonality .............................................................................................................................. 2 - 8

2.2.2 Cyclic Prefix ............................................................................................................................... 2 - 10

2.2.3 Multiple Access in OFDM .......................................................................................................... 2 - 12

V

2.2.4 OFDM versus Single Carrier ...................................................................................................... 2 - 14

2.2.5 Scalable OFDM Access (SOFDMA) ............................................................................................. 2 - 17

2.2.5.1 S-OFDMA parameters ........................................................................................................ 2 - 18

2.2.5.2 Other Complementary Features of S-OFDMA ................................................................... 2 - 18

2.2.5.3 SOFDMA frame structure ................................................................................................... 2 - 18

2.2.5.4 Advantages and Disadvantages of SOFDMA System ......................................................... 2 - 19

2.3 OFDM Parameters ............................................................................................................................ 2 - 19

2.3.1 Basic Terms in OFDM ................................................................................................................ 2 - 20

2.3.2 Basic OFDM Parameters ........................................................................................................... 2 - 22

2.3.3 Properties of OFDM .................................................................................................................. 2 - 24

2.3.4 OFDM Real Parameters ............................................................................................................. 2 - 26

2.3.5 Subchannelization ..................................................................................................................... 2 - 26

2.3.6 Frame Structure ........................................................................................................................ 2 - 28

2.3.7 From Bits to Carrier ................................................................................................................... 2 - 29

2.4 OFDM Generation and Reception .................................................................................................... 2 - 30

2.4.1 Serial to parallel conversion ...................................................................................................... 2 - 31

2.4.2 Modulation................................................................................................................................ 2 - 32

2.4.3 Frequency to time domain conversion ..................................................................................... 2 - 34

2.4.4 Guard Period ............................................................................................................................. 2 - 35

Chapter 3: Comparison between WiMAX and other Broadband access technologies 3.1 Comparison between WiMAX and 3G cellular................................................................................... 3 - 1

3.1.1 Introduction to 3G Technologies ................................................................................................ 3 - 1

3.1.1.1 THE STANDARDS FOR 3G ..................................................................................................... 3 - 1

3.1.1.2 3G STANDARDIZATION PROCESS ......................................................................................... 3 - 1

3.1.1.3 3GPP ..................................................................................................................................... 3 - 1

3.1.2 Competing Technologies ............................................................................................................. 3 - 2

3.1.2.1 CDMA Family ........................................................................................................................ 3 - 2

3.1.2.2 HSDPA .................................................................................................................................. 3 - 3

3.1.3 Roadmap for 3G Enhancements ................................................................................................. 3 - 3

3.1.4 Technological Comparison .......................................................................................................... 3 - 4

3.2 Comparing Mobile WiMAX to 1xEVDO and HSPA ............................................................................. 3 - 5

3.2.1 Common Features ....................................................................................................................... 3 - 6

VI

3.2.1.1 Adaptive Modulation and Coding (AMC) ............................................................................. 3 - 6

3.2.1.2 Hybrid ARQ ........................................................................................................................... 3 - 6

3.2.1.3 Fast Scheduling .................................................................................................................... 3 - 7

3.2.1.4 Bandwidth Efficient Handoff ................................................................................................ 3 - 7

3.1 Key Advantages of Mobile WiMAX .................................................................................................. 3 - 11

3.2.2 Tolerance to Multipath and Self-Interference .......................................................................... 3 - 11

3.2.3 Scalable Channel Bandwidth ..................................................................................................... 3 - 12

3.2.4 Orthogonal Uplink Multiple Access ........................................................................................... 3 - 12

3.2.5 Support for Spectral-Efficient TDD ............................................................................................ 3 - 12

3.2.6 Frequency Selective Scheduling ................................................................................................ 3 - 13

3.2.7 Fractional Frequency Reuse ...................................................................................................... 3 - 14

3.2.8 Quality of Service ...................................................................................................................... 3 - 14

3.2.9 Advanced Antenna Technology ................................................................................................ 3 - 15

3.2.10 Spectral Efficiency ................................................................................................................... 3 - 16

3.2.11 Throughput Comparison ......................................................................................................... 3 - 17

3.2.12 Base-Station Deployment ....................................................................................................... 3 - 17

3.2.13 Power control .......................................................................................................................... 3 - 18

3.2.13.1 Power control in 3G ......................................................................................................... 3 - 18

3.2.13.2 Power control in WiMAX .................................................................................................. 3 - 19

3.2.13.3 Comparison between Powers Controls on 3G versus WiMAX ......................................... 3 - 20

3.3 Comparison between WiMAX and WiFi ........................................................................................... 3 - 20

3.3.1 Introduction .............................................................................................................................. 3 - 20

3.3.2 Scalability .................................................................................................................................. 3 - 21

3.3.2.1 Improved user connectivity ............................................................................................... 3 - 21

3.3.2.2 Higher quality of service .................................................................................................... 3 - 21

3.3.2.3 Full support for WMAN service .......................................................................................... 3 - 21

3.3.2.4 Robust carrier-class operation ........................................................................................... 3 - 22

3.3.3 Relative Performance ................................................................................................................ 3 - 22

3.3.3.1 Channel Bandwidth ............................................................................................................ 3 - 22

3.3.3.2 Data rate ............................................................................................................................ 3 - 23

3.3.4 Quality of Service ...................................................................................................................... 3 - 23

3.3.4.1 Quality of Service in WiFi: .................................................................................................. 3 - 23

VII

3.3.4.2 Quality of Service in WiMAX .............................................................................................. 3 - 24

3.3.5 RANGE ....................................................................................................................................... 3 - 27

3.3.6 Coverage ................................................................................................................................... 3 - 29

3.3.7 WiMAX Security ........................................................................................................................ 3 - 30

3.4 Comparison between Mobile and Fixed WiMAX ............................................................................. 3 - 31

3.4.1 WiMAX Rollout .......................................................................................................................... 3 - 31

3.4.1.1 Features of IEEE 802.16a .................................................................................................... 3 - 31

3.4.1.2 General features of IEEE 802.16b ...................................................................................... 3 - 32

3.4.1.3 General features of IEEE 802.16c ....................................................................................... 3 - 32

3.4.1.4 IEEE 802.16d-2004 “Fixed WiMAX” ................................................................................... 3 - 32

3.4.1.5 IEEE 802.16e “Mobile WiMAX” .......................................................................................... 3 - 33

3.4.2 Types of WiMAX ........................................................................................................................ 3 - 33

3.4.2.1 Fixed WiMAX ...................................................................................................................... 3 - 33

3.4.2.2 Mobile WiMAX ................................................................................................................... 3 - 34

3.4.2.3 Backhaul ............................................................................................................................. 3 - 34

3.4.3 What is Fixed WiMAX? .............................................................................................................. 3 - 35

3.4.4 What is mobile WiMAX? ........................................................................................................... 3 - 35

3.4.5 Difference between Fixed vs. Mobile ....................................................................................... 3 - 37

3.4.5.1 Mobility Management and Handoff .................................................................................. 3 - 37

3.4.5.2 Technically both are based on OFDM ................................................................................ 3 - 37

3.4.5.3 Mobile WiMAX adds .......................................................................................................... 3 - 37

3.5 Conclusion ........................................................................................................................................ 3 - 39

Chapter 4: Coverage analysis of mobile WiMAX 4.1 Introduction ....................................................................................................................................... 4 - 1

4.2 Link Budget ......................................................................................................................................... 4 - 2

4.2.1 Why link budget? ........................................................................................................................ 4 - 3

4.2.2 What is a link? ............................................................................................................................. 4 - 3

4.2.3 Base Station ................................................................................................................................ 4 - 3

4.2.4 Customer Premises Equipment (CPE) ......................................................................................... 4 - 4

4.2.5 What is EIRP? .............................................................................................................................. 4 - 5

4.2.6 Receiver Sensitivity ..................................................................................................................... 4 - 6

4.2.6.1 The thermal noise ................................................................................................................ 4 - 6

VIII

4.2.6.2 The receiver SNR .................................................................................................................. 4 - 7

4.2.6.3 The noise figure ................................................................................................................... 4 - 7

4.2.6.4 The implementation loss ..................................................................................................... 4 - 8

4.2.7 Uplink Subchanneling Gain ......................................................................................................... 4 - 8

4.2.8 Margins ....................................................................................................................................... 4 - 8

4.2.9 Link Budget Calculation (Maximum Allowable Path Loss) .......................................................... 4 - 9

4.2.10 Effect of Adverse Weather Conditions ................................................................................... 4 - 10

4.2.11 Improving Coverage and Throughput ..................................................................................... 4 - 11

4.3 Propagation Model .......................................................................................................................... 4 - 12

4.3.1 Hata Model ............................................................................................................................... 4 - 13

4.3.2 COST-231 Hata Model ............................................................................................................... 4 - 15

4.3.3 Walfish-Ikegami Model ............................................................................................................. 4 - 16

4.3.4 Erceg Model .............................................................................................................................. 4 - 17

4.3.5 Ecc-33 path loss model ............................................................................................................. 4 - 19

4.3.6 COMPARISON WITH SIMULATION RESULTS ............................................................................. 4 - 19

4.4 Cell Area ........................................................................................................................................... 4 - 21

4.5 Bit Rate per Sector ........................................................................................................................... 4 - 22

4.6 Required Number of Sites and Sectors ............................................................................................ 4 - 22

4.7 Planning Tool: Graphical User Interface (GUI) ................................................................................. 4 - 23

4.8 Link budget sample .......................................................................................................................... 4 - 24

4.9 Conclusions ...................................................................................................................................... 4 - 25

Chapter 5: Numerical results of WiMAX 5.1 Introduction ....................................................................................................................................... 5 - 1

5.2 The BS antenna height and the modulation technique and coding rate ........................................... 5 - 2

5.3 Effect of different morphologies ........................................................................................................ 5 - 3

5.4 Effect of operating frequency ............................................................................................................ 5 - 4

5.5 Effect of channel bandwidth .............................................................................................................. 5 - 5

5.6 Effect of subchannelization ................................................................................................................ 5 - 6

5.6.1 The forward link versus reverse link cell radius in case of no subchannelization ...................... 5 - 6

5.6.2 The forward link versus reverse link cell radius in case of subchannelization ........................... 5 - 7

5.7 Comparison between Fixed and mobile WiMAX ............................................................................... 5 - 8

5.8 Comparison between Erceg A, B and C .............................................................................................. 5 - 9

IX

Chapter 6: Performance analysis of mobile WiMAX 6.1 Performance measures ...................................................................................................................... 6 - 1

6.2 Effect of modulation type and code rate ........................................................................................... 6 - 4

6.3 Effect of Cyclic prefix rate .................................................................................................................. 6 - 6

6.4 Effect of nominal bandwidth and operating frequency ..................................................................... 6 - 8

6.5 Effective subchannelization (Licensed operation) ........................................................................... 6 - 10

6.6 Effective subchannelization (Licensed-exempt operation) ............................................................. 6 - 12

6.7 Comparison between fixed WiMAX and Mobile WiMAX ................................................................ 6 - 14

Chapter 7: Practical part of mobile WiMAX coverage 7.1 Introduction ....................................................................................................................................... 7 - 1

7.2 Cellular structured WiMAX Network planning processes .................................................................. 7 - 1

7.2.1 Nominal or preliminary cell planning .......................................................................................... 7 - 1

7.2.2 Site surveys ................................................................................................................................. 7 - 2

7.2.3 Field measurements .................................................................................................................... 7 - 3

7.2.4 System design (or final cell plan) ................................................................................................ 7 - 3

7.2.5 System tuning ............................................................................................................................. 7 - 4

7.2.6 System growth ............................................................................................................................ 7 - 4

7.3 BS site choice ..................................................................................................................................... 7 - 4

7.4 Antenna configuration and cell type choice ...................................................................................... 7 - 5

7.5 Antenna selection .............................................................................................................................. 7 - 5

7.6 Uniform solution of cellular structured mobile WiMAX network coverage ...................................... 7 - 6

7.6.1 Case study one ............................................................................................................................ 7 - 6

7.6.2 Case study two ............................................................................................................................ 7 - 8

7.7 Non uniform solution of cellular structured mobile WiMAX network coverage ............................... 7 - 9

7.7.1 Rural area (RU) ............................................................................................................................ 7 - 9

7.7.2 Suburban area (SU) ................................................................................................................... 7 - 10

7.7.3 Urban area (UR) ........................................................................................................................ 7 - 11

7.7.4 Dense urban area (DU).............................................................................................................. 7 - 12

Chapter 8: Hardware implementation of RF Field strength meter 8.1 Introduction ....................................................................................................................................... 8 - 1

8.2 RF strength meter applications .......................................................................................................... 8 - 1

8.3 RF strength meter specifications ....................................................................................................... 8 - 1

X

8.3.1 Antenna specification ................................................................................................................. 8 - 1

8.3.2 Frequency range ......................................................................................................................... 8 - 2

8.3.3 Power supply ............................................................................................................................... 8 - 2

8.3.4 Power density ............................................................................................................................. 8 - 2

8.4 Block diagram of RF strength meter .................................................................................................. 8 - 3

8.5 RF strength meter Circuit diagram ..................................................................................................... 8 - 4

8.6 Circuit Operation ................................................................................................................................ 8 - 4

8.6.1 Whip antenna.............................................................................................................................. 8 - 4

8.6.2 Preamplifier ................................................................................................................................. 8 - 5

8.6.2.1 VHF-UHF preamplifier .......................................................................................................... 8 - 5

8.6.2.2 LF-HF preamplifier ................................................................................................................ 8 - 5

8.6.3 Chopper amplifier ....................................................................................................................... 8 - 6

8.6.4 Power supply ............................................................................................................................... 8 - 7

8.6.5 Bar graph display ......................................................................................................................... 8 - 7

8.7 Parts Placement of RF Field Strength Meter ...................................................................................... 8 - 8

8.8 PC Board Pattern for Solder Side of RF Field Strength Meter ............................................................ 8 - 9

8.9 Test Procedure of RF strength meter ............................................................................................... 8 - 10

8.10 RF Strength Meter parts List .......................................................................................................... 8 - 11

8.11 Packaging of RF field strength meter ............................................................................................. 8 - 12

8.12 Conclusions .................................................................................................................................... 8 - 14

Chapter 9: Mobility Management in WiMAX 9.1 Introduction ....................................................................................................................................... 9 - 1

9.2 Channel acquisition ............................................................................................................................ 9 - 1

9.3 Initial Ranging and Negotiation of SS Capabilities ............................................................................. 9 - 2

9.4 Authentication and Registration ........................................................................................................ 9 - 3

9.5 IP Connectivity ................................................................................................................................... 9 - 3

9.6 Idle mode management. .................................................................................................................... 9 - 4

9.7 Call procedure. ................................................................................................................................... 9 - 4

9.7.1 VoIP ............................................................................................................................................. 9 - 5

9.7.2 Session Initiation Protocol (SIP) .................................................................................................. 9 - 5

9.7.3 SIP network elements ................................................................................................................. 9 - 5

9.8 Radio Link Control (RLC) ..................................................................................................................... 9 - 8

XI

9.9 Hand over ......................................................................................................................................... 9 - 10

9.9.1 Hard Handover .......................................................................................................................... 9 - 10

9.9.2 Macro Diversity Handover ........................................................................................................ 9 - 11

9.9.3 Fast Base Station Switching ...................................................................................................... 9 - 11

9.10 Simulation ...................................................................................................................................... 9 - 12

Chapter 10: Conclusions and suggestions for future work 10.1 Introductions .................................................................................................................................. 10 - 1

10.2 Conclusions .................................................................................................................................... 10 - 1

10.3 Suggestions for future work ........................................................................................................... 10 - 3

10.3.1 WiMAX future ......................................................................................................................... 10 - 3

10.3.1.1 IMT-2000 & IMT-Advanced .............................................................................................. 10 - 3

10.3.1.2 IEEE 802.16m goals .......................................................................................................... 10 - 4

10.3.1.3 802.16m specifications. ................................................................................................... 10 - 4

10.3.1.4 IEEE 802.16m & LTE ......................................................................................................... 10 - 4

10.3.2 Mobility management suggestions ......................................................................................... 10 - 6

10.3.3 Hardware suggestions ............................................................................................................. 10 - 6

XII

Figures caption Chapter 1: Overview of WiMAX technology Figure1.1 WiMAX network ....................................................................................................................... 1 - 2 Figure1.2 WiMAX Standards .................................................................................................................... 1 - 3 Figure1.3 WiMAX Network Architecture ................................................................................................. 1 - 7 Figure1.4 WiMAX Network reference model .......................................................................................... 1 - 8 Figure1.5 Functions performed across reference points ....................................................................... 1 - 10 Figure1.6 WiMAX Various Topologies .................................................................................................... 1 - 11 Figure1.7 Point-to-point WiMAX Configurations ................................................................................... 1 - 11 Figure1.8 Point-to-Multipoint WiMAX Configurations .......................................................................... 1 - 12 Figure1.9 Mesh Network with Wi-Fi and/or WiMAX ............................................................................. 1 - 13 Figure1.10 The difference between line o f sight and non-line of sight ................................................ 1 - 14 Figure1.11 Different antenna types are designed for different applications ........................................ 1 - 14 Figure1.12 an Omni-directional antenna broadcasts 360 degrees from the base station .................... 1 - 15 Figure1.13 Sector antennas are focused on smaller sectors ................................................................. 1 - 15 Figure1.14 Panel antennas are most often used for point-to-point applications ................................. 1 - 16 Figure1.15 an mobile WiMAX CPE device .............................................................................................. 1 - 17 Figure1.16 Portable WiMAX CPE with PCMCIA ..................................................................................... 1 - 17 Figure1.18 Cellular Backhaul .................................................................................................................. 1 - 22 Figure1.19 Wireless Service Provider Backhaul ..................................................................................... 1 - 23 Figure1.20 Banking Networks ................................................................................................................ 1 - 24 Figure1.21 Education Networks ............................................................................................................. 1 - 25 Figure1.22 Public Safety ......................................................................................................................... 1 - 26 Figure1.23 Offshore Communications ................................................................................................... 1 - 27 Figure1.24 Campus Connectivity ........................................................................................................... 1 - 28 Figure1.25 Temporary Construction Communications .......................................................................... 1 - 29 Figure1.26 Theme Parks ......................................................................................................................... 1 - 30 Figure1.27 Wireless Service Provider Access Network .......................................................................... 1 - 31 Figure1.28 Rural Connectivity ................................................................................................................ 1 - 32

Chapter 2: Overview of OFDM Figure2.1 Conceptual scheme of a multi-carrier transmission system .................................................... 2 - 2 Figure2.2 parallel-data-transmission scheme .......................................................................................... 2 - 2 Figure2.3 Frequency response of the subcarriers in a 5 tone OFDM ...................................................... 2 - 3 Figure2.4 Concept of the OFDM signal .................................................................................................... 2 - 5 Figure2.5 TDMA scheme where each user is allocated a small ............................................................... 2 - 6 Figure2.6 Conventional CDMA PN Code sequence .................................................................................. 2 - 7 Figure2.7 (A) Basis functions of an OFDM signal with N=16 carriers represented in frequency domain 2 - 8 (B) Resulting spectrum from the basic functions. .................................................................................... 2 - 8 Figure2.8 Time domain construction of an OFDM signal ...................................................................... 2 - 10

XIII

Figure2.9 Cyclic Prefix in OFDM ............................................................................................................. 2 - 11 Figure2.10 Cyclic Prefix in OFDM ........................................................................................................... 2 - 11 Figure2.11 FDMA channelization ........................................................................................................... 2 - 13 Figure2.12 OFDMA channelization ........................................................................................................ 2 - 13 Figure2.13 Single carrier and OFDM ...................................................................................................... 2 - 14 Figure2.14 Single carrier and OFDM ...................................................................................................... 2 - 15 Figure2.15 Single carrier and OFDM received ....................................................................................... 2 - 15 Figure2.16 Single carrier and OFDM ...................................................................................................... 2 - 16 Figure2.17 Multi path Fading Channel ................................................................................................... 2 - 16 Figure2.18 OFDM sub carrier structure ................................................................................................. 2 - 17 Figure2.19 SOFDM structure ................................................................................................................. 2 - 18 Figure2.20 OFDM in Both Time and Frequency domains ...................................................................... 2 - 22 Figure2.21 The spectrum of an OFDM signal (without cyclic prefix) ..................................................... 2 - 24 Figure2.22 The spectrum of an OFDM signal (without cyclic prefix) ..................................................... 2 - 25 Figure2.23 Subchannelization with 4 used subchannels ....................................................................... 2 - 27 Figure2.24 The effect of sub-channelization ......................................................................................... 2 - 28 Figure2.25 OFDM frame structure ......................................................................................................... 2 - 28 Figure2.26 OFDM / OFDMA transmitter architecture (simplified) ........................................................ 2 - 29 Figure2.27 Block diagram showing a basic OFDM transceiver .............................................................. 2 - 31 Figure2.28 Adaptive Modulation ........................................................................................................... 2 - 33 Figure2.29 OFDM generation, IFFT stage .............................................................................................. 2 - 34 Figure2.30 Addition of a guard period to an OFDM signal .................................................................... 2 - 35

Chapter 3: Comparison between WiMAX and other Broadband access technologies Figure3.1 Cellular Network Evolution ...................................................................................................... 3 - 2 Figure3.2 Mobile WiMAX will be available before 3G – LTE .................................................................... 3 - 4 Figure3.3 Hard handover realization ....................................................................................................... 3 - 8 Figure3.4 Macro Diversity Handover ....................................................................................................... 3 - 8 Figure3.5 Fast Base Station Switching ..................................................................................................... 3 - 9 Figure3.6 Hard handoff ............................................................................................................................ 3 - 9 Figure3.7 Soft handoff ........................................................................................................................... 3 - 10 Figure3.8 Fractional Frequency Reuse with Mobile WiMAX ................................................................. 3 - 14 Figure3.9 Performance of Adaptive MIMO Switch (AMS) ..................................................................... 3 - 16 Figure3.10 Mobile WiMAX Versus 3G spectral efficiency comparison .................................................. 3 - 16 Figure3.11 Mobile WiMAX versus 3GNet Throughput Comparison ...................................................... 3 - 17 Figure3.12 Mobile WiMAX versus 3G Number of required sites ........................................................... 3 - 17 Figure3.13 Near-Far-problem ................................................................................................................ 3 - 18 Figure3.14 UGS scheduling service uplink grants allocation mechanism .............................................. 3 - 25 Figure3.15 rtPS scheduling service uplink grants allocation and request mechanismnon-real-time Polling Service (nrtPS) ........................................................................................................................................ 3 - 26 Figure3.16 Illustration of the nrtPS scheduling service uplink grants allocation and request mechanism. The SS may use contention request opportunities as well as unicast request opportunities ............... 3 - 26

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Figure3.17 Illustration of the BE scheduling service uplink grants allocation and request mechanism. The BS does not have any unicast uplink request polling obligation for a BE SS ......................................... 3 - 27 Figure3.18 WiMAX versus WiFi range .................................................................................................... 3 - 28 Figure3.19 WiMAX vs. WiFi coverage .................................................................................................... 3 - 29 Figure3.20 Mobile versus Fixed data rate .............................................................................................. 3 - 36

Chapter 4: Coverage analysis of mobile WiMAX Figure4.1 Link-budget for downlink ......................................................................................................... 4 - 1 Figure4.2 illustration of link budget ......................................................................................................... 4 - 2 Figure4.3 illustration of EIRP .................................................................................................................... 4 - 5 Figure4.4 Link analysis of a WiMAX system operating at 2.5 and 5GHz ................................................ 4 - 10 Figure4.5 Correction factor in small and medium size area .................................................................. 4 - 14 Figure4.6 Correction factor in large size area ........................................................................................ 4 - 14 Figure4.7 Path loss propagation in suburban area versus distance ...................................................... 4 - 15 Figure4.8 the Walfish-Ikegami model .................................................................................................... 4 - 16 Figure4.9 Comparison of path loss propagation for rural environments ............................................. 4 - 20 Figure4.10 Comparison of path loss propagation for suburban environments .................................... 4 - 20 Figure4.11 Comparison of path loss propagation for urban environments .......................................... 4 - 21 Figure4.12 Illustration of cell area calculation ....................................................................................... 4 - 21 Figure4.13 Range of the different modulation schemes, indicated by different colors. The lighter the color, the less data bits per symbol (cf. Table 4.4) ................................................................................ 4 - 22 Figure4.14 Graphical user interface of the planning tool ...................................................................... 4 - 23

Chapter 5: Numerical results of WiMAX Figure5.1 Modulation technique effect ................................................................................................... 5 - 2 Figure5.2 Morphology effect ................................................................................................................... 5 - 3 Figure5.3 Operating frequency effect ...................................................................................................... 5 - 4 Figure5.4 Channel bandwidth effect ....................................................................................................... 5 - 5 Figure5.5 FL versus RL cell radius in case of no subchannelization ......................................................... 5 - 6 Figure5.6 FL versus RL cell radius in case of no subchannelization ........................................................ 5 - 7 Figure5.7 Comparison between Fixed and mobile WiMAX cell radius .................................................... 5 - 8 Figure5.8 Comparison between Erceg A, B and C cell radius .................................................................. 5 - 9

Chapter 6: Performance analysis of mobile WiMAX Figure6.1 Maximum transmission data rate calculations ........................................................................ 6 - 3 Figure6.2 Effect of modulation type in data rate .................................................................................... 6 - 5 Figure6.3 Effect of cyclic prefix in data rate ............................................................................................ 6 - 7 Figure6.4 Effect of Bandwidth and operating frequency in data rate ..................................................... 6 - 9 Figure6.5 Effect of subchannelization for licensed operation ............................................................... 6 - 11 Figure6.6 Effect of subchannelization for licensed-exempt operation ................................................. 6 - 13 Figure6. 7 Effect of bandwidth in Mobile and Fixed WiMAX ................................................................. 6 - 15

Chapter 7: Practical part of mobile WiMAX coverage Figure7.1 Coverage of rural area ............................................................................................................. 7 - 7 Figure7.2 Coverage of dense urban area ................................................................................................. 7 - 8

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Figure7.3 Rural area coverage ............................................................................................................... 7 - 10 Figure7.4 Suburban area coverage ........................................................................................................ 7 - 11 Figure7.5 Urban area coverage .............................................................................................................. 7 - 12 Figure7.6 Dense urban area coverage ................................................................................................... 7 - 13

Chapter 8: Hardware implementation of RF Field strength meter Figure8.1 Block diagram of RF strength meter ........................................................................................ 8 - 3 Figure8.2 Schematic of RF Field Strength Meter ..................................................................................... 8 - 4 Figure8.3 VHF-UHF preamplifier .............................................................................................................. 8 - 5 Figure8.4 LF-HF preamplifier ................................................................................................................... 8 - 5 Figure8.5 Chopper amplifier .................................................................................................................... 8 - 6 Figure8.6 Bar graph display ..................................................................................................................... 8 - 7 Figure8.7 Parts Placement of RF Field Strength Meter Component Side ................................................ 8 - 8 Figure8.8 Parts Placement of RF Field Strength Meter Solder Side ......................................................... 8 - 9 Figure8.9 PC Board Pattern for Solder Side of RF Field Strength Meter ................................................ 8 – 9 Figure8.10 Packaging of RF field strength meter ................................................................................... 8 - 12 Figure8.11 Photo of Completed RF Field Strength Meter with Matching Antenna .............................. 8 - 13 Figure8.12 Photo of inside Completed RF Field Strength Meter Showing Battery Pack ....................... 8 - 13

Chapter 9: Mobility Management in WiMAX Figure9.1 Channel Acquisition, Ranging, and Negotiation of Subscriber Station Capabilities ................ 9 - 2 Figure9.2 Subscriber Station Authentication, Registration and IP connectivity ...................................... 9 - 3 Figure9.3 SIP Establishment of a peer to peer Call .................................................................................. 9 - 6 Figure9.4 Radio Link Control .................................................................................................................... 9 - 9 Figure9.5 Hard Handover realization ..................................................................................................... 9 - 10 Figure9.6 Macro Diversity Handover ..................................................................................................... 9 - 11 Figure9.7 Fast Base Station Switching ................................................................................................... 9 - 12 Figure 9.8 Welcome page ...................................................................................................................... 9 - 13 Figure 9.9 First view of HO simulation ................................................................................................... 9 - 13 Figure 9.10 the first step in HO procedure ............................................................................................ 9 - 14 Figure 9.11 the last step in HO procedure: ............................................................................................ 9 - 14

Chapter 10: Conclusions and suggestions for future work Figure 10.1 IMT-2000 & IMT-Advanced ................................................................................................. 10 - 3 Figure 10.2 3GPP & Mobile WiMAX Timeline ........................................................................................ 10 - 5

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Tables caption Chapter 2: Overview of OFDM Table2.1 scalable ODFM parameters ..................................................................................................... 2 - 18 Table2.2 Required SNR to maintain a BER below a given threshold ..................................................... 2 - 33

Chapter 3: Comparison between WiMAX and other Broadband access technologies

Table3.1 Theoretical throughputs of CDMA systems .............................................................................. 3 - 3 Table3.2 WiMAX, EVDO and HSPA Features - summary of comparative features .................................. 3 - 5 Table3.3 AMC Capability .......................................................................................................................... 3 - 6 Table3.4 Mobile WiMAX Applications and Quality of Service ............................................................... 3 - 15 Table3.5 Power Control on 3G versus WiMAX ...................................................................................... 3 - 20 Table3.6 WiMAX versus WiFi Scalability ................................................................................................ 3 - 22 Table3.7 WiMAX versus WiFi QOS ......................................................................................................... 3 - 27 Table3.8 Mobile versus Fixed ................................................................................................................ 3 - 38

Chapter 4: Coverage analysis of mobile WiMAX Table4.1 Base station parameters ........................................................................................................... 4 - 4 Table4.2 Coaxial feeder cable model (7/8”) diameter ............................................................................. 4 - 4 Table4.3 CPE parameters ......................................................................................................................... 4 - 4 Table4.4 Parameters per channel bandwidth.......................................................................................... 4 - 6 Table4.5 Parameters per modulation scheme......................................................................................... 4 - 7 Table4.6 Urban corrections ..................................................................................................................... 4 - 9 Table4.7 Parameters of Erceg Model ..................................................................................................... 4 - 18 Table4.8 Link budget sample ................................................................................................................. 4 - 24

Chapter 5: Numerical results of WiMAX Table5.1 Case studies ............................................................................................................................... 5 - 1 Table 5.2 The Estimated downlink coverage radius for different BTS heights in Km with different modulation techniques ............................................................................................................................ 5 - 2 Table 5.3 The Estimated downlink coverage radius for different BTS heights in Km with different morphologies ........................................................................................................................................... 5 - 3 Table 5.4 The Estimated downlink coverage radius for different BTS heights in Km with different operating frequency (licensed and license exempt) ................................................................................ 5 - 4 Table 5.5 The Estimated downlink coverage radius for different BTS heights in Km with different channel BW ............................................................................................................................................................ 5 - 5 Table 5.6 The Estimated downlink coverage radius for different BTS heights in Km at FL and RL without subchannelization .................................................................................................................................... 5 - 6 Table 5.7 The Estimated downlink coverage radius for different BTS heights in Km at FL and RL with subchannelization .................................................................................................................................... 5 - 7 Table 5.8 The Estimated downlink coverage radius for different BTS heights in Km at mobile WiMAX and fixed WiMAX ............................................................................................................................................ 5 - 8

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Table 5.9 The Estimated downlink coverage radius for different BTS heights in Km at with different Erceg models ...................................................................................................................................................... 5 - 9

Chapter 6: Performance analysis of mobile WiMAX Table6.1 Coding schemes ........................................................................................................................ 6 - 2 Table6.2 Effect of modulation type in data rate ...................................................................................... 6 - 4 Table6.3 Effect of cyclic prefix in data rate .............................................................................................. 6 - 6 Table6.4 Effect of Bandwidth and operating frequency in data rate ...................................................... 6 - 8 Table6.5 Effect of subchannelization for licensed operation ................................................................ 6 - 10 Table6.6 Effect of subchannelization for licensed-exempt operation ................................................... 6 - 12 Table6.7 Effect of bandwidth in Mobile and Fixed WiMAX ................................................................... 6 - 14

Chapter 7: Practical part of mobile WiMAX coverage Table7.1 the antenna selection for rural environment and for dense urban environment .................... 7 - 6

Chapter 8: Hardware implementation of RF Field strength meter Table8.1 RF Strength meter parts list .................................................................................................... 8 - 11

1xEV-DO 1x Evolution data optimized 1xEV-DV 1x Evolution data and voice 3DES Triple data encryption standard 3G Third generations3GPP Third-generation partnership project 3GPP2 Third generation partnership project-2 AAA Authentication, authorization, and accounting AAS Advanced antenna systems AC Admission control ACE Active constellation extension ADC Analog-to-digital converter ADSL Asymmetric digital subscriber loop AES Advanced encryption standard AF Application function AF Assured forwarding AK Authentication key AKA Authentication and key agreement AM Amplitude modulationAMC Adaptive modulation and coding AoA Angle of arrival AoD Angle of departure API Application programming interface AR Access routerARQ Automatic repeat request AS Angular spread ASN Access services network ASN-GW ASN gateway ASP Application service provider ATM Asynchronous transfer mode AWGN Additive white Gaussian noise AWS Advanced wireless services BE Best effort BEP Bit error probability BER Bit error rate BGCF Breakout gateway control function BLAST Bell Labs layered spaced time BLER Block error rate BPSK Binary phase shift keyingBRS Broadband radio services BS Base station BSC Base station controller BSN Block sequence number BTS Base station transceiversCBC Cipher-block chaining CBR Constant bit rate CC Convolution coding CCDF Complementary cumulative distribution functionCCI Cochannel interference

Abbreviation and Symbols

CDF Cumulative distribution function CDMA Code division multiple access CGI Common gateway interface CHAP Challenge handshake authentication protocol CID Connection identifier CLT Central limit theorem CM Cubic metric CMAC Cipher-based message authentication code CMAC Complexes multiply and accumulate CN Correspondent node CoA Care-of address COPS Common open policy service CP Cyclic prefix CPE Customer premise equipment CPL Call-processing language CQICH Channel-quality indicator channel CRC Cyclic redundancy check CQI Channel quality indicatorCS Convergence sublayer CSCF Call session control function CSI Channel state information CSMA Carrier sense multiple access CSN Connectivity services network CTC Convolution turbo code DAC Digital-to-analog converter DARS Digital audio radio services DC Direct current DCD Downlink channel descriptor DCF Distributed coordination function DECT Digital-enhanced cordless telephony DDFSE Delayed-decision-feedback sequence estimationDES Data encryption standard DFE Decision-feedback equalizer DFT Discrete Fourier transform DHCP Dynamic host control protocol DiffServ Differentiated services DL Downlink DNS Domain name systemDoA Direction of arrival DOCSIS Data over cable service interface specification DP Decision point DPF Data path function DRM Digital rights management DS Delay spread DSA Dynamic service allocation DSC Dynamic service change DSCP DiffServ code point DSD Dynamic service delete

DSL Digital subscriber line DSP Digital-signal processing DSTTD Double space/time transmit diversity DVB-H Digital video broadcasting-handheld EAP Extensible authentication protocol ECRM Effective code rate map EDGE Enhanced data rate for GSM evolution EESM Exponentially effective SINR map EF Expedited forwarding EGC Equal gain combining EIRP Effective isotopic radiated power EMSK Enhanced master session key EP Enforcement point ErtPS Extended real-time packet service ERT-VR Extended real-time variable-rate service ESP Encapsulating security payload ETH-CS Ethernet convergence sublayer ETRI Electronics and Telecommunications Research Institute

ETSI European Telecommunications Standards InstituteEVM Error vector magnitude FA Foreign agent FBSS Fast base station switching FCC Federal Communications Commission FCH Frame control header FDD Frequency division duplexing FDMA Frequency division multiple access FEC Forward error correction FEC Forward equivalence class FEQ Frequency-domain equalization FER Frame error rate FFT fast Fourier transform FHDC frequency-hopping diversity code FIB forward information base FIPS Federal Information Processing Standard FIR finite impulse response FM frequency modulation FSH fragmentation subheader FTP file transfer protocol FTTH fiber-to-the-homeFUSC full usage of subcarriers FWA fixed wireless access GMH generic MAC header GPRS GSM packet radio services GRE generic routing encapsulation GSM global system for mobile communications GW gateway HA home agent HARQ hybrid-ARQ

HDTV high-definition television HIPERMA high-performance metropolitan area network HHO hard handover HMAC hash-based message authentication code HO handover HoA home address HPA high-power amplifier HSDPA high-speed downlink packet access HSPA high-speed packet access HSS home subscriber server HSUPA high-speed uplink packet access HTTP hypertext transfer protocol HUMAN high-speed unlicensed metropolitan area network IBO input backoff ICI intercarrier interference ICMP Internet control message protocol I-CSCF interrogating call session control function IDFT inverse discrete Fourier transform IEEE Institute of Electrical and Electronics Engineers IETF Internet Engineering Task Force IFFT inverse fast Fourier transform IGMP Internet group management protocol IM instant messaging IMS IP multimedia subsystem IN intelligent network IntServ integrated services IP Internet protocol IP-CS IP convergence sublayer IPsec IP security IP-TV Internet protocol television IS Integrated services ISDN Integrated services digital network ISI Inter-symbol interferenceITU International Telecommunications Union JAIN Java for advanced intelligence network KEK Key encryption key LAN Local area network LDAP Lightweight directory access protocol LDPC Low-density parity codes

LDP-CR Label distribution protocol/constraint-based routing

LER Label-edge router LLR Log liklihood ratio LMOS Local multipoint distribution system LMMSE Linear minimum mean square error LOS Line of sight LPF Local policy function LR Location register

LS Least squares LSB Least significant bit LSP Label switched path LSR Label switching router LTE Long-term evolution MAC Media access control MAC Message-authentication code MAN Metropolitan area network MBS Multicast broadcast service MC-CDMA Multicarrier CDMA MCS Modulation and coding scheme MD5 Message-digest 5 algorithm MDHO Macro diversity handover MIMO Multiple input multiple outputs MIC Mean instantaneous capacity MIP Mobile IP MIP-HA Mobile IP home agent MISO Multiple input/single outputs ML Maximum likelihood MLD Maximum likelihood detection MLSD Maximum-likelihood sequence detection MMDS Multichannel multipoint distribution services MMS Multimedia messaging service MMSE Minimum mean square error MN Mobile node MPDU MAC protocol data unit MPEG Motion Picture Experts Group MPLS Multiprotocol label switching M-QAM Multilevel QAM MRC Maximal ratio combining MRT Maximum ratio transmission MS Mobile station MSB Most significant bit MSDU MAC service data unit MSE Mean square error MSK Master session key MSL Minimum signal levelMSR Maximum sum rate MUD Multiuser detection NAI Network access identifier NAP Network access provider NAS Network access server NAT Network address translation NLOS Non–line-of-sight NRM Network reference model nrtPS Non–real n time polling service NSP Network services provider NTP Network timing protocol

NWG Network Working Group OBO Output backoff OC Optimum combiner OCI Other-cell interference OFDM Orthogonal frequency division multiplexing OFDMA Orthogonal frequency division multiple access OSA Open systems architecture OSI Open systems interconnect O-SIC Ordered successive cancellation OSS Operational support systems OSTBC Orthogonal space/time block code PA Paging agent PAP Password authentication protocol PAPR Peak-to-average-power ratio PAR Peak-to-average ratio PC Paging controller PCS Personal communications services P-CSCF Proxy call session control function PDA Personal data assistant PDF Probability density function PDP Policy decision point PDU Packet data unit PEAP Protected extensible authentication protocolPEP Policy enforcement point PER Packet error rate PF Proportional fairness; policy function PG Paging group PHB Per hop behavior PHS Packet header suppression PHSF PHS field PHSI PHS index PHSM PHS mask PHSV PHS verify PKI Public key infrastructure PKM Privacy and key management PM Phase modulation PMIP Proxy mobile IPPMK Pair wise master key PN Pseudo noise PoA Point of attachment PPP Point-to-point protocol PR Policy rule PRC Proportional rate constraints P/S Parallel to serial PSH Packing subheader PSK preshared key PSTN Public switched telephone network PTS Partial transmit sequence

PUSC Partial usage of subcarriers QoS Quality of service QAM quadrature amplitude modulation QPSK quadrature phase shift keying RADIUS Remote access dial-in user service RF Radio frequency RFC Request for comments RMS Root mean square ROHC Robust header compression RP Reference point RR Radio resource RR Round-robin RRA Radio resource agent RRC Radio resource controller RRM Radio resource management RS Reed Solomon RSA Rivest-Shamir-Adleman RSS Received signal strengthRSSE Reduced-state sequence estimation RSSI Received signal strength indicator RSVP Resource reservation protocol RTCP Real-time control protocol RTP Real-time transport protocol rtPS Real-time polling service RTT Roundtrip time RUIM Removable user identity module SA Security association SC Selection combining S-CSCF Serving call session control function SCTP Stream control transport protocol SDP Session description protocol SDU Service data unit SET Secure electronic transactions SF Service flow; shadow fading SFA Service flow authorization SFBC Space/frequency block code SFID Service flow identifierSFM Service flow management SGSN Serving GPRS support node SH Sub header SHA Secure hash algorithm SIC Successive interference cancellation SII System identity information SIM Subscriber identity module SIMO Single input/multiple output SINR Signal-to-interference-plus-noise ratio SIP Session initiation protocol SIR Signal-to-interference ratio

SISO Single input/single output SLA Service-level agreement SLM Selected mapping SM Spatial multiplexing SME Small and medium enterprise SMS Short messaging service SNDR Signal-to-noise and distortion ratio SNR Signal-to-noise ratio SOFDMA Sealable OFDMA SOHO Small office/home office SOVA Soft input/soft output S/P Serial to parallel SPI Security parameter index SPID Sub packet identity SPM Spatial-channel model SPWG Service Provider Working Group SS Subscriber station SSL Secure sockets layerSTBC Space/time block code SUI Standford University Interim SVD Singular-value decomposition TCP Transport control protocol TD-SCDMA Time division/synchronous CDMA TDD Time division duplexing TDL Tap-delay line TDM Time division multiplexing TDMA Time division multiple access TE Traffic engineering TEK Traffic encryption key TLS Transport-layer security TOS Type of service TR Tone reservation TSD Transmit selection diversity TTLS Tunneled transport layer security TUSC Tile usage of subcarriers UA User agent UCD Uplink channel descriptorUDP User datagram protocol UGS Unsolicited grant services UHF Ultrahigh frequency UICC Universal integrated circuit card UL Uplink ULA Uniform linear array UMTS Universal mobile telephone system U-NII Unlicensed national information infrastructure URL Universal resource locator USIM Universal subscriber identity module VDSL Very high data rate digital subscriber loop

VHF Very high frequency VLAN Virtual local area networking VoD Video on demand VoIP Voice over Internet protocol VCI Virtual circuit identifier VPI Virtual path indicator VPN Virtual private network WAN Wide area network WAP Wireless access protocol WCDMA Wideband code division multiple access WCS Wireless communications services WiBro Wireless broadband Wi-Fi Wireless fidelity WiMAX Worldwide interoperability for microwave accessWISP Wireless Internet service provider WLAN Wireless local area network WLL Wireless local loop WMAN Wireless metropolitan area network WRAN Wireless regional area network WSS Wide-sense stationary WSSUS Wide-sense stationary uncorrelated scattering ZF Zero forcing

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1.1 Introduction After years of development and uncertainty, a standards based interoperable solution is

emerging for wireless broadband. A broad industry consortium, the Worldwide Interoperability for Microwave Access (WiMAX) Forum has begun certifying broadband wireless products for interoperability and compliance with a standard. WiMAX is based on wireless metropolitan area networking (WMAN) standards developed by the IEEE 802.16 group and adopted by both IEEE and the ETSI HIPERMAN group. In this chapter, we present a concise technical overview of the emerging WiMAX solution for broadband wireless.

We begin the chapter by summarizing the activities of the IEEE 802.16 group and its relation to WiMAX. Next, we discuss the salient features of WiMAX and briefly describe the physical and MAC-layer characteristics of WiMAX. Service aspects, such as quality of service, security, and mobility, are discussed, and reference network architecture is presented. The chapter ends with a brief discussion of expected WiMAX performance.

1.2 WiMAX WiMAX has the potential to replace a number of existing telecommunications infrastructures. In

a fixed wireless configuration, it can replace the telephone company's copper wire networks, the cable TV's coaxial cable infrastructure while offering Internet Service Provider (ISP) services. In its mobile variant, WiMAX has the potential to replace cellular networks. How do we get there?

1.2.1 What is WiMAX?

WiMAX is stand for (Worldwide Interoperability for Microwave Access) is an emerging technology that is designed to deliver fixed, and more recently, mobile broadband connectivity. The WiMAX trade name is used to group a number of wireless technologies that have emerged from the IEEE (Institute of Electrical and Electronics Engineers) 802.16 Wireless MAN (Metropolitan Area Network) standards. The main two standards are identified as 802.16-2004 (October 2004) and802.16e (December 2005), with 802.16e introducing mobility and currently receiving a great deal of interest in the telecoms world. The diagram below summarizes different environments in which WiMAX could be employed.

Chapter 1 Overview of WiMAX technology

Chapter 1 Overview of WiMAX technology

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Figure1.1 WiMAX network

1.2.2 WiMAX Standard

Like most IEEE standards, the 802.16 standard family consists of the basic 802.16 standard, and several, ever-increasing variations signified by adding a small alphabet to the basic specification name. The first 802.16 standard was published on 8 April 2002 and was followed by three amendments 802.16a to address issue of radio spectrum, 802.16b to address the issue of quality of service and 802.16c to address the issue of interoperability.

In September 2003, a revision project called 802.16REVd commenced aiming to align the standard with aspects of the European Telecommunications Standards Institute (ETSI) HYPERMAN standard as well as lay down conformance and test specifications. This project concluded in 2004 with the release of IEEE 802.16-2004 and the withdrawal of the earlier 802.16 documents including the a/b/c also an amendment to the standard, 802.16e, and addressing mobility was concluded in 2005. This is sometimes called “Mobile WiMAX”. The latest revisions in progress are 802.16f and g. These specifications try to address the management issues relating to 802.16 specifications, especially to 802.16e. The 802.16g defines the management plan procedures and services, and the 802.16f defines the management information base.

In addition there are amendments at pre-draft stage:

802.16 – Improved coexistence mechanisms for license-exempt operation. 802.16i - Mobile management information base.

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Figure1.2 WiMAX Standards

1.2.3 What is a Standard?

Is a published document that sets out specifications and procedures designed to ensure that a material, product, method, or service meets its purpose and consistently performs to its intended use.

1.2.4 Benefits of standardized WiMAX

Fewer product variants through a common subset of capabilities.

Less risk, lower system costs and greater return on investment.

Faster, cheaper access to more widely available, higher quality service.

Significant growth potential for broadband wireless deployment in underserved markets.

Equivalent delivery of services vs. wire line or fiber.

Guaranteed minimum performance levels.

Consistent levels of voice, video and data flow quality.

1.2.5 General features of IEEE 802.16

Broad bandwidth 70 Mbps throughput in 20 MHz channel (in WMAN-OFDM air interface).

Supports multiple services simultaneously with full QOS.

Bandwidth on demand (frame by frame).

MAC designed for efficient use of spectrum.

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Comprehensive, modern, and extensible security.

Supports frequency allocations from <1 to 66 GHz.

TDD and FDD (TDD dominates lately).

Link adaptation: Adaptive modulation and coding.

Point-to-multipoint topology, with mesh extensions.

Support for adaptive antennas and space-time coding.

Extensions to mobility.

1.2.6 General features of IEEE 802.16a

It was approved in January 2003.

It covers frequency band between 2GHz and11GHz (licensed and unlicensed).

Its lower frequencies make non-line of sight a possibility; hence, it makes the IEEE 802.16a standard the appropriate technology for last-mile application where obstacles like trees and buildings are often present and where base stations may need to be roofs of homes or buildings rather than towers on mountains.

Total data rate can be up to 75 Mb/s in each 20MHz channel.

It has up to 30 miles of range with a typical cell radius of 4-6 miles.

It provides an ideal wireless backhaul technology to connect 802.11 wireless LANs and commercial hotspots with the Internet.

It enables business to flexibly deploy new 802.11 hotspots in locations where traditional wired connection may be unavailable or time consuming to provide and offers service providers around the globe with a flexible new way to stimulate growth of the residential broadband access market segment.

It will be mostly used for small businesses, residential users and for backhaul or hotspot.

The most common 802.16 configurations consist of base station mounted on building or tower that communicates on a point to multi-point basis with subscriber station located in businesses and homes.

1.2.7 General features of IEEE 802.16b

IEEE 802.16b aims at the needs of license-exempt (unlicensed) applications around 5-6 GHz.

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1.2.8 General features of IEEE 802.16c

The IEEE Standards Board approved IEEE 802.16c in December 2002. The aim was to develop 10-66 GHz system profiles to aid interoperability specifications for Line-of-Sight broadband wireless access. Its peak (shared) data rate 70Mbits/s, with range up to 50km.

1.2.9 General features of IEEE 802.16d-2004 Fixed WiMAX

IEEE 802.16a has all but been forgotten as the focus recently has been on IEEE 802.16- 2004, which is also known as 802.16REVd .802.16-2004 is an improvement to the 802.16a Standard separately, 802.16-2004, was ratified in July 2004. 802.16-2004 is a wide-ranging standard that includes previous versions and covers both LOS and NLOS applications in the 2-66 GHz frequencies. The changes introduced in 802.16-2004 were focused on fixed and nomadic applications in the 2-11 GHz frequencies. Two multi-carrier modulation techniques are supported in 802.16-2004: OFDM with 256 carriers and OFDMA with 2048 carriers. IEEE 802.16-2004 is a fixed wireless access technology, meaning that it is designed to serve as a wireless DSL replacement technology, to compete with the incumbent DSL or broadband cable providers or to provide basic voice and broadband access in underserved areas where no other access technology exists; examples include developing countries and rural areas in developed countries where running copper wire or cable does not make economic sense.

802.16-2004 is also a viable solution for wireless backhaul for Wi-Fi access points or potentially for cellular networks, in particular if licensed spectrum is used. Finally, in certain configurations, WiMAX Fixed can be used to provide much higher data rates and therefore be used as a T1 replacement option for high-value corporate subscribers. 802.16-2004 can also support VoIP (Voice over Internet Protocol), and assuming that the G.729 (8kbps) codec is used, it reportedly supports up to 96 simultaneous voice calls in a 3.5MHz radio channel. The trade-off is increased path losses at frequencies such as 5.8GHz. It is unlikely that an operator would use 2.4GHz to offer voice services due to the higher probability that interference could develop (simple microwave ovens radiate RF in the 2.4GHz band).

1.2.10 General features of IEEE 802.16e Mobile WiMAX

IEEE 802.16e is the portable or mobile version of WiMAX, which promises to support voice and data sessions at vehicular speeds of up to 120 kilo-meters per hour. The current strategy within the WiMAX Forum is to launch 802.16e with portable features in order to achieve rapid time to market. As the technology and market opportunity matures, the forum intends to introduce full-scale mobility. The main features of mobile WiMAX are:

Approved on the 23th of September 2004.

Covers "Physical and Medium Access Control Layers for Combined Fixed and

Mobile Operation in Licensed Bands.

Optimized for and backwards compatible with fixed stations.

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Work on Licensed bands from 2 to 6 GHz.

The IEEE 802.16e introduces nomadic capabilities which allow users to connect to wireless Internet Service Provider (WISP) when they travel outside their home or business, or go to another city that also has a WISP.

It is targeted at mobile users, who will be able to keep their connection while moving or driving from 75 to 93 miles per hour.

It has proved to be the most controversial standard, as it overlaps with the authorization of the IEEE 802.20 group, which was establish before 802.16e.

Typical Channel BW < 5MHz.

Packet oriented architecture.

Channelization and control for multimedia services with QOS.

High efficiency data uplinks and downlinks Technology.

Low latency architecture.

1.3 WiMAX Spectrum Availability WiMAX 802.16-2004 and 802.16e operate at frequencies below 11GHz and 6GHz respectively.

So far the most viable spectrum is available at the unlicensed 2.4GHz and 5.8GHz bands, as well as the 2.3GHz, 2.5GHz and 3.5GHz licensed bands. In addition, it may be possible to use the700MHz analogue TV band (once released). With all these possible frequencies, the main issue is now one of worldwide interoperability and the fact that WiMAX devices may have to support multiple frequency bands to be globally compatible.

1.3.1 Licensed Band

The main issue with licensed spectrum is that it usually comes at a high price. It is however vital for operators carriers wanting to offer a high level quality service, ensuring exclusive use of the spectrum and thus protecting the users from unwanted interference.

700MHz Band - This band is currently utilized worldwide for analogue television broadcasters.

2.3GHz Band - In Australia, New Zealand and the United States, this band is currently utilized for other systems, such that the spectrum is not that attractive. It is also used in South Korea where it is used for WiBRO (Wireless Broadband), an early adoption of a WiMAX 802.16e standard.

2.5GHz Band - This band is gaining a lot of attention since it is available for use in North America and Latin America. It is also soon to be available across Europe, once the 3G (Third Generation)

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extension bands are auctioned off. This may cause issues since the band could be bought by 3G operator carrier wanting to improve their offering.

3.5GHz Band - This band is currently available for use in most countries with the exception of the United States. In many countries this band also has various regulator license restrictions, which in some cases limit the use of mobility.

1.3.2 Unlicensed Band

It is worth noting that the 2.4GHz and 5.8GHz are unlicensed bands and are currently being utilized by such technologies as Wi-Fi and Bluetooth. The term unlicensed spectrum implies that there is no regulation governing its use. However in Europe a concept of "light licensed" spectrum applies. In this scenario, the users have to indicate their intent to use this spectrum. The idea behind this is to enable regulators to identify usage and potentially control the number of licensees, thus minimizing unwanted loading and interference.

1.4 WiMAX Network Architecture The IEEE 802.16-2004 standard provides the air interface for WiMAX but does not define the full

end-to-end WiMAX network. The WiMAX Forum’s Network Working Group, is responsible for developing the end-to-end network requirements, architecture, and protocols for WiMAX, using IEEE 802.16e-2005 as the air interface.

The WiMAX NWG has developed a network reference model to serve as an architecture framework for WiMAX deployments and to ensure interoperability among various WiMAX equipment and operators.

The network reference model envisions unified network architecture for supporting fixed, nomadic, and mobile deployments and is based on an IP service model. Figure 2.3 shows a simplified illustration of IP-based WiMAX network architecture.

Figure1.3 WiMAX Network Architecture

Chapter 1 Overview of WiMAX technology

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1.4.1 WiMAX Network Reference Model (NRM)

WiMAX network reference model (NRM) is a logical representation of the network architecture (as shown Figure 1.4). The NRM identifies the functional entities in the architecture and the reference points between the functional entities over which interoperability is achieved. The NRM divides the end-to-end system into three logical parts:

1. Mobile Stations (MS) which used by the subscriber to access the network.

2. Access Service Network (ASN) which is owned by a NAP and comprises one or more base stations and one or more ASN gateways that form the radio access network.

3. Connectivity Service Network (CSN) which is owned by an NSP, and provides IP connectivity and all the IP core network functions. The subscriber is served from the CSN belonging to the visited NSP; the home NSP is where the subscriber belongs. In the no roaming case, the visited and home NSPs are the same.

Figure1.4 WiMAX Network reference model

The architecture allows for three separate business entities as we show in Figure 1.5

WiMAX Network Architecture

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1. Network Access Provider (NAP), which owns and operates the ASN.

2. Network Services Provider (NSP), which provides IP connectivity and WiMAX services. Subscribers using the ASN infrastructure provided by one or more NAPs.

3. Application Service Provider (ASP), which can provide value-added services such as multimedia applications. Using IMS (IP multimedia subsystem) and corporate VPN (virtual private networks) that on top of IP.

This separation between NAP, NSP, and ASP is designed to enable a richer ecosystem or WiMAX service business, leading to more competition and hence better services. The network reference model developed by the WiMAX Forum NWG defines a number of functional. Entities and interfaces between those entities. (The interfaces are referred to as reference points). Figure 1.4 shows some of the more important functional entities.

Base station (BS) The base station BS is responsible for providing the air interface to the MS. And additional

functions that may be part of the BS are micro mobility management functions, such as handoff triggering and tunnel establishment, radio resource management, QOS policy enforcement, traffic classification, DHCP (Dynamic Host Control Protocol) proxy, key management, session management, and multicast group management.

Access service network gateway (ASN-GW) The ASN gateway typically acts as a layer 2 traffic aggregation point within an ASN. Additional

functions that may be part of the ASN gateway include intra-ASN location management and paging, radio resource management and demission control, caching of subscriber profiles and encryption keys, AAA client functionality, establishment and management of mobility tunnel with base stations, QOS and policy enforcement, and foreign agent functionality for mobile IP, and routing to the selected CSN.

Connectivity service network (CSN) The CSN provides connectivity to the Internet, ASP, other public networks, and corporate

networks. The CSN is owned by the NSP and includes servers that support authentication for the devices, users, and specific services. The CSN also provides per user policy management of QOS and security. The CSN is also responsible for IP address management, support for roaming between different NSPs, location management between ASNs, and mobility and roaming between ASNs. Further, CSN can also provide gateways and interworking with other networks, such as PSTN (public switched telephone network), 3GPP, and 3GPP2.

The WiMAX architecture framework allows for the flexible decomposition and/or combination of functional entities when building the physical entities. For example, the ASN may be decomposed into base station transceivers (BST), base station controllers (BSC), and an ASNGW analogous to the GSM model of BTS, BSC, and Serving GPRS Support Node (SGSN). It is also possible to collapse the BS and ASN-GW into a single unit, which could be thought of as WiMAX router. Such a design is often referred

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to as a distributed, or flat, architecture. By not mandating a single physical ASN or CSN topology, the reference architecture allows for vendor/operator differentiation.

In addition to functional entities, the reference architecture defines interfaces, called reference points, between function entities. The interfaces carry control and management protocols mostly IETF-developed network and transport-layer protocols in support of several functions, such as mobility, security, and QOS, in addition to bearer data. Figure 1.5 shows an example. The WiMAX network reference model defines reference points between:

1. MS and the ASN, called R1, which in addition to the air interface includes protocols in the management plane.

2. MS and CSN, called R2, which provides authentication, service authorization, IP Configuration and mobility management.

3. ASN and CSN, called R3, to support policy enforcement and mobility Management.

4. ASN and ASN, called R4, to support inter-ASN mobility.

5. CSN and CSN, called R5, to support roaming across multiple NSP.

6. BS and ASN-GW, called R6, which consists of intra-ASN bearer paths and IP tunnels for mobility events.

7. BS to BS, called R7, to facilitate fast, seamless handover.

Figure1.5 Functions performed across reference points

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1.5 WIMAX Topologies

Figure1.6 WiMAX Various Topologies

1.5.1 Point-to-point (P2P)

Point to point is used where there are two points of interest: one sender and one receiver. This is also a scenario for backhaul or the transport from the data source (data center, co-Lo facility, fiber POP, Central Office, etc) to the subscriber or for a point for distribution using point to multipoint architecture. Backhaul radios comprise an industry of their own within the wireless industry. As the architecture calls for a highly focused beam between two points range and throughput of point-to point radios will be higher than that of point-to multipoint products, as shown in Figure 1.7.

Figure1.7 Point-to-point WiMAX Configurations

WiMAX Topologies

Point to Point (P2P)

Mesh Topology

Point to Multipoint

(P2MP)

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1.5.2 Point-to-Multipoint (PMP)

Point-to-multipoint is synonymous with distribution. One base station can service hundreds of dissimilar subscribers in terms of bandwidth and services, as shown in figure 1.8.

Figure1.8 Point-to-Multipoint WiMAX Configurations

1.5.3 Mesh Topology

Mesh topology is not supported by existing IEEE's wireless LAN standards but it becomes popular as city-wide (municipal) Wi-Fi network deployment gains more supporters day after day. In a mesh network, each node (i.e. base station or access point) connects to several neighboring nodes and on to a mesh gateway (i.e. a base station that aggregates the mesh network traffic and routes it to the Internet). Since each node has many routes to a mesh gateway, mesh network is very reliable. But mesh network is more complex to manage and poses interference challenge especially for operation in a license-exempt band such as in Wi-Fi case.

Line of sight (LOS) or Non-line of sight (NLOS)

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Figure1.9 Mesh Network with Wi-Fi and/or WiMAX

1.6 Line of sight (LOS) or Non-line of sight (NLOS) Earlier wireless technologies (LMDS, MMDS for example) were unsuccessful in the mass market

as they could not deliver services in non-line-of-sight scenarios. This limited the number of subscribers they could reach and, given the high cost of base stations and CPE, those business plans failed. WiMAX functions best in line of sight situations and, unlike those earlier technologies, offers acceptable range and throughput to subscribers who are not line of sight to the base station. Buildings between the base station and the subscriber diminish the range and throughput, but in an urban environment, the signal will still be strong enough to deliver adequate service. Given WiMAX's ability to deliver services non-line-of-sight, the WiMAX service provider can reach many customers in high-rise office buildings to achieve a low cost per subscriber because so many subscribers can be reached from one base station.

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Figure1.10 The difference between line o f sight and non-line of sight

1.7 WiMAX Antennas WiMAX antennas, just like the antennas for car radio, cell phone, FM radio, or TV, are designed

to optimize performance for a given application. The figure above illustrates the three main types of antennas used in WiMAX deployments. From top to bottom is an Omni directional, sector and panel antenna each has a specific function.

Figure1.11 Different antenna types are designed for different applications

1.7.1 Omni directional antenna

Omni directional antennas are used for point-to-multipoint configurations. The main drawback to an Omni directional antenna is that its energy is greatly diffused in broadcasting 360 degrees. This

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limits its range and ultimately signals strength. Omni directional antennas are good for situations where there are a lot of subscribers located very close to the base station. An example of Omni directional application is a Wi-Fi hotspot where the range is less than 100 meters and subscribers are concentrated in a small area.

Figure1.12 an Omni-directional antenna broadcasts 360 degrees from the base station

1.7.2 Sector antennas

A sector antenna, by focusing the beam in a more focused area, offers greater range and throughput with less energy. Many operators will use sector antennas to cover a 360-degree service area rather than use an Omni directional antenna due to the superior performance of sector antennas over an Omni directional antenna.

Figure1.13 Sector antennas are focused on smaller sectors

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1.7.3 Panel antennas

Panel antennas are usually a flat panel of about one foot square. They can also be a configuration where potentially the WiMAX radio is contained in the square antenna enclosure. Such configurations are powered via the Ethernet cable that connects the radio/antenna combination to the wider network.

That power source is known as Power over Ethernet (POE). This streamlines deployments, as there is no need to house the radio in a separate, weatherproof enclosure if outdoors or in a wiring closet if indoors. This configuration can also be very handy for relays.

Figure1.14 Panel antennas are most often used for point-to-point applications

1.8 Subscriber Stations The technical term for customer premise equipment (CPE) is subscriber station. The generally

accepted marketing terms now focus on either "mobile CPE" or "portable CPE". There are advantages and disadvantages to both deployment schemes as described below.

1.8.1 Mobile CPE

It is the CPE which can make a reliable connection during moving. It is required a hand off system to avoid interruption or cutting off the connection. Also mobile CPE has several restrictions in its size and the transmitted power.

Examples: mobile Handset as shown in figure 1.15

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Figure1.15 an mobile WiMAX CPE device

1.8.2 Portable CPE

It is the CPE that can be kept in bag and has a larger size than mobile CPE and its transmitted power is higher than mobile CPE. It doesn’t require hand off for its connection.

Examples: PCMCIA in laptop as shown in figure 1.16

Figure1.16 Portable WiMAX CPE with PCMCIA

1.9 WiMAX Technical specifications WiMAX is a wireless metropolitan broadband solution that offers a rich set of features with a lot

of flexibility in terms of deployment options and potential service offerings. Some of the more salient features that deserve highlighting in that section, the basic WiMAX features are:

OFDM-based physical layer The WiMAX physical layer (PHY) is based on orthogonal frequency division multiplexing, a

scheme that offers good resistance to multipath, and allows WiMAX to operate in NLOS conditions. OFDM is now widely recognized as the method of choice for mitigating multipath for broadband wireless.

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Very high peak data rates WiMAX is capable of supporting very high peak data rates. In fact, the peak PHY data rate can be

as high as 74Mbps when operating using a 20MHz2 wide spectrum. More typically, using a 10MHz spectrum operating using TDD scheme with a 3:1 downlink-to-uplink ratio, the peak PHY data rate is about 25Mbps and 6.7Mbps for the downlink and the uplink, respectively. These peak PHY data rates are achieved when using 64 QAM modulations with rate 5/6 error-correction coding. Under very good signal conditions, even higher peak rates may be achieved using multiple antennas and spatial multiplexing.

Scalable bandwidth and data rate support WiMAX has a scalable physical-layer architecture that allows for the data rate to scale easily

with available channel bandwidth. This scalability is supported in the OFDMA mode, where the FFT (fast Fourier transform) size may be scaled based on the available channel bandwidth. For example, a WiMAX system may use 128,512, or 1,048-bit FFTs based on whether the channel bandwidth is 1.25MHz, 5MHz, or10MHz, respectively. This scaling may be done dynamically to support user roaming across different networks that may have different bandwidth allocations.

Adaptive modulation and coding (AMC) WiMAX supports a number of modulation and forward error correction (FEC) coding schemes

and allows the scheme to be changed on a per user and per frame basis, based on channel conditions. AMC is an effective mechanism to maximize throughput in a time-varying channel. The adaptation algorithm typically calls for the use of the highest modulation and coding scheme that can be supported by the signal-to-noise and interference ratio at the receiver such that each user is provided with the highest possible data rate that can be supported in their respective links.

Link-layer retransmissions For connections that require enhanced reliability, WiMAX supports automatic retransmission

requests (ARQ) at the link layer. ARQ-enabled connections require each transmitted packet to be acknowledged by the receiver; unacknowledged packets are assumed to be lost and are retransmitted. WiMAX also optionally supports hybrid-ARQ, which is an effective hybrid between FEC and ARQ.

Support for TDD and FDD

IEEE 802.16-2004 and IEE802.16e-2005 supports time division duplexing and frequency division duplexing, as well as a half-duplex FDD, which allows for a low-cost system implementation.

TDD is favored by a majority of implementations because of its advantages:

Flexibility in choosing uplink-to-downlink data rate ratios.

Ability to exploit channel reciprocity.

Ability to implement in nonpayer spectrum.

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Less complex transceiver design. All the initial WiMAX profiles are based on TDD, except for two fixed WiMAX profiles in 3.5GHz.

Orthogonal frequency division multiple access (OFDMA) Mobile WiMAX uses OFDM as a multiple-access technique, whereby different users can be

allocated different subsets of the OFDM tones; OFDMA facilitates the exploitation of frequency diversity and multi-user diversity to significantly improve the system capacity.

Flexible and dynamic per user resource allocation Both uplink and downlink resource allocation are controlled by a scheduler in the base station.

Capacity is shared among multiple users on a demand basis, using a burst TDM scheme. When using the OFDMA-PHY mode, multiplexing is additionally done in the frequency dimension, by allocating different subsets of OFDM sub carriers to different users. Resources may be allocated in the spatial domain as well when using the optional advanced antenna systems (AAS). The standard allows for bandwidth resources to be allocated in time, frequency, and space and has a flexible mechanism to convey the resource allocation information on a frame-by-frame basis.

Support for advanced antenna techniques The WiMAX solution has a number of hooks built into the physical-layer design, which allows for

the use of multiple-antenna techniques, such as beam forming, space-time coding, and spatial multiplexing. These schemes can be used to improve the overall system capacity and spectral efficiency by deploying multiple antennas at the transmitter and/or the receiver.

Quality-of-service support The WiMAX MAC layer has a connection-oriented architecture that is designed to support a

variety of applications, including voice and multimedia services. The system offers support for constant bit rate, variable bit rate, real-time, and non-real-time Traffic flows, in addition to best-effort data traffic. WiMAX MAC is designed to support a large number of users, with multiple connections per terminal, each with its own QOS requirement.

Robust security WiMAX supports strong encryption, using Advanced Encryption Standard (AES), and has a robust

privacy and key-management protocol. The system also offers Avery flexible authentication architecture based on Extensible Authentication Protocol (EAP), which allows for a variety of user credentials, including username/password, digital certificates, and smart cards.

Support for mobility The mobile WiMAX variant of the system has mechanisms to support secure seamless

handovers for delay-tolerant full-mobility applications, such as VoIP. The system also has built-in support for power-saving mechanisms that extend the battery life of handheld subscriber devices. Physical-layer enhancements, such as more frequent channel estimation, uplink subchannelization, and power control, are also specified in support of mobile applications.

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IP-based architecture The WiMAX Forum has defined reference network architecture that is based on an all-IP

platform. All end-to-end services are delivered over an IP architecture relying on IP-based protocols for end-to-end transport, QOS, session management, security, and mobility. Reliance on IP allows WiMAX to ride the declining cost curves of IP processing, facilitate easy convergence with other networks, and exploit the rich ecosystem for application development that exists for IP.

1.10 WiMAX Advantages Flexible Architecture

WiMAX supports several system architectures, including Point-to-Point, Point to- Multipoint, and ubiquitous coverage. The WiMAX MAC (Media Access Control) supports Point-to-Multipoint and ubiquitous service by scheduling a time slot for each Subscriber Station (SS). If there is only one SS in the network, the WiMAX Base Station (BS) will communicate with the SS on a Point-to-Point basis. A BS in a Point-to-Point configuration may use a narrower beam antenna to cover longer distances.

High Security WiMAX supports AES (Advanced encryption Standard) and 3DES (Triple DES, where DES is the

Data Encryption Standard). By encrypting the links between the BS and the SS, WiMAX provides subscribers with privacy (against eavesdropping) and security across the broadband wireless interface. Security also provides operators with strong protection against theft of service. WiMAX also has built-in VLAN support, which provides protection for data that is being transmitted by different users on the same BS.

WiMAX QOS WiMAX can be dynamically optimized for the mix of traffic that is being carried. Four types of

service are supported.

Quick Deployment Compared with the deployment of wired solutions, WiMAX requires little or no external plant

construction. For example, excavation to support the trenching of cables is not required.

Operators that have obtained licenses to one of the licensed bands, or that plan to use one of the unlicensed bands, do not need to submit further applications to the Government. Once the antenna and equipment are installed and powered, WiMAX is ready for service. In most cases, deployment of WiMAX can be completed in a matter of hours, compared with months for other solutions.

Multi-Level Service The manner in which QOS is delivered is generally based on the Service Level Agreement (SLA)

between the service provider and the end-user. Further, one service provider can offer different SLAs to different subscribers, or even to different users on the same SS.

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Interoperability WiMAX is based on international, vendor-neutral standards, which make it easier for end-users

to transport and use their SS at different locations, or with different service providers. Interoperability protects the early investment of an operator since it can select equipment from different equipment vendors, and it will continue to drive the costs of equipment down because of mass adoption.

Portability As with current cellular systems, once the WiMAX SS is powered up, it identifies itself,

determines the characteristics of the link with the BS, as long as the SS is registered in the system database, and then negotiates its transmission characteristics accordingly.

Mobility The IEEE 802.16e amendment has added key features in support of mobility. Improvements

have been made to the OFDM and OFDMA physical layers to support devices and services in a mobile environment. These improvements, which include Scalable OFDMA, MIMO, and support for idle/sleep mode and hand-off, will allow full mobility at speeds up to 160 km/hr. The WiMAX Forum-supported standard has inherited OFDM’s superior NLOS (Non-Line Of Sight) performance and multipath-resistant operation, making it highly suitable for the mobile environment.

Cost-effective WiMAX is based on an open, international standard. Mass adoption of the standard, and the use

of low-cost, mass-produced chipsets, will drive costs down dramatically, and the resultant competitive pricing will provide considerable cost savings for service providers and end-users.

Wider Coverage WiMAX dynamically supports multiple modulation levels, including BPSK, QPSK, 16-QAM, and

64-QAM. When equipped with a high-power amplifier and operating with a low-level modulation (BPSK or QPSK, for example), WiMAX systems are able to cover a large geographic area when the path between the BS and the SS is unobstructed.

Non-Line-of-Sight Operation NLOS usually refers to a radio path with its first Fresnel zone completely blocked. WiMAX is

based on OFDM technology, which has the inherent capability of handling NLOS environments. This capability helps WiMAX products deliver broad bandwidth in a NLOS environment, which other wireless product cannot do.

High Capacity Using higher modulation (64-QAM) and channel bandwidth (currently 7MHz, with planned

evolution towards the full bandwidth specified in the (associated IEEE and ETSI standards), WiMAX systems can provide significant bandwidth to end users

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1.11 WiMAX Applications WiMAX technology will revolutionize the way we communicate. It will provide total freedom to

people who are highly mobile, allowing them to stay connected with voice, data and video services. WiMAX will allow people to go from their homes to their cars, and then travel to their offices or anywhere in the world, all seamlessly. To illustrate the ability of WiMAX to address the applications outlined in the preceding section, several representative usage scenarios, grouped into two broad categories – private and public networks are outlined in the following sections.

1.11.1 Private Networks

Private networks, used exclusively by a single organization, institution or business, offer dedicated communication links for the secure and reliable transfer of voice, data and video. Quick and easy deployment is generally a high priority, and configurations are typically Point-to-Point or Point-to-Multipoint.

1.11.2 Cellular Backhaul

The market for cellular services is becoming more and more competitive. To stay in the business, cellular operators are constantly looking for ways to reduce operating costs. Backhaul costs for cellular operators represent a significant portion of their recurring costs.

WiMAX can provide Point-to-Point links of up to 30 miles (50 km), with data rates capable of supporting multiple E1/T1s Cellular operators can therefore use WiMAX equipment to backhaul Base Station traffic to their Network Operation and Switching Centers, as shown in Figure 1.18

Figure1.18 Cellular Backhaul

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Note: Based on the availability of spectrum for WiMAX in different countries, the cellular backhaul application may or may not be able to handle nationwide networks.

Cellular traffic is a mix of voice and data, for which the built-in QOS feature of WiMAX is highly suited. Leasing backhaul facilities from local telephone companies can be cost prohibitive, and deploying a fiber solution, which is both costly and time consuming, could negatively impact rollout of service. Wired solutions for providing cellular backhaul are seldom cost-effective in rural or suburban areas, and most versions of DSL and cable technology cannot offer the required bandwidth, especially for backhauling upcoming 3G networks.

1.11.3 Wireless Service Provider Backhaul

Wireless Service Providers (WSPs) use WiMAX equipment to backhaul traffic from Base Stations in their access networks as shown in Figure 1.19.

Figure1.19 Wireless Service Provider Backhaul

Access networks may be based on Wi-Fi, WiMAX or any proprietary wireless access technology. If the access network uses Wi-Fi equipment, the overall WSP network is referred to as a Hot Zone. Since WSPs typically offer voice, data and video, the built-in QOS feature of WiMAX will help prioritize and optimize the backhauled traffic. WiMAX equipment can be deployed quickly, facilitating a rapid rollout of the WSP network.

As already illustrated, leasing backhaul facilities from the local telephone company will increase operating costs, and deployment of a fiber solution can be very costly and requires significant lead

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times, negatively impacting rollout. Furthermore, fiber, DSL and cable are not cost-effective in rural and suburban areas, and most versions of DSL and cable technology will not provide the capacity required for these networks.

1.11.4 Banking Networks

Large banks can connect branches and ATM sites to their regional office through a private WiMAX network carrying voice, data and video traffic, as shown in Figure 1.20 These banks are normally spread over a large area and need high security and bandwidth to handle the traffic.

Figure1.20 Banking Networks

WiMAX data encryption offers excellent link security, however, banks will most likely also need end-to-end security, such as that provided by SSL, to protect against undesired interception and manipulation of sensitive banking traffic.

The broad coverage and high capacity allows the bank’s regional office to be connected to a large number of diversely located brand offices and ATM sites. WiMAX networks also offer a high degree of scalability, so that low-data-rate traffic between the regional office and ATM machines can co-exist with the high levels of traffic needed to support branch-to-regional office communications. The WiMAX QOS, which is used to prioritize voice (telephony among branches), data (financial transactions, email,

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Internet, and intranet) and video (surveillance, CCTV) traffic make this possible. It is desirable for banks to own their own networks, for a number of reasons.

Besides eliminating the repeat costs charged by telephone companies, this will provide banks the ability to quickly redeploy their network if an ATM or branch is temporarily or permanently relocated. In addition to their inability to be quickly deployed, most versions of DSL and cable technology will not provide the bandwidth required to support and sustain branch-to-regional office communications.

1.11.5 Education Networks

School boards can use WiMAX networks to connect schools and school board offices within a district, as shown in Figure 1.21. Some of the key requirements for a school system are NLOS, high bandwidth (>15 Mbps), Point-to-Point and Point-to- Multipoint capability, and a large coverage footprint.

Figure1.21 Education Networks

WiMAX-based education networks, using QOS, can deliver the full range of communication requirements, including telephony voice, operating data (such as student records), email, Internet and

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intranet access (data), and distance education (video)between the school board office and all of the schools in the school district, and between the schools themselves.

In the above scenario, the camera at School B delivers real-time classroom instruction to School A, allowing the schools to simultaneously deliver instruction from a recognized subject-matter expert to a large number of students, eliminating the need for additional instructors. The WiMAX solution provides broad coverage, making it very cost-effective, particularly for rural schools, which may have little or no communications infrastructure, and which are widely dispersed when school boards.

Own and operate their own network, they can be responsive to changes in the location and layout of their facilities. This will significantly reduce the annual operating cost of leased lines. Wired solutions cannot offer a quickly deployable, low-cost solution, and most versions of DSL and cable technology do not have the throughput required by these education networks.

1.11.6 Public Safety

Government public safety agencies, such as police, fire, and search and rescue, can use WiMAX networks to support response to medical and other emergency situations, as shown in Figure 1.22.

Figure1.22 Public Safety

In addition to providing two-way voice communications between the dispatch center and on-site emergency response teams, the network relays video images and data from the site of the accident or disaster to the control center. This data can be relayed to expert teams of medical or emergency staff, who can analyze the situation in real-time, as if they were on site. WiMAX QOS allows the network to handle these diverse types of traffic.

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WiMAX solutions are highly deployable, so the initial response team can set up a temporary wireless network at the site of the accident, event, or natural disaster, in a matter of minutes. They can also relay traffic from this network back to a control or dispatch center, over an existing WiMAX network. Wired solutions are not appropriate situations like these, due to unpredictability and instability of accidents and disasters. As well, there may be a requirement for mobility, such as, for example, a police officer having to access a database from a moving vehicle, or a fireman having to download information about the best route to a fire scene or the architecture of the building on fire.

A video camera in the ambulance can offer advance information about the condition of a patient, before the ambulance reaches the hospital. In all of these cases, WiMAX provides support for mobility and high bandwidth, which narrowband systems cannot deliver.

1.11.7 Offshore Communications

Oil and gas producers can use WiMAX equipment to provide communication links from land-based facilities to oilrigs and platforms, to support remote operations, security, and basic communications, as shown in Figure 1.23.

Figure1.23 Offshore Communications

Remote operations include remote troubleshooting of complex equipment problems, site monitoring, and database access. For example, video clips of malfunctioning components or subassemblies can be transmitted to a land-based team of experts for analysis.

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Security includes alarm monitoring and video surveillance. Basic communications includes voice telephony, email, Internet access, and video conferencing. WiMAX networks are quickly and easily deployed.

The network can be set up or redeployed in a matter of hours, if not minutes, even when oilrigs and platforms are moved to other locations. Wired solutions are not appropriate for this scenario, because the facilities are offshore, and since oilrigs are temporarily located and moved regularly within the oil or gas field. In the event of having to temporarily abandon an offshore facility, communications for monitoring the status of the asset can continue to be maintained, using battery-backed WiMAX terminals.

1.11.8 Campus Connectivity

Government agencies, large enterprises, industrial campuses, transportation hubs, universities, and colleges, can use WiMAX networks to connect multiple locations, sites and offices within their campus, as shown in Figure 1.24.

Campus systems require high data capacity, low latency, a large coverage footprint, and high security. Like other usage scenarios, campus networks carry a mix of voice, data, and video, which the WiMAX QOS helps prioritize and optimize.

It takes less time and resources to interconnect a campus through a WiMAX network, since excavation and external construction are not required. Some campuses have been around for a long time, and digging trenches for cable may not be permitted. In such cases, WiMAX solutions may be one of the most effective ways to interconnect campus buildings.

Even if wired installations are permitted, the lead-time to deploy a wired solution is much longer than the lead-time to deploy a WiMAX solution, without offering any accompanying benefits.

Figure1.24 Campus Connectivity

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1.11.9 Temporary Construction Communications

Construction companies can use WiMAX networks to establish communication links between the company head office, construction sites, offices of other project participants, such as architectural and engineering firms, and storage facilities, as shown in Figure 1.25.

The fast deploy ability of WiMAX networks is also important in this scenario, since it allows for quick provision of communications to the construction site, including voice (telephony) and data (emails, engineering drawings, and Internet access). Surveillance video can also be carried over the network to support monitoring of the site or areas of the site that are otherwise difficult to access. A local Hotspot can also be set up at the construction site, allowing personnel at the site to communicate and exchange data and schedule information. Like the other usage scenarios, the WiMAX built-in QOS will prioritize network traffic and optimize the communications channel. Construction sites include, but are not limited to, office buildings, residential land development, and oil and gas facilities. Since construction activity at these sites is temporary, wired solutions are usually not appropriate. WiMAX equipment, being highly portable, can be redeployed and reused at other construction sites.

Figure1.25 Temporary Construction Communications

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1.11.10 Theme Parks

Theme park operators can use WiMAX to deliver a broad range of communication services for their amusement parks, expositions, hospitality and operation censers, and buses and service vehicles, as shown in Figure 1.26. The above network can support a wide range of communications traffic, including two-way dispatch from a control center, video surveillance throughout the park, reservation data, inventory database access and update, site status monitoring, video on demand, and voice telephony. Some of the key requirements for a system like this are support for fixed and mobile operations, high security, scalable architecture and low latency.

The broad coverage range of WiMAX means an entire park can be covered from only 2 numbers of Base Stations, scalable upwards as capacity requirements increase. The WiMAX QOS MAC will prioritize and optimize the communications channel, based on the operator's requirements. Re-deployment of the network, in response to changes in theme park facilities, is straightforward and simple, unlike the changes that would be required had the park been served by wired facilities, such as DSL or cable. WiMAX mobility capability will support two way voice and data communications to the theme park’s tour buses and service vehicles. Real-time video can be broadcast to tour buses, providing tourist information, promotions, and weather to passengers.

Figure1.26 Theme Parks

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1.11.11 Public Networks

In public network, resources are accessed and shared by different users, including both businesses and private individuals. Public networks generally require a cost-effective means of providing ubiquitous coverage, since the location of the users is neither predictable nor fixed. The main applications of public networks are voice and data communication, although video communication is becoming increasingly popular.

Security is a critical requirement, since many users share the network. Built-in VLAN support and data encryption address these concerns several usage scenarios involving public networks.

1.11.12 Wireless Service Provider Access Network

Wireless Service Providers (WSPs) use WiMAX networks to provide connectivity to both residential (voice, data and video) and business (primarily voice and Internet) customers, as shown in Figure 1.27.

The WSP could be a CLEC (Competitive Local Exchange Carriers) that is starting its business with little or no installed infrastructure. Since WiMAX is easy to deploy, the CLEC can quickly install its network and be in position to compete with the ILEC (Incumbent Local Exchange Carrier). The WiMAX built-in QOS mechanism is highly suited for the mix of traffic carried by the CLEC. The QOS MAC also offers multi-level service to address the variety of customer service needs. A common network platform, offering voice, data and video, is highly attractive to end customers, because it presents a one-stop shop and a single monthly bill.

Figure1.27 Wireless Service Provider Access Network

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Support for multiple service types allows for different revenue streams, yet it reduces customer acquisition cost, and increases ARPU (Average Revenue per User). The WSP needs only one billing system and one customer database. Cellular operators may also be interested in applying WiMAX in their networks. These operators already have towers, billing infrastructure and a customer base in place, but the deployment of a WiMAX solution will expand their market presence in their service area.

All of the wired solutions, including fiber, DSL, and cable, require substantial upfront costs for implementing the wired infrastructure. In particular, wired solutions are not suited for markets in developing countries, where there is very little infrastructure, or in the less-populated areas of developed countries, such as rural areas, small towns or the suburban edges of major centers.

1.11.13 Rural Connectivity

Service providers use WiMAX networks to deliver service to underserved markets in rural areas and the suburban outskirts of cities, as shown in Figure 1.28.

The delivery of rural connectivity is critical in many developing countries and underserved areas of developed countries, where little or no infrastructure is available. Rural connectivity delivers much-needed voice telephony and Internet service. Since the WiMAX solution it provides extended coverage; it is a much more cost-effective solution than wired technology in areas with lower population densities.

WiMAX solutions can be deployed quickly, providing communication links to these underserved areas, providing more secure environment, and helping to improve their local economies.

Figure1.28 Rural Connectivity

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1.12 Conclusion WiMAX offers benefits for wire line operators who want to provide last mile access to

residences and businesses, either to reduce costs in their own operating areas, or as a way to enter new markets. 802.16e offers cost reductions to mobile operators who wish to offer broadband IP services in addition to 2G or 3G voice services, and allows operators to enter new markets with competitive services, despite owning disadvantaged spectrum. The capital outlay for WiMAX equipment will be less than for traditional 2G and 3G wireless networks, although the supporting infrastructure of cell sites, civil works, and towers and so on will still be needed. WiMAX’s all-IP architecture lends itself well to high bandwidth multi-media applications, and with QOS will support mobile voice and messaging services, re-using the mobile networks IP core systems.

The latest developments in the IEEE 802.16 group are driving a broadband wireless access (r) evolution thanks to a standard with unique technical characteristics. In parallel, the WiMAX forum, backed by industry leaders, helps the widespread adoption of broadband wireless access by establishing a brand for the technology. Initially, WiMAX will bridge the digital divide and thanks to competitive equipment prices, the scope of WiMAX deployment will broaden to cover markets with high DSL unbundling costs or poor copper quality, which have acted as a brake on extensive high-speed Internet and voice over broadband. WiMAX will reach its peak by making Portable Internet a reality.

When WiMAX chipsets are integrated into laptops and other portable devices, it will provide high-speed data services on the move, extending today's limited coverage of public WLAN to metropolitan areas. Integrated into new generation networks with seamless roaming between various accesses, it will enable end-users to enjoy an "Always Best Connected" experience.

The combination of these capabilities makes WiMAX attractive for a wide diversity of people: fixed operators, mobile operators and wireless ISPs (Internet Service Provider), but for many vertical markets and local authorities. Alcatel, the worldwide broadband market leader with a market share in excess of 37%, is committed to offer complete support across the entire investment and operational cycle required for successful deployment of WiMAX services.

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2.1 Introduction 2.1.1 History of OFDM

Orthogonal frequency-division multiplexing, or OFDM, is a process of digital modulation that is used in communication technology today. During the last few years wireless communication system has been transferred from low data-rate system to high data-rate system containing of voice, images and even to videos.

The goal of third and fourth generation mobile networks is to provide users with a high data rate, and to provide a wider range of services, such as voice communications, videophones, and high speed Internet access. The higher data rate of future mobile networks will be achieved by increasing the amount of spectrum allocated to the service and by improvements in the spectral efficiency. OFDM is a potential candidate for the physical layer of fourth generation mobile systems. This thesis presents techniques for improving the spectral efficiency of OFDM systems applied in WLAN and mobile networks.

The history of OFDM goes back to the 1960’s. At the time, there was a need to make more efficient use of bandwidth transmissions without creating situations where signals would be subject to a phenomenon referred to as crosstalk.

The concept dates back some 40 years. This brief history of OFDM cites some landmark dates.

At 1960: The OFDM technique was used in several high-frequency military systems such as KINEPLEX, ANDEFT, and KATHRYN.

At 1966: Chang shows that multicarrier modulation can solve the multipath problem without reducing data rate. This is generally considered the first official publication on multicarrier modulation. Some earlier work was Hollinger's 1964 MIT dissertation and some of Gallager's early work on water filling.

At 1971: Weinstein and Ebert show that multicarrier modulation can be accomplished using a DFT.

At 1985: Cimini at Bell Labs identifies many of the key issues in OFDM transmission and does a proof-of-concept design.

At 1993: DSL adopts OFDM, also called discrete multi tone, following successful field trials/competitions at Bellcore versus equalizer-based systems.

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At 1999: The IEEE 802.11 committee on wireless LANs releases the 802.11a standard for OFDM operation in 5GHz UNI band.

At 2002: The IEEE 802.16 committee releases an OFDM-based standard for wireless broadband access for metropolitan area networks under revision 802.16a.

At 2003: The IEEE 802.11 committee releases the 802.11g standard for operation in the 2.4GHz band.

At 2004: The multiband OFDM standard for ultra-wideband is developed, showing OFDM's usefulness in low SNR systems.

2.1.2 What is OFDM?

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique that has recently found wide adoption in a widespread variety of high-data rate communication systems, including digital subscriber lines, wireless LANs (802.11a/g/n), digital video broadcasting, and now

WiMAX (802.16e/f/g/k) and other emerging wireless broadband systems as shown in Figure 2.1.

Figure2.1 Conceptual scheme of a multi-carrier transmission system

OFDM is one of the applications of a parallel-data-transmission reduces the influence of multipath fading and makes complex equalizers unnecessary as shown in Figure 2.2.

Figure2.2 parallel-data-transmission scheme

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In OFDM systems, the spectrum of individual subcarrier is overlapped with minimum frequency spacing, which is carefully designed so that each subcarrier is orthogonal to the other subcarriers. The bandwidth efficiency of OFDM is another advantage as shown in Figure 2.3.

Figure2.3 Frequency response of the subcarriers in a 5 tone OFDM

OFDM is a multiplexing technique that subdivides the bandwidth into multiple frequency sub-carriers.

In an OFDM system, the input data stream is divided into several parallel sub-streams of reduced data rate (thus increased symbol duration) and each sub-stream is modulated and transmitted on a separate orthogonal sub-carrier.

OFDM can be viewed as either a modulation technique or a multiplex technique. In case of Modulation technique, it viewed by the relation between input and output signals. On the other hand from Multiplex technique, OFDM is viewed as the output signal which is the linear sum of the modulated signal.

OFDM is a method of using many carrier waves instead of only one, and using each carrier wave for only part of the message.

OFDM uses the principles of FDM to allow multiple messages to be sent over a single radio channel. It is however in a much more controlled manner, allowing an improved spectral efficiency.

Each carrier in an OFDM signal has a very narrow bandwidth (i.e. 1 kHz), thus the resulting symbol rate is low. This results in the signal having a high tolerance to multipath delay spread, as the delay spread must be very long to cause significant inter-symbol interference (e.g. > 100 ms).

2.1.3 Advantages and Disadvantages

Advantages:

Immunity to delay spread and multipath, Robust against Inter-symbol interference (ISI) and fading caused by multipath propagation.

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Resistance to frequency selective fading.

Simple equalization, Robust against narrow-band co-channel interference.

Efficient bandwidth usage, High spectral efficiency.

Robust against Inter-symbol interference (ISI) and fading caused by multipath propagation.

Low sensitivity to time synchronization errors.

Efficient implementation using FFT.

Tuned sub-channel receiver filters are not required (unlike conventional FDM).

Multiuser diversity: OFDMA allows different users to transmit over different portions of the broadband spectrum (traffic channel).

Receiver simplicity: OFDMA has the merit of easy decoding at the receiver side, as it eliminates the intra-cell interference avoiding CDMA type of multi-user detection.

Disadvantages:

Sensitive to carrier frequency offset and phase noise .

The Peak-to-Average Ratio (PAG) which tends to reduce the power efficiency of the radio frequency (RF) amplifier.

Sensitive to Doppler shift.

Nonlinear effects generated by the power amplifier may introduce intercarrier- interference and thus destroy the orthogonality.

2.1.4 Comparison among different multiplexing techniques

2.1.4.1 OFDM versus FDM

OFDM is different from FDM in several ways. In conventional broadcasting each radio station transmits on a different frequency, effectively using FDM to maintain a separation between the stations. There is however no coordination or synchronization between each of these stations.

With an OFDM transmission such as Digital Audio Broadcasting (DAB), the information signals from multiple stations are combined into a single multiplexed stream of data. This data is then transmitted using an OFDM ensemble that is made up from a dense packing of many subcarriers. All the subcarriers within the OFDM signal are time and frequency synchronized to each other, allowing the interference between subcarriers to be carefully controlled.

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These multiple subcarriers overlap in the frequency domain, but do not cause Inter-Carrier Interference (ICI) due to the orthogonal nature of the modulation.

Typically with FDM the transmission signals need to have a large frequency guard band between channels to prevent interference. This lowers the overall spectral efficiency. However with OFDM the orthogonal packing of the subcarriers greatly reduces this guard band, improving the spectral efficiency.

In FDM the total signal frequency band is divided into N non-overlapping frequency subchannels. Each subchannel is modulated with a separate symbol, and then the N subchannels are frequency multiplexed. It seems good to avoid spectral overlap of channels to eliminate inter-channel interference. However, this leads to inefficient use of the available spectrum.

OFDM use parallel data and FDM with overlapping subchannels, in which each, carrying a signaling rate b, is spaced b apart in frequency to avoid the use of high-speed equalization and to combat impulsive noise and multipath distortion, as well as to use the available bandwidth fully.

Figure 2.4 show the difference between the conventional non-overlapping multicarrier technique and the overlapping multicarrier modulation technique.

By using the overlapping multicarrier modulation technique, we save almost 50% of bandwidth. To realize this technique, however, we need to reduce cross talk between SCs, which means that we want orthogonality between the different modulated carriers, this overcomes the problem of overhead carrier spacing required in FDMA.

Figure2.4 Concept of the OFDM signal

(a) Conventional multicarrier technique (FDM). (b) Orthogonal multicarrier modulation.

2.1.4.2 OFDM versus TDM

TDM systems transmit data in a buffer and burst method, thus the transmission of each channel is non-continuous. The input data to be transmitted is buffered over the previous frame and burst transmitted at a higher rate during the time slot for the channel.

(a) (b)

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TDMA cannot send analog signals directly due to the buffering required, thus are only used for transmitting digital data. TDMA can suffer from multipath effects as the transmission rate is generally very high, resulting in significant inter-symbol interference.

There is an overhead associated with the change over between users due to time slotting on the channel. A change B over time must be allocated to allow for any tolerance in the start time of each user, due to propagation delay variations and synchronization errors. This limits the number of users that can be sent efficiently in each channel. In addition, the symbol rate of each channel is high (as the channel handles the information from multiple users) resulting in problems with multipath delay spread as shown in Figure 2.5.

Figure2.5 TDMA scheme where each user is allocated a small

OFDM exploits the frequency diversity of the multipath channel by coding and interleaving the information across the sub-carriers prior to transmissions. Complex equalizers are not required to compensate for frequency selective fading.

OFDMA therefore, is very well-suited to support smart antenna technologies. The increased symbol duration improves the robustness of OFDM to delay spread.

Furthermore, the introduction of the cyclic prefix (CP) can completely eliminate Inter-Symbol Interference (ISI) as long as the CP duration is longer than the channel delay spread. OFDM splits the available bandwidth into many narrow band channels (typically 100-8000).

Because of this there is no great need for users to be time multiplex as in TDMA, thus there is no overhead associated with switching between users.

2.1.4.3 OFDM versus CDMA

The CDMA signal is generated by modulating the data by the PN sequence. The modulation is performed by multiplying the data (XOR operator for binary signals) with the PN

sequence as shown in Figure 2.6.

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Figure2.6 Conventional CDMA PN Code sequence

CDMA is achieved by modulating the data signal by a pseudo random noise sequence (PN code), which has a chip rate higher than the bit rate of the data. The PN code sequence is a sequence of ones and zeros.

CDMA can suffer from two problems, Near Far Problem (NFP) so in CDMA cellular, the base station uses a fast closed-loop power control scheme to tightly control each mobile's transmit power, And the other problem Multiple Access Interference (MAI) These PN sequences are statistically uncorrelated, and the sum of a large number of PN sequences results in Multiple Access Interference (MAI) that is approximated by a Gaussian noise process. If all of the users are received with the same power level, then the variance (e.g., the noise power) of the MAI increases in direct proportion to the number of users.

At OFDM the carriers for each channel are made orthogonal to one another, allowing them to be spaced very close together.

OFDM was found to perform very well compared with CDMA, with it out-performing CDMA in many areas for a single and multi-cell environment. OFDM was found to allow up to 2-10 times more users than CDMA in a single cell environment and from 0.7 – 4 times more users in a multi-cellular environment. The difference in user capacity between OFDM and CDMA was dependent on whether cell sectorization and voice activity detection is used.

2.1.5 Applications

Broadcasting:

DAB (Digital Audio Broadcasting)

DVB (Digital Video Broadcasting)

WLAN (Wireless Local Area Networks):

IEEE 802.11a

Hyper LAN/2

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Wireless MAN (Wireless Metropolitan Area Networks)

IEEE 802.16 (WiMAX)

2.2 Basics of OFDM 2.2.1 Orthogonality

The subcarriers are orthogonal to each other when we multiply the waveforms of any two subcarriers and integrate over the symbol period the result is zero. The orthogonality of the carriers means that each carrier has an integer number of cycles over a symbol period. Due to this, the spectrum of each carrier has a null at the centre frequency of each of the other carriers in the system as shown in Figure 2.7.

Figure2.7 (A) Basis functions of an OFDM signal with N=16 carriers represented in frequency domain

(B) Resulting spectrum from the basic functions.

This results in no interference between the carriers, allowing then to be spaced as close as theoretically possible. This overcomes the problem of overhead carrier spacing required in OFDM.

Signals are orthogonal if they are mutually independent of each other. Orthogonality is a property that allows multiple information signals to be transmitted perfectly over a common channel and detected without interference.

OFDM achieves orthogonality in the frequency domain by allocating each of the separate information signals onto different subcarriers.

OFDM signals are made up from a sum of sinusoids, with each corresponding to a sub carrier.

(A) (B)

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The base band frequency of each sub carrier is chosen to be an integer multiple of the inverse of the symbol time, resulting in all subcarriers having an integer number of cycles per symbol. As a consequence the subcarriers are orthogonal to each other.

Sets of functions are orthogonal to each other if they match the conditions in equation 2.1. If any two different functions within the set are multiplied, and integrated over a symbol period, the result is zero, for orthogonal functions.

0 (2.1)

Another way of thinking of this is that if we look at a matched receiver for one of the orthogonal functions, a sub carrier in the case of OFDM, then the receiver will only see the result for that function. The results from all other functions in the set integrate to zero, and thus have no effect, and equation 2.2 shows a set of orthogonal sinusoids, which represent the subcarriers for an unmodulated real OFDM signal. sin 2 0 1,2,3 … 0 (2.2)

Where: f0 is the carrier spacing, M is the number of carriers, T is the symbol period. Since the highest frequency component is Mf0 the transmission bandwidth is also Mf0 .

Figure 2.8 shows the construction of an OFDM signal with four subcarriers. (1a), (2a), (3a) and (4a) show individual subcarriers, with 1, 2, 3, and 4 cycles per symbol respectively. The phase on all these subcarriers is zero.

Note that each sub carrier has an integer number of cycles per symbol making them cyclic. Adding a copy of the symbol to the end would result in a smooth join between symbols

(1b), (2b), (3b) and (4b) show the FFT of the time waveforms in (1a), (2a), (3a) and (4a) respectively. (4a) and (4b) shows the result for the summation of the 4 sub carriers.

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Figure2.8 Time domain construction of an OFDM signal

This results in sum and difference frequency components, which will always be integer sub carrier frequencies, as the frequency of the two mixing subcarriers has integer number of cycles. Since the system is linear we can integrate the result by taking the integral of each frequency component separately then combining the results by adding the two sub integrals.

The two frequency components after the mixing have an integer number of cycles over the period and so the sub-integral of each component will be zero, as the integral of a sinusoid over an entire period is zero.

Both the sub-integrals are zeros and so the resulting addition of the two will also be zero, thus we have established that the frequency components are orthogonal to each other. Orthogonal frequency division multiplexing is then the concept of typically establishing a communications link using a multitude of carriers each carrying an amount of information identical to the separation between the carriers.

A more detailed understanding of Orthogonal arises when we observe that the bandwidth of a modulated carrier has a so called "Sinc" shape with nulls spaced by the bit rate. In OFDM, the carriers are spaced at the bit rate, so that the carriers fit in the nulls of the other carriers. Another view of Orthogonal is that each carrier has an integer number of sine wave cycles in one bit period.

2.2.2 Cyclic Prefix

The increased symbol duration in OFDMA improves the delay spread while the Inter Symbol Interference (ISI) is completely eliminated by introduction of a Cyclic Prefix (some data). CP is a repetition of the last samples of the data portion that is appended at the beginning of the data payload.

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The ISI is completely eliminated as long as the CP duration is longer than the channel delay spread. A drawback of the CP is that it introduces overhead, which effectively reduces bandwidth efficiency. Since OFDM signal power spectrum has a sharp fall off at the edge of channel, a larger fraction of the allocated channel bandwidth can be utilized for data transmission which compensates the loss in efficiency due to the cyclic prefix. The concept of CP in OFDMA is explained as shown in Figure 2.9.

Figure2.9 Cyclic Prefix in OFDM

The total length of the symbol is Ts=TG + TFFT, where Ts is the total length of the symbol in samples, TG is the length of the guard period in samples, and TFFT is the size of the IFFT used to generate the OFDM signal.

The strength of OFDM is maximized by the introduction of a guard period among the transmitted symbols. The guard period allows time for multi-path signals from the earlier symbol to gradually disappear before the information from the present symbol is get together. Cyclic extension is the most essential guard to period to employ. Cyclic extension is necessary to decode the symbol by using the FFT. This satisfies the multi-path resistance and the symbol time synchronization tolerance.

Figure2.10 Cyclic Prefix in OFDM

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For a given system bandwidth the symbol rate for an OFDM signal is much lower than a single carrier transmission scheme. For example for a single carrier BPSK modulation, the symbol rate corresponds to the bit rate of the transmission.

However for OFDM the system bandwidth is broken up into Nc subcarriers, resulting in a symbol rate that is Nc times lower than the single carrier transmission. This low symbol rate makes OFDM naturally resistant to effects of Intersymbol Interference (ISI) caused by multipath propagation.

Multipath propagation is caused by the radio transmission signal reflecting off objects in the propagation environment, such as walls, buildings, mountains, etc. These multiple signals arrive at the receiver at different times due to the transmission distances being different. This spreads the symbol boundaries causing energy leakage between them. The effect of ISI on an OFDM signal can be further improved by the addition of a Cyclic Prefix to the start of each symbol. This guard period is a cyclic copy that extends the length of the symbol waveform.

Each subcarrier, in the data section of the symbol, (i.e. the OFDM symbol with no guard period added, which is equal to the length of the IFFT size used to generate the signal) has an integer number of cycles. Because of these placing copies of the symbol end-to-end results in a continuous signal, with no discontinuities at the joins. Thus by copying the end of a symbol and appending this to the start results in a longer symbol time.

2.2.3 Multiple Access in OFDM

Multiple access schemes are used to allow many simultaneous users to use the same fixed bandwidth radio spectrum. In any radio system, the bandwidth that is allocated to it is always limited. For mobile phone systems the total bandwidth is typically 50 MHz, which is split in half to provide the forward and reverse links of the system.

Sharing of the spectrum is required in order increase the user capacity of any wireless network. FDMA, TDMA and CDMA are the three major methods of sharing the available bandwidth to multiple users in wireless system. There are many extensions, and hybrid techniques for these methods, such as OFDMA, and hybrid TDMA and FDMA systems.

However, an understanding of the three major methods is required for understanding of any extensions to these methods.

OFDMA is similar to FDMA in that the multiple user access is achieved by subdividing the available bandwidth into multiple channels, which are then allocated to users as shown in Figure 2.11. However, OFDMA uses the spectrum much more efficiently by spacing the channels much closer together. This is achieved by making all the carriers orthogonal to one another, preventing interference between the closely spaced carriers.

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Figure2.11 FDMA channelization

Before the digital implementation of OFDMA, FDMA can only be realized using multiple analog RF modules if one terminal is occupying multiple frequency bands. FDMA therefore was deemed unsuitable for broadband communications. However, the rise of OFDM, and in particular, its IFFF/FFT implementation, give FDMA a new life as a broadband multiple access scheme.

The use of IFFF /FFT allows terminals to arbitrarily combine multiple frequencies (subcarriers) at the baseband, leading to orthogonal frequency division multiple access (OFDMA) scheme as shown in Figure 2.12.

Figure2.12 OFDMA channelization

An OFDMA system is defined as one in which each terminal occupies a subset of subcarriers (termed an OFDMA traffic channel), and each traffic channel is assigned exclusively to one user at any time PI.

In OFDMA, users are not overlapped in frequency domain at any given time. However, the frequency bands assigned to a particular user may change over the time as shown in Figure 2.12.

The IEEE 802.16a-e has an OFDMA mode with bandwidth options of 1.25, 5, 10 or 20 MHz depending on the bandwidth, the entire spectrum is divided into 128, 512, 1024 or 2048 subcarriers.

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For example, a 20 MHz band with 2048-FFT yields a subcarrier spacing of 9.8 KHz. In time domain, the resource is further divided into frames and sub frames that can be allocated to different users.

2.2.4 OFDM versus Single Carrier

Orthogonal frequency division multiplexing (OFDM) technology provides operators with an efficient means to overcome the challenges of NLOS propagation. The WiMAX OFDM waveform offers the advantage of being able to operate with the larger delay spread of the NLOS environment. By virtue of the OFDM symbol time and use of a cyclic prefix, the OFDM waveform eliminates the inter-symbol interference (ISI) problems and the complexities of adaptive equalization. Because the OFDM waveform is composed of multiple narrowband orthogonal carriers, selective fading is localized to a subset of carriers that are relatively easy to equalize.

An example is shown in Figure 2.13 and Figure 2.14 as a comparison between an OFDM Multi carrier signal and a single carrier signal, with the information being sent in parallel for OFDM and in series for single carrier.

Figure2.13 Single carrier and OFDM

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Figure2.14 Single carrier and OFDM

The ability to overcome delay spread, multi-path, and ISI in an efficient manner allows for higher data rate throughput. As an example it is easier to equalize the individual OFDM carriers than it is to equalize the broader single carrier signal as shown in Figure 2.15 and Figure 2.16.

Figure2.15 Single carrier and OFDM received

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Figure2.16 Single carrier and OFDM

In radio transmissions, the channel spectral response is not flat. In the frequency domain large delay spreads translate into frequency-selective fading.

Signals on some frequencies arrive at the receiver in phase while signals at some other frequencies arrive out of phase. This results in "frequency selective fading" as shown in Figure 2.17. NLOS channels may also vary in time significantly, due to moving transceivers in mobile communications. Also time variation of NLOS channels is caused by other moving objects in the paths of signals. This results in time selective fading as shown in Figure 2.17.

Figure2.17 Multi path Fading Channel

The OFDMA symbol structure consists of three types of sub-carriers as shown in Figure 2.18.

Data sub-carriers for data transmission.

Pilot sub-carriers for estimation and synchronization purposes.

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Null sub-carriers for no transmission; used for guard bands and DC carriers.

Figure2.18 OFDM sub carrier structure

Active (data and pilot) sub-carriers are grouped into subsets of sub-carriers called subchannels. The WiMAX OFDMA PHY supports sub-channelization in both DL and UL.

The minimum frequency-time resource unit of sub channelization is one slot, which is equal to 48 data tones (sub-carriers).

There are two types of sub-carrier permutations for sub-channelization; diversity and contiguous. The diversity permutation draws sub-carriers pseudo-randomly to form a subchannel. It provides frequency diversity and inter-cell interference averaging.

2.2.5 Scalable OFDM Access (SOFDMA)

Scalable OFDMA is the OFDMA mode is used in Mobile Wi-MAX defined in IEEE 802.16e. Scalability is supported by adjusting the size of FFT size while fixing the sub-carrier frequency spacing in 10.94 kHz. It supports channel bandwidths ranging from 1.25 MHz to 20 MHz.

SOFDMA adds scalability to OFDMA. With bandwidth scalability, Mobile Wi-MAX technology can comply with various frequency regulations worldwide.

When designing OFDMA wireless systems the optimal choice of the number of subcarriers per channel bandwidth is a tradeoff between protection against multipath, Doppler shift, and design cost/complexity.

Increasing the number of subcarriers leads to better immunity to the inter-symbol interference (ISI) caused by multipath (due to longer symbols); on the other hand it increases the cost and complexity of the system (it leads to higher requirements for signal processing power and power amplifiers with the capability of handling higher peak-to-average power ratios).

Having more subcarriers also results in narrower subcarrier spacing and therefore the system becomes more sensitive to Doppler shift and phase noise.

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2.2.5.1 S-OFDMA parameters

Smaller FFT size is given to lower bandwidth channels, while larger FFT size to wider channels. By making the sub-carrier frequency spacing constant, SOFDMA reduces system complexity of smaller channels and improves performance of wider channels. In order to keep optimal sub-carrier spacing, the FFT size should scale with the bandwidth. This concept is introduced in Scalable OFDMA (SOFDMA).This results in the property that the number of sub-channels scales with FFT/bandwidth. Various scalable parameters in SOFDMA along with the fixed parameters are given in the table below.

PARAMETERS VALUES

System Channel Bandwidth (MHz) 20 10 5 1.25

Sampling frequency Fp in MHz 22.4 11.2 5.6 1.4

FFT Size (Nfft) 2048 1024 512 128

Number of Sub-Channels 32 16 8 2

Sub-Carrier Frequency Spacing 10.94KHz

Useful symbol Time ( Tb=1/f) 91.4 microsecond

Guard Time (Tg=Tb/8) 11.4 microsecond

OFDMA symbol duration (Ts=Tb+Tg) 102.9 microsecond

Number of OFDMA Symbols (5ms Frame) 48 Table2.1 scalable ODFM parameters

2.2.5.2 Other Complementary Features of S-OFDMA

Advanced Modulation and Coding(AMC) Hybrid Automatic Repeat Request (H-ARQ) high-efficiency uplink subchannel structures, Multiple-Input-Multiple Output (MIMO)

2.2.5.3 SOFDMA frame structure

Figure2.19 SOFDM structure

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2.2.5.4 Advantages and Disadvantages of SOFDMA System

Advantages

1. Combating ISI and Reducing ICI

When signal passes through a time-dispersive channel, the orthogonality of the signal can be lost. CP helps to maintain orthogonality between the sub carriers. Initially guard interval-empty space between two OFDM symbols served as a buffer for the multi path reflection. But the empty guard time introduces Inter Carrier Interference (ICI) that is crosstalk between different sub carriers. A better solution is cyclic extension of OFDM symbol or CP. It ensures that the delayed replicas of the OFDM symbols will always have a complete symbol within the FFT interval (often referred as FFT window).

At the receiver side, CP is removed before any processing starts. As long as the length of CP interval is larger than maximum expected delay spread, all reflections of previous symbols are removed and orthogonality is restore

2. Spectral Efficiency

In the case of OFDM, a better spectral efficiency is achieved by maintaining orthogonality between the sub-carriers.

Disadvantages

1. Strict Synchronization Requirement

OFDMA is highly sensitive to time and frequency synchronization errors. Demodulation of an OFDM signal with an offset in the frequency can lead to a high bit error rate.

2. Peak-to-Average Power Ratio (PAPR)

Peak to Average Power Ratio (PAPR) is proportional to the number of sub-carriers used for OFDM systems. An OFDM system with large number of sub-carriers will thus have a very large PAPR when the sub-carriers add up coherently. Large PAPR of a system makes the implementation of Digital-to-Analog Converter (DAC) and Analog-to-Digital Converter (ADC) to be extremely difficult. The design of RF amplifier also becomes increasingly difficult as the PAPR increases .

2.3 OFDM Parameters The IEEE 802.16-2004 standard specified OFDM as the transmission method for NLOS

connections. The OFDM signal is made up of many orthogonal carriers, and each individual carrier is digitally modulated with a relatively slow symbol rate. This method has distinct advantages in multipath

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propagation because, in comparison with the single carrier method at the same transmission rate, more time is needed to transmit a symbol.

The BPSK, QPSK, 16QAM, and 64QAM modulation modes are used, and the modulation is adapted to the specific transmission requirements. Transmission rates of up to 75 Mbps are possible. Unlike WiMAX’s "little brother" WLAN, the bandwidth is not constant and can vary between 1.25 MHz and 28 MHz. In IEEE 802.16-2004, a distinction is made between two methods: OFDM and OFDMA.

In the normal OFDM mode, 200 carriers are available for data transmission and both TDD and FDD methods are used. In the OFDMA mode, various subscribers can be served simultaneously by assigning each subscriber a specific carrier group (subchannelization) that carries the data intended for that subscriber.

The number of carriers is also significantly increased. The 802.16e standard is a further expansion of WiMAX in the frequency range up to 6 GHz with the objective of allowing mobile applications and even roaming. In addition, the number of carriers can vary over a wide range depending on permutation zones and FFT base (128, 512, 1024, and 2048). The Korean standard WiBRO is a special case of 802.16e.

OFDM is a combination of modulation and multiplexing. Multiplexing generally refers to independent signals, those produced by different sources. So it is a question of how to share the spectrum with these users. In OFDM the question of multiplexing is applied to independent signals but these independent signals are a sub-set of the one main signal.

In OFDM the signal itself is first split into independent channels, modulated by data and then re-multiplexed to create the OFDM carrier. OFDM is a special case of Frequency Division Multiplex (FDM). As an analogy, a FDM channel is like water flow out of a faucet, in contrast the OFDM signal is like a shower. In a faucet all water comes in one big stream and cannot be sub-divided. OFDM shower is made up of a lot of little streams.

Think about what the advantage might be of one over the other? One obvious one is that if I put my thumb over the faucet hole, I can stop the water flow but I cannot do the same for the shower. So although both do the same thing, they respond differently to interference.

In OFDM system, the subcarriers must be orthogonal. The independent sub-channels can be multiplexed by frequency division multiplexing (FDM), called multi-carrier transmission or it can be based on a code division multiplexing (CDM), in this case it is called multi-code transmission.

2.3.1 Basic Terms in OFDM

The WiMAX standard describes different modes of operation:

Single Carrier (SC / SCa).

Orthogonal Frequency Division Multiplex (OFDM / OFDMA).

OFDM Parameters

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OFDM is one step in the evolution of transmitting information over a physical media:

The easiest way to send information is bit-by-bit in time at one particular carrier frequency. With this method, you start with the first bit, transmit it, send the second bit, transmit it, and so on. This is done by means of ASK modulation for example.

A more complex method is to group a certain number of bits together to form a symbol and then to transmit such symbols symbol-by-symbol. QPSK (two bits form 1 QPSK symbol) or 16QAM (four bits form one 16QAM symbol) are examples of this modulation.

OFDM is an even more complex method of transmitting information over a physical channel. The basic concept is to use ''multiple carriers'' (e.g. 256 carriers) to transmit a large number of symbols at the same time, and distributing information blocks containing a certain number of bits to a certain number of carriers.

Using OFDM has many advantages, including high spectrum efficiency, resistance against multipath interference (particularly in wireless communications), and ease of filtering out noise (if a particular range of frequencies is affected by interference, the carriers within that range can be disabled or made to run slower). Also, the upstream and downstream speeds can be varied by allocating a higher or lower number of carriers for each purpose.

An extremely important benefit from using multiple subcarriers is that because each carrier operates at a relatively low bit rate, the duration of each symbol is relatively long. For example, if you send a million bits per second over a single baseband channel, then the duration of each bit must be under a microsecond. This imposes severe constraints on synchronization and removal of ''multipath interference''.

If the same million bits per second are spread among N subcarriers, the duration of each bit can be extended by a factor of N, and the constraints of timing and multipath sensitivity are greatly relaxed. For moving vehicles, the Doppler Effect on signal timing is another constraint that causes difficulties for some other modulation schemes.

The more complex the technique and the greater the information bandwidth (one parameter is "bit/Hz", which indicates how many useful bits can be transmitted when using 1 Hz bandwidth), the more sensitive the systems are to ''disturbing effects'' (such as fading, noise, transmitter and receiver imperfections).

Overcome these problems, more sophisticated techniques to ''recover errors'' have to be introduced (advanced protocols, multipath receivers such as Rake receivers, high-performance receiver frontends, advanced error coding and error recovery methods such as turbo codes, Viterbi decoders, etc).

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2.3.2 Basic OFDM Parameters

In order to describe an OFDM system, a number of terms are used to specify the parameters of the physical properties. In The following few words, we will explain and illustrate the basic terms related to OFDM.

Figure2.20 OFDM in Both Time and Frequency domains

Nominal channel bandwidth BWn (Hz) The bandwidth which is allocated by the governmental authorities Values are 1.5 MHz, 5

MHz or 20 MHz, the bandwidth is defined in OFDM as (2.3)

Where: Fs is the sampling frequency, n is the sampling factor.

Used bandwidth BW (Hz) The bandwidth is the area which is physically occupied by the WiMAX signal in

frequency domain.

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(2.4)

Where: Δf is the sampling frequency, Nused (max) is the maximum number of used subcarriers. Note: The used bandwidth must be smaller than the nominal BW.

Sampling frequency FS (Hz) The sampling frequency is the "core" frequency of the transmission system, that means

the frequency at which e.g. of the D/A converter generates new samples. (2.5)

Note: The sampling frequency is always greater that Bandwidth BW.

Sampling factor n The sampling factor is the ratio of sampling frequency to channel bandwidth (2.6)

Note: The Typical factors used in OFDM are 8/7 (recommended), 28/25, 86/75…etc

FFT size (NFFT) In OFDM, signals are very often processed using fast Fourier transformation (FFT). NFFT

specifies the number of samples for this processing step and is always a power of 2. Subcarrier spacing Δf (Hz)

Is the distance between two adjacent physical OFDM carriers. The value is calculated by Δf that given by: ∆ (2.7)

Useful symbol time Tb (sec) The time a symbol is "valid", which means the correct and undisturbed carrier

modulation state (also called the "orthogonality interval") is present, and it can be given as: (2.8)

Note: For FFT analysis, this is the analyzed interval length.

Guard period ratio / interval G, cyclic prefix (CP) time Tg (sec) In order to collect multipath information, a particular ratio of the useful symbol is added

to the OFDM symbol. This ratio is called ''guard period'' and the absolute time is called ''cyclic prefix' . (2.9)

Note: Typical values of G: , , ,

Chapter 2 Overview of OFDM

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(Overall) OFDM symbol time Ts (sec) The duration of the complete OFDM symbol with useful symbol time and cyclic prefix

time, where: (2.10)

Number of used subcarriers (Nused) Due to the shape of the transmission filter, the outer carriers of an OFDM signal may be

attenuated and thus be disturbed. Also, the DC carrier cannot be used. Consequently, the outer carriers do not carry any modulation data. Nused may vary, depending on special transfer modes.

DC subcarrier The DC subcarrier is the carrier at the transmission frequency and is not used for data

transmission (set to 0). Pilot carriers

Pilot carriers are used to synchronize the receiver to the transmitter by means of phase, frequency and timing. Note: For OFDM, 8 pilot carriers are used.

Guard subcarriers NGuard(left) and NGuard(right) The guard subcarriers are the outer carriers, which are not used for transmission. 1 (2.11)

2.3.3 Properties of OFDM

Unshaped QPSK signal produces a spectrum such that its bandwidth is equal to (1+ α) Rs. In OFDM, the adjacent carriers can overlap in the manner shown here. The addition of two carriers, now allows transmitting 3Rs over a bandwidth of -2Rs to 2Rs or total of 4Ts. This gives a bandwidth efficiency of 4/3 Hz per symbol for 3 carriers and 6/5 for 5 carriers.

As more and more carriers are added, the bandwidth approaches bits per Hz.

Figure2.21 The spectrum of an OFDM signal (without cyclic prefix)

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Figure2.22 The spectrum of an OFDM signal (without cyclic prefix)

So the larger the number of carriers is better. Here is a spectrum of an OFDM signal and note that the out of band signal is down by 50 dB without any pulse shaping.

Comparing this to the spectrum of a QPSK signal, not how much lower the sidebands are for OFDM and how much less are the variance.

Bit Error Rate performance

The BER of an OFDM is only exemplary in a fading environment. We would not use OFDM is a straight line of sight link such as a satellite link. OFDM signal due to its amplitude variation does not behave well in a non-linear channel such as created by high power amplifiers on board satellites. Using OFDM for a satellite would require a fairly large back off, on the order of 3 dB, so there must be some other compelling reason for its use such as when the signal is to be used for a moving user.

Peak to average power ratio (PAPR)

If a signal is a sum of N signals each of max amplitude equal to 1 v, then it is conceivable that we could get max amplitude of N that is all N signals add at a moment at their max points. The PAPR is defined as: | |

(2.12)

Where: R: Peak to average power ratio x(t): Peak power Pavg: average power

For an OFDM signal that has 128 carriers, each with normalized power of 1 w, then the max PAPR can be as large as log (128) or 21 dB. This is at the instant when all 128 carriers combine at their maximum point, unlikely but possible. The RMS PAPR will be around half this number or 10-12 dB. This same PAPR is seen in CFDM signals as well.

Chapter 2 Overview of OFDM

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When the signal has to go through amplifier non-linearity's, Large back off is required in such cases. This makes use of OFDM just as problematic as Multi-carrier FDM in high power amplifier applications such as satellite links.

Synchronization

The other problem is that tight synchronization is needed. Often pilot tones are served in the subcarrier space. These are used to lock on phase and to equalize the channel.

Coding

The sub-carriers are typically coded with convolution coding prior to going through IFFT. The coded version of OFDM is called COFDM or Coded OFDM.

2.3.4 OFDM Real Parameters

The OFDM use has increased greatly in the last 10 years. It is now proposed for radio broadcasting such as in Eureka 147 standard and Digital Radio Mondiale (DRM). OFDM is used for modem/ADSL application where it coexists with phone line. For ADSL use, the channel, the phone line, is filtered to provide a high SNR. OFDM here is called Discrete Multi Tone (DMT.)

(Remember the special filters on your phone line if you have cable modem.) OFDM is also in use in your wireless internet modem and this usage is called 802.11a. Let’s take a look at some parameters of this application of OFDM. The summary of these are given below.

Data rates: 6 Mbps to 48 Mbps

Modulation: BPSK, QPSK, 16 QAM and 64 QAM

Coding: Convolution concatenated with Reed Solomon

FFT size: 64 with 52 sub-carriers uses, 48 for data and 4 for pilots.

Subcarrier frequency spacing: 20 MHz divided by 64 carriers or .3125 MHz

FFT period: Also called symbol period, 3.2 μsec = 1/Δf

Guard duration: One quarter of symbol time, 0.8 μsec

Symbol time: 4 μsec

2.3.5 Subchannelization

As WiMAX is designed to operate as an infrastructure network, resource allocation is also an important topic. Within WiMAX (OFDM and OFDMA), subchannelization allows you to group the complete number of OFDM carriers into blocks and assign each block to a different segment of a base

OFDM Parameters

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station. The blocks are spread over the complete frequency range and contain a number of adjacent carriers.

The subchannel index controls the use of the different blocks over the entire spectrum.

The complete number of data subcarriers (192) can be divided into 2, 4, 8 or 16 subchannels. All subcarriers are spread in four different "regions" of the available frequency range.

If, four subchannels are used (as in the example below), there will be 16/4 = 4 different subchannel indices and 192/4 = 48 subcarriers per subchannel, which are distributed over four different "regions", thus yielding 48/4 = 12 adjacent subcarriers per subchannel block.

Figure 2.23 below shows the concept of subchannelization with the example of four used subchannels. Subchannel index 12 (green) is used as an example.

Figure2.23 Subchannelization with 4 used subchannels

As shown in figure 2.24 Subchannelization in the uplink is an option within WiMAX. Without sub channelization, regulatory restrictions and the need for cost effective CPEs, typically cause the link budget to be asymmetrical, this causes the system range to be up link limited. Sub channeling enables the link budget to be balanced such that the system gains are similar for both the up and down links. Subchanneling concentrates the transmit power into fewer OFDM carriers; this is what increases the system gain that can either be used to extend the reach of the system, overcome the building penetration losses, and or reduce the power consumption of the CPE. The use of sub channeling is further expanded in orthogonal frequency division multiple access (OFDMA) to enable a more flexible use of resources that can support nomadic or mobile operation.

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Figure2.24 The effect of sub-channelization

2.3.6 Frame Structure

Frame structure is illustrated in Figure 2.25 that shows the frame structure of an WiMAX OFDM transmission. A frame is divided into a DL and a UL sub frame. The DL and UL sub frames start with the preamble 8 a known symbol with a limited number of carriers 8 to recover information about the transmission channel and allow the receiver to recover the channel response. The FCH and DL MAP contain information about the frame content (location and modulation of the individual bursts) and is BPSK-modulated.

Figure2.25 OFDM frame structure

OFDM Parameters

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2.3.7 From Bits to Carrier

To get a basic impression of how OFDM / OFDMA transmission works, the path from bits to the carrier is described as shown in Figure 2.26 that shows a 802.16-2004 OFDM transmitter (with parts of the OFDMA transmitter) and is just an overview; the detailed implementation may vary.

First, data from upper layers pass the randomizer, which converts long 0's or 1's sequences into randomly scrambled data, showing better coding performance in the next steps of transmission. The initialization value consists of the base station ID, DL or UL interval usage code (DIUC/UIUC) and frame number. The randomizer is implemented as a feedback register.

Figure2.26 OFDM / OFDMA transmitter architecture (simplified)

After that, the Forward Error Correction (FEC) coder adds redundancy to the signal. This is a means of correcting errors that may occur during signal transmission. The coder is implemented as a

Chapter 2 Overview of OFDM

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''Reed-Solomon coder'' as inner coding and a ''Convolution coder'' as outer coder. The total number of bits after encoding is higher than the number of bits before encoding.

Alternatively, ''turbo coding'' can be added as a block turbo coder or convolution turbo coder, which performs better but is also more complex.

The signal's number of bits must now be reduced. This is done within the puncturing device. It removes parts of the two output streams of the FEC and joins them in a defined way depending on the selected coding rate.

The interleaver now takes the bit stream and rearranges the data in a different order. This is done to protect against burst (or block) errors that can occur due to fading, signal level drops or other RF conditions.

The bit sequence leaving the interleaver is converted from serial to parallel (width depends on the FFT size) and applied to a modulator that performs a specific modulation scheme on the data (BPSK, 16QAM, etc).

For OFDMA, the data from one user occupies a certain amount of frequency and time resource. This mapping depends on different parameters such as amount of data to transmit, zone type, segment, subchannel group, etc.

A logical carrier can be built up from more than one physical carrier, which are normally non-adjacent physical carriers. This mapping is done by a burst mapper, which arranges the data in accordance with the rules defined in the standard.

All operations up to now lead to a complex-value and symbol-based representation of the data in frequency domain. This frequency domain data is now transformed to the time domain by means of an FFT block, which takes a certain number of data carriers, maps them to the FFT inputs (where the mapping rule may depend on complex rules) and adds a certain number of pilot carriers.

The pilot carriers are used to recover the absolute phase and phase response of the transmission channel, and allow the receiver to recover information about the transmission channel. The output data is now complex values in the time domain.

After the FFT block, the Guard Period is inserted into the IQ stream to overcome the problem of multipath effects on the OFDM signal, is then filtered by a baseband filter and passed to the D/A converter section, where it is converted to the transmission frequency and finally transmitted.

2.4 OFDM Generation and Reception OFDM signals are typically generated digitally due to the difficulty in creating large banks of

phase lock oscillators and receivers in the analog domain. Figure 2.27 shows the block of typical OFDM Transceiver.

OFDM Generation and Reception

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Figure2.27 Block diagram showing a basic OFDM transceiver

The transmitter section converts digital data to be transmitted, into a mapping of sub carrier

amplitude and phase.

It then transforms this spectral representation of the data into the time domain using an Inverse

Discrete Fourier Transform (IDFT).

The Inverse Fast Fourier Transform (IFFT) performs the same operations as an IDFT, except that

it is much more computationally efficiency, and so is used in all practical systems. In order to transmit

the OFDM signal the calculated time domain signal is then mixed up to the required frequency.

The receiver performs the reverse operation of the transmitter, mixing the RF signal to base

band for processing, then using a Fast Fourier Transform (FFT) to analyze the signal in the frequency

domain. The amplitude and phase of the subcarriers is then picked out and converted back to digital

data.

The IFFT and the FFT are complementary function and the most appropriate term depends on

whether the signal is being received or generated. In cases where the signal is independent of this

distinction then the term FFT and IFFT is used interchangeably.

2.4.1 Serial to parallel conversion

Data to be transmitted is typically in the form of a serial data stream. In OFDM, each symbol

typically transmits 40 – 4000 bits, and so a serial to parallel conversion stage is needed to convert the

input serial bit stream to the data to be transmitted in each OFDM symbol.

Chapter 2 Overview of OFDM

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The data allocated to each symbol depends on the modulation scheme used and the number of sub carriers. For example, for a sub carrier modulation of 16-QAM each subcarrier carries 4 bits of data, and so for a transmission using 100 sub carriers the number of bits per symbol would be 400.

For adaptive modulation schemes the modulation scheme used on each subcarrier can vary and so the number of bits per subcarrier also varies. As a result the serial to parallel conversion stage involves filling the data payload for each subcarrier. At the receiver the reverse process takes place, with the data from the sub carriers being converted back to the original serial data stream.

When an OFDM transmission occurs in a multipath radio environment, frequency selective fading can result in groups of sub carriers being heavily attenuated, which in turn can result in bit errors. These nulls in the frequency response of the channel can cause the information sent in neighboring carriers to be destroyed, resulting in a clustering of the bit errors in each symbol.

Most Forward Error Correction (FEC) schemes tend to work more effectively if the errors are spread evenly, rather than in large clusters, and so to improve the performance most systems employ data scrambling as part of the serial to parallel conversion stage.

This is implemented by randomizing the subcarrier allocation of each sequential data bit. At the receiver the reverse scrambling is used to decode the signal. This restores the original sequencing of the data bits, but spreads clusters of bit errors so that they are approximately uniformly distributed in time.

This randomization of the location of the bit errors improves the performance of the FEC and the system as a whole.

2.4.2 Modulation

Most OFDM systems use a fixed modulation scheme over all sub carriers for simplicity. However each subcarrier in a multi-user OFDM system can potentially have a different modulation scheme depending on the channel conditions. Any coherent or differential, phase or amplitude modulation scheme can be used including BPSK, QPSK, 8-PSK, 16-QAM, 64-QAM, etc, each providing a trade-off between spectral efficiency and the bit error rate. The spectral efficiency can be maximized by choosing the highest modulation scheme that will give an acceptable Bit Error Rate (BER).

In a multipath radio channel, frequency selective fading can result in large variations in the received power of each subcarrier. For a channel with no direct signal path this variation can be as much as 30 dB in the received power resulting in a similar variation in the SNR.

In addition to this, interference from neighboring cells can cause the SNR to vary significantly over the system bandwidth. To cope with this large variation in SNR over the system sub carriers, it is possible to adaptively allocate the subcarrier modulation scheme, so that the spectral efficiency is maximized while maintaining an acceptable BER.

As shows in Figure 2.28 an example of applying adaptive modulation to an individual subcarrier as the channel SNR varies with time.

OFDM Generation and Reception

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Figure2.28 Adaptive Modulation (The modulation scheme is set based on the SNR of the channel)

The SNR must be greater than the threshold (chosen from Table 2.1) to maintain a maximum BER. Excess SNR results in the BER being lower than the BER threshold. This diagram assumes that the modulation scheme is updated continuously and with no delay.

Using adaptive modulation has a number of key advantages over using static modulation. In systems that use a fixed modulation scheme the subcarrier modulation must be designed to provide an acceptable BER under the worst channel conditions.

This results in most systems using BPSK or QPSK. However these modulation schemes give a poor spectral efficiency (1 - 2 b/s/Hz) and result in an excess link margin most of the time. Using adaptive modulation, the remote stations can use a much higher modulation scheme when the radio channel is good.

Modulation Scheme (Coherent)

Spectral Efficiency (b/s/Hz)

Required SNR(dB) BER < 10−2 BER < 10−4 BER < 10−5 BER < 10−6

BPSK 1 4.32 8.41 9.61 10.42 QPSK 2 7.33 11.41 12.58 13.48 8-QAM 3 11.38 15.3 16.45 17.35 16-QAM 4 13.9 18.22 19.46 20.43 32-QAM 5 17.75 21.58 22.74 23.58 64-QAM 6 19.94 24.39 25.6 26.52 128-QAM 7 23.62 27.6 28.76 29.83 256-QAM 8 25.74 30.34 31.6 32.61 512-QAM 9 29.44 33.54 34.54 35.65 1024-QAM 10 31.54 36.29 37.58 38.59 2048-QAM 11 35.23 39.49 40.67 41.75

Table2.2 Required SNR to maintain a BER below a given threshold

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Thus as a remote station approaches the base station the modulation can be increased from 1 b/s/Hz (BPSK) up to 4 - 8 b/s/Hz (16-QAM – 256-QAM), significantly increasing the spectral efficiency of the overall system.

Using adaptive modulation can effectively control the BER of the transmission, as sub carriers that have a poor SNR can be allocated a low modulation scheme such as BPSK or none at all, rather than causing large amounts of errors with a fixed modulation scheme. This significantly reduces the need for Forward Error Correction.

2.4.3 Frequency to time domain conversion

After the subcarrier modulation stage each of the data sub carriers is set to an amplitude and phase based on the data being sent and the modulation scheme; all unused sub carriers are set to zero.

This sets up the OFDM signal in the frequency domain. An IFFT is then used to convert this signal to the time domain, allowing it to be transmitted.

Figure 2.29 shows the IFFT section of the OFDM transmitter. In the frequency domain, before applying the IFFT, each of the discrete samples of the IFFT corresponds to an individual subcarrier. Most of the sub carriers are modulated with data.

The outer sub carriers are unmodulated and set to zero amplitude. These zero sub carriers provide a frequency guard band before the nyquist frequency and effectively act as an interpolation of the signal and allows for a realistic roll off in the analog anti-aliasing reconstruction filters.

Figure2.29 OFDM generation, IFFT stage

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2.4.4 Guard Period

The strength of OFDM is maximized by the introduction of a guard period among the transmitted symbols. The guard period allows time for multi-path signals from the earlier symbol to gradually disappear before the information from the present symbol is get together. Cyclic extension is the most essential guard to period to employ. Cyclic extension is necessary to decode the symbol by using the FFT. This satisfies the multi-path resistance and the symbol time synchronization tolerance.

For a given system bandwidth the symbol rate for an OFDM signal is much lower than a single carrier transmission scheme. For example for a single carrier BPSK modulation, the symbol rate corresponds to the bit rate of the transmission. However for OFDM the system bandwidth is broken up into Nc sub carriers, resulting in a symbol rate that is Nc times lower than the single carrier transmission. This low symbol rate makes OFDM naturally resistant to effects of Inter-Symbol Interference (ISI) caused by multipath propagation.

Multipath propagation is caused by the radio transmission signal reflecting off objects in the propagation environment, such as walls, buildings, mountains, etc. These multiple signals arrive at the receiver at different times due to the transmission distances being different. This spreads the symbol boundaries causing energy leakage between them.

The effect of ISI on an OFDM signal can be further improved by the addition of a

guard period to the start of each symbol. This guard period is a cyclic copy that extends the length of the symbol waveform. Each subcarrier, in the data section of the symbol, (i.e. the OFDM symbol with no guard period added, which is equal to the length of the IFFT size used to generate the signal) has an integer number of cycles. Because of these placing copies of the symbol end-to-end results in a continuous signal, with no discontinuities at the joins. Thus by copying the end of a symbol and appending this to the start results in a longer symbol time. Figure 2.30 shows the insertion of a guard period.

Figure2.30 Addition of a guard period to an OFDM signal

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The total length of the symbol is Ts=TG + TFFT, where Ts is the total length of the symbol in samples, TG is the length of the guard period in samples, and TFFT is the size of the IFFT used to generate the OFDM signal. In addition to protecting the OFDM from ISI, the guard period also provides protection against time-offset errors in the receiver.

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3.1 Comparison between WiMAX and 3G cellular 3.1.1 Introduction to 3G Technologies

3.1.1.1 THE STANDARDS FOR 3G

Third Generation (3G) is the mobile phone systems that will be begin to be available commercially in the year 2001. The idea behind 3G is to unify the disparate standards that today’s second generation wireless networks use. Instead of different network types being adopted in The Americas, Europe and Japan, the plan is for a single network standard to be agreed and implemented.

3.1.1.2 3G STANDARDIZATION PROCESS

In 1998, the International Telecommunications Union (ITU) called for Radio Transmission Technology (RTT) proposals for IMT-2000 (originally called Future Public Land Mobile Telecommunications Systems (FPLMTS)), the formal name for the Third Generation standard. Many different proposals were submitted: the DECT and TDMA/ Universal Wireless Communications organizations submitted plans for the RTT to be TDMA-based; whilst all other proposals for non-satellite based solutions were based on wideband CDMA- the main submissions were called Wideband CDMA (WCDMA) and cdma2000. The ETSI/ GSM players including infrastructure vendors such as Nokia and Ericsson backed WCDMA. The North American CDMA community, led by the CDMA Development Group (CDG) including infrastructure vendors such as Qualcomm and Lucent Technologies, backed cdma2000.

3.1.1.3 3GPP

In December 1998, the Third Generation Partnership Project (3GPP) was created following an agreement between six standards setting bodies around the world including ETSI, ARIB and TIC of Japan, ANSI of the USA and the TTA of Korea. This unprecedented cooperation into standards setting made 3GPP responsible for preparing, approving and maintaining the Technical Specifications and Reports for a Third Generation mobile system based on evolved GSM core networks and the Frequency Division Duplex (FDD) and Time Division Duplex (TDD) radio access technology. For example, ETSI SMG2 activities on UMTS have been fully transferred to 3GPP. The Chinese and the CDMA Development Group were unfortunately not original

Chapter 3 Comparison between WiMAX and other Broadband access technologies

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members of the 3GPP. In the first half of 1999, much progress was made in agreeing a global IMT-2000 standard that met the political and commercial requirements of the various technology protagonists- GSM, CDMA and TDMA. In late March 1999, Ericsson purchased Qualcomm’s CDMA infrastructure division and Ericsson and Qualcomm licensed each other’s key Intellectual Property Rights and agreed to the ITU’s “family of networks” compromise to the various standards proposals.

3.1.2 Competing Technologies

The 3G partnership project (3GPP) and 3G partnership project 2 (3GPP2) have been defining standards for enhancements to today’s 3G systems. The objective is to add network capacity and features enabling operators to offer new data-oriented services over their existing networks. The extensions are discussed below:

Figure3.1 Cellular Network Evolution

3.1.2.1 CDMA Family

CDMA 2000 represents a family of technologies that includes CDMA2000 1X and CDMA2000 1xEV.CDMA2000 1X can double the voice capacity of CDMA One networks and delivers peak packet data speeds of 307 Kbps in mobile environments. CDMA2000 1xEV includes:

CDMA2000 1xEV-DO is a high-speed data only system for 1.25 MHz FDD channels and delivers peak data speeds of 2.4Mbps supporting applications such as MP3 transfers and video conferencing.

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CDMA2000 1xEV-DV provides integrated voice and simultaneous high-speed packet data multimedia services at speeds of up to 3.09 Mbps.

Wideband code division multiple access (WCDMA) uses direct sequence spread spectrum (DSSS) to spread the signal over a 5 MHz spectrum. It is based on 3GPP Release 99 and provides data rates of 384 Kbps for wide area coverage and up to 2 Mbps for hot-spot areas. In addition to the use of orthogonal spreading codes, it uses quadrature phase shift keying (QPSK) for its modulation

Family

Technology

Theoretical Throughput Forward link

(Kbps) Return link (Kbps)

CDMA

1 x 1.25MHz 614

614

1 x EV-DO Rev 0 (1.25MHz) 2458

153

1 x EV-DO Rev A (1.25MHz) 3072 1800

1 x EV-DO Rev B (1.25MHz) 14745 5400

WCDMA

GPRS (200KHz) 163

163

EDGE (200KHz) 474

474

WCDMA Rel 99 (5MHz) 2688

2304

HSDPA Rel 5 (5MHz) 14400

2300

HSUPA Rel 5 (5MHz) 14400 5000 Table3.1 Theoretical throughputs of CDMA systems

3.1.2.2 HSDPA

3GPP Release 5 extends the WCDMA specification with high speed downlink packet access (HSDPA).HSDPA includes advanced features such as adaptive modulation and coding (AMC), hybrid automatic repeat request (HARQ), and de-centralized scheduling architecture. The 3GPP has also defined WCDMA enhancements for the uplink path. This enhancement is known as high speed uplink packet access (HSUPA); the combination of HSDPA and HSUPA is simply known as HSPA (high speed packet Access).

3.1.3 Roadmap for 3G Enhancements

1xEVDO Rev 0 had initial success in Korea and Japan beginning in 2003 with additional major deployments following in 2004 and 2005.The initial launch for EV-DO Rev A with CDMA2000 UL enhancements took place in Korea and Japan in 2005.

A further enhancement to the CDMA2000 standard is 1xEVDO-Rev B (also known as DO Multi-Carrier).

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This enhancement will increase the DL peak over the air data rate for a 1.25 MHz carrier to 4.9 Mbps and, by aggregating 3 carriers (known as 3xEVDO) in a nominal 5 MHz channel bandwidth, will provides peak DL rate of 14.7 Mbps and a peak UL data rate of 5.4 Mbps. Commercial deployments for 1xEVDO-Rev B are not anticipated until 2008.

HSUPA/HSPA availability is not expected until 2007-2008. The 3GPP envisions additional long term WCDMA enhancements leading to UMTS terrestrial radio access node long term evolution (known as 3GPP-LTE or UTRAN LTE) also referred to as 3.99G or evolved UMTS. 3GPP2 is on a similar path with LTE forCDMA2000. Since approved standards for LTE are not expected until 2007, it is unlikely that products will be available until 2009 or later.

Figure3.2 Mobile WiMAX will be available before 3G – LTE

3.1.4 Technological Comparison

3G enhancements have evolved from the 3G experiences and as a result, inherit both the advantages and limitations of legacy 3G systems. WiMAX on the other hand was initially developed for fixed broadband wireless access and is optimized for broadband data services.

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3.2 Comparing Mobile WiMAX to 1xEVDO and HSPA

Attribute 1xEVDO Rev A HSPA Mobile WiMAX

Base Standard

CDMA2000/IS-95 WCDMA IEEE 802.16e

Duplex Method

FDD FDD TDD (FDD optional)

Downlink

TDM CDM- TDM OFDMA

Uplink Multiple Access

CDMA CDMA OFDMA

Channel BW 1.25 MHz 5.0 MHz Scalable: 4.375, 5,7, 8.75, 10 MHz

DL

UL

Frame Size

1.67 milliseconds 2 milliseconds 5milliseconds TDD

6.67 milliseconds 2, 10 milliseconds

5 milliseconds TDD

Modulation DL

QPSK/8PSK/ 16QAM

QPSK/16QAM QPSK/16QAM/ 64QAM

Modulation UL

BPSK,QPSK/8PSK BPSK/QPSK QPSK/16QAM

Coding CC, Turbo CC, Turbo CC, Turbo DL Peak Over

the Air Data Rate

Rev A: 3.1 Mbps Rev B: 4.9 Mbps

14 Mbps 46(1:1)~54 (3:1) Mbps (DL/UL combined (32,14),

(46, 8)) UL Peak Over

the Air Data Rate

Rev 0: 0.15 Mbps Rev A,B: 1.8 Mbps

5.8 Mbps

H-ARQ Fast 4-Channel Synchronous IR

Fast 6-Channel Asynchronous

CC

Multi-Channel Asynchronous CC

Scheduling

Asynchronous CC Fast Scheduling in the DL

Fast Scheduling in DL and UL

Handoff Virtual Soft Handoff Network Initiated Hard Handoff

Network Optimized Hard Handof

Tx Diversity and MIMO

Simple Open Loop Diversity

Simple Open & Closed

Loop Diversity

STBC, SM

Beamforming No Yes (Dedicated Pilots)

Yes

Table3.2 WiMAX, EVDO and HSPA Features - summary of comparative features

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3.2.1 Common Features

Several features, designed to enhance data throughput, are common to EVDO, HSPDA / HSPA and mobile WiMAX including:

Adaptive modulation and coding (AMC)

Hybrid ARQ (HARQ)

Fast scheduling

Bandwidth efficient handoff

3.2.1.1 Adaptive Modulation and Coding (AMC)

1xEVDO-Rev B introduces 64QAM to further increase the peak downlink data rate. 1xEVDO-Rev A and

HSUPA introduce adaptive coding and modulation in the uplink to enhance uplink data rate with a finite number of specific packet sizes.

Mobile WiMAX supports AMC in both downlink and uplink with variable packet size. The uplink supports 16QAM modulation or 64QAM due to OFDMA orthogonal uplink sub-channels.

Technology

DL Modulation

DL Code Rate UL Modulation

UL Code Rate

Mobile WiMAX

QAM64 QAM16 QPSK

Turbo, CC, Repetition

1/12, 1/8, 1/4, 1/2, 2/3, 3/4, 5/6

QAM16 QPSK

QAM64

Turbo, CC, Repetition:

1/12, 1/8, 1/4, 1/2, 2/3, 3/4, 5/6

HSDPA

QAM16 QPSK

Turbo, CC: 1/4, 1/2, 3/4, 4/4

BPSK BPSK

BPSK HSPA (DPA+UPA)

BPSK QPSK

Turbo, CC: 2/3, 3/4, 4/4

Table3.3 AMC Capability

3.2.1.2 Hybrid ARQ

All systems support HARQ as an important means to improve the robustness of data transmission over the wireless channel.

Chase combining (CC) or incremental redundancy (IR) can be implemented at the receiver to jointly process the packets in error and new retransmission to improve the packet reception. HARQ CC is supported by mobile WiMAX and HSPA; HARQ IR is supported by 1xEVDO. Multi-channel HARQ operation is supported by all systems.

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3.2.1.3 Fast Scheduling

Mobile WiMAX, HSPA and 1xEVDO all apply fast scheduling in the downlink. HSPA uplink supports.

Autonomous scheduling - all uplink transmissions can randomly occur in parallel with controlled rates; Dedicated scheduling. However, due to no orthogonal uplink, the quality of an individual link cannot be easily controlled even with dedicated scheduling.

Mobile WiMAX applies fast scheduling in both downlink and uplink. Furthermore, WiMAX performs scheduling on a per-frame basis and broadcasts the downlink/uplink scheduling in the MAP messages at the beginning of each frame. This is especially well suited for busty data traffic and rapidly changing channel conditions.

3.2.1.4 Bandwidth Efficient Handoff

1xEVDO depends on the DSC signal for feedback on link conditions to accomplish “Virtual” Soft Handoff. HSPA does not support soft handoff but rather uses a more bandwidth efficient “Network Initiated Hard Handoff”, which can be optimized for reduced delay. Mobile WiMAX supports “Network Optimized Hard Handoff” for bandwidth-efficient handoff with reduced delay, achieving a handoff delay of less than 50ms. Mobile WiMAX also supports fast base station switch (FBSS) and macro diversity handover (MDHO) as options to further reduce the handoff delay.

Handover types in WiMAX

The basic mean of WiMAX handover is to provide the continuous connection when a Mobile Station (MS) migrates from an air-interface of one BS to another air-interface provided by another BS. In the IEEE 802.16e are defined three types of handover hard handover, Macro Diversity Handover (MDHO) and Fast Base Station Switching (FBSS). Hard handover is mandatory in WiMAX systems .Other two types of handover are optional.

Hard Handover:

During hard handover the MS communicates with only just one BS in each time. Connection with the old BS is broken before the new connection is established. Handover is executed after the signal strength from neighbor’s cell is exceeding the signal strength from the current cell. This situation is shown in Fig. 3.3 Red thick line at the boarder of the cells presents the place where the hard handover is realized.

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Figure3.3 Hard handover realization

Macro Diversity Handover

When MDHO is supported by MS and by BS, the “Diversity Set” is maintained by MS and BS. Diversity set is a list of the BS’s, which are involved in the handover procedure. Diversity set is defined for each of MS’s in network. MS communicates with all BS’s in the diversity set (see Fig. 3.4). For downlink in MDHO, two or more BS’s transmit data to MS such that diversity combining can be performed at the MS. For uplink in MDHO, MS transmission is received by multiple BS’s where selection diversity of the received information is performed. The BS, which can receive communication among MS’s and other BS’s, but the level of signal strength is not sufficient is noted as “Neighbor BS”.

Figure3.4 Macro Diversity Handover

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Fast Base Station Switching

In FBSS, the MS and BS diversity set is maintained similar as in MDHO. MS continuously monitors the base stations in the diversity set and defines an “Anchor BS”. Anchor BS is only one base station of the diversity set that MS communicates with for all uplink and downlink traffic including management messages (see Fig. 3.5).This is the BS where MS is registered, synchronized, performs ranging and there is monitored downlink channel for control information. The anchor BS can be changed from frame to frame depending on BS selection scheme. This means every frame can be sent via different BS in diversity set.

Figure3.5 Fast Base Station Switching

Handover types in 3G

There are following categories of handover.

Hard Handover

Hard handover means that all the old radio links in the UE are removed before the new radio links are established. Hard handover can be seamless or non-seamless. Seamless hard handover means that the handover is not perceptible to the user. In practice a handover that requires a change of the carrier frequency (inter-frequency handover) is always performed as hard handover.

Figure3.6 Hard handoff

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Soft Handover

Soft handover means that the radio links are added and removed in a way that the UE always keeps at least one radio link to the UTRAN. Soft handover is performed by means of macro diversity, which refers to the condition that several radio links are active at the same time. Normally soft handover can be used when cells operated on the same frequency are changed.

Figure3.7 Soft handoff

Softer handover

Softer handover is a special case of soft handover where the radio links that are added and removed belong to the same Node B (i.e. the site of co-located base stations from which several sector-cells are served. In softer handover, macro diversity with maximum ratio combining can be performed in the Node B, whereas generally in soft handover on the downlink, macro diversity with selection combining is applied.

MAHO: Mobile Assisted Handoff

Mobile Assisted Handoff (MAHO) is a handoff technique involving feedback from the mobile station as part of the handoff process. The feedback is usually in

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the form of signal level and quality measurements on the downlink and signal level measurements from neighbor cells.

3.1 Key Advantages of Mobile WiMAX Unlike the CDMA-based 3G systems, which have evolved from voice-centric systems, WiMAX

was designed to meet the requirements necessary for the delivery of broadband data services as well as voice. The Mobile WiMAX physical layer is based on Scalable OFDMA technology. The new technologies employed for Mobile WiMAX result in lower equipment complexity and simpler mobility management due to the all-IP core network and provide Mobile WiMAX systems with many other advantages over CDMA- based 3G systems including:

Tolerance to Multipath and Self-Interference

Scalable Channel Bandwidth

Orthogonal Uplink Multiple Access

Support for Spectrally-Efficient TDD

Frequency-Selective Scheduling

Fractional Frequency Reuse

Fine Quality of Service (QoS)

Advanced Antenna Technology

3.2.2 Tolerance to Multipath and Self-Interference

With OFDMA systems, the sub-channels maintain their orthogonality in a multipath channel. The number of multipath components does not limit the performance of the system as long as the multipaths are within the cyclic prefix window. OFDMA systems therefore are robust to multipath effects. The sub-channel orthogonality within the cyclic prefix window also relaxes the time synchronization requirement.

In CDMA systems, RAKE receivers are usually employed to combat multipath fading. However, in addition to multipath, other impairments such as frequency offset, Doppler Effect and lack of time synchronization can cause CDMA systems to suffer from intra-cell interference between users in the same cell and even self-interference in the absence of other users. This interference can be mitigated by employing a time domain equalizer. The equalizer however, cannot completely remove interference as in OFDMA and does not scale well with channel bandwidth since the complexity increases with channel bandwidth and increased delay spread. Therefore, in broadband wireless systems where multipath effect is prevalent, OFDMA systems are more robust and the equipment less complex than CDMA systems.

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3.2.3 Scalable Channel Bandwidth

Scalability is one of the most important advantages of OFDMA. With the OFDMA sub-carrier structure, it can support a wide range of bandwidths. The scalability is achieved by adjusting the FFT size7 to the channel bandwidth while fixing the sub-carrier frequency spacing.By fixing the sub-carrier spacing and symbol duration, the basic unit. of physical (time and frequency) resource is fixed. Therefore, the impact to higher layers is minimal when scaling the bandwidth.

One immediate advantage stemming from scalability is the flexibility of deployment. With little modification to air interface, OFDMA systems can be deployed in various frequency band intervals to flexibly address the need for various spectrum allocation and usage model requirements. Mobile WiMAX supports channel bandwidths of 5 MHz, 7 MHz, 8.75 MHz, and 10 MHz and can optionally support channel bandwidths ranging from 1.25 MHz to 20 MHz

With the flexibility to support a wider bandwidth, Mobile WiMAX also enjoys high aggregate sector throughput, which allows more efficient multiplexing of data traffic, lower latency and better QoS.

The CDMA-based systems such as 1xEVDO and HSPA on the other hand, are optimized for a specific channel plan (1.25 MHz for 1xEVDO and 5 MHz for HSPA). These systems are very sensitive to bandwidth change, because the signals occupy the entire bandwidth and do not have the same modular property as the OFDMA signals in the frequency domain. Both the CDMA code and frame structure may have to be re-optimized for the new channel bandwidth. Therefore, 1xEVDO and HSPA and do not provide scalability in a natural manner.

3.2.4 Orthogonal Uplink Multiple Access

When considering multiple access benefits, sub-channel orthogonality provides OFDMA with a distinct advantage over CDMA. Since with OFDMA, users are allocated different portions of the channel, there is no (or little) multiple access interference (MAI) between multiple users. OFDMA therefore, can support higher order uplink modulations and achieve higher uplink spectral efficiency. With CDMA, on the other hand, each user transmits over the entire channel. Even though it is possible to construct orthogonal spreading codes, due to the uplink synchronization issues, asynchronous CDMA is used in the uplink in most practical CDMA systems. With asynchronous CDMA, the users interfere with each other during uplink multiple accesses and MAI significantly reduces uplink spectral efficiency. Uplink capacity, in fact, is the bottleneck in most CDMA systems. WiMAX with OFDMA on the other hand, is capable of providing balanced downlink/uplink throughput. Orthogonal uplink sub-channels also enables the uplink scheduler to provide better control of the uplink quality and uplink resource allocation. Therefore the uplink performance is more predictable and QoS is better enforced.

3.2.5 Support for Spectral-Efficient TDD

Both HSDPA and 1xEVDO are FDD-based, whereas Mobile WiMAX supports TDD and optionally, Full and Half-Duplex FDD. To counter interference issues, TDD does require system-wide frame

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synchronization; nevertheless, TDD is the preferred duplexing mode for broadband services for the following reasons:

TDD enables adjustment of the downlink/uplink ratio on a per cluster basis to efficiently support asymmetric downlink/uplink traffic while maintaining frame synchronization. With traffic becoming more and more dominated by data, downlink traffic will generally be dominant. With FDD, downlink and uplink always have fixed and generally, equal DL and UL bandwidths. Either the downlink channel or the uplink channel will be underutilized when the traffic is asymmetric resulting in a net decrease in overall spectral efficiency.

TDD assures channel reciprocity for better support of link adaptation, MIMO and other closed loop advanced antenna technologies.

Unlike FDD, which requires a pair of channels, TDD only requires a single channel for both downlink and uplink providing greater flexibility for adaptation to varied global spectrum allocations.

Transceiver design for TDD implementations is less complex and therefore less expensive.

It should be noted that there are TDD solutions for 3G as well. UMTS-TDD or TD-CDMA uses a combined time division code division access scheme based on a radio access approach defined by the ETSI Delta group. TD-CDMA is designed for operation at a 3.84 Mbps chip rate in a 5 MHz channel. TD-CDMA can also use AMC features developed for HSDPA to further enhance channel capacity. Specifications for TD-CDMA were approved by 3GPP in 1999 and continue to evolve. TD-SCDMA was proposed by the China Wireless Telecommunications Standards group (CWTS) and approved by the ITU in 1999. TD-SCDMA adds a synchronization mechanism and is designed to operate at a 1.28 Mcps chip rate in a 1.6 MHz channel. Both TD-CDMA and TD-SCDMA were adopted by 3GPP as part of UMTS Release 4 in 2001. To date, worldwide adoption of these systems has been limited and therefore, is not discussed in greater detail in this paper. Nevertheless, given the favorable attributes of TDD for data-centric services these systems can also be expected to play an important part in the ongoing evolution of 3G networks.

3.2.6 Frequency Selective Scheduling

Both 1xEVDO and HSPA signals occupy the entire bandwidth. Mobile WiMAX signals on the other hand only occupy a portion of the bandwidth. In broadband wireless channels, propagation conditions can vary over different portions of the spectrum in different ways for different users. Mobile WiMAX supports frequency selective scheduling to take full advantage of multi-user frequency diversity and improve QoS. WiMAX with adjacent sub-carrier permutation makes it possible to allocate a subset of sub-carriers to mobile users based on relative signal strength. By allocating a subset of sub-carriers to each MS for which the MS enjoys the strongest path gains, this multi-user diversity technique can achieve significant capacity gains over TDMA/CDMA.

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3.2.7 Fractional Frequency Reuse

Mobile WiMAX, 1xEVDO and HSPA all support frequency reuse one, i.e. all cells/sectors operate on one frequency channel to maximize spectrum utilization. However, due to heavy interference in frequency reuse one deployment, users at the cell edge may suffer low connection quality. 1xEVDO and HSPA address the interference issue by adjusting the loading of the network. However, the same loading factor is applied to all users within the coverage area, leading to capacity loss by “over-protecting” users that are closer to the base station. Since in WiMAX, users operate on sub-channels, which only occupy a small fraction of the channel bandwidth, the cell edge interference problem can be easily addressed by reconfiguration of the sub-channel usage without resorting to traditional frequency planning. In Mobile WiMAX, the flexible sub-channel reuse is facilitated by sub-channel segmentation and permutation zone. A segment is a subdivision of the available OFDMA sub-channels (one segment may include all sub-channels). One segment is used for deploying a single instance of MAC. Permutation Zone is a number of contiguous OFDMA symbols in DL or UL that use the same permutation. The DL or UL sub- frame may contain more than one permutation zone. The sub-channel reuse pattern can be configured so that users close to the base station operate on the zone with all sub-channels available. While for the edge users, each cell sector operates on the zone with a fraction of all sub-channels available. In Figure 3, F1, F2 and F3 are different sets of sub-channels in the same frequency channel. In this configuration, the full load frequency reuse of one is maintained for center users to maximize spectral efficiency while fractional frequency reuse is achieved for edge users to improve edge user connection quality and throughput. The sub-channel reuse planning can be adaptively optimized across sectors or cells based on network load and interference conditions on a per frame basis. All the cells sectors can operate on the same frequency channel and no frequency planning is required.

Figure3.8 Fractional Frequency Reuse with Mobile WiMAX

3.2.8 Quality of Service

WiMAX was developed from the outset to meet the stringent requirements for the delivery of broadband services. The WiMAX QoS is specified for each service flow. The connection-oriented QoS therefore, can provide accurate control over the air interface. Since the air interface is usually the bottleneck, the connection-oriented QoS can effectively enable the end-to-end QoS control. The service flow parameters can be dynamically managed through MAC messages to accommodate the dynamic

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service demand. Service flows provide the same control mechanism in both the DL and UL to improve QoS in both directions. Furthermore, since the sub-channels are orthogonal, there is no intra-cell interference in either DL or UL. Therefore, the DL and UL link quality and QoS can be easily controlled by the base station scheduler. The high system throughput also allows efficient multiplexing and low data latency. Therefore, with fast air link, high system throughput, symmetric downlink/uplink capacity, fine resource granularity and flexible resource allocation Mobile WiMAX can support a wide range of data services and applications with varied QoS requirements as summarized in Table 3.

Support for QoS in 3G systems, on the other hand, is more limited. Using a priority-based technique to support Conversational Class, Streaming Class, Interactive Class, and Background Class services, higher priority traffic may completely starve lower priority traffic during periods of high usage.

QoS Category

Applications QoS

Specifications

UGS Unsolicited Grant

Service

VoIP Maximum Sustained Rate Maximum Latency

Tolerance Jitter Tolerance

rtPS Real-Time Polling

Service

Streaming Audio or Video

Minimum Reserved Rate Maximum Sustained Rate

Maximum Latency Tolerance

Traffic Priority ErtPS

Extended Real-Time Polling Service

Voice with Activity Detection (VoIP)

Minimum Reserved Rate Maximum Sustained Rate

Maximum Latency Tolerance Jitter Tolerance Traffic Priority

nrtPS Non-Real-Time

Polling Service

File Transfer Protocol (FTP)

Minimum Reserved Rate Maximum Sustained Rate

Traffic Priority

BE Best-Effort Service

Data Transfer, We Browsing, etc.

Maximum Sustained Rate Traffic Priority

Table3.4 Mobile WiMAX Applications and Quality of Service

3.2.9 Advanced Antenna Technology

In CDMA-based systems, the signals occupy the entire bandwidth. Since the processing complexity for smart antenna technologies scales with the channel bandwidth, supporting advanced antenna technologies in broadband wireless channels poses a more significant challenge than it does with Mobile WiMAX [23]. Both 1xEVDO and HSPA support simple transmit diversity and the HSPA standard has an option to support Beam forming. In general however, the use of advanced antenna technologies in current 1xEVDO and HSPA solutions has been limited.

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Mobile WiMAX on the other hand, is based on smart antenna friendly OFDM/OFDMA technology. OFDM/OFDMA converts a frequency selective wideband channel into multiple flat narrow band sub-carriers and allows smart antenna operations to be performed on vector flat sub-carriers. Complex equalizers are not required to compensate frequency selective fading. With OFDM/OFDMA systems therefore, it is far easier to support smart antenna technologies. Mobile WiMAX supports a full range of smart antenna technologies to enhance performance including Beam forming, STC and SM [24, 25, 26, and 27]. These technologies can improve both system coverage and capacity.

WiMAX also supports dynamic switching between the smart antenna technologies to maximize the benefit based on channel conditions. SM for example, improves peak throughput but, when channel conditions are poor, the Packet Error Rate (PER) can be high and thus the coverage area where target PER is met may be limited. STC on the other hand provides large coverage regardless of the channel condition but does not improve the peak throughput. Mobile WiMAX supports Adaptive MIMO Switching (AMS) between multiple MIMO modes to maximize spectral efficiency with no reduction in coverage area as illustrated in Figure 3.9.

Figure3.9 Performance of Adaptive MIMO Switch (AMS)

3.2.10 Spectral Efficiency

Mobile WiMAX, as a 4G technology, deployments has higher spectral efficiency and will outperform EVDO and HSPA

Figure3.10 Mobile WiMAX Versus 3G spectral efficiency comparison

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3.2.11 Throughput Comparison

Mobile WiMAX provides much better throughput than EVDO and HSxPA. Mobile WiMAX (with MIMO) provides 3 times more throughput than HSPA or EVDO Rev B in the same occupied spectrum. Mobile WiMAX (with SIMO) has 100% DL throughput advantage over EV-DO Rev B and a ~130% advantage over HSPA.

3G-LTE is the only 3G technology which may put a real match to WiMAX. However, it will not be commercially available until at least 2010/2011. Furthermore, 3G-LTE does not provide an EVOLUTIONARY path from existing 3G networks, but does require an effort closer to “fork-lift” revolution in the sense that it is a completely new network and requires entirely new devices.

Figure3.11 Mobile WiMAX versus 3GNet Throughput Comparison

3.2.12 Base-Station Deployment

The throughput and spectral efficiency advantages of mobile WiMAX result in fewer base stations to achieve the same performance. Since deploying Radio Access Networks (base-stations) is a significant percentage of the capital investment and operational expenses of the deployment, this has a substantial impact on the business case of deploying a mobile Personal Broadband network, and far-reaching ramifications on the service provider’s business and pricing model.

Figure3.12 Mobile WiMAX versus 3G Number of required sites

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3.2.13 Power control

3.2.13.1 Power control in 3G

Power control is used to overcome near-far-problem (NFP) in 3G.

Power control means the received power from all MS’s are nearly equal regardless their location whether near or far.

Figure3.13 Near-Far-problem

Open loop power control

It depends on MS only each BS transmits pilot continuously. The MS receive pilot, measure its signal strength and adjust. Its transmitted power increase proportional to the pilot signal without feedback to BS.

Closed loop power control

Reverse closed loop power control

The MS transmits & Bs receives. The Bs measures the receive signal and compare it with certain threshold and generate power control command (Up or Down) to MS the MS responds and the process continue until power control is full filled.

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Reverse closed loop power control

The BS transmits & MS receives. The MS measures the receive signal and compare it with certain threshold and generate power control command (Up or Down) to BS the BS responds and the process continue until power control is full filled.

Combination of closed loop and open loop power control

Prior to any transmission, the MS measure the pilot signal from BS and adjust its transmitted power.

Additional refinement, The BS receives the signal from MS, measure it and compare it with threshold and generate power control command. The MS responds and the process continue until power control is full filled.

3.2.13.2 Power control in WiMAX

Power control algorithms are used to improve the overall performance of the system; it is implemented by the base station sending power control information to each of the CPEs to regulate the transmit power level so that the level received at the base station is at a pre-determined level. In a dynamical changing fading environment this pre-determined performance level means that the CPE only transmits enough power to meet this requirement. The converse would be that the CPE transmit level is based on worst-case conditions. The power control reduces the overall power consumption of the CPE and the potential interference with other co-located base stations. For LOS the transmit power of the CPE is approximately proportional to its distance from the base station, for NLOS it is also heavily dependent on the clearance and obstructions.

Open loop power control

The MS could determine the transmit power for the first attempt based on the transmit power information sent by the BS and the measured DL signal strength.

Closed loop power control

The MS could determine the transmit power based on the power control information feed backed by the BS.

The fast-moving MS

Due to the very dynamic changes of the channel response, the power control would not be able to compensate the fast fading channel effect. As a result, the power control shall be used to compensate the distance-dependent path loss and slow fading only. Moreover, the fast-

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moving MS could request to change the power control mode from open loop to closed loop and vice versa. The BS could also send the unsolicited power control mode change command to the MS. 3.2.13.3 Comparison between Powers Controls on 3G versus WiMAX

Items

3G

WiMAX

Aim (UL)

To solve near-far problem

To mitigate interference

Interference

Inter-cell Interference

Intra-cell Interference

Priority

High

Low

Scheduler

N/A

Tightly Coupled

Table3.5 Power Control on 3G versus WiMAX

3.3 Comparison between WiMAX and WiFi 3.3.1 Introduction

There is lots of confusion among both WiMAX and WiFi technologies. There are many reasons for that; one could be both technologies starts with W letter that makes some people think that they both are same technologies with different names. There is one more major reason why it makes confusing, they both belong from standard setter IEEE and there standards first 3 letter are same “802”, and both WiFi and WiMAX technologies belong from Wireless connectivity family. Here it will be explained these two technologies may have few visible similarities but how much they are different from each other when considered practically.

WiFi: WiFi is used for developing wireless LAN to access high speed internet or access just a network for file sharing and software services.

WiMAX: WiMAX is quite latest technology and it can do far more than just developing wireless networks for high speed internet. It is also refer as Wireless broadband access, which can transfer not only data, but voice data, video data etc and at much higher rates.

WiFi: WiFi is capably for short range data transfer, which can be within hundred of meters range using non licensed spectrum to access network. WiFi is mostly connected to network in certain area which may not be connected to internet; it can be used for file sharing only.

WiMAX: WiMAX is designed for long distance coverage and it covers distance in kilometers, it uses licensed spectrum and unlicensed also in some case. WiMAX delivers point-to-point connection to the

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internet from service provide to as user. In WiMAX there are multiple standards of 802.16 a, b etc, so they are used for different types of access from mobile connectivity to fixed location connections.

WiFi: WiFi has introduced a quality of service similar to fixed Ethernet, where packets are priorities on their tags. This shows that quality of service (QoS) is relative to packet flow.

WiMAX: WiMAX uses technology based on setting up connection between end users’ device and base station. Special algorithm is scheduled for specific connection. This shows that Quality of Services (QoS) parameters can be guaranteed for each flow.

WiFi is deployed much more than WiMAX because of its ease of installation and cost effectiveness. It is easily deployed within the building or room for providing internet access by third party internet service providers. Many public places, hotels, coffee shops have installed Wi-fi access points providing high speed internet to their customers

3.3.2 Scalability

The WiMAX standard relies upon a grant-request access protocol that, in contrast to the contention-based access used under WiFi doesn’t allow data collisions and, therefore, uses the available bandwidth more efficiently. No collisions means no loss of bandwidth due to data retransmission. All communication is coordinated by the base station. Other characteristics of the WiMAX standards include:

3.3.2.1 Improved user connectivity

The WiMAX standards keep more users connected by virtue of its flexible channel widths and adaptive modulation. Because it uses channels narrower than the fixed 20-MHz channels used in WiFi, the WiMAX standards can serve lower- data-rate subscribers without wasting bandwidth. When subscribers encounter noisy conditions or low signal strength, the adaptive modulation scheme keeps them connected when they might otherwise be dropped.

3.3.2.2 Higher quality of service

This standard also enables WISPs to ensure QoS for customers that require it and to tailor service levels to meet different customer requirements. For example, the Wimax standards can guarantee high bandwidth to business customers or low latency for voice and video applications, while providing only best-effort and lower-cost service to residential Internet surfers.

3.3.2.3 Full support for WMAN service

From its inception, the WiMAX standards were designed to provide WMAN service. Hence, it is able to support more users and deliver faster data rates at longer distances than last-mile implementations based on the 802.11g standard.

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3.3.2.4 Robust carrier-class operation

The standard was designed for carrier-class operation. As more users join, they must share the aggregate bandwidth and their individual throughput decreases linearly. The decrease, however, is much less dramatic than what is experienced fewer than WiFi. This capability is termed “efficient multiple access.”

We Conclude that: WiFi uses 20 MHz channels; WiMAX is flexible allowing channels from 1.5 MHz to 20 MHz, with

spectral efficiency superior to that of 802.11 a and g, but lower than that of 802.11n.

WiFi WiMAX

Wide (20MHz) frequency channels MAC layer designed to support

10’s of users

Channel bandwidths can be chosen by operator (e.g. for sectorization)

1.5 MHz to 20 MHz width channels. MAC designed for scalability. independent of channel bandwidth

MAC layer designed to support

thousands of users.

Table3.6 WiMAX versus WiFi Scalability

3.3.3 Relative Performance

3.3.3.1 Channel Bandwidth

WiMAX: the approved WiMAX Forum profiles for Mobile WiMAX currently support channel bandwidths of 5, 7, 8.75, and 10MHz. The IEEE802.16e 2005 standard, on which Mobile WiMAX technology is based, supports channel bandwidths from 1.25 to 20MHz, leaving open the possibility for additional WiMAX channel profiles in the future. In some cases local regulatory requirements will dictate the choice of channel bandwidth by limiting the amount of spectrum available to individual licensees or by specifying a specific channel plan From an equipment-complexity and cost point of view there will be little or no difference in selecting a 5MHz versus a10MHz channel bandwidth .Since the wider channel bandwidth will have greater capacity it will , in most cases , be more cost effective to deploy the largest channel bandwidth support able by local regulatory requirements , the desired reuse factor , and desire to conserve spectrum for future overlays.

WiFi: Standardization is a process driven by market forces. Interoperability issues between non-Wi-Fi brands or proprietary deviations from the standard can still disrupt connections or lower throughput speeds on all users’ devices that are within range, to include the non-Wi-Fi or

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proprietary product. Moreover, the usage of the ISM band in the 2.45 GHz range is also common to Bluetooth, WPAN-CSS and any new system will take its share.

Wi-Fi pollution, or an excessive number of access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other access points by others, caused by overlapping channels in the 802.11g/b spectrum, as well as with decreased signal-to-noise ratio (SNR) between access points. This can be a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points. Additionally, other devices use the 2.4 GHz band: microwave ovens, security cameras, Bluetooth devices and (in some countries) Amateur radio, video senders, cordless phones and baby monitors, all of which can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a Wi-Fi 5 GHz product, (802.11a, or the newer 802.11n if it has 5 GHz support) because the 5 GHz band is relatively unused, and there are many more channels available. This also requires users to set up the 5 GHz band to be the preferred network in the client and to configure each network band to a different name (SSID). It is also an issue when municipalities,[16] or other large entities such as universities, seek to provide large area coverage. This openness is also important to the success and widespread use of 2.4 GHz WiFi.

3.3.3.2 Data rate

WiFi versus WiMAX Efficiency: Given the data rates supported on its 25 MHz channel (1 M to 11 Mbps), 802.11b

delivers bandwidth efficiency between 0.04 and 0.44 bps/Hertz. The 6 M to 54 Mbps transmission rate supported on an 802.11a or g 20 MHz channel yields a bandwidth efficiency between .24 and 2.7 bps/Hertz. In WiMAX, the combination of modulation and coding schemes yields bandwidth efficiency up to 5- bits/Hertz. That would deliver a 100-Mbps transmission rate on a 20-MHz radio channel. The bandwidth efficiency will decrease as the transmission range increases, so a maximum of 3.5 bits/Hertz or 70 Mbps on a 20 MHz channel would be more realistic.

3.3.4 Quality of Service

3.3.4.1 Quality of Service in WiFi:

There are plans to incorporate quality of service (QoS) capabilities in Wi-Fi with the adoption of the IEEE 802.11e standard. The 802.11e standard will include two operating modes, either of which can be used to improve service for voice:

Wi-Fi Multimedia Extensions (WME)-Mandatory.

Wi-Fi Scheduled Multimedia (WSM)-Optional.

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Wi-Fi Multimedia Extensions (WME): This uses a protocol called Enhanced Multimedia Distributed Control Access (EDCA),

which is Extensions an enhanced version of the Distributed Control Function (DCF) defined in the original 802.11 MAC.

The enhanced part is that EDCA will define eight levels of access priority to the shared wireless channel. Like the original DCF, the EDCA access is a contention-based protocol that employs a set of waiting intervals and back-off timers designed to avoid collisions. However, with DCF, all stations use the same values and hence have the same priority for transmitting on the channel.

With EDCA, each of the different access priorities is assigned a different range of waiting intervals and back-off counters. Transmissions with higher access priority are assigned shorter intervals. The standard also includes a packet-bursting mode that allows an access point or a

mobile station to reserve the channel and send 3- to 5-packets in sequence.

Wi-Fi Scheduled Multimedia (WSM):

True consistent delay services can be provided with the optional Wi-Fi Scheduled Multimedia (WSM). WSM operates like the little used Point Control Function (PCF) defined with the original 802.11 MAC.

In WSM, the access point periodically broadcasts a control message that forces all stations to treat the channel as busy and not attempt to transmit. During that period, the access point polls each station that is defined for time sensitive service.

To use the WSM option, devices must first send a traffic profile describing bandwidth, latency. If the access point does not have sufficient resources to meet the traffic profile, it will return a busy signal.

3.3.4.2 Quality of Service in WiMAX

The IEEE 802.16 standard provides powerful tools in order to achieve different QoS constraints. The 802.16 standard MAC Layer provides QoS differentiation for the different types of applications that might operate over 802.16 networks, through five defined scheduling service types, also called QoS classes.

This classification into these scheduling service classes facilitates bandwidth sharing between different users. Every user has a quality of scheduling service class, also known as QoS class. According to this parameter, the BS scheduler allocates the necessary amount of bandwidth required for each application. This mechanism allows an efficient and adapted distribution of the existing resources. Therefore, a real-time application, such as a video application, will have the priority in bandwidth allocation in comparison with FTP (File Transfer

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Protocol) or email applications. This is not the case; for example, with the presently used WiFi (WLAN) system where all services have exactly the same level of QoS.

Scheduling services represent the data handling mechanisms supported by the MAC scheduler for data transport on a given connection. Uplink request (grant) scheduling is performed by the BS based on the scheduling service type, with the intent of providing each subordinate SS with a bandwidth for uplink transmissions and opportunities to request this bandwidth, when needed. As already mentioned in this book, each connection is associated with a single data service flow and each service flow is associated with a set of QoS parameters. These parameters are managed using the DSA and DSC MAC management messages dialogues four scheduling services were defined in 802.16e:

Unsolicited Grant Service (UGS):

The UGS scheduling service type is designed to support real-time data streams consisting of fixed-size data packets issued at periodic intervals. This would be the case, for example, for TI/EI classical PCM (Pulse Coded Modulation) phone signal transmission and Voice over IP without silence suppression.

In a UGS service, the BS provides fixed-size data grants at periodic intervals. This eliminates the overhead and latency of SS requests. Figure 11.7 illustrates the UGS mechanism. The BS provides Data Grant Burst IEs (UL-MAP_IEs) to the SS at periodic intervals based upon the maximum sustained traffic rate of the service flow. The size of these grants is sufficient to hold the fixed-length data associated with the service flow, taking into account the associated generic MAC header and grant management sub header.

Figure3.14 UGS scheduling service uplink grants allocation mechanism

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Real-time Polling Service (rtPS):

The rtPS scheduling service type is designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals. This would be the case, for example, for MPEG (Moving Pictures Experts Group) video transmission. In this service, the BS provides periodic unicast (uplink) request opportunities, which meet the flow's real-time needs and allow the SS to specify the size of the desired grant. This service requires more request overheads than UGS, but supports variable grant sizes for optimum real-time data transport efficiency.

Figure3.15 rtPS scheduling service uplink grants allocation and request mechanismnon-real-time Polling Service (nrtPS)

Non-Real-Time Polling Service (nrtPS):

The nrtPS is designed to support delay-tolerant data streams consisting of variable-size data packets for which a minimum data rate is required. The standard considers that this would be the case, for example, for an FTP transmission. In the nrtPS scheduling service, the BS provides unicast uplink request polls on a ‘regular’ basis, which guarantees that the service flow receives request opportunities even during network congestion. The standard states that the BS typically polls nrtPS CIDs on an interval on the order of one second or less. In addition, the SS is allowed to use contention request opportunities, i.e. the SS may use contention request opportunities as well as unicast request opportunities.

Figure3.16 Illustration of the nrtPS scheduling service uplink grants allocation and request mechanism. The SS may use contention request opportunities as well as unicast request opportunities

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Best Effort (BE):

The BE service is designed to support data streams for which no minimum service guarantees are required and therefore may be handled on a best available basis. The SS may use contention request opportunities as well as unicast request opportunities when the BS sends any. The BS do not have any unicast uplink request polling obligation for BE SSs. Therefore, a long period can run without transmitting any BE packets, typically when the network is in the congestion state.

Figure3.17 Illustration of the BE scheduling service uplink grants allocation and request mechanism. The BS does not have any unicast uplink request polling obligation for a BE SS

WiFi WiMAX Standard cannot currently guarantee

latency for Voice, Video Designed to support Voice and Video from ground up

Standard does not allow for differentiated levels of service on a per-

user basis

• Supports differentiated service levels: e.g. T1 for business customers; best

effort for residential.

802.11e (proposed) QoS is prioritization only Centrally-enforced QoS

Table3.7 WiMAX versus WiFi QOS

3.3.5 RANGE

WiMAX range:

In the early days of WiMAX it was common to see statements in the media describing WiMAX multipoint coverage extending 30 miles. In a strict technical sense (in some spectrum ranges) this is correct, with even greater ranges being possible in point to point links. In practice (and especially in the license-free bands) this is wildly overstated especially where non line of sight (NLOS) reception is concerned.

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Due to a variety of factors explained in more detail in other FAQ answers, the average cell ranges for most WiMAX networks will likely boast 4-5 mile range (in NLOS capable frequencies) even through tree cover and building walls. Service ranges up to 10 miles (16 Kilometers) are very likely in line of sight (LOS) applications (once again depending upon frequency). Ranges beyond 10 miles are certainly possible, but for scalability purposes may not be desirable for heavily loaded networks. In most cases, additional cells are indicated to sustain high quality of service (QOS) capability. For the carrier class approach, especially in regards to mobility, cells larger than this seem unlikely in the near future. The primary WiMAX focused US carrier Clear wire has stated that its cell sites are planned at about 1.5 miles apart for mobile purposes. This choice is clearly one intended to meet NLOS requirements. In licensed frequencies, expect similar performance or better for WiMAX than in traditional cellular systems.

WiFi range:

Wi-Fi range is used for low-cost, unregulated point-to-point connections, as an alternative to cellular networks, microwave or satellite links. The use of the term "long range WiFi" as depicted on this page for extreme ranges is not in any way endorsed by the Wi-Fi Alliance and is not in any way tested or certified by the WiFi Alliance for interoperability or performance.

The average range of WiFi is 100 meters. And it considers small range and this is disadvantage. The advantage in this small range it avoid “near-far” compensation and the delay spread about 0.8μ seconds and it is small.

Figure3.18 WiMAX versus WiFi range

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3.3.6 Coverage

WiMAX operates on the same general principles as WiFi -- it sends data from one computer to another via radio signals. A computer (either a desktop or a laptop) equipped with WiMAX would receive data from the WiMAX transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access.

The fastest WiFi connection can transmit up to 54 megabits per second under optimal conditions. WiMAX should be able to handle up to 70 megabits per second. Even once those 70 megabits is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent of cable-modem transfer rates to each user.

The biggest difference isn't speed; it's distance. WiMAX outdistances WiFi by miles. WiFi's range is about 100 feet (30 m). WiMAX will blanket a radius of 30 miles (50 km) with wireless access. The increased range is due to the frequencies used and the power of the transmitter. Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in some circumstances, but the potential is there to cover huge tracts of land.

IEEE 802.16 Specifications:

Range - 30-mile (50-km) radius from base station

Speed - 70 megabits per second

Line-of-sight not needed between user and base station

Frequency bands - 2 to 11 GHz and 10 to 66 GHz (licensed and unlicensed bands)

Defines both the MAC and PHY layers and allows multiple PHY-layer specifications

Figure3.19 WiMAX vs. WiFi coverage

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3.3.7 WiMAX Security

How do we establish a security environment for the use of the network and for the messages exchanged in it? Base Stations perform authentication using credentials to control the access of users to the network. Connections use security associations to indicate the way they will protect their messages.

Example: Line does a lot of Instant Messaging with her friends but there are a lot of impostors in the network, trying to get identity information. She is afraid to talk to some people because of this. She also wants to keep her messages confidential.

Context Fixed or mobile stations in wireless networks distributed in relatively large geographic areas, where WiFi cannot reach.

Problem How do we establish a security environment for the use of the network and for the messages exchanged in it? Subscribers need to exchange messages without exposing them to eavesdroppers. They also need to know they are talking to authentic subscribers. The network company only wants to authorize legitimate subscribers to use the links. The possible solution is constrained by the following forces:

We need to restrict access to the network only to registered subscribers. Otherwise it would be difficult to guarantee bandwidth and performance to legitimate users.

Subscriber needs to exchange confidential messages, authenticated messages, and messages with guarantees that they have not been modified in transit. These are important issues for business use.

The approach should be transparent or very easy for the users.

Solution

Base Stations perform authentication using credentials to control the access of users to the network. Connections use security associations to indicate the way they will protect their messages. Security is closely tied to connections and connection types. WiMAX defines two connection types, management and data. Management connections are further subdivided into basic, primary, and secondary. Stations perform authentication using credentials, X.509 certificates in the current standard. Once authenticated, a user is given a token to access the system.

802.16 define a Privacy and Key Management (PKM) protocol to address the goals of subscriber station confidentiality and preventing theft of provider service.

The PKM uses Security Associations (SAs), of which there are two types. A data SA specifies how messages between the base station and subscriber station are to be encrypted, which algorithms will be used, the keys to be used and related information. By using additional SAs different methods of encryption may be used for different groups of messages. An authorization SA is used for management and update.

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3.4 Comparison between Mobile and Fixed WiMAX To make a comparison between mobile and fixed WiMAX we should to know what’s WiMAX

rollout ?,what’s the type of WiMAX ?,what’s mobile WiMAX ? and what’s fixed WiMAX?

3.4.1 WiMAX Rollout

WiMAX Standards Like most IEEE standards, the 802.16 standard families consists of the basic 802.16 standard, and several, ever-increasing variations signified by adding a small alphabet to the basic specification name. The first 802.16 standard was published on 8 April 2002 and was followed by three amendments 802.16a to address issue of radio spectrum, 802.16b to address the issue of quality of service and 802.16c to address the issue of interoperability.

In September 2003, a revision project called 802.16REVd commenced aiming to align the standard with aspects of the European Telecommunications Standards Institute (ETSI)

HYPERMAN standard as well as lay down conformance and test specifications. This project concluded in 2004 with the release of IEEE 802.16-2004 and the withdrawal of the earlier 802.16 documents including the a/b/c also an amendment to the standard, 802.16e, and addressing mobility was concluded in 2005. This is sometimes called “Mobile WiMAX”. The latest revisions in progress are 802.16f and g.

These specifications try to address the management issues relating to 802.16 specifications, especially to 802.16e. The 802.16g defines the management plan procedures and services, and the 802.16f defines the management information base.

3.4.1.1 Features of IEEE 802.16a

It was approved in January 2003.

It covers frequency band between 2GHz and11GHz (licensed and unlicensed).

Its lower frequencies make non-line of sight a possibility; hence, it makes the IEEE 802.16a standard the appropriate technology for last-mile application where obstacles like trees and buildings are often present and where base stations may need to be roofs of homes or buildings rather than towers on mountains.

Total data rate can be up to 75 Mb/s in each 20MHz channel.

It has up to 30 miles of range with a typical cell radius of 4-6 miles.

It provides an ideal wireless backhaul technology to connect 802.11 wireless LANs and commercial hotspots with the Internet.

It enables business to flexibly deploy new 802.11 hotspots in locations where traditional wired connection may be unavailable or time consuming to provide and offers service providers

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around the globe with a flexible new way to stimulate growth of the residential broadband access market segment.

It will be mostly used for small businesses, residential users and for backhaul or hotspot. The most common 802.16 configurations consist of base station mounted on building or tower that communicates on a point to multi-point basis with subscriber station located in businesses and homes.

3.4.1.2 General features of IEEE 802.16b

IEEE 802.16b aims at the needs of license-exempt (unlicensed) applications around 5-6 GHz.

3.4.1.3 General features of IEEE 802.16c

The IEEE Standards Board approved IEEE 802.16c in December 2002. The aim was to develop 10-66 GHz system profiles to aid interoperability specifications for Line-of-Sight broadband wireless access. Its peak (shared) data rate 70Mbits/s, with range up to 50km.

3.4.1.4 IEEE 802.16d-2004 “Fixed WiMAX”

IEEE 802.16a has all but been forgotten as the focus recently has been on IEEE 802.16- 2004, which is also known as 802.16REVd .802.16-2004 is an improvement to the 802.16a Standard separately, 802.16-2004, was ratified in July 2004. 802.16-2004 is a wide-ranging standard that includes previous versions and covers both LOS and NLOS applications in the 2-66 GHz frequencies. The changes introduced in 802.16-2004 were focused on fixed and nomadic applications in the 2-11 GHz frequencies. Two multi-carrier modulation techniques are supported in 802.16-2004: OFDM with 256 carriers and OFDMA with 2048 carriers. IEEE 802.16-2004 is a fixed wireless access technology, meaning that it is designed to serve as a wireless DSL replacement technology, to compete with the incumbent DSL or broadband cable providers or to provide basic voice and broadband access in underserved areas where no other access technology exists; examples include developing countries and rural areas in developed countries where running copper wire or cable does not make economic sense.

802.16-2004 is also a viable solution for wireless backhaul for Wi-Fi access points or potentially for cellular networks, in particular if licensed spectrum is used. Finally, in certain configurations, WiMax Fixed can be used to provide much higher data rates and therefore be used as a T1 replacement option for high-value corporate subscribers. 802.16- 2004 can also support VoIP (Voice over Internet Protocol), and assuming that the G.729 (8kbps) codec is used, it reportedly supports up to 96 simultaneous voice calls in a 3.5MHz radio channel. The trade-off is increased path losses at frequencies such as 5.8GHz. It is unlikely that an operator would use 2.4GHz to offer voice services due to the higher probability that interference could develop (simple microwave ovens radiate RF in the 2.4GHz band).

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3.4.1.5 IEEE 802.16e “Mobile WiMAX”

IEEE 802.16e is the portable or mobile version of WiMAX, which promises to support voice and data sessions at vehicular speeds of up to 120 kilo-meters per hour. The current strategy within the WiMAX Forum is to launch 802.16e with portable features in order to achieve rapid time to market. As the technology and market opportunity matures, the forum intends to introduce full-scale mobility. The main features of mobile WiMAX are: Approved on the 23th of September 2004. Covers "Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands. Optimized for and backwards compatible with fixed stations. Work on Licensed bands from 2 to 6 GHz. The IEEE 802.16e introduces nomadic capabilities which allow users to connect to wireless Internet Service Provider (WISP) when they travel outside their home or business, or go to another city that also has a WISP. It is targeted at mobile users, who will be able to keep their connection while moving or driving from 75 to 93 miles per hour. It has proved to be the most controversial standard, as it overlaps with the authorization of the IEEE 802.20 group, which was establish before 802.16e. Typical Channel BW < 5MHz.

Packet oriented architecture. Channelization and control for multimedia services with QoS. High efficiency data uplinks and downlinks Technology. Low latency architecture.

3.4.2 Types of WiMAX

WiMAX Forum anticipates rollout of its technology in 3 phases:

Phase 1: Fixed Location, Private Line Services, Hot Spot Backhaul. Phase 2: Broadband Wireless Access/Wireless DSL Phase 3: Mobile/Nomadic Users

The WiMAX family of standards concentrates on two types of usage models a fixed usage model and a mobile usage model. The basic element that differentiates these systems is the ground speed at which the systems are designed to manage. Based on mobility, wireless access systems are designed to operate on the move without any disruption of service; wireless access can be divided into three classes; stationary, pedestrian and vehicular.

A mobile wireless access system is one that can address the vehicular class, whereas the fixed serves the stationary and pedestrian classes. This raises a question about the nomadic wireless access system, which is referred to as a system that works as a fixed wireless access system but can change its location.

3.4.2.1 Fixed WiMAX

Service and consumer usage of WiMAX for fixed access is expected to reflect that of fixed wire-line service, with many of the standards-based requirements being confined to the air interface. Because communications takes place via wireless links from Customer Premise

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Equipment (CPE) to a remote Non Line-of-sight (NLOS) base station, requirements for link security are greater than those needed for a wireless service. The security mechanisms within the IEEE 802.16 standards are sufficient for fixed access service.

Another challenge for the fixed access air interface is the need to set up high performance radio links capable of data rates comparable to wired broadband service, using equipment that can be self installed indoors by users, as is the case for Digital Subscriber Line (DSL) and cable modems. IEEE 802.16 standards provide advanced physical (PHY) layer techniques to achieve link margins capable of supporting high throughput in NLOS environment

3.4.2.2 Mobile WiMAX

The 802.16a extension, refined in January 2003, uses a lower frequency of 2 to 11 GHz, enabling NLOS connections. The latest 802.16e task group is capitalizing on the new capabilities this provides by working on developing a specification to enable mobile WiMAX clients. These clients will be able to hand off between WiMAX base stations, enabling users to roam between service areas.

3.4.2.3 Backhaul

Backhaul is actually a connection system from the Access Point (AP) back to the provider and to the connection from the provider to the network. A backhaul can set out any technology and media provided; it connects the system to the backbone. In most of the WiMAX deployments circumstances, it is also possible to connect several base stations with one another by use of high speed backhaul microware links. This would also allow for roaming by a WiMAX subscriber from one base station coverage area to another, similar to roaming enabled by cellular phone companies

There can be two cases of portability; full mobility or limited mobility. The effortless case of portable service involves a user transporting a WiMAX modem to a different location. Provided this visited location is serve by wireless broadband service, in this scenario the user re-authenticates and manually re-establishes new IP connections and is afforded broadband service at the visited location.

In the fully mobile scenario, user expectations for connectivity are comparable to facilities available in third generation (3G) voice/data systems. Users may move around while engaged in a broadband data access or multimedia streaming session. Mobile wireless systems need to be robust against rapid channel variation to support vehicular speeds.

There are significant implications of mobility on the IP layer owing to the need to maintain rout-ability of the host IP address to preserve in-flight packets during IP handoff. This may require authentication and handoff for uplink and downlink IP packets and Medium Access Control (MAC) frames. The need to support low latency and low packet loss handovers of data streams as users transition from one base station to another is clearly a challenging task. For

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mobile data services, users will not easily adapt their service expectations because of environmental limitations that are technically but not directly relevant to the mode of user. For these reasons, the network and air interface must be designed to anticipate these user expectations and deliver accordingly.

3.4.3 What is Fixed WiMAX?

IEEE 802.16a has all but been forgotten as the focus recently has been on IEEE 802.16- 2004, which is also known as 802.16REVd .802.16-2004 is an improvement to the 802.16a Standard separately, 802.16-2004, was ratified in July 2004. 802.16-2004 is a wide-ranging standard that includes previous versions and covers both LOS and NLOS applications in the 2-66 GHz frequencies. The changes introduced in 802.16-2004 were focused on fixed and nomadic applications in the 2-11 GHz frequencies. Two multi-carrier modulation techniques are supported in 802.16-2004: OFDM with 256 carriers and OFDMA with 2048 carriers. IEEE 802.16-2004 is a fixed wireless access technology, meaning that it is designed to serve as a wireless DSL replacement technology, to compete with the incumbent DSL or broadband cable providers or to provide basic voice and broadband access in underserved areas where no other access technology exists; examples include developing countries and rural areas in developed countries where running copper wire or cable does not make economic sense. 802.16-2004 is also a viable solution for wireless backhaul for Wi-Fi access points or potentially for cellular networks, in particular if licensed spectrum is used. Finally, in certain configurations, WiMAX Fixed can be used to provide much higher data rates and therefore be used as a T1 replacement option for high-value corporate subscribers. 802.16- 2004 can also support VoIP (Voice over Internet Protocol), and assuming that the G.729 (8kbps) codec is used, it reportedly supports up to 96 simultaneous voice calls in a 3.5MHz radio channel. The trade-off is increased path losses at frequencies such as 5.8GHz. It is unlikely that an operator would use 2.4GHz to offer voice services due to the higher probability that interference could develop (simple microwave ovens radiate RF in the 2.4GHz band).

3.4.4 What is mobile WiMAX?

The IEEE 802.16 Working Group on broadband wireless access standards, established by the IEEE Standards Board in 1999, prepared the formal specie actions for broadband wireless metropolitan area networks (Wireless MAN, the 802.16 family of standards is the basis of Mobile WiMAX). IEEE 802.16-2004 (also called 802.16d) provides support for non-line-of-sight (NLOS) and indoor end-user terminals for fixed wireless broadband. The IEEE 802.16e-2005 supports both time division duplexing (TDD) and frequency division duplexing (FDD) modes. In 2005, the standard was amended (IEEE 802.16e-2005 or 802.16e) to add support for data mobility. IEEE 802.16e or Mobile WiMAX improves on the modulation schemes used in the original (Fixed) WiMAX standard by introducing scalable orthogonal frequency-division multiple access (SOFDMA).The system profile in IEEE 802.16e-2005 is not backward compatible with the Fixed WiMAX system profile. The charter of the WiMAX Forum, which has more than 400 members, is to promote and certify the compatibility and interoperability of broadband wireless access equipment that conforms to IEEE 802.16 and the ETSI Hyper MAN standard.

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The WiMAX Forum defines and conducts conformance and interoperability testing to ensure that different vendor systems work seamlessly with each other. WiMAX certification profile les specify characteristics such as spectrum band, duplexing and channelization. Several profiles exist for Fixed and Mobile WiMAX.

There are currently two waves of certification planned for Mobile

WiMAX equipment:

Wave 1: Mobile WiMAX system profile with single-input single-output (SISO) terminals for the 2.3GHz and 3.5GHz bands

Wave 2: Mobile WiMAX system profile with multiple-input multiple-output (MIMO) terminals and beam-forming support for the 2.6GHz band (sometimes referred to as the 2.5GHz band).

Because IEEE 802.16 standardization only covers basic connectivity up to the media access (MAC) level, the WiMAX Forum also addresses network architecture issues for Mobile WiMAX networks. The first network architecture specification (Release 1.0) focused on delivering a wireless internet service with mobility.

Release 1.5 introduced support for telecom-grade mobile services, supporting full IMS interworking, carrier-grade VoIP, broadcast applications, such as mobile TV, and over-the-air provisioning. While Mobile WiMAX offers the promise of high-speed wireless broadband services, it is still very much in its infancy and real-life performance has yet to be proved.

Figure3.20 Mobile versus Fixed data rate

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Conclusion:

It’s based on standard of IEEE 802.16e

It’s cell radius from 2-7 km

It’s range up to 20 km

It’s bit rate up to 15 Mbps

Full Mobility Access

3.4.5 Difference between Fixed vs. Mobile

3.4.5.1 Mobility Management and Handoff

The simplest explanation for the difference between the fixed and mobile variants of WiMAX boil down to the fact that the mobile variant enables a hand-off from one base station to another as the user, in one session, moves from the coverage zone of one base station to another. This is also known as “mobility management”. To make this happen, vendors must engineer the mobility management technology into their base stations at considerable cost over the fixed WiMAX technology. Service providers should assess what portion of their target market requires the mobility management piece when weighing fixed vs. mobile. From a high view, “mobile” means the service functions at 70 MPH while performing competent hand-offs. Service providers should assess what percentage of their subscribers will require that level of service.

3.4.5.2 Technically both are based on OFDM

Fixed WiMAX mostly 3.5 GHz FDD Mobile WiMAX mostly 2.5 and 3.5 GHz TDD

3.4.5.3 Mobile WiMAX adds

Link adaptation and power control

Paging

Handover mechanisms

Mobile IP architecture

Scalable OFDMA

Mobility

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fixed mobile

Standard IEEE 802.16a-2004 IEEE 802.16e-2005

Spectrum 2 -11 GHz (3.5 GHZ,5.8 GHZ) < 6 GHz (2.5 GHZ,3.5 GHZ, 5.8 GHZ)

Channel Conditions

Line of Sight, Non light of sight Line of Sight, Non light of sight

Bit Rate Up to 75 Mbps Up to 15 Mbps

Modulation OFDM 256 sub-carriers QPSK, 16QAM, 64QAM

SOFDMA 2048 sub-carriers QPSK, 16QAM and 64QAM ,BPSK

Mobility Fixed, nomadic fixed , portable ,Nomadic, Mobility

Channel Bandwidths

Scalable 1.5 to 20 MHz

Scalable 1.25 to 20 MHz

Typical Cell Radius

7 to 10 km Max range 50 km

2-5 km Max range 20 km

Hard and soft handoff

No handoff Hand-off

FDD/TDD TDD Duplexing technique

OFDM/OFDMA TDM OFDM

Multiplexing technique

Yes No Sub-channeling

Turbo Coding CC Error correction

Yes (up to 6 times) No Repeating coding

Yes No H-ARQ

optional No Beam forming

21dBm 23dBm SS Tx power

-1dBi 2dBi SS Tx gain

YES NO Head body loss

Table3.8 Mobile versus Fixed

Conclusion

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3.5 Conclusion In this Chapter, we outlined a high-level overview of the different broadband access

technologies by presenting a brief overview of each and compare them according to spectrum usage, capacity, coverage, and limitations.

Broadband technologies either fixed or wireless are developed to face the rapid growth challenges in telecommunication industry. Broadband systems can be used to deliver a variety of applications and services to both fixed and mobile subscribers. WiMAX could potentially deployed in a variety of spectrum bands: 2.3GHz, 2.5GHz, 3.5GHz and 5.8GHz. WiMAX faces a number of competitive challenges from both fixed line and third generation mobile broadband alternatives.

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4.1 Introduction In order to investigate the feasibility of a WiMAX rollout, one has to be able to assess the

number of base stations that will be needed in a specific area, dependent on the offered services and the number of active users. This is possible with the developed planning tool based on an accurate technical model. The tool takes into account the major technical characteristics of Mobile WiMAX together with the desired service specifications. It also has a certain degree of flexibility to introduce adaptations like e.g. new hardware.

To start, we discuss the calculation of the link budget, which indicates to what extent the signal may weaken (Figure 4.1). Then, a propagation model is proposed to determine the range, by taking into account the link budget. Based on this range, we illustrate the calculation of the cell coverage area. In a next step, we calculate the bit rate per cell sector and finally, the cell areas and bit rates are combined to estimate the required number of base stations.

Figure4.1 Link-budget for downlink

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4.2 Link Budget You are planning a vacation. You estimate that you will need $1000 dollars to pay for the hotels,

restaurants, food etc... You start your vacation and watch the money get spent at each stop. When you get home, you pat yourself on the back for a job well done because you still have $50 left in your wallet.

We do something similar with communication links, called creating a link budget. The traveler is the signal and instead of dollars it starts out with power. It spends its power (or attenuates, in engineering terminology) as it travels, is it wired or wireless.

Just as you can use a credit card along the way for extra money infusion, the signal can get extra power infusion along the way from intermediate amplifiers such as microwave repeaters for telephone links or from satellite transponders for satellite links. The designer hopes that the signal will complete its trip with just enough power to be decoded at the receiver with the desired signal quality.

In our example, we started our trip with $1000 because we wanted a budget vacation. But what if our goal was a first-class vacation with stays at five-star hotels, best shows and travel by QE2? A $1000 budget would not be enough and possibly we will need instead $5000. The quality of the trip desired determines how much money we need to take along.

With signals, the quality is measured by the Bit Error Rate (BER). If we want our signal to have a low BER, we would start it out with higher power and then make sure that along the way it has enough power available at every stop to maintain this BER.

A link budget is the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc.) to the receiver in a telecommunication system (Figure 4.2). It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feed line and miscellaneous losses. Randomly varying channel gains such as fading are taken into account by adding some margin depending on the anticipated severity of its effects. The amount of margin required can be reduced by the use of mitigating techniques such as antenna diversity or frequency hopping.

Figure4.2 illustration of link budget

Link Budget

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The link budget depends on several parameters, which are discussed in this paragraph. Different parameter values can be chosen in the planning tool, and for both the downlink and the uplink a separate link budget is calculated. We also indicate which values are selected for the business modeling study.

4.2.1 Why link budget?

To determine or calculate the maximum allowable (or available, or accepted) path loss (MAPL) where communication is achieved reliably or that will provide adequate signal strength at the cell boundary for acceptable voice quality over 90% of the coverage area it is flat or 75% if it is hilly. To determine the radius of the cell, to determine the location of cell sites as well as the spacing between them to ensure reliable uninterrupted communication as mobile station move through the coverage area of interest.

The link budget is dependent on several parameters, which are discussed in this paragraph. Different parameter values can be chosen in the planning, and for both the downlink and the uplink are separate link budget is calculated.

There are two link budget: reverse link budget i.e.as signal is transmitted from subscriber station (SS) and received by base station (BS) and forward link budget as signal is transmitted from the (BS) and received by the subscriber station(SS)

4.2.2 What is a link?

A link consists of three parts:

1. Transmitter (is BS in FL communication and is CPE in RL communication). 2. Receiver (is BS in RL communication and is CPE in FL communication). 3. Media.

The very simplest form of a link equation is written as:

(4.1)

This equation of course only talks about the signal power. We have not accounted for noise yet.

4.2.3 Base Station

We consider a base station (BS) with three sectors, and there is a choice from three BS profiles:

Standard BS. BS with 2 x 2 MIMO. BS with 2 x 2 MIMO and 2 element AAS.

Most base stations which are now entering the market belong to the category “BS with 2 x 2 MIMO” (which is considered in our study). Every profile contains the values for six different parameters

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required for the link budget calculation. Table 4.1 gives an overview of them, where DL and UL stands for downlink and uplink respectively, and Tx and Rx for transmitter and receiver.

Note that additionally a BS feeder loss of 0.5 dB is taken into account.

Standard BS BS with 2 x 2 MIMO

BS with 2 x 2 MIMO and 2 element AAS

DL Tx power 35 dBm 35 dBm 35 dBm DL Tx antenna gain 16 dBi 16 dBi 16 dBi Other DL Tx gain 0 dB 9 dB 15 dB UL Rx antenna gain 16 dBi 16 dBi 16 dBi Other UL Rx gain 0 dB 3 dB 6 dB UL Rx noise figure 5 dB 5 dB 5 dB

Table4.1 Base station parameters

There are several parameters affect on BS received power or transmitted power.

BS receiver cable feeder: The BS receiver feeder cable is dependent on the feeder type and the length of the feeder run table 4.2 shows the typical feeder type used.

Frequency coaxial feeder cable model ( 7/8" ) diameter 1000 MHz 32 dB2000 MHz 55 dB

Table4.2 Coaxial feeder cable model (7/8”) diameter

BS receiver cable and connector losses: Losses are nominally taken to be 3dB. When the cable length and diameter (and hence attenuation/feet) are known, the actual cable losses may be substituted in the link budget along with an additional margin of 0.5 dB for connector losses. Typically cable diameters used are 7/8’ and 1 5/8” and corresponding attenuations are 6.15 dB /100 meters and 3.84 dB /100 meters. 4.2.4 Customer Premises Equipment (CPE)

With regard to the CPE, we can choose from two profiles: Portable CPE. Mobile CPE.

The first type is comparable with e.g. as usual cable modem: they are installed indoors, have their own power supply and are usually connected via an Ethernet cable to the computer. They do not guarantee any form of mobility. Solutions with PCMCIA cards and receivers integrated in e.g. a laptop belong then to the second type. Every profile contains again six parameters (Table 4.3).

Portable CPE Mobile CPE UL Tx power 27 dBm 27 dBm UL Tx antenna gain 6 dBi 2 dBi Other UL Tx gain 0 dB 0 dB DL Rx antenna gain 6 dBi 2 dBi Other DL Rx gain 0 dB 0 dB DL Rx noise figure 6 dB 6 dB

Table4.3 CPE parameters

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From the above six parameters for BS and CPE, we calculate Equivalent isotropically radiated power (EIRP).

There is parameter called “body loss” may affect on CPE received power or transmitted power.

Body loss: Body loss or body proximity loss affects both uplink and downlink. A human body near the mobile antenna affects the radiation pattern of the MS antenna. The loss measured against the best direction depends on the MS antenna type, location of the antenna and frequency. For planning purposes the loss of 4–6 dB could be used. However, in the worst direction the loss can be well over 10 dB.

4.2.5 What is EIRP?

In radio communication systems, Equivalent isotropically radiated power (EIRP) or, alternatively, Effective isotropically radiated power is the amount of power that a theoretical isotropic antenna (that evenly distributes power in all directions) would emit to produce the peak power density observed in the direction of maximum antenna gain. EIRP can take into account the losses in transmission line and connectors and includes the gain of the antenna. The EIRP is often stated in terms of decibels over a reference power emitted by an isotropic radiator with equivalent signal strength. The EIRP allows comparisons between different emitters regardless of type, size or form. From the EIRP, and with knowledge of a real antenna's gain, it is possible to calculate real power and field strength values.

Figure4.3 illustration of EIRP (4.2) Then,

For FL communication ,BS is the transmitter and its EIRP can be calculated from Table 4.1 as: – (4.3)

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For RL communication ,CPE is the transmitter and its EIRP can be calculated from Table 4.2 as: – /

(4.4)

4.2.6 Receiver Sensitivity

The receiver sensitivity is defined by:

The thermal noise. The receiver SNR. The noise figure (Table 4.1 and Table 4.2). The implementation loss.

Now, the receiver sensitivity can be calculated as: (4.5)

4.2.6.1 The thermal noise

The thermal noise is dependent on the channel bandwidth and can be estimated as (in dBm): (4.6) Where Δf is the bandwidth in hertz over which the noise is measured. As physical

bandwidth (BW), there is a choice from 1.25 MHz, 5 MHz, 10 MHz and 20 MHz, where today 10 MHz is the most standard value. For the calculation of the thermal noise, the bandwidth Δf has to be scaled to the effectively used bandwidth. So the value of BW has to be multiplied by the ratio between the numbers of used subcarriers (NUsed) and the total number of OFDM subcarriers or FFT size (NFFT), and the sampling factor (n). For each bandwidth, the model contains different values for NFFT and NUsed (Table 4.4).

Note that NUsed is equal to the sum of the number of data subcarriers (NData) and pilot subcarriers (NPilot), together with the DC carrier. Table 4.3 also shows NData (used to determine the bit rates, Section 4.5) and the number of subchannels (NSubCh, used to calculate the subchanneling gain, Section 4.2.7).

NFFT NUsed NDataDL NDataUL NSubChDL NSubChUL 1.25 MHz 128 85 72 56 3 4 5 MHz 512 421 360 280 15 17 10 MHz 1024 841 720 560 30 35 20 MHz 2084 1681 1440 1120 60 70

Table4.4 Parameters per channel bandwidth

The sampling factor n determines the subcarrier spacing (in conjunction with the bandwidth and used data subcarriers), and the useful symbol time. This value is set to 28/25 for

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channel bandwidths that are a multiple of any of 1.25, 1.5, 2 or 2.75 MHz (which is applicable in our case). The thermal noise is then determined by: (4.7)

1000 147

Where, K is Boltzmann constant in joule/Kelvin and T is the room temperature in Kelvin

4.2.6.2 The receiver SNR

The receiver SNR depends on the modulation scheme and the corresponding values are shown in Table 4.5, for two different forward error correction (FEC) methods (convolution code (CC) and convolution turbo code (CTC)) in an additive white Gaussian noise (AWGN) channel at a bit error rate (BER) of 10−6. As WiMAX adaptively selects the modulation scheme per user, the appropriate SNR value used in the link budget calculation is dynamically adapted. The modulation scheme also defines the number of data bits per symbol, but this parameter only influences the bit rate per sector which will be discussed further in this chapter (Section 4.5).

Modulation scheme SNR CC

(AWGN, BER 10-6) SNR CTC

(AWGN, BER 10-6) Data bit

per symbol QPSK 1/2 5 dB 2.5 dB 1

QPSK 3/4 8 dB 6.3 dB 1.5

16-QAM 1/2 10.5 dB 8.6 dB 2

16-QAM 3/4 14 dB 12.7 dB 3

64-QAM 1/2 16 dB 13.8 dB 3

64-QAM 2/3 18 dB 16.9 dB 4

64-QAM 3/4 20 dB 18 dB 4.5 Table4.5 Parameters per modulation scheme

4.2.6.3 The noise figure

Noise figure (NF) is a measure of degradation of the signal to noise ratio (SNR), caused by components in the RF signal chain. The noise figure is the ratio of the output noise power of a device to the portion thereof attributable to thermal noise in the input termination at standard noise temperature T0 (usually 290 K). The noise figure is thus the ratio of actual output noise to that which would remain if the device itself did not introduce noise. It is a number by which the performance of a radio receiver can be specified. (4.8)

Note: In our calculations, the assumed values of NF in Table 4.1 and Table 4.2.

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4.2.6.4 The implementation loss

The implementation loss includes non-ideal receiver effects such as channel estimation errors, tracking errors, quantization errors, and phase noise. The assumed value is 2 dB.

4.2.7 Uplink Subchanneling Gain

In the uplink direction, it will hardly occur that data is sent over all subcarriers simultaneously. To set off this effect, an uplink subchanneling gain is taken into account, based on the number of used subchannels per user and defined by: 10 (4.9) NSubChUL is already given in Table 4.3 and NUsedSubChUL is based on the number of subchannels required for the offered uplink data rate per user, and will also depend on the modulation scheme (Section 4.5).

4.2.8 Margins

Is defined as the amount by which a received signal level may be reduced without causing system performance to fall below a specified threshold value.

To calculate the link budget, we have to consider several margins, such as the fade margin, the interference margin and a Building penetration loss (BPL) factor.

1. Fading margin: Fading covers the effect of the variation of the signal strength during the time on a fixed location. In contrast to shadowing which takes into account the variation of the signal strength between different locations on the same distance from the transmitter, fading is not incorporated in the propagation model.

Slow fading margin (lognormal fading margin):

Slow fading or log-normal fading is the variation of the local mean signal level over a wider area, and has been observed by Young. The local mean is the mean value of the Rayleigh or Rician fading signal amplitude. This log-normal fading is caused by the obstacles (buildings, trees, etc.) that changes the average received signal level and thus bring about shadowing. The variation of the signal amplitude local mean value over the wider area is log-normally distributed and thus it is called lognormal fading. , , (4.10)

Fast fading margin: The mobile station or base station receives in one moment the same signal arriving via different radio paths as mentioned in the previous section. The total received signal is a

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contribution of all the arrived signal multipath components based on the superposition principle. The different signal components, arriving via different radio paths, have different amplitude and phase due to the different lengths of the radio path and

different reflection and diffraction properties. Thus, the sum of the received signals can be constructive or a destructive depending on the phases of the multipath

components. The assumed value for fast fading margin is 3 dB.

2. Interference margin: Due to co-channel interference (CCI) in frequency reuse deployments, users at the cell edge or the sector boundaries may suffer degradation in connection quality. The assumed interference margin is 2 dB for DL and 3 dB for UL respectively.

3. Building penetration loss (BPL): Buildings obstruct the transmitted electromagnetic signals. Since the used propagation model does not sufficiently take into account this effect, an extra correction on the link budget is added. The different possibilities are summarized in Table 4.6.

Urban type Correction Rural 12 dB Suburban 15 dBUrban 18 dB Dense urban 20 dB

Table4.6 Urban corrections

4.2.9 Link Budget Calculation (Maximum Allowable Path Loss)

With the data discussed in the previous sections, it is possible to calculate the link budget.

For the downlink communication MAPL is specified as: / (4.11)

For uplink communication MAPL is specified as: (4.12)

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Figure4.4 Link analysis of a WiMAX system operating at 2.5 and 5GHz

4.2.10 Effect of Adverse Weather Conditions

It is important to research any unusual weather conditions that are common to the site location. These conditions can include excessive amounts of rain or fog, wind velocity, or extreme temperature ranges. If extreme conditions exist that may affect the integrity of the radio link, it is recommended that these conditions be taken into consideration early in the planning process.

Rain and Fog: Except in extreme conditions, attenuation (weakening of the signal) due to rain does not require serious consideration for frequencies up to the range of 6 or 8 GHz. When frequencies are at 11 or 12 GHz or above, attenuation due to rain becomes much more of a concern, especially in areas where rainfall is of high density and long duration. If this is the case, shorter paths may be required.

In most cases, the effects of fog are considered to be much the same as rain. However, fog can adversely affect the radio link when it is accompanied by atmospheric conditions such as temperature inversion, or very still air accompanied by stratification. Temperature inversion can negate clearances, and still air along with stratification can cause severe refractive or reflective conditions, with unpredictable results. Temperature inversions and stratification can also cause ducting, which may increase the potential for interference between systems that do not normally interfere with each other. Where these conditions exist, it is recommended to have shorter paths and adequate clearances.

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Atmospheric Absorption: A relatively small effect on the link is from oxygen and water vapor. It is usually significant only on longer paths and particular frequencies. Attenuation in the 2 to 14 GHz frequency range, which is approximately 0.01 dB/mile, is not very significant.

Wind: Any system components mounted outdoors will be subject to the effect of wind. It is important to know the direction and velocity of the wind common to the site. Antennas and their supporting structures must be able to prevent these forces from affecting the antenna or causing damage to the building or tower on which the components are mounted. Antenna designs react differently to wind forces, depending on the area presented to the wind. This is known as wind loading. Most antenna manufacturers will specify wind loading for each type of antenna manufactured.

Lightning: The potential for lightning damage to radio equipment should always be considered when planning a wireless link. A variety of lightning protection and grounding devices are available for use on buildings, towers, antennas, cables, and equipment, whether located inside or outside the site that could be damaged by a lightning strike. Lightning protection requirements are based on the exposure at the site, the cost of link down-time, and local building and electrical codes. If the link is critical, and the site is in an active lightning area, attention to thorough lightning protection and grounding is critical.

Lightning Protection: To provide effective lightning protection, install antennas in locations that are unlikely to receive direct lightning strikes, or install lightning rods to protect antennas from direct strikes. Make sure that cables and equipment are properly grounded to provide low-impedance paths for lightning currents. Install surge suppressors on telephone lines and power lines. Lightning protection is recommended for both coaxial and control cables leading to the wireless device. The lightning protection should be placed at points close to where the cable passes through the bulkhead into the building, as well as near the wireless device. All smart Bridges products include grounding wires, so please make sure that the antenna is properly grounded.

4.2.11 Improving Coverage and Throughput

Select data rate according to the actual utilization; with lower data rate allows longer distances to be achieved.

Selection of Autofall back mode. Keeping the transmit power of equipment low and using a higher gain antenna will improve the

data rate and coverage. Selecting equipment with RF interference mitigation capabilities. Selecting equipment that takes care of multi-path issues. Using MAC based authentication only for security and disabling a WEP/WPA/AES if higher end

security standards are not required. This will improve the throughput. Selection of sector can improve the range of coverage in a particular direction.

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4.3 Propagation Model Median pathloss in a radio channel is generally estimated using analytical models based on

either the fundamental physics behind radio propagation or statistical curve fitting of data collected via field measurements. For most of the practical deployment scenarios, particularly nonline- of-sight scenarios, statistical models based on empirical data are more useful. Although most of the statistical models for pathloss have been traditionally developed and tuned for a mobile environment, many of them can also be used for an NLOS fixed network with some modification of parameters. In the case of a line-of-sight-based fixed network, the free-space radio propagation model can be used to predict the median pathloss. Since WiMAX as a technology has been developed to operate efficiently even in an NLOS environment, we focus extensively on this usage model for the remainder of the appendix. We describe a few of the pathloss models that are relevant to NLOS WiMAX deployments.

One of the most important issues in the design, implementation and operation of land mobile system is the knowledge of the received signal and its fluctuations. Propagation models take into account the type of the environment, the materials. The propagation models can be broadly classified in 3 types:

Statistical models.

Theoretical models.

Semi-empirical models.

Statistical model: Also named Empirical models, Empirical models are usually set of equations, the model parameters are derived from extensive field measurements data. They are accurate for environments with the same characteristics as those where measurements were made.

The input parameters for empirical models are usually qualitative and not very specific e.g. dense urban (DU), urban (UR), suburban (SU) and rural (RU) areas and so on. One of the main drawbacks of empirical models is that they cannot be used for different environment without modifications. The output parameters are basically range specific. Empirical models examples are Okumura model and Hata model.

Theoretical model: They are derived physically assuming some ideal conditions for example over roof top diffractions model is derived using physical optics assuming uniform heights and spacing of buildings. Theoretical models examples are Walfisch and Bertoni model, Ikegami model and free space model.

Semi-empirical model: The parameters of the theoretical models are empirically corrected to fit measurement data. Semi-empirical models examples are COST 231- Wolfish Ikegami model and COST 231 Okumura Hata model.

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4.3.1 Hata Model

The Hata model is an analytical formulation based on the pathloss measurement data collected by Okumura in 1968 in Japan. The Hata model is one of the most widely used models for estimating median pathloss in macrocellular systems. The model provides an expression for median pathloss as a function of carrier frequency, BS and mobile station antenna heights, and the distance between the BS and the MS. The Hata model is valid only for the following range of parameters:

150MHz ≤ f ≤ 1500MHz 30m ≤ hb ≤ 200m 1m ≤ hm ≤ 10m 1km ≤ d ≤ 20km

In these parameters, f is the carrier frequency in MHz, hb is the BS antenna height in meters, hm

is the MS antenna height in meters, and d is the distance between the BS and the MS in km. According to the Hata model, the median pathloss in an urban environment is given by: 69.55 26.16 13.82 44.9 6.55 (4.13)

Where is expressed in the dB scale, and is the MS antenna-correction factor. For a large city with dense building clutter and narrow streets, the MS antenna-correction factor is given by: 8.29 1.54 0.8 300 (4.14a) 3.20 11.75 4.97 300 (4.14b)

For a small- or medium-size city, where the building-clutter density is smaller, the MS antenna-correction factor is given by: 1.11 0.7 1.56 0.8 (4.15)

For a suburban area, the same MS antenna-correction factor as used for small cities is applicable, but the median pathloss is modified to be:

2 5.4 (4.16)

For a rural area, the same MS antenna-correction factor as used for small cities is applicable, but the median pathloss is modified to be: 4.78 18.33 40.98 (4.17)

The model may also be generalized to any clutter environment, such that the median pathloss is modified from that of a small urban city as: (4.18)

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Figure4.5 Correction factor in small and medium size area

Figure4.6 Correction factor in large size area

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Figure4.7 Path loss propagation in suburban area versus distance

4.3.2 COST-231 Hata Model

The Hata model is widely used for cellular networks in the 800MHz/900MHz band. As PCS deployments begin in the 1,800MHz/1,900MHz band, the Hata model was modified by the European COST (Cooperation in the field of Scientific and Research) group, and the extended pathloss model is often referred to as the COST-231 Hata model. This model is valid for the following range of parameters:

150MHz ≤ f ≤ 2000MHz 30m ≤ hb ≤ 200m 1m ≤ hm ≤ 10m 1km ≤ d ≤ 20km

The median pathloss for the COST-231 Hata model is given by: 46.3 33.9 13.82 44.9 6.55 (4.19)

The MS antenna-correction factor, a(hm), is given by: 1.11 0.7 1.56 0.8 (4.20)

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For urban and suburban areas, the correction factor CF is 3dB and 0dB, respectively. The WiMAX Forum recommends using this COST-231 Hata model for system simulations and network planning of macrocellular systems in both urban and suburban areas for mobility applications. The WiMAX Forum also recommends adding a 10dB fade margin to the median pathloss to account for shadowing.

4.3.3 Walfish-Ikegami Model

The Hata model and its COST-231 extension are suitable for macrocellular environments, but not for smaller cells that have a radius less than 1 km. The Walfish-Ikegami model applies to these smaller cells and is recommended by the WiMAX Forum for modeling microcellular environments. The model assumes an urban environment with a series of buildings as depicted in Figure 4.5, with the building heights, interbuilding distance, street width, and so on, as parameters. In this model, diffraction is assumed to be the main mode of propagation, and the model is valid for the following ranges of parameters:

800MHz ≤ f ≤ 2000MHz 4m ≤ hb ≤ 50m 1m ≤ hm ≤ 3m 0.2km ≤ d ≤ 5km

Figure4.8 the Walfish-Ikegami model

The model is made up of three terms: (4.21)

Where, Lfs is the free-space loss, Lrts is the rooftop-to-street diffraction loss, and Lmsd is the multiscreen loss. The model provides analytical expressions for each of the terms for a variety of scenarios and parameter settings. For the standard NLOS case, with BS antenna height 12.5m, building height 12m, building-to-building distance 50m, width 25m, MS antenna height 1.5m, orientation 30° for all paths, and in a metropolitan center, the equation simplifies to:

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65.9 38 24.5 . (4.22)

This equation is recommended by the WiMAX Forum to be used for system modeling. The use of an additional 10dB for fading margin is also recommended with this model.

The Walfish-Ikegami model also provides an expression for the urban canyon case, which has a LOS component between the BS and the MS. For the LOS case, the median pathloss expression is: 31.4 26 20 (4.23) 4.3.4 Erceg Model

The Erceg model is based on extensive experimental data collected at 1.9GHz in 95 macrocells across the United States. The measurements were made mostly in suburban areas of New Jersey, Seattle, Chicago, Atlanta, and Dallas. The Erceg model is applicable mostly for fixed wireless deployment, with the MS installed under the eave/window or on the rooftop. The model, adopted by the IEEE 802.16 group as the recommended model for fixed broadband applications, has three variants, based on terrain type.

1. Erceg A is applicable to hilly terrain with moderate to heavy tree density. 2. Erceg B is applicable to hilly terrain with light tree density or flat terrain with moderate to heavy

tree density. 3. Erceg C is applicable to flat terrain with light tree density.

The Erceg model is a slope-intercept model given by: 10 (4.24)

Where is the median pathloss, PL is the instantaneous attenuation, and X is the shadow fades, A is the intercept and is given by free-space pathloss at the desired frequency over a distance of d0 = 100 m: 20 (4.25)

and α is the pathloss exponent and is modeled as a random variable with a Gaussian distribution around

a mean value of . The instantaneous value of the pathloss exponent is given by: (4.26)

Where x is a Gaussian random variable with zero mean and unit variance, and σα is the standard deviation of the pathloss exponent distribution. The parameters of the Erceg model, A, B, C, and σα for the various terrain categories, are given in Table 4.7.

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Parameters Erceg Model A Erceg Model B Erceg Model C

a 4.6 4 3.6

b 0.0075 0.0065 0.005

c 12.6 17.1 20

sa 0.57 0.75 0.59

μS 10.6 9.6 8.2

σS 2.3 3 1.6 Table4.7 Parameters of Erceg Model

Unlike the Hata model, which predicts only the median pathloss, the Erceg model has both a median pathloss and a shadow-fading component, χ, a zero-mean Gaussian random variable expressed as y σ, where y is a zero-mean Gaussian random variable with unit variance, and σ is the standard deviation of χ. The standard deviation σ is, in fact, another Gaussian variable with a mean of μS and a standard deviation of σS, such that σ = μS + z σS, z being a zero-mean unit variance Gaussian random variable.

Strictly speaking, this base model is valid only for frequencies close to 1,900MHz, for an MS with omnidirectional antennas at a height of 2 meters and BS antenna heights between 10 meters and 80 meters. The base model has been expanded with correction factors to cover higher frequencies, variable MS antenna heights, and directivity. The extended versions of the Erceg models are valid for the following range of parameters:

• 1900MHz ≤ f ≤ 3500MHz

• 10m ≤ hb ≤ 80m

• 2m ≤ hm ≤ 10m

• 0.1km ≤ d ≤ 8km The median pathloss formula for the extended version of the Erceg model is expressed as: 10 log ∆ ∆ ∆ (4.27)

The various correction factors in previous Equation corresponding to frequency, MS height, and MS antenna directivity are given by: ∆ 6 log (4.28)

∆ 10.8 log (4.29a)

∆ 20 log (4.29b)

∆ 0.64 ln 0.54 ln (4.30)

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Where ΔPLMS is often referred to as the antenna-gain reduction factor and accounts for the fact that the angular scattering is reduced owing to the directivity of the antenna. The antenna-gain reduction factor can be quite significant; for example, using a 20° antenna can contribute to a ΔPLMS of 7 dB.

4.3.5 Ecc-33 path loss model

Initial Experimental of Okumura model are done suburban areas at Tokyo. A partition of urban areas has let authors reporting 2 categories for towns such:

Large towns (like Tokyo, New York, etc...)

Medium towns (like Berlin, Rome, etc...).

A correction factor for open and suburban’s areas was also defined. Even if the Okumura-Hata model is well known for UHF frequency bands, it’s a validity for High Frequencies (HF) is however discussable. The COST-231 model extends this to frequencies up to 2GHz, where mobile system is supposed equipped with Omni-directional antenna installed more than 3 m above the ground.

ECC-33 model is an empirical model composed from four terms and known as following :

(4.31)

Where, , , , are, respectively the free space attenuation, the basic median path loss, the BS

height gain factor and the terminal (CPE) height gain factor. They are individually defined in (Erceg, 2003; Kabaou, 2006). 92.4 20 log 20 log (4.32) 20.41 9.83 log 7.894 log 9.56 log (4.33) log . 13.958 5.8 log (4.34)

For medium city environment

42.57 13.7 log log 0.585 (4.35)

The medium city model is more appropriate for European cities whereas the large cities environment should be used only for cities having tall buildings.

4.3.6 COMPARISON WITH SIMULATION RESULTS

After presented the different path loss models, we entered a comparative study to compare the path loss model results obtained through appropriate parameters in rural, urban and suburban environments. Figure 4.9 compares the path loss obtained in rural environment. It clearly shows that the COST-231 Hata model predict a higher path loss than the Standard University Interim model (SUI).

Chapter 4 Coverage analysis of Mobile WiMAX

4 - 20

Figure4.9 Comparison of path loss propagation for rural environments

Figure4.10 Comparison of path loss propagation for suburban environments

Cell Area

4 - 21

Figure4.11 Comparison of path loss propagation for urban environments

Note that the SUI model does not specifically have a classification for urban environment, but terrain type B is considered the most appropriate.

The assumptions for urban and medium city are used for the COST-231 Hata model and the ECC-33. The SUI model in comparison with the ECC-33 and COST-231 model are shown in Figure 4.10. The SUI model shows the lowest path loss for a BS antenna height of 30 m in suburban environment.

The results of comparison between three path loss models in urban environment are shown in Figure 4.11. The BS antenna height is considered equal to 20 m. The ECC-33 model grossly over predict the path loss at 20 m, however the SUI model shows the lowest path loss.

4.4 Cell Area Mobile WiMAX uses a cellular network structure and we consider a hexagonal cell area, defined as: 3 X d2 X sin(π/3), with d the coverage range as indicated in Figure 4.12.

Figure4.12 Illustration of cell area calculation

Chapter 4 Coverage analysis of Mobile WiMAX

4 - 22

4.5 Bit Rate per Sector Both the channel bandwidth and the modulation scheme have an important influence on the bit

rate, and these two parameters were already discussed above (Table 4.3 and Table 4.4). Besides, the bit rate is also determined by the guard time, the overhead and the TDD down/up ratio. The guard time is intended to overcome multi path effects and in the planning tool the user can select a fraction from a particular set, specified in the standard (1/8 is used in our study). The overhead is defined as the percentage of time that no data is sent and is the time used for e.g. initialization and synchronization, and it also covers the headers (we assume an overhead of 20%). Finally, the ratio between the downlink and uplink time is defined by a TDD down/up ratio parameter (fixed at 3:1 in our model). The downlink bit rate is then given by: / (4.36)

4.6 Required Number of Sites and Sectors The final goal of the planning tool is to deliver the number of sites and sectors required to cover

a particular region, and this information will then be used to formulate different business scenarios. The area of the region, the user density and the desired downlink and uplink bit rate per user are additional input parameters. Operators also take into account that not every user simultaneously uses his connection, and for this purpose a parameter for simultaneous usage (overbooking) is introduced, which defines the percentage of the users that effectively use the service (we assume 5%). As already mentioned, WiMAX dynamically selects the best possible modulation scheme per user, which is illustrated in Figure 4.13.

Figure4.13 Range of the different modulation schemes, indicated by different colors. The lighter the color, the less data bits per symbol (cf. Table 4.4)

Planning Tool: Graphical User Interface (GUI)

4 - 23

4.7 Planning Tool: Graphical User Interface (GUI) Figure 4.14 shows the graphical user interface of the planning tool, and the main blocks are

discussed below.

Figure4.14 Graphical user interface of the planning tool

Our planning tool divided into 6 blocks: CPE parameters: it contains the parameters of CPE. BS parameters: it contains the parameters of BS. OFDM parameters: it contains parameters of OFDM for UL and DL connection. Margins: it contains all margin variables. System parameters: contains other system specification like MS antenna height an BS antenna

height. Results: after providing inputs from user and pressing Calculate button, the results will appears

for UL and DL in this block. Note that user can type equations instead of numbers as input to the tool and he can change this equation later.

Clear button is used to remove all inputs and results to reset the tool for new values.

Chapter 4 Coverage analysis of Mobile WiMAX

4 - 24

4.8 Link budget sample Table 4.8 shows a sample link budget for a WiMAX system for two deployment scenarios. In the

first scenario, the mobile WiMAX case, service is provided to a portable mobile handset located outdoors; in the second case, service is provided to a fixed desktop subscriber station placed indoors. The fixed desktop subscriber is assumed to have a switched directional antenna that provides 6 dBi gain.

Table4.8 Link budget sample

Conclusions

4 - 25

4.9 Conclusions We have presented in this chapter a comparative study between different path loss models.

Each one of these models is described by an appropriate parameters and a specific environment of propagation. The ECC-33 model showed quite large path loss in urban and suburban environment. The COST-231 models predict a higher path loss in rural environment.

Finally, physical models (Walfish-Ikegami) can attain a greater degree of accuracy than a statistical model (Okumura-Hata), because researcher can retain his electromagnetism’s laws knowledge that he has. Statistical Models are easier to be used than the physical ones. They don’t need e.g. geographic databases. However, validity domain is often limited: Okumura-Hata model can’t, e.g., be used for distances less than 1Km.

5 - 1

5.1 Introduction

Scenario Description Parameters

A Licensed operation

BW: 1.75, 7 MHz Fc: 3.5 GHz Nsubchannel: 16 (without sub channelization) Modulation technique: BPSK, QPSK, 16-QAM and 64-QAM Coding rate: 1/2, 2/3 and ¾ Morphology classes: RU, SU, UR and DU

B Licensed operation

BW: 1.75, 7 MHz Fc: 3.5 GHz Nsubchannel: 4 Modulation technique: BPSK, QPSK, 16-QAM and 64-QAM Coding rate: 1/2, 2/3 and 3/4 Morphology classes: RU, SU, UR and DU

C Licensed-exempt operation

BW: 10, 20 MHz Fc: 5.8 GHz Nsubchannel: 16 (without sub channelization) Modulation technique: BPSK, QPSK, 16-QAM and 64-QAM Coding rate: 1/2, 2/3 and ¾ Morphology classes: RU, SU, UR and DU

D Licensed-exempt operation

BW: 10, 20 MHz Fc: 5.8 GHz Nsubchannel: 2 Modulation technique: BPSK, QPSK, 16-QAM and 64-QAM Coding rate: 1/2, 2/3 and 3/4 Morphology classes: RU, SU, UR and DU

Table5.1 Case studies

We study the effecting of eight parameters on the coverage prediction:

1. The BS antenna height. 2. The modulation technique and coding rate. 3. The different morphologies. 4. The operating frequency. 5. The channel bandwidth. 6. The sub channelization technique. 7. Comparison between Fixed and mobile WiMAX. 8. Comparison between Erceg.

Chapter 5 Numerical results of WiMAX

Chapter 5 Numerical results of WiMAX

5 - 2

5.2 The BS antenna height and the modulation technique and coding rate We observe that:

At operating frequency 3.5GHz, BW 1.75, without subchannelization, morphology Dense urban and link direction is reverse link.

Hbs (m) 10 20 30 40 50 60 70 BPSK 1/2 1.111794 1.553071 1.828066 2.047452 2.247144 2.442878 2.643326QPSK 1/2 0.688743 0.900249 1.025857 1.123369 1.210331 1.294087 1.378489QPSK 3/4 0.641124 0.829716 0.940909 1.026879 1.103313 1.176736 1.250548

16QAM 1/2 0.52126 0.655492 0.732996 0.792215 0.844402 0.894156 0.94382416QAM 3/4 0.485221 0.604135 0.672299 0.724169 0.76974 0.813072 0.85622564QAM 2/3 0.405651 0.492665 0.541645 0.578538 0.610703 0.641088 0.6711666QAM 2/3 0.379111 0.456128 0.499184 0.53149 0.559575 0.58604 0.612177

Table 5.2 The Estimated downlink coverage radius for different BTS heights in Km with different modulation techniques

Figure5.1 Modulation technique effect

We conclude that:

Cell radius increases as BS antenna height increases. Cell radius changes with different modulation techniques; BPSK has higher cell radius while 64-

QAM has lower cell radius. Each modulation type has a certain required S/N so, it has a certain receiver sensitivity which a

dominant factor in the MAPL so the cell radius changes among the modulation types.

10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3

hbs

cell

radi

us

mobile reverse link

BPSK 1/2QPSK 1/2QPSK 3/416-QAM 1/216-QAM 3/464-QAM 2/364-QAM 3/4

Effect of different morphologies

5 - 3

5.3 Effect of different morphologies We observe that:

At operating frequency 3.5GHz, code rate 0.5, BW 1.75, with subchannelization (N subchannel=2),

modulation type BPSK and link direction is reverse link.

hbs (m) 10 20 30 40 50 60 70 80 rural 1.434794 2.076482 2.486716 2.818773 3.124331 3.426641 3.738904 4.070312

suburban 1.200201 1.694464 2.004851 2.253552 2.480668 2.703907 2.933113 3.174973urban 1.15221 1.617523 1.908538 2.141175 2.353252 2.561398 2.774814 2.999715

denseurban 1.111794 1.553071 1.828066 2.047452 2.247144 2.442878 2.643326 2.854319Table 5.3 The Estimated downlink coverage radius for different BTS heights in Km with different morphologies

Figure5.2 Morphology effect

We conclude that:

Cell radius changes for different morphologies. Ruler has higher Cell radius due to have lower BPL ( lower standard deviation of lognormal ),

then suburban, urban, dense has lower cell radius.

10 20 30 40 50 60 70 801

1.5

2

2.5

3

3.5

4

4.5

hbs

cell

radi

us

mobile reverse link

RuralSuburbanUrbanDenseurban

Chapter 5 Numerical results of WiMAX

5 - 4

5.4 Effect of operating frequency We observe that:

At BW 1.75, code rate 0.5, no sub channel, modulation type BPSK and link direction is reverse link, morphology Dense urban.

hbs (m) 10 20 30 40 50 60 70 80 3.5 GHz 1.111794 1.553071 1.828066 2.047452 2.247144 2.442878 2.643326 2.8543195.8 GHz 0.886004 1.199279 1.390107 1.54039 1.675863 1.807552 1.941385 2.08123

Table 5.4 The Estimated downlink coverage radius for different BTS heights in Km with different operating frequency (licensed and license exempt)

Figure5.3 Operating frequency effect

We conclude that:

At higher operating frequency the coverage prediction is decreased.

Since:

1. The frequency correction factor of the model is increased. 2. Increasing frequency decrease the wave length which decrease the cell radius.

10 20 30 40 50 60 70 800.5

1

1.5

2

2.5

3

hbs

cell

radi

us

mobile reverse link

F =3.5 GHzF =5.8 GHz

Effect of channel bandwidth

5 - 5

5.5 Effect of channel bandwidth We observe that:

At operating frequency 3.5GHz, code rate 0.5, with subchannelization (N subchannel=4), modulation type

BPSK and link direction is reverse link, morphology Dense urban.

hbs(m) 10 20 30 40 50 60 70 80 1.75 MHz 0.986252 1.354981 1.58202 1.761915 1.924826 2.083810 2.245967 2.415994

7 MHz 0.776096 1.031377 1.184819 1.304751 1.412255 1.516250 1.621469 1.730943 10 MHZ 0.734528 0.968707 1.108686 1.217754 1.315289 1.409451 1.504544 1.603308 20 MHz 0.651586 0.845151 0.959464 1.047927 1.126632 1.202282 1.278373 1.357096

Table 5.5 The Estimated downlink coverage radius for different BTS heights in Km with different channel BW

Figure5.4 Channel bandwidth effect

We conclude that:

As channel bandwidth increase, the coverage radius decreases.

Since: increasing the channel BW increases the receiver sensitivity (due to increasing of effective channel BW).

10 20 30 40 50 60 70 80

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

hbs

cell

radi

us

mobile reverse link

BW = 1.75 MHzBW = 7 MHzBW = 10 MHzBW = 20 MHz

Chapter 5 Numerical results of WiMAX

5 - 6

5.6 Effect of subchannelization 5.6.1 The forward link versus reverse link cell radius in case of no subchannelization

We observe that:

At operating frequency 3.5GHz, BW 1.75MHz, code rate 0.5, no sub channel, modulation type BPSK and, morphology Dense urban.

hbs (m) 10 20 30 40 50 60 70 80 RL 0.746424 0.986593 1.130385 1.242527 1.342879 1.439818 1.537769 1.639553FL 1.06324 1.476069 1.732186 1.935993 2.121151 2.302343 2.48762 2.682362

Table 5.6 The Estimated downlink coverage radius for different BTS heights in Km at FL and RL without subchannelization

Figure5.5 FL versus RL cell radius in case of no subchannelization

We conclude that:

There is unbalance between forward link and reverse link.

Since:

1. Antenna gain of SS is low , but BS antenna gain is very high. 2. Transmitted power of SS is low. 3. SS antenna height is low. 4. SS is battery powered.

10 20 30 40 50 60 70 800.5

1

1.5

2

2.5

3

hbs

cell

radi

us

mobile reverse link

RLFL

Effect of subchannelization

5 - 7

5.6.2 The forward link versus reverse link cell radius in case of subchannelization

We observe that:

At operating frequency 3.5GHz, BW 1.75MHz, code rate 0.5, modulation type BPSK, morphology Dense urban.

hbs 10 20 30 40 50 60 70 80 RL 1.069287 1.485634 1.74408 1.949807 2.136754 2.319735 2.506877 2.703616Fl 1.06324 1.476069 1.732186 1.935993 2.121151 2.302343 2.48762 2.682362

Table 5.7 The Estimated downlink coverage radius for different BTS heights in Km at FL and RL with subchannelization

Figure5.6 FL versus RL cell radius in case of no subchannelization

We conclude that:

By using the subchannelization technique there is balance forward link and reverse link.

10 20 30 40 50 60 70 801

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

hbs

cell

radi

us

mobile reverse link

RLFL

Chapter 5 Numerical results of WiMAX

5 - 8

5.7 Comparison between Fixed and mobile WiMAX We observe that:

At operating frequency 3.5GHz, BW 1.75MHz, code rate 0.5, with subchannelization, modulation type BPSK and link direction is reverse link, morphology Dense urban.

hbs 10 20 30 40 50 60 70 80 mobile WiMAX 1.05153 1.41847 1.61349 1.74531 1.84821 1.93635 2.01670 2.09317 fixed WiMAX 2.94367 4.58068 5.58647 6.34279 6.98928 7.58868 8.17451 8.76759

Table 5.8 The Estimated downlink coverage radius for different BTS heights in Km at mobile WiMAX and fixed WiMAX

Figure5.7 Comparison between Fixed and mobile WiMAX cell radius

We conclude that:

The cell radius of Fixed WiMAX is higher than the cell radius of the mobile WiMAX.

Since:

1. SS transmission and reception antenna gain in fixed WiMAX is high. 2. SS transmitted power in fixed WiMAX is high. 3. LOS capabilities in fixed WiMAX is more than mobile WiMAX . 4. Most fixed SS is AC powered. 5. SS in mobile WiMAX able to has a certain speed up to 120km/s, where in fixed WiMAX

it’s speed is zero , so in mobile WiMAX must have a robust connection.

10 20 30 40 50 60 70 801

2

3

4

5

6

7

8

9

hbs

cell

radi

us

mobile reverse link

Mobile WiMAXFixed WiMAX

Comparison between Erceg A, B and C

5 - 9

5.8 Comparison between Erceg A, B and C We observe that:

At operating frequency 3.5GHz, BW 1.75MHz, code rate 0.5, with subchannelization (N subchannel=2),

modulation type BPSK and link direction is reverse link, morphology Dense urban.

hbs 10 20 30 40 50 60 70 80 Erceg A 1.069726 1.486327 1.744943 1.950809 2.137887 2.320997 2.508275 2.705159Erceg B 1.134486 1.820447 2.296108 2.683837 3.035887 3.378423 3.727026 4.092648Erceg C 1.418877 2.104684 2.795109 3.363212 3.871011 4.353209 4.831213 5.319809

Table 5.9 The Estimated downlink coverage radius for different BTS heights in Km at with different Erceg models

Figure5.8 Comparison between Erceg A, B, C cell radius

We conclude that:

The largest cell radius in Erceg C, then Erceg B, and the smallest cell radius Erceg A.

Since:

Erceg A is applicable to hilly terrain with moderate to heavy tree density . Erceg B is applicable to hilly terrain with light tree density or flat terrain with moderate

to heavy tree density. Erceg c is applicable to flat terrain with light tree density.

10 20 30 40 50 60 70 801

2

3

4

5

6

7

8

hbs

cell

radi

us

mobile reverse link

Erceg AErceg BErceg C

6 - 1

6.1 Performance measures We can evaluate the performance of mobile WiMAX system in terms of user capacity,

throughput, bit error rate (BER), and the maximum transmission data rate uplink data rate

User capacity:

User capacity the maximum number of user that can be served simultaneously by the system with predefined in a certain geographic area.

Throughput and delay:

For transmission in communication networks, a packet communication schedule can be more efficient than using a circuit switched protocol. In a packet network, throughput and delay are appropriate parameters.

Throughput is the average rate of successful message delivery per time slot giving a certain amount of traffic for a certain amount of throughput it is important to know what will be the average of a packet Delay .The throughput is usually measured in bits per second (bit/s or bps), and sometimes in data packets per second or data packets per time slot.

Bit error rate (BER):

BER in telecommunication is defined as a ratio of the number of the bit incorrectly receives to the total number of bit sent during a specified time interval is called BER.

The most commonly encountered ratio is the bit error rate (BER), also sometimes referred to as a bit error ratio. Examples of bit error rate are transmission BER, i.e., the number of erroneous bits received divided by the total number of bit transmitted.

Maximum transmission data rate:

In telecommunication data rate is the number of bits that are conveyed or processed per unit of time. The data rate is usually measured in “bits per second “(bit/s or bps).

Chapter 6 Performance analysis of mobile WiMAX

Chapter 6 Performance analysis

6 - 2

The maximum transmission data rate is given by: (6.1) (6.2) 1 (6.3)

(6.4) ∆ (6.5) ∆ (6.6)

(6.7)

Where:

R is Maximum transmission data rate

Cr is code rate

bm is Number of bits per symbol

Nused is data subcarrier

Ts is sample duration

G: is the cyclic prefix rate

ΔF is the sub carrier spacing

NFFT is fast Fourier transform size

Fs is Sampling frequency

n is sampling frequency.

Modulation and coding schemes:

Modulation type Cr bm

BPSK 1/2 1 QPSK 1/2 2

3/4 2 16-QAM 1/2 4

3/4 4 64-QAM 2/3 6

3/4 6 Table6.1 Coding schemes

Performance measures

6 - 3

Flow chart of the maximum transmission data rate calculations:

Figure6.1 Maximum transmission data rate calculations

We study Effects of following Parameters on mobile WiMAX System:

Effect of Modulation Type

Effect of Cyclic Prefix Rate

Effect of Channel Bandwidth

Effect of Subchannelization (Case 1& Case 2)

Effect of Subchannelization (Case 3 & Case 4)

Comparison between Fixed and Mobile WiMAX

Chapter 6 Performance analysis

6 - 4

6.2 Effect of modulation type and code rate

We take case of F = 5.8GHz and BW = 20MHz but in different modulation types with different code rates.

Modulation type BPSK QPSK 16QAM 64QAM

code rate 1/2 1/2 ¾ 1/2 3/4 2/3 3/4

Nsubcahnnel 16 16 16 16 16 16 16

Nused 1120 1120 1120 1120 1120 1120 1120

n( sampling factor) 1.15 1.15 1.15 1.15 1.15 1.15 1.15

Fs 23.04 23.04 23.04 23.04 23.04 23.04 23.04

FFT size 2048 2048 2048 2048 2048 2048 2048

∆F 0.01125 0.01125 0.01125 0.01125 0.01125 0.01125 0.01125

Tb 88.88889 88.88889 88.88889 88.88889 88.88889 88.88889 88.88889

G 0.03125 0.03125 0.03125 0.03125 0.03125 0.03125 0.03125

TS 91.66667 91.66667 91.66667 91.66667 91.66667 91.66667 91.66667

bm 1 2 2 4 4 6 6

R 6.109091 12.21818 18.32727 24.43636 36.65455 48.87273 54.98182

Table6.2 Effect of modulation type in data rate

We observe that:

At BPSK, r = 1/2 Data rate = 6.1 Mbps. At QPSK, r = 1/2 Data rate = 16.8Mbps. At QPSK, r = 3/4 Data rate = 36.6Mbps. At 16-QAM, r= 1/2 Data rate = 24.4Mbps. At 16-QAM, r=3/4 Data rate = 36.6 Mbps. At 64-QAM, r= 2/3 Data rate = 48.8Mbps. At 64-QAM, r=3/4 Data rate = 75.4Mbps.

Effect of modulation type and code rate

6 - 5

Figure6.2 Effect of modulation type in data rate

We conclude that:

The highest data rate is achieved for 64QAM, with rate ¾ since the 64QAM is the highest level of modulation type.

The lowest data rate is achieved for BPSK with rate ½, since BPSK is the lowest level of modulation.

0

10

20

30

40

50

60

6.109090909

12.21818182

18.32727273

24.43636364

36.65454545

48.87272727

54.98181818

max

imum

tran

smis

sion

dat

a ra

te

(Mbp

s)

modulation type & code rate

Effective of modulation type & code rate (f=5.8 GHz , BW=20MHz ,G=1/32,no

subchannelization)

Chapter 6 Performance analysis

6 - 6

6.3 Effect of Cyclic prefix rate

We take case of F = 5.8GHz, BW = 20MHz and 64-QAM modulation type but with different G values.

G 0.03125 0.0625 0.125 0.25

code rate 3/4 3/4 3/4 3/4

Nsubcahnnel 16 16 16 16

Nused 1120 1120 1120 1120

n( sampling factor) 1.15 1.15 1.15 1.15

Fs 23.04 23.04 23.04 23.04

FFT size 2048 2048 2048 2048

∆F 0.01125 0.01125 0.01125 0.01125

Tb 88.88888889 88.88888889 88.88888889 88.88888889

G 0.03125 0.0625 0.125 0.25

TS 91.66666667 94.44444444 100 111.1111111

bm 6 6 6 6

R 54.98181818 53.36470588 50.4 45.36

Table6.3 Effect of cyclic prefix in data rate

We observe that:

The maximum data rate at G = 1/32 is 54.9 Mbps The maximum data rate at G = 1/16 is 53.3 Mbps The maximum data rate at G = 1/8 is 50.4 Mbps The maximum data rate at G = 1/ 4 is 45.3 Mbps

Effect of Cyclic prefix rate

6 - 7

Figure6.3 Effect of cyclic prefix in data rate

We conclude that:

The higher level cyclic prefix index (1/32), has over head occurs, the throughput is achieved.

0

10

20

30

40

50

60

G=1/32 G=1/16 G=1/8 G=1/4

54.9818181853.36470588

50.4

45.36

max

imum

tra

nsm

issi

on d

ata

rate

(M

bps)

Cyclic prefix

Effect of Cyclic prefix rate (64Qam,r=3/4,f=5.8GHz,without

subchannelization

Chapter 6 Performance analysis

6 - 8

6.4 Effect of nominal bandwidth and operating frequency

We take case of 64-QAM modulation type but with different bandwidth and operating frequency.

Nominal bandwidth 20 MHZ 10MHz 7 MHz 1.75MHz

code rate 3/4 3/4 3/4 3/4

F 5.8*10^9 5.8*10^9 3.5*10^9 3.5*10^9

Bandwidth 20 10 7 1.75

Nsubcahnnel 16 16 16 16

Nused 1120 560 280 56

n( sampling factor) 1.15 1.15 1.14 1.14

Fs 23.04 11.52 8 2

FFT size 2048 1024 512 128

∆F 0.01125 0.01125 0.015625 0.015625

Tb 88.88888889 88.88888889 64 64

G 0.03 0.03125 0.03125 0.03125

TS 91.66666667 91.66666667 66 66

bm 6 6 6 6

R 54.98181818 27.49090909 19.09090909 3.818181818

Table6.4 Effect of Bandwidth and operating frequency in data rate

We observe that:

At nominal channel bandwidth = 1.75MHz, Data rate = 3.8 Mbps. At nominal channel bandwidth = 7 MHz, Data rate = 19.09 Mbps. At nominal channel bandwidth = 10 MHz, Data rate = 27.4 Mbps. At nominal channel bandwidth = 20 MHz, Data rate = 54.9 Mbps.

Effect of nominal bandwidth and operating frequency

6 - 9

Figure6.4 Effect of Bandwidth and operating frequency in data rate

We conclude that:

The higher nominal channel bandwidth produce higher data rate. As the nominal channel bandwidth increase data rate increase. We conclude that that the operation in licensed band (3.5 GHz) has lower. Throughput than the licensed excepted band (5.8GHz) narrower channel bandwidth available

for licensed operation.

0

10

20

30

40

50

60

1.75 MHz 7 MHz 10 GHz 20 GHz

3.818181818

19.09090909

27.49090909

54.98181818

max

imum

tra

nsm

issi

on d

ata

rate

(M

bps)

Channel bandwidth

Effect of nominal bandwidth & operating frequency

(64QAM,r=3/4,no subchannelization)

Chapter 6 Performance analysis

6 - 10

6.5 Effective subchannelization (Licensed operation)

We take case of 64-QAM modulation type but for two different case studies [case study A (without subchannelization) and case study B (with subchannelization)]

Case Study Case study A Case study B

code rate 3/4 3/4 3/4 3/4

F 3.50 3.50 3.50 3.50

bandwidth 1.75 7 7 1.75

Nsubcahnnel 16 16 4 4

Nused 56 280 280 56

n( sampling factor) 1.14 1.14 1.14 1.14

Fs 2 8 8 2

FFT size 128 512 512 128

∆F 0.015625 0.015625 0.00390625 0.00390625

Tb 64 64 256 256

G 0.03125 0.03125 0.03125 0.03125

TS 66 66 264 264

bm 6 6 6 6

R 3.818181818 19.09090909 4.772727273 0.954545455

Table6.5 Effect of subchannelization for licensed operation

We observe that:

At nominal channel bandwidth 1.75 MHz case study A (without subchannelization), maximum data rate 3.8 Mbps and Case study B (with subchannelization) maximum data rate is 0.95 Mbps.

At nominal channel bandwidth 7 MHz case study A (without subchannelization), maximum data rate 19.09 Mbps and Case study B (with subchannelization) maximum data rate is 4.7 Mbps.

Effective subchannelization (Licensed operation)

6 - 11

Figure6.5 Effect of subchannelization for licensed operation

We conclude that:

The maximum data rate that can be achieved in case study two is significantly lower than that for case study one by about 1/16 due to subchannelization.

0

2

4

6

8

10

12

14

16

18

20

1.75MHZ 7MHz

3.818181818

19.09090909

0.954545455

4.772727273

max

imum

tra

nsm

issi

on d

ata

rate

(M

bps)

nominal channel bandwidth(MHz)

Effective subchannelization (Case A& Case B )(64-QAM , r=3/4)

with no subchannelization

with subchannelization

Chapter 6 Performance analysis

6 - 12

6.6 Effective subchannelization (Licensed-exempt operation)

We take case of 64-QAM modulation type but for two different case studies [case study C (without subchannelization) and case study D (with subchannelization)].

Case Study Case study C Case study D

code rate 3/4 3/4 3/4 3/4

F 5.8*10^9 5.8*10^9 5.8*10^9 5.8*10^9

bandwidth 20 10 20 10

Nsubcahnnel 16 16 2 2

Nused 1120 560 1120 560

n( sampling factor) 1.15 1.15 1.15 1.15

Fs 23.04 11.52 23.04 11.52

FFT size 2048 1024 2048 1024

∆F 0.01125 0.01125 0.00140625 0.00140625

Tb 88.88888889 88.88888889 711.1111111 711.1111111

G 0.03 0.03125 0.03125 0.03125

TS 91.66666667 91.66666667 733.3333333 733.3333333

bm 6 6 6 6

R 54.98181818 27.49090909 6.872727273 3.436363636

Table6.6 Effect of subchannelization for licensed-exempt operation

We observe that:

At nominal channel bandwidth 10 MHz case study one without subchannelization, maximum data rate 27.4 Mbps and Case study tow with subchannelization maximum data rate is 3.4 Mbps.

At nominal channel bandwidth 20 MHz case study one without subchannelization, maximum data rate 54.9 Mbps and Case study tow with subchannelization maximum data rate is 6.8 Mbps.

Effective subchannelization (Licensed-exempt operation)

6 - 13

Figure6.6 Effect of subchannelization for licensed-exempt operation

We conclude that:

The maximum data rate for case study four is significantly lower than that in case study three is about 1/8 or 12.5%.

The maximum data rate for case study four is about 1/8 or 12.5%. The maximum data rates achieved in case study three.

0

10

20

30

40

50

60

10MHZ 20MHz

27.49090909

54.98181818

3.4363636366.872727273

max

imum

tran

smis

sion

dat

a ra

te

(Mbp

s)

nominal channel bandwidth(MHz)

Effective of subchannelization (Case 3 & Case 4)(64QAM,r=3/4,f=5.8GHz.G=1/32)

with no subchannelization

with subchannelization

Chapter 6 Performance analysis

6 - 14

6.7 Comparison between fixed WiMAX and Mobile WiMAX

Here we study the effect of bandwidth on Data rate for Mobile WiMAX and Fixed WiMAX.

Bandwidth 1.75MHz 7MHz 10MHz 20MHz

Mobile WiMAX 3.818181818 19.09090909 27.49090909 54.98181818

Fixed WiMAX 6.647727273 26.59090909 37.70181818 75.40363636

Table6.7 Effect of bandwidth in Mobile and Fixed WiMAX

We observe that:

At nominal channel bandwidth 1.75 MHz in maximum data rate in fixed WiMAX is 6.64Mbps and in mobile WiMAX are 3.8Mbps.

At nominal channel bandwidth 7 MHz in maximum data rate in fixed WiMAX is 26.5Mbps and in mobile WiMAX are 19.09Mbps.

At nominal channel bandwidth 10 MHz in maximum data rate in fixed WiMAX is 37.7 Mbps and in mobile WiMAX are 27.4 Mbps.

At nominal channel bandwidth 20 MHz in maximum data rate in fixed WiMAX is 75.4 Mbps and in mobile WiMAX are 54.9 Mbps.

Comparison between fixed WiMAX and Mobile WiMAX

6 - 15

Figure6. 7 Effect of bandwidth in Mobile and Fixed WiMAX

We conclude that:

The maximum data rate can be achieved in Fixed WiMAX and it occur in Bandwidth 20MHz. The data rate in Mobile WiMAX less than in Fixed WiMAX (In different bandwidth).

0

10

20

30

40

50

60

70

80

1.75MHz 7MHz 10MHz 20MHz

3.8181

19.0909

27.4909

54.9818

6.6477

26.5909

37.7018

75.4036

max

imum

tra

nsm

issi

on d

ata

rate

(M

bps)

nominal channel bandwidth(MHz)

Comparison between fixed WiMAX & Mobile WiMAX

(no subchannelization,G=1/32,r=3/4,64QAM)

Mobile WiMAX

Fixed WiMAX

7 - 1

7.1 Introduction When planning cellular structured WiMAX system, you have to determine:

The minimum number of base stations (BSs) to cover the whole area of interest.

The type of the base stations that includes choice of BS, antenna configuration cell type.

The radius of each cell.

The location of base stations as well as the spacing between them,

The height of antenna at each base station.

Network planning is an ongoing process or a continuous process. It occurs periodically after certain period of time. You have to make network planning in the following cases:

When you install a new system.

To meet a new requirement either to extend coverage to other areas or to increase the number of subscribers.

When the new techniques appear or are developed and become commercially available such as smart antennas that will lead to increase in cell site capacity and it will reduce the number of cell sites or new techniques that will lead to increase in data rate.

7.2 Cellular structured WiMAX Network planning processes The cellular structured WiMAX network planning processes include the following:

7.2.1 Nominal or preliminary cell planning

A nominal or preliminary cell plan can be produced from the data compiled from coverage and traffic analysis. The nominal cell plains a graphical representation of the network and looks like a cell pattern on a map. During nominal cell planning, do not care about the position of the sites taking only in consideration the separation distance between sites.

Chapter 7 Practical part of mobile WiMAX coverage

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To simplify the network planning, hexagonal shaped cells are adopted although they are artificial or fictitious and do not exist in real world but it have become a widely promoted symbols for cellular structured system. Nominal cell plans are the first cell plans and forms the basis for further planning.

In reality, each company has a planning tool which is a work station equipped with a software package based on link budget calculations and using certain propagation model to determine the cell radius and the results are displayed on the map using different colors. An up to date digital three dimensional map with high resolutions for the area where the network is to be planned is used to import the actual environment data that include the terrain fluctuations (height information), clutter distribution, dense degree of the area of interest. The area of interest is divided into different sub regions according to different environment definitions. Each sub region has its own characteristics. The classification is based on the dense of buildings and their heights in the sub region.

Each sub region is classified into one of the four categories: dense urban (DU), urban (UR), suburban (SU) and rural (RU).The planning tool determines the classification of each sub region. It is possible to import data from site survey files. Data can also be imported from field measurements files to tune the propagation model as will be explained in the following subsections.

The area where the network is to be planned to be covered with cellular structured system is used. Two study cases are investigated:

Coverage oriented environment represent suburban and rural environments.

Capacity oriented environment represent dense urban and urban environments.

Using the software program developed by us the maximum allowable path loss (MAPL) is calculated using reverse link budget and forward link budget and the link balance was made and the least value was taken as an input to the propagation model. Thus, the cell radius was calculated using coverage criterion.

The classification of sub regions according to their building density and heights is determined by us during site survey by observing the area features, landmarks and terrain in each sub region.

7.2.2 Site surveys

Once the nominal cell planning has been completed, site surveys can be performed for all the proposed site locations by the site survey team. The site survey includes: site search, candidate sites are chosen, the site survey team check the validity of each location of the sites, contact with the site owner, site location lease agreement, get permission of the new sites, and carry out the construction of the civil works, tower erection, transmission and interconnection between the network entities. Finally site acquisition.

The following items must be checked for each site:

Cellular structured WiMAX Network planning processes

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The space for the equipment including: antennas, cable runs and power facilities. The exact site locations (with some shifts)are fed back to the network planning team to modify the network planning by shifting the locations of the sites such that no dead zones were introduced and overlap between sites were reduced as much as possible.

7.2.3 Field measurements

The purpose of the field measurements is to correct the propagation model to reflect the propagation status of wireless signal in the environment of the area of interest, thus making the model more practical meet the coverage requirement.

To conduct field tests, the following steps have to be followed:

1. You have to choose the frequency of the measurement. If there is interference on the frequency point to be used, choose a frequency point without interference. The transmission characteristics are almost the same when frequency difference is 10 MHz or so.

2. Field measurements site choice: You have to choose the field measurements site. The field measurements site should not be too much higher than the surrounding buildings and 10 meters are suitable. To obtain as much data as possible for correcting various clutters, two or three field measurements sites with similar surrounding clutters (building heights, site height, and so on) can be chosen to carry out field measurements and data from several sites can be synthesized to execute the correction of the various clutters.

3. Choose pertinent parameters of the field measurements site i.e. use omnidirectional antenna, choose proper transmission power, no obstruction surrounding the field measurements site, and clean the frequency point.

4. The tools for field measurements includes: transmitter or CW transmitter, scanner or field strength meter and GPS handset.

5. Before field measurements, you have to span antennas, install transmitter, and adjust output power and frequency point to proper values and transmitting signal.

6. After field measurements, the field measurements data is put into a form acceptable for the planning tool load the field measurements file into the planning tool and correct the model.

7.2.4 System design (or final cell plan)

The actual and the exact site locations are used to produce the final cell planning which is used for network installations, provided that no dead zones and overlap between sites is small as possible 2.5 System diagnosis The test team via the driving test and using test mobile system which is a testing tool. The testing tool includes mobile test units (MTUs) in cars and fixed test units geographically distributed. The testing tool consists of a MS with special software, a portable personal computer (PC) and a global positioning system (GPS) receiver and mobile traffic recording (MTR) and cell traffic recording (CTR). The

Chapter 7 Practical part of mobile WiMAX coverage

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MS is used in active and idle mode. The PC is used for presentation, control and measurement data storage. The GPS receiver provides the exact position of the measurement site by utilizing satellites. When the satellite signals are shadowed, the GPS system switches to dead reckoning. Dead reckoning consists of a speed sensor and a gyro. This provides the position if satellite signals are lost temporarily. The measurement data can be imported to the planning tool and can be displayed on a map to compare the measured handoffs with the predicted cell boundaries for example to check the network performance, to evaluate the customer complaints, to verify that the final cell planning was implemented successfully.

7.2.5 System tuning

After installation of the network, it is continuously monitored to determine how well it meets the coverage and capacity requirement using the measured data, parameters are changed. Other measurements can be taken if necessary.

The parameters to be changed are such as BS transmitted power, BS antenna height, antenna down tilting angle, antenna type (gain, horizontal HPBW, and so on). Change handoff parameters, change, add or decrease channels.

7.2.6 System growth

Cell planning is an ongoing process. If the network needs to be expanded to extend coverage due to increase in traffic of because or change in the environment. Starting with a new capacity or traffic and coverage or power analysis.

7.3 BS site choice When choosing BS site, the following rules should be obeyed:

1. Antenna height should be higher to some degree than the surroundings.

2. Ensure that there is no obvious obstruction in surrounding environments.

3. Ensure that there is no obstruction surrounding the position of setting the global positioning (GPS) antenna.

4. Meet coverage goal requirement concerning the effective coverage of the BS.

5. Predict traffic distribution in the coverage area and set the BS sites on the places of real traffic need.

6. Utilize existent sites such as telecom Egypt centrals in case of rural communication network and use other communication resources as possible such as towers, buildings.

7. Guarantee necessary space separation concerning the interference from other systems.

Antenna configuration and cell type choice

7 - 5

8. Avoid strong wireless transmitter, radar or other serious interference.

9. Choose places with convenient traffic, reliable electricity plant, if not available use generators or solar cell panels.

10. Avoid being near the flammable or explosive buildings.

11. Avoid being near the industrial manufactories with poisonous gas or smoke and dust.

12. Avoid hospitals, educational buildings, military zones, church, mosques, and entertainment areas.

7.4 Antenna configuration and cell type choice The choice of BS antenna should concern with the following factors: site type, dense degree of BS

and relative positions between them and dense degree of the area and so on. The following rules b. d be obeyed when choosing antennas:

1. In dense urban (DU) and urban (UR) areas i.e. in capacity oriented areas, sectorized cells or directional antennas with narrow power beam width (HPBW) angle can be chosen and large gain can be chosen to reduce the other cell interference and increase the capacity.

2. In suburban areas and rural areas with low capacity where user or population density is low i.e. In coverage oriented areas, Omni cells with Omnidirectional antennas with high antenna height can be chosen.

3. In suburban areas and rural areas, when the capacity increases, directional antennas with wide half power beam width (HPBW) angle and large gain value can be chosen to increase coverage.

4. In highways, where there is no need to cover towns along the road, or at border area or at the coast, 2 sector configuration is the optimal solution with two directional antennas with narrower width and higher gain antennas.

5. Three sector cells is the optimum solution to meet both capacity and coverage in all morphologies.

6. Dual polarization is usually used in dense urban (DU) and urban (UR) areas and space diversity is usually used in suburban (SU) rural (RU) areas.

7.5 Antenna selection Antenna selection is very important part of WiMAX network planning and is mainly based on

coverage and installation space. Table (7.1) shows the antenna selection for rural environment representing coverage oriented case study and for dense urban (DU) environment representing capacity

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7 - 6

oriented case study. It shows also the antenna type (Omni directional and directional) and typical antenna height.

case study Antenna gain (dBi)

polarization

Half power band width (HPBW) (degrees

Antenna type Antenna height

environment

coverage oriented case

12 vertical 360 omnidirectional50 meters

rural

Capacity oriented case

18 Dual polarization 45

65 directional 30 meters

Dense urban

Table7.1 the antenna selection for rural environment and for dense urban environment

7.6 Uniform solution of cellular structured mobile WiMAX network coverage

We consider two study cases and calculate the cell radius in each case study according to coverage criterion.

Case study one: rural area.

Case study two: dense urban area

7.6.1 Case study one

Assume: All the region of interest to be covered by WiMAX system is rural (RU) environment.

All the cells are omnicells

The BS antenna used is omnidirectional

The BS antenna used has gain 15dBi

The BTS antenna height is 50 meters

We calculate the cell radius according to coverage criterion Covered area is 115.461Km2

The cell radius is 2.90126443268447Km

The cell area is 31.868878Km2

Number of cells is 5.47 cells

Uniform solution of cellular structured mobile WiMAX network coverage

7 - 7

Figure7.1 Coverage of rural area

Cell site information of Case study one

Site ID Site name Site coordinates Longitude(E) Latitude(N)

1 Burtus 31° 8'9.45"E 30°10'1.33"N 2 Ausim 31° 9'58.57"E 30° 7'3.37"N

3 Mansuirya 31° 2'5.44"E 30° 6'55.66"N 4 Mansuirya 31° 2'5.44"E 30° 6'55.66"N 5 Dhat al kwam 31° 3'29.12"E 30°10'2.06"N

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7.6.2 Case study two

Assume:

All the region of interest of the map to be covered by mobile WiMAX system is dense urban (DU) environment

All the cells are 3 sector cells

The BS antenna is directional antenna with gain 15 dBi

The BS antenna height is 30 meters

We calculate the cell radius according to coverage criterion

Covered area is 129.535Km2

The cell radius is 1.705908403Km

The cell area is 7.560722584Km2

Number of cells is 17.2 cells

Figure7.2 Coverage of dense urban area

Non uniform solution of cellular structured mobile WiMAX network coverage

7 - 9

Cell site information of Case study one

Site ID Site name Site coordinates

Longitude(E) Latitude(N) 1 El hegaz 31°20'22.76"E 30° 6'44.69"N 2 El Matarya 31°18'41.07"E 30° 6'44.25"N 3 El Kablat 31°17'9.69"E 30° 6'43.80"N 4 El Hagan 31°15'33.45"E 30° 6'41.24"N 5 Shobra 31°14'24.41"E 30° 5'42.63"N 6 El Oboor 31°16'24.86"E 30° 5'41.00"N 7 Saraya el koba 31°18'8.33"E 30° 5'38.84"N 8 Haroun el Rasheed 31°19'37.88"E 30° 5'44.00"N 9 Almaza airport 31°21'17.15"E 30° 5'46.52"N

10 Kobry el nozha 31°20'21.36"E 30° 4'38.52"N 11 Nafaq el taiaran 31°18'54.85"E 30° 4'38.60"N 12 Sarya el zafaran 31°17'14.43"E 30° 4'37.11"N 13 Ahmed helmy 31°15'11.01"E 30° 4'36.12"N 14 El anteqkhana sq 31°14'9.23"E 30° 3'18.64"N 15 El tarabeshy 31°16'4.81"E 30° 3'25.95"N 16 Extended Ramses 31°17'59.74"E 30° 3'32.69"N 17 El Nahda 31°19'43.77"E 30° 3'33.12"N 18 Mostafa el nahas 31°21'21.19"E 30° 3'31.43"N

7.7 Non uniform solution of cellular structured mobile WiMAX network coverage 7.7.1 Rural area (RU)

Covered area is 115.461Km2

The cell radius is 2.623326272Km

The cell area is17.87954669Km2

Number of cells is 6.4577cells

Assume that the BS height is 40 meters

Chapter 7 Practical part of mobile WiMAX coverage

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Figure7.3 Rural area coverage

7.7.2 Suburban area (SU)

Covered area is 173.542Km2

The cell radius is 2.097296742 Km

The cell area is11.42803734 Km2

Number of cells is 15.18563467 cells

Assume that the BS height is 40 meters

Non uniform solution of cellular structured mobile WiMAX network coverage

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Figure7.4 Suburban area coverage

7.7.3 Urban area (UR)

Covered area is 6.8 Km2

The cell radius is 1.992711699 Km

The cell area is10.31670061 Km2

Number of cells is 1 cell

Chapter 7 Practical part of mobile WiMAX coverage

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Assume that the BS height is 40 meters

Figure7.5 Urban area coverage

7.7.4 Dense urban area (DU)

Covered area is 115.461 Km2

The cell radius is 2.623326272 Km

The cell area is17.87954669 Km2

Number of cells is 6.4577 cells

Assume that the BS height is 40 meters

Non uniform solution of cellular structured mobile WiMAX network coverage

7 - 13

Figure7.6 Dense urban area coverage

8 - 1

8.1 Introduction Due to Field measurements in Network planning of WIMAX cellular structured system we make

measurements is to correct the propagation model to reflect the propagation status of wireless signal in the environment of the area of interest, thus making the model more practical meet the coverage requirement so we use RF field strength meter to do this measurement.

8.2 RF strength meter applications 1. Set up and adjust antennas. 2. Test the operation of remote control for garage door openers and other low-power

transmitters. 3. It is also useful for checking ham and CB antennas and low-power transmitters, in the FM and

AM bands. 4. It will also spot sources of RF and RF interference from devices such as light dimmers,

fluorescents, and switching supplies. 5. It even checks the electronic car “keys” used by many new cars for RF output. 6. It is also useful for checking small transmitters such as cell phones, amateur radio walkie-talkies,

family radio (UHF walkie-talkies), and CB transmitters. 7. It even checks microwave ovens for leakage and can detect an operating microwave oven 10–12

feet away. 8. Reveal the possible RF hazards from these devices as well. 9. It can check wireless computer peripherals such as mice and keyboards, and PCS devices 10. Detects small FM transmitters and other “bugs”.

11. And also detect 900-MHz wireless video cameras ,video transmitters, low-power FM stereo

transmitters and so on.

8.3 RF strength meter specifications 8.3.1 Antenna specification

Small, relatively high-power (1–5 watt) VHF and UHF transceivers are common. The high operating frequency of these handheld devices allows small antennas of 5–20 cm length to be used. The

Chapter 8 Hardware implementation of RF Field strength meter

Chapter 8 Hardware implementation of RF Field strength meter

8 - 2

result of this is the generation of an intense RF field in close proximity to the antenna. The antenna may be as close as a few centimeters from vital body structures, such as the brain or the eyes. This may be the case when a cell phone or walkie-talkie is held close to your face, as is often done because the microphone and speakers are integrated into these units. The allowable RF power density that might be harmful is easily exceeded in such cases.

So in this project we use short (2-foot) adjustable whip antenna is used for pickup, and this antenna can be removed via a BNC connector.

8.3.2 Frequency range

This system detects signals over a range of 500 kHz to 500 MHz, with usable sensitivity from 100 kHz to 3 GHz. As with any untuned broadband detector, the strongest signal in the area will dominate. Hidden transmitters can be detected with this device, but their signals must be stronger than any other signal or a false indication may occur. For optimum performance, two separate active preamplifiers are used; one for LF and HF (100 kHz to about 30 MHz) and another for 30 MHz or higher VHF and UHF (30 MHz to 3GHz) A front panel switch select which preamplifier is used.

8.3.3 Power supply

Power is supplied from the circuit using two 6- or 9-volt batteries.

8.3.4 Power density

Assume that the antenna of a low-power transmitter in use is located 10 cm (4 inches) from the body and that 500 milliwatts (mW) is being radiated from the antenna. Consider a sphere of 10-cm radius around the antenna. The total area of this sphere is equal to Area 4 πr 4 3.14159 125.6 cm (8.1)

Because 500 mW is being radiated, the average power density crossing the surface of this sphere is: Power Unit area 500 125.6 3.98 mW/cm (8.2)

This is almost four times the 1 mW/ that is thought to be hazardous, and this assumes an ideal isotropic radiator. (In Australia, a power density level of 0.2 mW/ or more is considered hazardous.) In practice, there are peaks and valleys in any antenna and ground (composed of the device PC board and case assembly plus other metal parts), and at distances closer than about 0.159 wavelengths from the antenna, the near-field components must be considered. Note that this equals 1/2π wavelengths and is a mathematical approximation, and no real sharp boundary exists between near- and far-field regions. Nevertheless, the radiated power still has to cross this spherical surface. In addition, note that 5-watt VHF and UHF walkie-talkies are common, and antennas are often held closer than 4 inches from the body. So you can see that it is easily possible to develop power density levels of more than 1mW/ with any of these devices. The safe exposure limit is not known to any degree of accuracy. The authors have seen various low-cost devices available to measure power density level.

Block diagram of RF strength meter

8 - 3

An X-band (around 10 GHz) waveguide has a cross-sectional area of around 0.33 square inches or 2.3 square centimeters. A transistor oscillator putting out 10 mW would produce a power density of 4.3 mW/ A 1-watt transmitter would produce 430 mW/ . As anyone who has been on the bench has learned, 1 watt in a small area (for instance, a transistor with no heat sink, dissipating 1 watt of power), can get very hot. Someone who would be foolish enough to look straight into this X-band waveguide carrying 1 watt could definitely fry an eyeball. The moral of the story is obvious: Power density, not power level, is the culprit.

8.4 Block diagram of RF strength meter

Figure8.1 Block diagram of RF strength meter

Chapter 8 Hardware implementation of RF Field strength meter

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8.5 RF strength meter Circuit diagram

Figure8.2 Schematic of RF Field Strength Meter

8.6 Circuit Operation 8.6.1 Whip antenna

A 2-foot (60-cm), collapsible whip antenna connected to J1 picks up RF signal. This signal can be anywhere in the 100 kHz to 3 GHz range. Higher-frequency signals (more than 30 MHz) tend to be opposed by L1 and are coupled to preamplifier Q1 via C1. Lower-frequency signals see C1 as high impedance in series with the low-input impedance of Q1, and L1 as low impedance. The low-frequency signals are coupled to the gate of FET Q2 via C9. The gate of Q2 has very high-input impedance (more than 100K Ωs) to lower-frequency signals, and C9, although small, has a negligible effect.

Circuit Operation

8 - 5

8.6.2 Preamplifier

8.6.2.1 VHF-UHF preamplifier

Figure8.3 VHF-UHF preamplifier

The VHF-UHF preamplifier consists of Q1 and a few bias resistors. R3, R1, and R2 bias Q1, a BFR90 UHF bipolar, to about 3 volts and 5 mA collector current. The gain of the bipolar preamplifier is approximately two to three times voltage gain. FB1 acts as an RF choke, and signal is coupled to voltage doublers /detector diodes D1 and D2. These are hot carrier diodes for better sensitivity. R5 provides a slight DC bias for improved sensitivity to low-level signals. C4 is an RF bypass, and the detected signal is taken off via R6 to be amplified by IC2.

8.6.2.2 LF-HF preamplifier

Figure8.4 LF-HF preamplifier

The low-frequency preamplifier is fed from source follower Q2. R22 returns the gate of Q2 to ground, while R23 provides source bias. C10 couples signal into a feedback pair amplifier consisting of Q3, Q4, and bias resistors R24, R26, and feedback resistor R25. The overall gain of the LF preamplifier is about three to five times voltage gain (antenna to detector). C12 couples RF signal to detector diode D3, which is also a hot carrier diode. Because the preamplifier gain is higher than the Q1 stage, a voltage doublers configuration is not needed here. D3 is also a hot carrier diode and is slightly forward biased by R27. Detected signal is taken off through R28.

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Both preamplifiers are fed chopped from timer IC IC1, an ICM7555. This is a CMOS version of the popular 555 timer IC. R19, R20, and C8 form an RC network to produce a nearly symmetrical square wave. C7 is a bypass capacitor for noise suppression, and C6 is a bypass capacitor also for noise suppression. is fed to pins 4 and 8, and chopped appears at pin 3.C3 is a despiking capacitor to reduce fast transients. R4 and C3 control wave shaping to preamplifier Q1, and R21 and C11 do the same for the lower-frequency preamplifier. The effect of using a chopped supply for both preamplifiers is to amplitude modulates their RF outputs. This allows an AC component to appear on the detected signal, which is later amplified rather than the DC component. The lower limit of delectability is about 5–10 mV at the detector, which is limited by the presence of chopping noise spikes and the square law effect of the detector at low levels.

8.6.3 Chopper amplifier

Figure8.5 Chopper amplifier

With the preamplifiers, this allows 2-mV input signal levels to be detected.IC2 is a TLO81 FET op-amp that performs all of the amplification functions needed in this circuit. It is powered by two supplies: a positive and a negative battery supply. This simplifies biasing, and battery life is long, approaching shelf life for the negative battery supply BT2. The positive battery supply BT1 has to carry the preamplifiers and LED display and must provide 20–30 mA, but for the intermittent nature of the use of this device, the battery life should be long here also. S2 is the power switch for the battery supply. S1 is a selector switch that connects one of the detector outputs to the AC amplifier IC2. This op-amp is biased to 6–9 volts and is set for a gain of between 30 times and 600 times via gain control R7 and limiting resistor R8.D4, D5, and R10 compensate for the nonlinearity of the rectifier diode D6. Amplifier

Circuit Operation

8 - 7

output is coupled to D6 via C15. DC output is fed to network R12, C16, and R13, which filter the output and remove AC components and determine the ballistic characteristics of the “meter” formed by the LED display.

8.6.4 Power supply

Power is supplied from the circuit using two 6- or 9-volt batteries. A voltage divider or active splitter using an op-amp would permit only one battery to be used, but it was not really worth the extra parts because large decoupling capacitors would be needed. Only a few milliamperes of negative supply are needed, and the battery life will approach shelf life with such a light drain. The positive supply must handle 20–30 mA. We used two sets of four AA batteries, which are cheap and simple and fit the case perfectly. Alternately, two 9-volt batteries could also have been used. The circuit operates down to 3.5 volts or so. But In order to test the circuit board, a power supply of ±5 to 9 volts should be used.

8.6.5 Bar graph display

Figure8.6 Bar graph display

The meter acts like an analog mechanical movement. The meter has a full-scale deflection of around 3 volts. At full gain setting, this allows an RF input signal of 5–10 mV to produce a full-scale indication. This corresponds to maximum gain setting of R7 (minimum resistance).The meter consists of IC3 and IC4, a pair of LM3914 LED segment drivers, and two 10-segment LED bar graph assemblies cascaded to give a 20-segment meter This is sufficient resolution (5 percent full scale) for our purposes.

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Red LEDs were used, but any other color or combinations of colors may be used as long as all LEDs are driven with the same DC current levels. The use of separate, individual LEDs is permissible. R14 and R15, with R16 set up the LM3914s for cascaded dot mode operation. Bar graph mode operation could be used, but battery drain when 20 LEDs are lit (full scale) would approach 200 mA. Dot mode saves battery drain because only one or two segments at a time are lit. R17 cuts off LED10 when any of the LEDs 11 to 20 are lit and C17 with R18 form a filter network to suppress a tendency for the display to be unstable because of possible RF oscillation. In addition, R17 limits the maximum possible LED current in case of a

short circuit, avoiding damage to individual segments.

A voltage divider or active splitter using an op-amp would permit only one battery to be used, but it was not really worth the extra parts because large decoupling capacitors would be needed. Only a few milliamperes of negative supply are needed, and the battery life will approach shelf life with such a light drain. The positive supply must handle 20–30 mA. We used two sets of four AA batteries, which are cheap and simple and fit the case perfectly. Alternately, two 9-volt batteries could also have been used. The circuit operates down to 3.5 volts or so before beginning A magnifier is helpful to see certain color codes and small part numbers. Check any dubious items with a VOM to be sure. Low-profile DIP sockets can be used to facilitate experimentation and replacement of ICs and LED bar graph displays. Sockets are recommended if you prefer to avoid directly soldering IC chips in the board. The long lead on Q1 is the collector. When trimming it to length, it is a good idea to cut the end diagonally to distinguish it from the other leads. The center lead is the emitter, and this lead is soldered directly to the ground plane, with the lead as short as possible. If you like, you may mount the board in a case with batteries and jacks before testing; however, if any assembly errors are found, access to the circuit board will be more difficult.

8.7 Parts Placement of RF Field Strength Meter

Figure8.7 Parts Placement of RF Field Strength Meter Component Side

PC Board Pattern for Solder Side of RF Field Strength Meter

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Figure8.8 Parts Placement of RF Field Strength Meter Solder Side

8.8 PC Board Pattern for Solder Side of RF Field Strength Meter

Figure8.9 PC Board Pattern for Solder Side of RF Field Strength Meter

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8.9 Test Procedure of RF strength meter In order to test the circuit board, a power supply of ±5 to 9 volts should be used. Note that this

is actually two separate supplies of the same voltage but with opposite polarity.

Connect the power supplies to the circuit board at the points shown in the parts placement diagrams. Make sure S2 is in the OFF position when connecting the power supplies. After checking your wiring, turn on S2. The LED display should flash briefly and return to 0. Rotate R7 fully counter clockwise (minimum gain).

Check for the following voltages:

Pin 7 IC2: +5 to +6 volts

Pin 4 IC2: –5 to –6 volts

Pin 6 IC2: 0–1 volt

Pins 4 and 8 IC1: +5 to +6 volts

Pin 3 IC1: +2.2 to +3.0 volts

Collector Q1: +1.1 to +1.7 volts

Base Q1: +0.3 to +0.4 volt

Drain Q2: +1.3 to +1.8 volts

Source Q2: +0.7 to +1.3 volts

Collector Q4: +1.3 to +1.8 volts

Base Q3: +0.3 to +0.4 volt

Emitter Q4: +0.35 to +0.5 volt

Pins 6, 7 of IC4: +1.2 to +1.5 volts

Pin 4 IC4: +0.6 to +0.8 volt

Pin 6 IC3: +0.6 to +0.8 volt

Pin 7 IC3: +1.25 volts

Pin 3 IC3: +4.5 to +5.7 volts

Note that this test was made with 5–6 volts. You may later use a 9-volt battery supply for both batteries if desired, but the meter should work with somewhat less than 5 volts, to allow for gradual battery exhaustion.

RF Strength Meter parts List

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8.10 RF Strength Meter parts List Component Item name VALUE QuantityIntegrated Circuits

IC1 ICM7555 IC2 TLO81N IC3,IC4 LM3914N

1 1 2

Transistors Q1 BFR90 Q2 MPf107 Q3 2N3565 Q4 2N3565

1 1 1 1

Diodes D1 through D3 HP 5082-2800 or 5082-2835 D4 through D6 1N914B or 1N4148

3 3

Capacitors C1, C12 C2, C9 C3, C11 C4 C7, C10, C14 C13 C15,C6 C16, C17 C5 C8

10 pf NPO 4.7 pf NPO .1 Mylar 50V 47 pf NPO .01 μf 50V ceramic .022 μf Mylar 50V 1 μf 35V elec 10 μf 16V elec Not used .001 Mylar

2 2 2 1 3 1 2 2 1 1

Resistors 1/4W 5%

R1, R25 R2 R3, R4, R21 R5, R9, R27 R6, R28 R7 PT10 pot R8 R10, R12, R17 R11, R20, R22 R14, R15 R16 R18 R19 R23, R24 R26 R13

6.8 KΩ 3.3 KΩ 470 Ω 3.3 MΩ 22 KΩ 100 KΩ 4.7 KΩ 10 KΩ 1 MΩ 1 KΩ 1.2 KΩ 33 Ω 100 KΩ 2.2 KΩ 330 Ω 33 KΩ

2 1 3 3 2 1 1 3 3 2 1 1 1 2 1 1

Miscellaneous Ferrite bead (FB) S1, S2 J1 L1 BT1, BT2

DPDT slide switch BNC Jack-or other 4 T #22 Bare wire 1/4 inch dia 6 to 9 volts

1 2 1 1 2

Table8.1 RF Strength meter parts list

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8.11 Packaging of RF field strength meter It is recommended to package the meter in a plastic or metal case. Use a 1:1 size layout of the

PC board to locate the holes for the display and the switches and R7. A BNC jack can be mounted on top of the meter to use as an antenna connection. A 2-foot, collapsible whip antenna is recommended, and this should be fitted with a BNC connector to mate with J1. A suitable antenna can be purchased from the source shown at the end of this chapter. A case and a complete kit of parts and a drilled and etched board are also available from the same source. Packaging is not critical, and you can do this to suit your own preferences. Battery supplies (6–9 volt) are required, and you can use AA, AAA, or 9-volt alkaline types with suitable holders. The battery holders can be mounted inside the case, in the rear half, with the circuit board mounted as shown to the front half of the case. Three wires are needed from the battery pack to the circuit board, and a lead from the antenna jack J1 should run to the preamplifier inputs. A short length of coaxial cable is used to connect the VHF-UHF preamplifier directly to J1, and a length of #20 wire is used to both form L1 (not critical) and connect to the LF-HF preamplifier input as shown in the figures. If a plastic case is used, this wire will form an adequate UHF pickup antenna for 400–3000 MHz A metal case will shield this pickup, so an external antenna will be needed at J1. If you prefer, a plastic filter can be used over the LED display (use red for red LEDs, or a matching color for other LEDs you may use, for best visibility). We did not use a filter because none was found necessary

Figure8.10 Packaging of RF field strength meter

Packaging of RF field strength meter

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Figure8.11 Photo of Completed RF Field Strength Meter with Matching Antenna

Figure8.12 Photo of inside Completed RF Field Strength Meter Showing Battery Pack

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8.12 Conclusions Among the newer RF devices on the consumer market are a wide variety of low power

transmitters. These include more application.

The meter in this project uses an active antenna preamplifier and Schottky barrier diodes for improved sensitivity. A chopper system converts the detected signal to a 700-Hz AC signal. This is amplified with a high-gain op-amp AC amplifier (up to 600 times), and the AC signal is rectified and used to drive a 20-segment LED bar graph display in the dot mode for reduced battery drain. Diodes in the feedback loop compensate for rectifier nonlinearity. This system detects signals as low as –40 dBm (2.2 mV into 50 ohms) over a range of 500 kHz to 500 MHz, with usable sensitivity from 100 kHz to 3 GHz. As with any untuned broadband detector, the strongest signal in the area will dominate. Hidden transmitters can be detected with this device, but their signals must be stronger than any other signal or a false indication may occur. For optimum performance, two separate active preamplifiers are used, one for LF and HF (100 kHz to about 30 MHz) and another for 30 MHz or higher. A front panel switch selects which preamplifier is used. A gain control allows optimum adjustment of sensitivity.

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9.1 Introduction The IEEE 802.16 standard, the Worldwide Interoperability for Microwave Access (WiMAX), is a

broadband wireless technology that offers all packet-switched services for fixed, nomadic, portable, and mobile accesses. The first specification (i.e., IEEE 802.16-2004) that was ratified by IEEE in 2004 targets fixed and nomadic accesses in line-of-sight (LOS) and non-line-of-sight (NLOS) environment. With the amendment of IEEE 802.16e-2005, IEEE 802.16e, also called Mobile WiMAX, further provides handover, sleep mode, idle mode, robust security, and roaming functions for mobiles. Similar to other IEEE 802 standards, IEEE 802.16 only specifies media access control (MAC) and physical (PHY) layer functions and lacks networking support. To address the demands for establishing an interoperable WiMAX network, the WiMAX Forum was formed to promote WiMAX and certify WiMAX products, and also proposed an end-to-end network architecture and service operations for WiMAX and Mobile WiMAX. With these efforts from IEEE 802.16 and other organizations, WiMAX and Mobile WiMAX are not only PHY and MAC layer technologies, but also a complete network solution for a broadband wireless access system beyond third generation (3G).

Mobility management is one of the essential functions for a mobile network. In Mobile WiMAX, mobility management schemes that handle link and network layer handover have been jointly developed by IEEE 802.16e and the Network Working Group (NWG) of the WiMAX Forum. This chapter provides an overview of mobility management in a Mobile WiMAX network.

Based on the network architecture, location management of a mobile station (MS) in idle mode, link layer mobility management (also called access service network [ASN]- anchored mobility management), and network layer mobility management (i.e., connectivity service network [CSN]-anchored mobility management) are presented. Finally, mobility management in Mobile WiMAX is summarized.

9.2 Channel acquisition The MAC protocol includes an initialization procedure designed to eliminate the need for

manual configuration. In other words, the subscriber takes the SS out of the box, plugs in power and Ethernet, and connects almost immediately to the network. The following paragraphs describe how that is possible without laborious user setup or service provider truck roll.

Upon installation, the SS begins scanning its frequency list to find an operating channel. It may be preconfigured by the service provider to register with a specified BS. This feature is useful in dense

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deployments where the SS might hear a secondary BS due to spurious signals or when the SS picks up a sidelobe of a nearby BS antenna. Moreover, this feature will help service providers avoid expensive installations and subsequent truck rolls.

After selecting a channel or channel pair, the SS synchronizes to the DL transmission from the BS by detecting the periodic frame preambles. Once the PHY is synchronized, the SS will look for the periodically broadcasted DCD and UCD messages that enable the SS to determine the modulation and FEC schemes used on the BS’s carrier.

9.3 Initial Ranging and Negotiation of SS Capabilities Once the parameters for initial ranging transmissions are established, the SS will scan the UL-

MAP messages present in every frame for ranging information. The SS uses a backoff algorithm to determine which initial ranging slot it will use to send a ranging request (RNG-REQ) message. The SS will then send its burst using the minimum power setting and will repeat with increasingly higher transmission power until it receives a ranging response. Based on the arrival time of the initial RNG-REQ and the measured power of the signal, the BS adjusts the timing advance and power to the SS with the ranging response (RNG-RSP). The response provides the SS with the basic and primary management CIDs. Once the timing advance of the SS transmissions has been correctly determined, the ranging procedure for fine-tuning the power is done via a series of invited transmissions. WiMAX transmissions are made using the most robust burst profile.

To save bandwidth, the SS next reports its PHY capabilities, including which modulation and coding schemes it supports and whether, in an FDD system, it is half-duplex or full duplex. The BS, in its response, can deny the use of any capability reported by the SS. It should be noted here how complex this setup procedure is. The purpose thus far is to ensure a high quality connection between the SS and the BS.

Figure9.1 Channel Acquisition, Ranging, and Negotiation of Subscriber Station Capabilities

Authentication and Registration

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9.4 Authentication and Registration Wi-Fi has been dogged with a reputation for lax security. Perhaps the best “horror story” deals

with a computer retailer who installed a wireless LAN. A customer purchased a Wi-Fi equipped laptop and, anxious to enjoy it, powered it up in the parking lot of the retailer.

The new laptop owner was immediately able to tap into the retailer’s Wi-Fi network and was able to capture some customer credit card information. Fortunately, the new laptop owner was a journalist, not a con artist. The story, much to the chagrin of the national retailer and the Wi-Fi industry, made the national news. The Wi-Fi industry has had to work hard to shake the reputation of having loose security measures. A similar story will not easily, if ever, occur with WiMAX.

Each SS contains both a manufacturer-issued factory-installed X.509 digital certificate and the certificate of the manufacturer. The SS in the Authorization Request and Authentication Information messages sends these certificates, which set up the link between the 48-bit MAC address of the SS and its public RSA key, to the BS. The network is able to verify the identity of the SS by checking the certificates and can subsequently check the level of authorization of the SS. If the SS is authorized to join the network, the BS will respond to its request with an authorization reply containing an authorization key (AK) encrypted with the SS’s public key and used to secure further transactions.

Upon successful authorization, the SS will register with the network. This will establish the secondary management connection of the SS and determine capabilities related to connection setup and MAC operation. The version of IP used on the secondary management connection is also determined during registration.

9.5 IP Connectivity After registration, the SS attains an IP address via DHCP and establishes the time of day via the

Internet Time Protocol. The DHCP server also provides the address of the TFTP server from which the SS can request a configuration file. This file provides a standard interface for providing vendor-specific configuration information.

Figure9.2 Subscriber Station Authentication, Registration and IP connectivity

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9.6 Idle mode management. While an MS does not have any connection for a period, an MS might want to turn off its

WiMAX interface to save power and switches to idle mode. Similar to other mobile communication systems, Mobile WiMAX also defines its own idle-mode operations and a paging network architecture. Four logical entities for idle-mode and paging operations are defined in a Mobile WiMAX network. First, a paging controller (PC) is associated with a paging group (PG) which comprises one or several paging agents (PAs) in the same NAP. The major task of a PC is to administer the activities of all idle-mode MSs situated in the PG managed by the PC. A PC can function as an anchor PC, which is in charge of the paging and idle-mode management, or a relay PC, which only forwards paging-related messages between PAs and an anchor PC. A PC could either collocate with a PA (i.e., a PC is implemented on a BS) or a PC can be implemented on a network node such as an ASN-GW and uses the R6 interface to communicate with its PAs. PAs which are normally implemented on BSs interact with the PC to perform paging functions. Finally, a PC can access a distributed database, called a location register (LR), which contains information such as paging parameters for idle-mode MSs. When an MS decides to switch to the idle mode, it first sends a deregistration message (DREG-REQ) to the ASN-GW. The serving BS/PA and ASN-GW/PC release resources such as the data path occupied by the MS and update the information of the MS to the LR. Meanwhile, the PA and PC negotiate, configure, and inform the paging parameters, such as paging cycle, paging offset, paging interval length, anchor PC identifier, and paging group identifier for the MS. Based on the paging cycle (PAGING CYCLE), paging offset (PAGING OFFSET), and paging interval length, the MS derives the BS paging listening interval. A BS paging listening interval begins from the PAGING OFFSET frame in every paging cycle and each paging listening interval lasts for the paging interval length. The MS has to stay awake during the entire BS paging listening interval in order to receive BS broadcasting paging messages (MOV PAG-ADV). An MS performs a location update (LU) based on four LU evaluation conditions (i.e., paging group update, timer update, power-down update, and MAC hash skip threshold update). The paging group update is activated when an MS detects a change in the paging group. The timer update is a periodic LU, and an MS performs an LU when the idle-mode timer expires. When an MS turns off or the MS MAC hash skip counter exceeds the MAC hash skip threshold, the MS also has to perform LUs. After a BS receives LU messages, the BS/PA updates the MS information to the PC/LR. While receiving an incoming packet sent to an idle MS, the ASN-GW/FA first obtains information of the MS from the LR and informs the PC to page the MS. Then the PC generates a paging announcement message and sends it to the relay PC or PA. Based on the paging parameters of the MS, PAs/BSs send BS broadcasting paging messages (MOV PAG-ADV) to the MS. Once an MS is paged, the MS exits idle mode, performs ranging with the serving BS, and completes network (re)entry procedures.

9.7 Call procedure. The IEEE 802.16 standard simply addresses the air interface specification between BS and SS,

the WiMAX Forum defines an end-to-end WiMAX network architecture, based on an all-IP platform.

Call procedure.

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9.7.1 VoIP

The emergence of VoIP raises a wide range of possibilities. By virtue of transporting voice over a data stream, VoIP frees the voice stream from the confines of a voice-specific network and its associated platforms. VoIP can be received and transmitted via PCs, laptops, IP, and Wi-Fi handsets. Where there is IP, there can be VoIP.

Here we explain how VoIP call is done .thus we need to identify what is called the SIP.

9.7.2 Session Initiation Protocol (SIP)

is a signaling protocol, widely used for setting up and tearing down multimedia communication sessions such as voice and video calls over Internet Protocol (IP). Other feasible application examples include video conferencing, streaming multimedia distribution, instant messaging, presence information and online games. The protocol can be used for creating, modifying and terminating two-party (unicast) or multiparty (multicast) sessions consisting of one or several media streams. The modification can involve changing addresses or ports, inviting more participants, adding or deleting media streams, etc.

9.7.3 SIP network elements

A SIP user agent (UA) is a logical network end-point used to create or receive SIP messages and thereby manage a SIP session. A SIP UA can perform the role of a User Agent Client (UAC), which sends SIP requests, and the User Agent Server (UAS), which receives the requests and returns a SIP response. These roles of UAC and UAS only last for the duration of a SIP transaction.

A SIP phone is a hardware-based or software-based SIP user agent, that provides call functions such as dial, answer, reject, hold/unhold, and call transfer. Examples

include softphones like Ekiga, KPhone, Twinkle, Windows Live Messenger, X-Lite, and hardware phones from vendors like Avaya, Cisco, Leadtek, Polycom, Snom, and Nokia.

Each resource of a SIP network, such as a User Agent or a voicemail box, is identified by a Uniform Resource Identifier (URI), based on the general standard syntax also used in Web services and e-mail. A typical SIP URI is of the form: sip:username:password@host:port. The URI scheme used for SIP is sip:. If secure transmission is required, the scheme sips: is used and SIP messages must be transported over Transport Layer Security (TLS).

In SIP, as in HTTP, the User Agent may identify itself using a message header field 'User-Agent', containing a text description of the software/hardware/product involved. The User-Agent field is sent in request messages, which means that the receiving SIP server can see this information. SIP network elements sometimes store this information[8], and it can be useful in diagnosing SIP compatibility problems.

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SIP also defines server network elements. Although two SIP endpoints can communicate without any intervening SIP infrastructure, which is why the protocol is described as peer-to-peer, this approach is often impractical for a public service.

RFC 3261 defines these server elements:

A proxy server "is an intermediary entity that acts as both a server and a client for the purpose of making requests on behalf of other clients. A proxy server primarily plays the role of routing, which means its job is to ensure that a request is sent to another entity "closer" to the targeted user. Proxies are also useful for enforcing policy (for example, making sure a user is allowed to make a call). A proxy interprets, and, if necessary, rewrites specific parts of a request message before forwarding it."

"A registrar is a server that accepts REGISTER requests and places the information it receives in those requests into the location service for the domain it handles."

"A redirect server is a user agent server that generates 3xx responses to requests it receives, directing the client to contact an alternate set of URIs. The redirect server allows SIP Proxy Servers to direct SIP session invitations to external domains."

The RFC specifies: "It is an important concept that the distinction between types of SIP servers is logical, not physical."

Other SIP related network elements are:

Session border controllers (SBC), they serve as "man in the middle" between UA and SIP server, see the article SBC for a detailed description.

Various types of gateways at the edge between a SIP network and other networks (as a phone network)

Figure9.3 SIP Establishment of a peer to peer Call

Call procedure.

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SIP Messages SIP is a text-based protocol with syntax similar to that of HTTP. There are two different types of

SIP messages: requests and responses. The first line of a request has a method, defining the nature of the request, and a Request-URI, indicating where the request should be sent. The first line of a response has a response code.

For SIP requests, RFC 3261 defines the following methods:

REGISTER: Used by a UA to notify its current IP address and the URLs for which it would like to receive calls.

INVITE: Used to establish a media session between user agents.

ACK: Confirms reliable message exchanges.

CANCEL: Terminates a pending request.

BYE: Terminates a session between two users in a conference.

OPTIONS: Requests information about the capabilities of a caller, without setting up a call.

The SIP response types defined in RFC 3261 fall in one of the following categories:

Provisional (1xx): Request received and being processed.

Success (2xx): The action was successfully received, understood, and accepted.

Redirection (3xx): Further action needs to be taken (typically by sender) to complete the request.

Client Error (4xx): The request contains bad syntax or cannot be fulfilled at the server.

Server Error (5xx): The server failed to fulfil an apparently valid request.

Global Failure (6xx): The request cannot be fulfilled at any server.

9.7.4 SIP in WiMAX

A specific Connectivity Service Controller (CSC) is located in each NRM entity (MS, ASN and CSN) in order to coordinate and to process the QoS signaling, and to perform the resource reservation in the related segment.

SIP Proxy handles SIP signaling, intercepts Session Description Protocol (SDP) messages and interacts with the CSC_ASN to request resource reservation for SIP applications.

AAA (Authentication, Authorization, and Accounting) Server provides functionalities for user authentication and QoS authorization, interacting with the SIP Proxy and the CSC_ASN.

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SIP signaling is initiated by a standard SIP User Agent (UA) on the MS and is intercepted and processed by the Application Function (AF) of the SIP Proxy located in the CSN.

9.8 Radio Link Control (RLC) RLC runs simultaneously to channel acquisition and service flow to maintain a steady link. The

WiMAX PHY requires equally advanced RLC, particularly the capability of the PHY to transition from one burst profile to another. The RLC controls this capability as well as the traditional RLC functions of power control and ranging.

RLC begins with periodic BS broadcast of the burst profiles that have been chosen for the UP and DL. The particular burst profiles used on a channel are chosen based on a number of factors, such as rain region and equipment capabilities. Burst profiles for the DL are each tagged with a Downlink Interval Usage Code (DIUC). Those for the UL are each tagged with an UIUC.

During initial access, the SS performs initial power leveling and ranging using RNG-REQ messages transmitted in initial maintenance windows. Adjustments to the SS’s transmit time advance and power adjustments are returned to the SS in RNG-RSP messages.

For ongoing ranging and power adjustments, the BS may transmit unsolicited RNG-RSP messages commanding the SS to adjust its power or timing.

During initial ranging, the SS also requests to be served in the DL via a particular burst profile by transmitting its choice of DIUC to the BS. The SS performs the choice before and during initial ranging based on received DL signal quality measurements. The BS may confirm or reject the choice in the RNG-RSP. Similarly, the BS monitors the quality of the UL signal it receives from the SS. The BS commands the SS to use a particular UL burst profile simply by including the appropriate burst profile UIUC with the SS’s grants in UL-MAP messages.

After initially determining UP and DL burst profiles between the BS and a particular SS, RLC continues to monitor and control the burst profiles. Harsher environmental conditions, such as rain fades, can force the SS to request a more robust burst profile. Alternatively, exceptionally good weather may allow an SS to temporarily operate with a more efficient burst profile. The RLC continues to adapt the SS’s current UL and DL burst profiles, always striving to achieve a balance between robustness and efficiency.

As the BS controls and directly monitors the UL signal quality, the protocol for changing the UL burst profile for an SS is simple: the BS specifies the profile’s UIUC whenever granting the SS bandwidth in a frame. This eliminates the need for an acknowledgment, as the SS will always receive both the UIUC and the grant or neither. This negates the possibility of UL burst profile mismatch between the BS and SS.

In the DL, the SS monitors the quality of the receive signal and knows when to change its DL burst profile. The BS still has ultimate control of the change. The SS has two available methods to

Radio Link Control (RLC)

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request a change in DL burst profile, depending on whether the SS operates in the grant per connection (GPC) or grant per SS (GPSS) mode .The first method would apply (based on the discretion of the BS scheduling algorithm) only to GPC SSs. In this case, the BS may periodically allocate a station maintenance interval to the SS. The SS can use the RNG-REQ message to request a change in DL burst profile. The preferred method is for the SS to transmit a DL burst profile change request (DBPC-REQ). In this case, which is always an option for GPSS SSs and can be an option for GPC SSs, the BS responds with a DBPC-RSP message confirming or denying the change. Because messages may be lost due to irrecoverable bit errors, the protocols for changing an SS’s DL burst profile must be carefully structured. The order of the burst profile change actions is different when transitioning to a more robust burst profile than when transitioning to a less robust one. The standard takes advantage of the fact that an SS is always required to listen to more robust portions of the DL as well as the profile that was negotiated.

Figure9.4 Radio Link Control

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9.9 Hand over The handover in WiMAX can be a hard handover, a hard handover with fast base station

switching (FBSS) support, or a microdiversity handover (MDHO).

9.9.1 Hard Handover

During hard handover the MS communicates with only just one BS in each time. Connection with the old BS is broken before the new connection is established. Handover is executed after the signal strength from neighbor’s cell is exceeding the signal strength from the current cell. This situation is shown in the figure. Red thick line at the boarder of the cells presents the place where the hard handover is realized.

Figure9.5 Hard Handover realization

Hand over

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9.9.2 Macro Diversity Handover

When MDHO is supported by MS and by BS, the “Diversity Set” is maintained by MS and BS. Diversity set is a list of the BS’s, which are involved in the handover procedure. Diversity set is defined for each of MS’s in network. MS communicates with all BS’s in the diversity set (see the figure). For downlink in MDHO, two or more BS’s transmit data to MS such that diversity combining can be performed at the MS. For uplink in MDHO, MS transmission is received by multiple BS’s where selection diversity of the received information is performed. The BS, which can receive communication among MS’s and other BS’s, but the level of signal strength is not sufficient is noted as “Neighbor BS”.

Figure9.6 Macro Diversity Handover

9.9.3 Fast Base Station Switching

In FBSS, the MS and BS diversity set is maintained similar as in MDHO. MS continuously monitors the base stations in the diversity set and defines an “Anchor BS”. Anchor BS is only one base station of

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the diversity set that MS communicates with for all uplink and downlink traffic including management messages (see the figure). This is the BS where MS is registered, synchronized, performs ranging and there is monitored downlink channel for control information. The anchor BS can be changed from frame to frame depending on BS selection scheme. This means every frame can be sent via different BS in diversity set.

Figure9.7 Fast Base Station Switching

Handover in a Mobile WiMAX network can be further classified into ASN-anchored and CSN-anchored handover.

ASN-anchored handover, also called micromobility, implies that an MS moves from one BS and another BS without a need to update its care-of address (CoA).

CSN-anchored handover, on the other hand, defines macro mobility, which involves MSs to change its serving ASN-GW/FA and their CoAs. CSN-anchored handover facilitates network-layer mobility in both IPv4 and IPv6 networks.

9.10 Simulation Here we simulate the previous concepts by animation

First we have a welcome page where we can choose the simulation type

Simulation

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Figure 9.8 Welcome page

An example for simulation:

If we choose the “HO” simulation the following window will appear:

Figure 9.9 First view of HO simulation

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Using the controls to go to the next and the previous step .also to back to the welcome page, go to the next procedure and control the time line(play, pause and stop)

Figure 9.10 the first step in HO procedure

Figure 9.11 the last step in HO procedure:

Also we can choose “one scenario” from the welcome page to play all procedures for a MS in the order each one.

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10.1 Introductions In this project we studies the "mobile WiMAX" that is based on IEEE 802.16e and target mobile and nomadic subscribers in wireless metropolitan area (WMAN) and studied the effect of the main parameters on its performance and coverage.

10.2 Conclusions The fixed version of the WiMAX standard, 802.16-2004, addresses a particular market need, that

being the availability of a low-cost, standards-based solution that can provide basic voice and broadband access in regions of the world where the economics of a fixed wire line service do not make sense. Additionally, the fixed standard can help drive the proliferation of Wi-Fi access points while at the same time reducing operating [backhaul] costs and improving the user experience through higher data rates.

While these market opportunities are readily available and worth pursuing, much of the industry focus is on the portable/mobile standard, 802.16e, and its potential to offer mobile broadband wireless service. At this juncture, there is still a large amount of work remaining to be done before the .16e standard is commercially ready and before operators can seriously consider utilizing the technology. To the extent that WiBro can be considered within the WiMAX family [it arguably is], South Korea could have the first network available in early 2006, although the availability of end-user devices is a major uncertainty. In that regard, it is important to recognize that even after the portable/mobile standard is ratified, there remains much work to be done as chipsets, followed by base stations and CPEs, still need to be developed, the network architecture still needs to be defined, security issues need to be addressed, and the technology still needs to be proven in a field trial. After successful field trials by the equipment providers, the technology will then be ready for extensive operator trials which could then lead to broader-scale commercial deployments. It goes without saying that operator trials don't always lead to commercial rollouts.

The jump to full mobility is still a bit tenuous, even after the .16e standard is ratified. In all probability it will take far longer than currently predicted for the technology to be commercially and economically feasible - the timing depends to a large degree on the final complexity of the network architecture. In the absence of compelling content and services, consumers who already utilize 3G and Wi-Fi services will be hard pressed to abandon their cellular service provider and adopt WiMAX. Those

Chapter 10 Conclusions and suggestions

for future work

Chapter 10 Overview of WiMAX technology

10 - 2

that do adopt WiMAX as a broadband data pipe will likely continue using their cellular service provider, which at best indicates that WiMAX complements 3G while trying to compete with already inexpensive Wi-Fi services. To some extent, WiMAX wi also have to compete with the 3G/Wi-Fi combination in order to find room in next-generation notebook computers. Those non-traditional operators that currently lack a mobile offering are the most likely candidates to use the portable/mobile capabilities of WiMAX. However, they will still be challenged by the requisite need for WiMAX-enabled user equipment and in some instances by their lack of suitable spectrum. Further, these operators will be challenged by the technical hurdles that are inherent in deploying any new wireless technology and by the economic challenges associated with offering a service that must attract interest from consumers that are already familiar with the 3G/Wi-Fi combo of services. Ultimately, the technical challenges can be addressed and the market opportunity for a portable/mobile WiMAX service can then begin to develop. WiMAX success in the market, given its high dependence upon the need for successful operator-driven business models, is a bit more suspect and could in the end prove to be the single biggest detriment.

In this project we studied the coverage prediction and performance evaluation of WiMAX.

The following parameters were discussed:

1. The effect of different channel bandwidth.

2. The effect of licensed and license-exempted operating frequency bands.

3. The impact of the type of adaptive modulation and coding schemes.

4. The effect of BTS antenna height.

5. The effect of using sub-channelization.

6. The effect of different terrains

We conclude that:

As the channel bandwidth increases the coverage radius decreases since the channel bandwidth increases, the effective channel bandwidth increases, the receiver sensitivity increases i.e. it degrades.

Without sub-channelization, the links are unbalanced. The reverse link coverage radius is always smaller than the forward link coverage radius. With sub-channelization, the reverse link coverage radius is increased thus mitigates link unbalance but at the expense of reduction of the data rate that can be achieved.

In license-exempt frequency band, coverage radius is degraded due to higher frequency (5.8 GHz) and larger channel bandwidth while license frequency band (3.5 GHz) provides better coverage radius due to narrower channel bandwidth.

Suggestions for future work

10 - 3

As the BTS antenna height increases the coverage radius increases in all scenarios. The highest data rate is achieved for 64-QAM and coding schemes but provides the worst coverage radius. The lowest data rate is achieved for BPSK and coding schemes but provides wider coverage radius.

The coverage cell radius in Erceg A model is the largest while is lower in Erceg B. The lowest coverage cell radius is Erceg C due to terrain as obstacles.

10.3 Suggestions for future work 10.3.1 WiMAX future

IEEE 802.16d(fixed WiMAX) and IEEE 802.16e(mobile WiMAX) available in USA, UK, Spain, France, Germany, South Korea and many countries. But the expectable to implement in the next years is IEEE 802.16m which will achieve the IMT-Advanced 2000.

10.3.1.1 IMT-2000 & IMT-Advanced

IMT-Advanced, also known as “systems beyond IMT-2000” is expected to offer constant higher data rates with high mobility to assure likely growing need for mobile WiMAX services that goes beyond what IMT-2000 can afford to provide. IMT- Advanced is awaiting technology that will require 3 to 5 years in the future with target maximum data rates, for research and examination, of up to 100 Mbits/sec in high mobility applications and up to 1 Gbit/sec in low mobility or nomadic applications. The capacity expected by IMT-Advanced is often referred to as 4G. It is commonly acknowledged that Orthogonal Frequency Division Multiple Access (OFDMA) technology will be integrated in IMT-Advanced in near future to get more the maximum benefits from the WiMAX.

IMT-Advanced is a continuing effort. The full criteria, being extended within ITU-R Working Party 8F, are not expected until 2008. The specification of IMT-Advanced technologies will probably not be completed until at least 2010. In preparation for IMT-Advanced, the IEEE 802.16 Working Group has moved to initiate a new project designated as “802.16m” with the intent of developing enhancements to IEEE STD 802.16 to ensure suitability as an IMT-Advanced proposal.

Figure 10.1 IMT-2000 & IMT-Advanced

Chapter 10 Overview of WiMAX technology

10 - 4

10.3.1.2 IEEE 802.16m goals

Increase system capacity

Coverage improvement (at cell edge)

Reduce MAC overhead

Mobile client power efficiency

Enhance mobility

Improve Quality of Service

Meet IMT-Advance Standard requirements (not yet defined)

It will also be 4G compatible with the future wireless networks offering much higher speeds.

10.3.1.3 802.16m specifications.

Amendment for advanced air interface.

Looking to the future.

It is anticipated that it will provide:

Data rates of 100 Mbps for mobile applications and 1 Gbps for fixed applications.

Cellular, macro and micro cell coverage.

16m and 16e shall be able to operate on the same RF carrier, with the same/different channel bandwidth

Operating frequencies: less than 6 GHz

Operating bandwidths: 5 to 20 MHz and more.

Duplex schemes: TDD and FDD, HFDD

Modulation (OFDMA - downlink and uplink), support smart antennas

10.3.1.4 IEEE 802.16m & LTE

LTE stands for long term evolution.

Suggestions for future work

10 - 5

LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) which will be introduced in 3rd Generation Partnership Project (3GPP) Release 8 in March 2009.

Much of 3GPP Release 8 will focus on adopting 4G mobile communications technology.

Both LTE and IEEE 802.16m are all IP networks based on OFDM technology.

Both support FDD and TDD.

Both support higher order MIMO antenna solutions.

In contrast to the forthcoming first generation LTE

there have already been two releases of WiMAX profiles:

the IEEE 802.16d fixed WiMAX standard released in 2004

the IEEE 802.16e mobile WiMAX standard released in 2005

Both of those standards have been implemented and there are compliant networks and devices/ products available.

As for speeds, LTE will be faster than the current generation of WiMax, but 802.16m that should be ratified in 2009 is fairly similar in speeds.

New spectrum required for either LTE or WiMAX to support wider channel BW Multi-Band/Multi-Mode subscriber devices required in either case for internetwork connectivity and global roaming

Figure 10.2 3GPP & Mobile WiMAX Timeline

Chapter 10 Overview of WiMAX technology

10 - 6

10.3.2 Mobility management suggestions

Ability to make the user to put the MS in any part and the program can detect the appropriate action and execute it.

10.3.3 Hardware suggestions

Improving sensitivity of circuit by replacing some components by other has a low tolerance and adding some circuits to decrease noise.

Design a selectivity system to select a certain band of frequency by adding band pass filter.

Changing display by LCD to add some features and information.

References [1] 3GPP TSG-RAN-1. Effective SIR computation for OFDM system-level simulations. Document R1- 03-1370, November 2003.

[2] 3GPP TSG-RAN1. System level simulation of OFDM—further considerations. Document R1-03- 1303, November 2003.

[3] V. Erceg, et.al. An empirically based pathloss model for wireless channels in suburban environments IEEE Journal on Selected Areas of Communications, 17(7), July 1999.

[4] European Cooperation in the Field of Scientific and Technical Research EURO-COST 231. Urban transmission loss models for mobile radio in the 900 and 1800MHz bands, rev. 2. The Hague, 1991.

[5] L. J. Greenstein and V. Erceg. Gain reductions due to scatter on wireless paths with directional antennas. IEEE Communications Letters, 3(6), June 1999.

[6] M. Hata. Empirical formula for propagation loss in land mobile radio services. IEEE Transactions on Vehicular Technology, 29(3):317–325, August 1980.

[7] IEEE. Standard 802.16.3c-01/29r4. Channel models for fixed wireless applications. tap:// www.ieee802.org/16.

[8] IEEE. Standard 802.16e-2005, Part 16: Air interface for fixed and mobile broadband wireless access systems.

[9] Y. Lin and V. W. Mark. Eliminating the boundary effect of a large-scale personal communication service network simulation. ACM Transactions on Modeling and Computer Simulations, 4(2), April 1994.

[10] Y. Okumura, Field strength and its variability in UHF and VHF land-mobile radio service. Review Electrical Communication Laboratory, 16(9–10):825–873, September–October 1968.

[11] A. Paulraj, R. Nabar, and D. Gore. Introduction to Space-Time Wireless Communications, Cambridge University Press, 2003.

[12] J. W. Porter and J. A. Thewatt. Microwave propagation characteristics in the MMDS frequency band. Proceedings of the ICC 2000 Conference, June 2000.

[13] T. S. Rappaport. Wireless Communications: Principles and Practice, 2nd ed. Prentice Hall, 2002.

[14] W. H. Tranter, K. S. Shanmugam, T. S. Rappaport, and K. L. Kosbar. Principles of Communication System Simulation with Wireless Applications. Prentice Hall, 2002.

[15] WiMAX Forum. Mobile WiMAX—Part 1: A technical overview and performance evaluation. June 2006.

[16] WiMAX Forum Technical Working Group. WiMAX Forum mobile system profile, February 2006.

[17] Y. R. Zheng and C. Xiao. Improved models for the generation of multiple uncorrelated Rayleigh fading waveforms, IEEE Communications Letters, 6(6), June 2002.

[18] Fundamentals of WiMAX understanding broadband wireless networking.

[19] Mobile WiMAX Toward Broadband Wireless Metropolitan Area Networks.

[20] WiMAX handbook mcgraw hill communications.

:ذا المشروع على النحو التالي وينظم ه

والجوانب النظام، وبنية النظام ، و مواصفات شكل الشبكات المختلفة أساس معايير تقنية واي ماآس ، و الفصل األوليصف اي ماآس الو الرئيسية بين الفروق ثالثالفصل الويبين . OFDM سياتأسا الفصل الثانيويعرض .الرئيسية لهذه التكنولوجيا

الفصل ويناقش . آيفية تغطية الواي ماآس المتنقل يشرح الفصل الرابع. ذات النطاق العريض وغيرها من التكنولوجيات المتنقلمختلفة مما معايير الفصل السادسويناقش . العدديةالنواتج و تنقلتغطية الواي ماآس الممختلفة مما يؤثر في معايير مساخال

واي ماآس الحل موحد للتخطيط لشبكة الفصل السابعويعرض . العدديةالنواتج و على األداء في واي ماآس المتنقل يؤثريناقش المهام الممكنه سعاتالالفصل ويناقش . حساب قوة االشارة السلكياعرض جهاز ل مناثالالفصل ويتضمن . المحمول .مستقبللل اتاستنتاجات واقتراح شراعالالفصل ويتضمن .تنقلالم واي ماآسالثابت إلى ال واي ماآسلتحويل ال

الملخص ميلالمشكلة لحل ابرزت واي ماآس . متزايد بسبب تطبيقاتها ومزاياهاهتمام واي ماآس في اآلونة األخيرة اآتسبت االتقنية

بينى على نطاق واسع عالميًا للنفاذ بالموجات الدقيقة و هى تعنى التشغيل ال واي ماآسوال. االخير وتكنولوجيا النطاق العريضواجهة لخدمات النفاذ إلى الخطوط الالسلكية ذات النطاق العريض فهى . IEEE 802.16 القياسية تعتمد على المواصفات

)FBWA (العاصمة شبكات في منطقة)MAN ( والحزمة العريضة الالسلكية النقالة الوصول)MBWA ( لتكون جزءا ال . يتجزأ من األجهزة المحمولة مثل أجهزة الكمبيوتر المحمول

لواي ماآس ، وجرى النظر في مختلف اص ائتؤخذ في االعتبار خص , بما في حساب الميزانية لتغطيةا لتنبؤ ةالرئيسيالعناصر النظر في الشروط والقواعد التنظيمية الستخدام طيف و تشغيل سيناريوهات محددة تقوم على العالم الواقعي وتم.االفتراضات

مثلعدة نماذج التنبؤ و استخدام .خلية ال قطر النموذج المناسب لحسابواستخدام ص يرختالى من عفالم المرخص والترددات المؤقت جامعة ستانفورد نموذجو COST231 Walfischنموذج Hata COST231 Okumura الفضاء الحر ، نموذج

)SUI ( خط البصر فى حالة الفضاء الحر نموذجولكن سنرآز على)LOS (المؤقت جامعة ستانفورد ونموذج )SUI (فى حالة وأخيرا ، يتم تقييم أداء النظام من حيث الحد األقصى لمعدل . غيغاهرتز ٦ يصل إلىتردد و )(NLOSخط البصر ال وجود ل

. نقل البيانات

:تأثير المعالم الرئيسية للنظام على نطاق التغطية و االداء مثل

المستخدم معدةتأثير نوع

قاعديةمحطة الالتأثير نوع

ناة االتصالتأثير عرض ق

تأثير حيز التردد المستخدم سواء التي تحتاج الى ترخيص او المعافاه من الترخيص

تأثير نوع التعديل المتوافق ومعدل التكوين المستخدمين

تأثير ارتفاع المحطة القاعدية

تأثير قدرة االرسال و استخدام اسلوب قنوات االتصال الفرعية في نظام الواي ماآس

ع معدة المستخدمتأثير ارتفا

مقارنة بين النماذج المختلفة

:األتية الخصائص تأثير دراسة طريق عن ماآس الواى نظام أداء تقييم تم ثم المستخدمين التكويد معدل وآذا التعديل نوع تأثير.

تأثير ال .Cyclic Prefix

التردد حيز و الرمزى اإلتصال نطاق عرض تأثير.

اإلتصال قنوات عدة إلى اإلتصال قناة تقسيم تأثير.