BENT 3163 Chapter 6 Wireless Communication

UNIVERSITI TEKNIKAL MALAYSIA MELAKAKompetensi Teras Kegemilangan

BENT 3163TELECOMMUNICATION SYSTEM ENGINEERING

CHAPTER 6WIRELESS COMMUNICATION

FAUZI HJ ABDUL WAHAB2_2011/2012


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OBJECTIVE

Students able to:

analyse wireless communication system.


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Chapter Outline

1. Introduction

2. Cellular Mobile Telephone systems

o Network

o Personal Communications Systems

3. Analogue vs Digital Access

4. 3G Network & Access


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Introduction

• Growing at exponential rate.

o Demand for “information at your fingertip”.

• Communications, monitoring or control system

o Electromagnetic waves carry signals through atmospheric space (rather than

along wires).

• Characteristics of radio (or EM wave) propagations over geographical area

influence design and performance.

• Earth’s atmospheric (troposphere & ionosphere) affect.


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Introduction

• Troposphere effects, (15 km range) include atmospheric precipitation:

o fog, raindrops, snow & hail

• Wireless system use RF or IR

• IR more appealing due to no licensing requirement

o FCC, ITU, etc.

• Competing standards for communication protocols, interfaces and networks.


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Cellular Mobile Telephone System

• Early development, mainly applied to military and public safety services until end

of WW II.

• Mobile Telephone System first introduced to public in 1946.

• Started with simplex system and manual operations.

• Full duplex automatic switching system (IMTS – Improved Mobile Telephone

System in 1964) using 450 MHz band.

• Rapid and high demand causes AMPS (Advanced Mobile Phone Service) being

introduced in 1983.


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• First digital cellular services made available

• More efficient utilisation of bandwidth (voice compression)

o FM modulation, FDMA, TDMA, CDMA

• General concept evolution:

o Global System for Mobile communication(GSM)

o Personal Communication System (or GSM II)

o Satellite based, Personal Communication Satellite System (PCSS)


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• To build GSM system, certain specification must be followed.

o Several network operators in each country (why?)

o Open system (well – defined interfaces)

o GSM network built must not cause major changes to PSTN.

• Other demands

o Pan European System

o Good speech quality

o Use radio frequencies efficiently

o High/adequate capacity.

o Compatible with ISDN & other data comm. Specifications

o Good security.


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• Advantages (summarised):

o GSM uses RF efficiently, due to digital radio path, intercell disturbance

tolerance.

o Average speech quality achieved better than analogue cellular systems.

o Data transmission supported.

o Speech is encrypted and subscriber information guaranteed security.

o New services (or more) than analogue system.

o International roaming possible.

o Market increases (investment and usage)


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GSM World Evolution

Phase Year Event

I

1982 CEPT initiated new cellular system. Reserve 900 MHz band GSM allowing roaming.

1985 CEPT made decision on time schedule and action plan.

1986 CEPT tested 8 experimental systems in Paris.

1987 MoU of frequency allocations (890 – 915 uplink), (935 – 960 downlink)

1988 ETSI formed

1989 Final recommendations and specifications for GSM Phase I


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GSM World Evolution

Phase Year Event

II

1990Validation systems implemented (1st GSM world congress in Rome – 650 participants)

1991 First official world’s GSM call (1st July).

1992World’s First GSM Network launched (Finland). 13 network operating in 7 areas. New frequency allocations for GSM 1800 (DCS 1800), (1710 – 1785 – uplink), (1805 – 1880 downlink)

III

1993 First roaming (include 32 GSM networks operating in 18 areas)

1994GSM II launched (data/fax bearer) include 69 GSM networks. MoU change to Association with 156 members from 86 areas. GSM World Congress held in Madrid with 1400 participants.

1995 117 GSM network operating around the world. Fax, data, SMS roaming implemented.


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Cellular Networks

• Any mobile communication network with series of overlapping hexagonal cells in

a honeycomb pattern.

• Cellular technology

o short–wave analogue or digital transmission where users have wireless

connection from MS to relative nearby base station.

• Mobile station

o transmitter, receiver, controller and antenna system and wireless link to MSC.

• Base station coverage span called cell


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Honeycomb Cell Pattern


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• Cells can be

o Small (individual building)

o Large (20 miles across)

o Or any size in between

• As cellular device, or MS moves from one cell coverage to another,

o MSC sense weakening signals and automatically hands–off (or handover) calls

to next BSC or.

o BSC hands–off calls to next cells.

• Cellular systems allocate a set number of frequencies for each cell.


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• 2 cells can use same frequency as long as cell are not adjacent to each other.

• New development is to have several sizes in the honeycomb cell patterns.

• Macrocell, microcell, picocell.

o Small cells works best with omni–directional antennas.

• How to optimise frequencies allocations: frequency reuse.

• 2 cells can use the same frequency for different conversations as long as the cells

are not adjacent to each other.

• Every 7th cell use the same set of channels or frequencies.


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o Mathematically, total number of cellular channels available in a cluster:

(6.1)F - number of cellular channelsG - number of channels in a cellN - number of cells in a cluster

o When clusters are duplicated m times within given service area, total number

of channels

(6.2)C - total channel capacitym - number of clustersG - number of channels in a cellN - number of cells in a cluster.

GNF

mGNC


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• This is useful for determining total number of channels can be used and reused.

• To determine the channel allocations, frequency planning should be done.

• Cellular concept:

o System with many low power transmitter. (Why low power?)

• Each base station assigned to different groups of channels

o Interference between base stations minimised

• (co–channel & adjacent–channel interference)


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• So what is frequency reuse?

o Planned frequencies so that high capacity achieved with interference under

specific level.

• Subscribers may use same sets of channels in non–adjacent cells.

o Same frequency?

• Frequency reuse factor (number of users) can be expressed as

(6.3)

N - number of channels in an area (full duplex)

C - number of channel in a cell (full duplex)

C

NFRC


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Channel Assignment

• GSM 900

880 890 915 935 960 925

E-GSM900 UPLINK

GSM900 UPLINK

GSM900 DOWNLINK

E-GSM900 DOWNLINK

45 MHz

45 MHz


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Channel Assignment

• GSM 1800

1710 1785

DCS1800

UPLINK

1805 1880

DCS1800 DOWNLINK

Guard Band

95 MHz


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Absolute Radio Frequency Channel Number

• Guard band

o 20 MHz for GSM I and GSM II

o 10 MHz for E–GSM

• Channel separation (Uplink–Downlink)

o 45 MHz for GSM I and E–GSM

o 95 MHz for GSM II

• Each channel (or carrier) bandwidth

o 200 kHz


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• Proper channel allocations is very crucial as frequency spectrum very limited.

• Mathematically, to determine corresponding frequency (GSM 900):

(6.4)

(6.5)

(1 ≤ N ≤ 124)

ft - transmit frequency (downlink) MHz

fr - receive frequency (uplink) MHz

N - channel number

Nft )2.0(890

45 tr ff


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• For GSM II (GSM 1800)

(6.6)

(6.7)

(512 ≤ N ≤ 885)

• GSM I (900) - 124 channels

• GSM II (1800) - 374 channels

)512)(2.0(1710 Nft

95 tr ff


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• Automatic Frequency Planning

o Feature offered to assist rapidly channel assignment work and reliable channel

assignment.

o Complex algorithm solving based on interference, field strength and density.

o Solving cell boundaries disputes.

o Useful for big and complex network.

• Frequency Hopping

o Successive TDMA burst of connection transmitted via different frequencies

(belonging to respective cell).

o Link quality may change


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Personal Communication System

o New bread of cellular

o Intelligent network + cellular

o FCC defines as

“family of mobile communication services for individuals and business integrating

variety of competing network”

o Better quality of service and smaller in size.

o Some declared it as 3rd generation cellular phone and also microcellular

system.

o But drawback is expensive system (smaller cells) disadvantage setback


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• Goals to provide:

o Voice, data & video

o Close to universal access irrespective of time, location & mobility patterns

• Three categories

o Broadband (cellular & cordless handset services)

o Narrowband (enhancing paging functions)

o Unlicensed (short–distance operations)


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• PCS networks & existing cellular networks complement each other (instead of

competing).

• Architecture resembles cellular network & enhanced:

o Speech quality

o Radio – link architecture flexibility

o Economics serving high–user density

o Handsets with lower power consumption


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• PCS variable sizes and hierarchical cell structure:

o Picocell (low–power indoor applications)

o Microcell (lower – power outdoor pedestrian applications)

o Macrocell (for high – power vehicular applications)

o Supermacro cells (satellites)


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• Cells Architecture

Illustration courtesy of Gokhale, Introduction to Telecommunications


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Analogue vs Digital Access

• Three modes of wireless access:

o Frequency–Division Multiple Access (FDMA)

o Time–Division Multiple Access (TDMA)

o Code–Division Multiple Access (CDMA)

• Analogue system

o Actual sound (caller’s voice pattern) transmitted over the airwaves.

• Digital system

o Better coverage o More calls per channel

o Broadband communications o Less noise interference

o Ability to add new features & functions


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Analogue vs Digital AccessCellular system Generation

Advantage Disadvantage

1st Generation (FDMA)

Widest coverage including rural PowerSecurityNot optimised for dataLimited capacity

2nd Generation (TDMA)

Better securityHigher capacity

May experience interruption during hand–off

3rd Generation (CDMA)

Very high securityImproved capacityGreater interference immunitySoft hand–off (no interruption)

Limited coverage.


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3G Network & Access

• New demand made future mobile cellular systems as individuals and business

way.

• Access to internet become more important.

• New services required more than speech and data

o Video other multimedia applications.

o High–speed data -> 3rd Generation Mobile.

• European 3rd Gen. System

o Universal Mobile Telecommunications System (UMTS)

o ETSI

o Radio “air interface” based on W–CDMA.


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3G Network & Access

• ITU named 3rd Gen. Mobile System as IMT–2000 (frequency band in region of

2000 MHz).

o Seamless

o Global communication service through small, lightweight terminals.

o Radio frequency range of 1885 ~ 2200 MHz.

o GSM system evolve towards UMTS progressively in steps.

GSM HSCSD GPRS EDGE

3rd Gen. UMTS

High Speed Circuit Switched Data, General Packet Radio Services

Enhanced Data rates for GSM Evolution


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3G Network & Access

HSCSD

o Modified air interface timeslots of TDMA (9.6 kbits/s) to 14.4 kbits/s.

o Increase data calls speed by means of multi timeslot usage.

o Combine 4 TDMA timeslots to provide 57.6 kbits/s transfer rate. (multiple

bursts).

o May cost more for subscribers/users but time required is shorter.

o At that time, mostly no hardware change (for MSC) required.


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3G Network & Access

GPRS

o Gives direct link for mobile communication to internet.

o Gives subscribers/users same experience as if they are connected to LAN.

o Charged by actual amount of data transfer.

o Higher transmission speed.

o Cost efficient for operators too.

o Allowing faster download, increases average usage levels (radio resources).

o Require modification to network:

• SGSN (serving GPRS Support Node) – maintain location of mobile station

• GGSN (Gateway GPRS Support Node) – enables data packets passed to

switch.


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3G Network & Access

EDGE

o Bridge from GSM to 3rd Gen mobile network.

o Advanced GSM modulation technique to provide 384 kbits/s at 200 kHz GSM

channel (6 X 64 kbits/s), and same structure of TDMA frame structure.

o Extra capacity achieved by increasing data capacity of single GSM timeslot 9.6

kbits/s to 48 kbits/s (or some may reach 70 kbits/s)

o Flexible timeslots to allow several simultaneous services.

o Handles:

• Internet/intranet, Video conferencing, Fast email

o Require minor changes to network hardware/software


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3G Network & Access

• GSM and 3G network interworking solution

Illustration courtesy of Nokia Telecommunication Oy.


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3G Network & Access

• Actual 3rd Gen. Network (W–CDMA)

Illustration courtesy of Nokia Telecommunication Oy.

Documents

BENT 3163 Chapter 6 Wireless Communication