April 25, 2005 Topic 5 1
Telecommunications EngineeringTopic 5: Wireless ArchitecturesJames K Beard, Ph.D.
http://astro.temple.edu/~jkbeard/
Topic 5 2April 25, 2005
Essentials Text: Simon Haykin and Michael Moher, Modern
Wireless Communications SystemView
Use the full version in E&A 603A for your term project Web Site
URL http://astro.temple.edu/~jkbeard/ Content includes slides for EE320 and EE521 SystemView page A few links
Office Hours E&A 349 Hours Tuesday afternoons 3:00 PM to 4:30 PM MWF 10:30 AM to 11:30 AM Others by appointment; ask by email
Topic 5 3April 25, 2005
Topics
Architecture topicsOpen System Interconnection (OSI) modelPower controlHandoverThe Network Layer
Other areas from earlier chapters are reviewed
Topic 5 4April 25, 2005
Open System Interconnection (OSI) Model Seven-layer model
Physical layer (modem)Data link layerNetwork layerTransport layer (packetizing, ACK/NAK)Session layer (Service selection and access)Presentation layer (encryption, compression)Application layer (HMI)
Layers designed together as a system
Topic 5 5April 25, 2005
Example 7.1: E-mail and the Seven-Layer Model Application layer – e-mail client software Presentation layer – compression and
encryption (SSH) Session layer – interface with host Transport layer – TCP interface, IP addressing Network layer – routing, adds header Data link layer – adds header and addresses of
host, adds CRD bits; medium access layer (MAC) selects free channel and passes to…
Physical layer – FEC and modulation, yet another header
Topic 5 6April 25, 2005
Power Control Architectures
Open Loop Mobile terminals measure strength of pilot channel Transmit power decreased for strong pilot channels Fast and simple, but must be approximate
Closed Loop Base station measures mobile terminal signal strength Mobile station receives signal strength by downlink Accurate but delay and averaging must be smaller than channel
coherence time Outer Loop Control
Base station uses expected signal strength in control algorithm Complexity can result in a slow loop
Topic 5 7April 25, 2005
Power Control: Summary
Power control minimizes SINR in busy cells Handset power control minimizes SINR in the
base station but not at the mobile terminal Methods still evolving Next generation standards will implement
Newer techniques such as outer-loop control Base station power control for SINR control at the
mobile station
Topic 5 8April 25, 2005
Example 7.3: The Near-Far Problem Mobile terminal distance to base station varies
from 100 m to 10 km Power differences
Given a path loss exponent of 4 Difference in received power at base station is 80 dB
Spreading rate of 128 million required to prevent jamming of weaker user
Solution is power control
Topic 5 9April 25, 2005
Handover Issues
PurposeAddress operational transition of mobile
terminals between cellsMaintain continuity of calls
Calls are dropped in handover becauseMobile station signal strength drops too low
before handover is completedThe new cell doesn’t have a free channel
Topic 5 10April 25, 2005
Handover Techniques
Start handover when signal strength is decreasing but a margin still exists Common technique with first-generation systems Margin can be small with second-generation systems
that switch cells quickly Mobile assisted
Use base station signal strength in handover logic Avoids cell dragging in which mobile station operates
well into another cell, and causes interference with other mobile stations
Topic 5 11April 25, 2005
Handover Multiple-Access Issues FDMA and TDMA
Mobile station must change signaling channels and traffic channels in handover
Called hard handover CDMA
Signaling channels are the same during handover Called soft handover
SDMA Switch stations when mobile station transitions
between beam boundaries Can become complex when base station tracks users
with steerable beams
Topic 5 12April 25, 2005
The Network Layer Components Base station
RF links to mobile terminals RF, wire, fiber or other links to mobile switching
center
Switching Center Handles billing and authorization Executes interconnects between base stations, other
networks, or land line telecommunications
Topic 5 13April 25, 2005
Mobile Switching Center Functions Billing and authorization
Counts the minutes Determines roaming status and finds home station/account Rings the cash register Modifies routing where appropriate
Interface between cellular and public land line telephone networks
Overall supervision of mobile access control (MAC) wireless communications network Power control functions Handover Provide data capability to mobile terminals
Topic 5 14April 25, 2005
Indoor LANs
TerminologyCells are service setsUser terminals are stationsBase stations are stations
PeculiaritiesOften design and growth is ad hoc without
planningDissimilar packet sizes through networkWired and 802.11 terminals on same station
Topic 5 15April 25, 2005
Physical Layer for Various MAC Standards (Table 7.2 p. 470) GPRS WCDMA IEEE 802.11b Bluetooth IEEE 802.11a Frequency Band
935-960 MHz (F) 890-915 MHz (R)
1920-1980 MHz (F) 2110-2117 MHz (R)
2.4 GHz 2.4-2.4385 GHz
5.2 GHz
Channel BW 200 kHz 5 MHz 50 MHz 80 MHz 20 MHz Modulation GMSK QPSK BPSK/QPSK
FH or DS GMSK/FH BPSK,…,64-
QAM/OFDM Data rates Up to 116 kbps Up to 2 Mbps Up to 11 Mbps M 1 Mbps Up to 54 Mbps Access strategy
FDMA/TDMA FDMA/CDMA/FDD FDMA/CDMA/TDD
CSMA/CA FH/TDD FDMA/CSMA
Cell size Up to 35 km < 35 km 1-20 m 1-1- m 1-100 m FEC Variable, including
rate-1/2 convolutional
Variable, including rate-1/2, 1/3 convolutional
Rate ½, 1/3 convolutional
Variable; repetition, Hamming, ARQ
Rate ½, 1/3, 3/4 convolutional
Frame size 4.61 ms 10 ms Up to 20 ms n X 625 μs n=1,2,3,4,5
24 μs to 5 mx
Diversity Frequency hopping Space-time block coding with transmit diversity
Dual antenna None Dual antenna
Network topology
Point-to-multipoint/cellular
Point-to-multipoint/cellular
Point-to-multipoint
Point-to-point connection and connectionless
Point-to-multipoint
Topic 5 16April 25, 2005
Physical Layer for Various Data Network Standards (Table 7.3) DECT GSM IS-95 WCDMA Frequency Band 1880-1900 MHz 935-960 MHz (F)
890-915 MHz (R) 869-894 MHz (F) 824-849 (R)
1920-1980 MHz (F) 2110-2117 MHz (R)
Channel BW 1.728 MHz 200 kHz 1.25 MHz 5 MHz Modulation GMSK GMSK BPSK QPSK Data rates 1.152 Mbps 270.8 kbps 1200-9600 bps Up to 2 Mbps Access strategy FDMA/TDMA/TDD FDMA/TDMA/FH FDMA/CDMA FDMA/CDMA/FDD
FDMA/CDMA/TDD Cell size < 300 m < 35 km < 35 km < 35 km FEC None (16-bit CRC) Variable, including
rate-1/2 convolutional
Variable, including rate-1/2, 1/3 convolutional
Variable, including rate-1/2, 1/3 convolutional
Frame size 10 ms 4.61 ms 20 ms 10 ms Voice encoding ADPCM at 32 kHz RELP at 13 kbps CELP at 9.6 kbs
and 14.4 kbps Adaptive multirate ACELP 4.75 to 12.2 kbps
Traffic channels per RF channel
12 8 Up to 63 Depends on data rate
Diversity Antenna diversity at base station
Frequency hopping Spread spectrum with RAKE receiver
Space-time block coding with transmit diversity
Topic 5 17April 25, 2005
Theme Example 5: 802.11(Wi-Fi) Pages 328-331 Timeline
User station (STA) logs onto local base station (AP), AP authenticates STA and provides ID
STA listens Inactive channel – STA sends RTS, AP sends CTS Active channel – listens for gap and sends packet
STA fragments and sends packet AP reassembles packet and sends to network layer AP disassembles packet from network layer and
sends to STA Random time access (like Ethernet)
Topic 5 18April 25, 2005
(5)(7) Convolutional Code with Hard Decoding
SystemView
0
0
2
2
4
4
6
6
8
8 1.00e+0
1.00e-1
1.00e-2
1.00e-3
1.00e-4
BER
Eb/No in dB
w3, PSK (coherent)
Topic 5 19April 25, 2005
(5)(7) Convolutional Code with Soft Decoding
SystemView
0
0
2
2
4
4
6
6
8
8 1.00e+0
1.00e-1
1.00e-2
1.00e-3
1.00e-4
BER
Eb/No in dB
w3, PSK (coherent)
Topic 5 20April 25, 2005
Problem 2.59 Page 102
When G. Marconi made the first radio transmission in 1899 across the Atlantic Ocean, he used all of the spectrum available worldwide to transmit a few bits per second. It has been suggested that, in the period since then, spectrum usage (bits/s/Hz worldwide) has increased by a factor of a million. List the factors that have resulted in this substantial increase. Which factor will likely result in the largest increase in the future?
Topic 5 21April 25, 2005
Factor Comment Antenna gain More directionality means more frequency reuse Modulation Increased spectral efficiency leads to a more compact spectrum and
less interference with adjacent channel users. Constant envelope schemes are immune to amplifier nonlinearities, therefore less spectral growth. Modulated pulse schemes provide more compact spectra.
Filters Match filtering improvements allow for steeper band rolloffs and a more compact spectral shape
Oscillators Crystal oscillators allow operation in the high GHz range. Stability and accuracy of oscillators also help improve compactness of spectrum.
Semiconductor technology
Improved switching speeds and good immunity to RFI and EMI. Circuit design methods have improved, thus reducing susceptibility to interference.
Digital processing Advanced algorithms have been deployed to track phase and gain with great efficiency resulting in low implementation losses. Also, advanced algorithms allow operation in environments with higher levels of interference; thereby increasing the amount of frequency reuse.
Coding Error correcting codes such as Viterbi and Turbo Codes allow large improvements in spectral efficiency. Receivers that use ECC can operate at lower power and in the presence of more interference than those receivers without ECC.
Factors That Increase Spectral Usage
Topic 5 22April 25, 2005
Problem 3.2 Page 110
Consider the sinusoidal modulating signal
Show that the use of double sideband, suppressed carrier (DSB-SC) modulation produces a pair of side frequencies, one at fc+fm and the other at fc-fm, where fc is the carrier frequency. What is the condition that the modulator has to satisfy in order to make sure that the two side-frequencies do not overlap?
cos 2m mm t A f t
Topic 5 23April 25, 2005
Solution for Problem 3.2
cos 2
cos 2 cos 2
1cos 2 cos 2
2
c c
c m m c
c m c m c m
s t A m t f t
A A f t f t
A A f f f f
Topic 5 24April 25, 2005
Polynomial Arithmetic Modulo 2
Integer arithmetic modulo 2 Add, subtract, multiply integers Take this result modulo 2 Solution is always 0 or 1 Division? Reciprocal of odd numbers is 1
Polynomial arithmetic modulo 2 Integers are coefficients of polynomials Perform polynomial arithmetic as usual Take coefficients of result modulo 2
Topic 5 25April 25, 2005
Examples
Two polynomials
Multiplying them
Taking the result modulo 2
5 3
4 3 2
1 101011
1 011101
x x x
x x x
9 8 7 6 5 4 3 22 3 2 3 1x x x x x x x x x
9 8 6 5 3 2 1 1101101111x x x x x x x
Topic 5 26April 25, 2005
Finite Fields
Example Integer arithmetic modulo 7Elements are {0,1,2,3,4,5,6}Reciprocals pairs are (1,1), (2,4), (3,5), (6,6)Division is defined as multiplication by
reciprocal All integer arithmetic modulo a prime
defines a finite field
Topic 5 27April 25, 2005
Vector Extensions of Finite Fields Sometimes called polynomial fields or Galois
fields The exist for orders N equal to any power k of a
prime p: N=pk
Arithmetic Elements are characterized as the coefficients of a
polynomial of order k-1 Addition and subtraction is done modulo p Multiplication is defined as modulo a generating
polynomial of order k
Topic 5 28April 25, 2005
Defining Characteristics of Galois Fields Successive multiplication by x
Begin with 1 Steps through all N elements except zero A sequence of length N-1
A reciprocal Defined as producing 1 as a product Always exists
Division is defined as multiplication by reciprocal
Topic 5 29April 25, 2005
Special Case for Signal Processing Galois fields of order 2k
The series of coefficients is a sequence of k zeros and ones
Addition and subtraction Are identical operations in this field Result is a bit-by-bit XOR
Multiplication Modulo a generating polynomial of order k Generating polynomial can be added or subtracted Table 5.1 page 272 lists some generating polynomials
Topic 5 30April 25, 2005
Generation with Shift Registers
Basis is a shift register with k latches Shifting is equivalent to multiplication by x A 1 shifted out
Fed back in according to the 1s in the generating polynomial
Addition is done with an XOR
Topic 5 31April 25, 2005
Example
2xx 3x
Generating Polynomial:
3 1x x
Topic 5 32April 25, 2005
Definitions of Orthogonality
Vectors with arithmetic modulo 2 Addition of two orthogonal vectors gives the zero
vector A set of vectors that is closed on addition has the
properties Sum of any two is another in the set The zero vector is always included
A basis set has the property Sum of any two is never another in the basis set or zero The opposite of closed on addition
Orthogonal signals
1,
0,i j
i js t s t dt
i j
Topic 5 33April 25, 2005
Next Time
Assignment:Look at the study guideGo over the slides to dateLook particularly at Chapters 4 and 7Make up a list of questionsSend them to me by email: