![Page 1: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/1.jpg)
UNIT V
ADVANCED TRANSCEIVER SCHEMESRef.: Wireless Communication, Molisch
![Page 2: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/2.jpg)
Multiple access
![Page 3: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/3.jpg)
Contents
• Interference and spectrum efficiency
• Frequency-division multiple access (FDMA)
• Time-division multiple access (TDMA)
• Packet radio
![Page 4: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/4.jpg)
Freq.-division multiple access (FDMA)
Assume that each channelhas a bandwidth of Bfch Hz.
If the system has a totalbandwidth Btot, thenthe number of availablefrequency channels is
N fch
B=B
tot
fch
Applying a cellular structure,using frequency reuse,we can have more thanNfch simultaneous active users.
![Page 5: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/5.jpg)
Time-division multiple access (TDMA)
TDMA is usually combinedwith FDMA, where eachfrequency channel is sub-divided in time to providemore channels.
Users within one cell useTDMA, while different cellsshare the radio resourcein frequency.
One cell can have more thanone frequency channel.
![Page 6: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/6.jpg)
PACKET RADIO
![Page 7: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/7.jpg)
Principle and application
• Data are broken into packets
• Each packet has to fight for its own resources
• Each packet can go from TX to RX via different relays
• Used for, e.g.,- Wireless computer networks: internet is packet radio by definition
- Sensor networks: routing over different relay nodes gives betterreliability
- Voice over IP: allows to have one consistent MA principle for dataand voice
![Page 8: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/8.jpg)
ALOHA (1)
• Basic principle: send out data packets whenever TX hasthem, disregarding all other TXs
• When collision occurs, packet is lost
Copyright: IEEE
![Page 9: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/9.jpg)
ALOHA (2)
• Probability that there are n packets within time duration t
p
ptn expptPrn, t
n!
where is the packet rate of arrival
• Probability of collision
Pr0, t expp t
• Total throughput: pTp exp2pTp
• Maximum throughput: 1/(2e)
• Slotted ALOHA: all packets start at certain discrete times
![Page 10: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/10.jpg)
Carrier sense multiple access
• Principle: first determine whether somebody else transmits,send only when channel is free
• Why are there still collisions?- Delays are unavoidable: system delay and propagation delay
- Collision, when there is a signal on the air, but device cannot senseit, because (due to delay) it has not reached it yet
• What does system do when it senses that channel is busy?- WAIT
- Different approaches to how long it should wait
![Page 11: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/11.jpg)
Performance comparison
Copyright: Ericsson
![Page 12: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/12.jpg)
DUPLEXING
![Page 13: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/13.jpg)
DUPLEXFrequency-division Duplex (FDD)
TransmitterDuplex
filterReceiver
Frequency
FDD gives a more complexsolution (the duplex filter).
Can be used for continuoustransmission.
Examples: Nodic Mobile Telephony (NMT), Global System for Mobile communications (GSM),Wideband CDMA (WCDMA)
![Page 14: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/14.jpg)
DUPLEXTime-division duplex (TDD)
Transmitter
ReceiverTime
TDD gives a low complexitysolution (the duplex switch). Duplex
switchCannot be used for continuoustransmission.
Examples: Global System for Mobile communications (GSM),Wideband CDMA (WCDMA)
![Page 15: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/15.jpg)
INTERFERENCE ANDSPECTRUM EFFICIENCY
![Page 16: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/16.jpg)
Interference and spectrum efficiencyNoise and interference limited links
NOISE LIMITED
TX RX
Power
C
(C/N)min
From Chapter 3
(C/I)min
N
Distance
INTERFERENCE LIMITED
TX RX TX
Power
C I
N
Distance
Max distance Copyright: Ericsson Max distance
![Page 17: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/17.jpg)
Interference and spectrum efficiencyCellular systems
D
R
Ncluster
(D/R)2=
3
![Page 18: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/18.jpg)
Interference and spectrum efficiencyCellular systems, cont.
Cluster size: Ncluster = 4 Cluster size: Ncluster = 13
D/R = 3.5 D/R = 6.2Copyright: Ericsson
![Page 19: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/19.jpg)
Interference and spectrum efficiencyCellular systems, cont.
Where do we get thenecessary D/R?
BS-3
Received useful power is−ηC∝P dTX 0
BS-4
BS-0
BS-2With 6 co-channel cells interfering, atdistances d1, d2, ... d6, from the MS, thereceived interference is
6−η
BS-5 MSI
BS-1∝∑
i=1
P dTX i
Knowing that d0<R and d1,...,d6>D - R,we get
BS-6 C PTXd−η
0 PTX−ηR 1 R −η
=I 6
∑i=1
P dTX i
>−η
6
∑i=1
PTX
=−η
(D−R)
6
D−R
![Page 20: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/20.jpg)
Interference and spectrum efficiencyCellular systems, cont.
Assume now that we have a transmission system, which requires(C/I)min to operate properly. Further, due to fading and requirementson outage we need a fading margin M.
Using our bound
C 1 R
We get−η
1/η>I
6D−R
D≥
6M
C +1
Rwe can solve for a“safe” D/R by requiring
−η
I min
1 R ≥M
C 6 D−R I min
![Page 21: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/21.jpg)
Interference and spectrum efficiencyCellular systems, cont.
N 3cluster
4 7 9 12 13 16 19 21 25 27
D/R= 3Ncluster 3 3.5 4.6 5.2 6 6.2 6.9 7.5 7.9 8.7 9
TDMA systems, Analog systems,like GSM like NMT
![Page 22: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/22.jpg)
Interference and spectrum efficiencyCellular systems, cont.
Erlang-B
Relation betweenblocking probabilityand offered trafficfor different numberof available speechchannels in a cell.
![Page 23: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/23.jpg)
Spread Spectrum
![Page 24: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/24.jpg)
PRINCIPLES OFSPREAD SPECTRUM
![Page 25: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/25.jpg)
Spread spectrum for multiple access
![Page 26: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/26.jpg)
Single Carrier
The traditional wayTransmitted signal
DataMod.
fC
Radio spectrum
fC
t
f
![Page 27: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/27.jpg)
Spread Spectrum Techniques
Power density spectrum [W/Hz]
Single carrierbandwidth
Spread spectrum bandwidth
Singlecarriersignal
Noise andinterference
Spreadspectrum
signalf
![Page 28: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/28.jpg)
Spread Spectrum Techniques
Spectrum Spectrum
f f
InformationSpreading
Noise andinterference
Spectrum Spectrum
InformationDespreading
f f
![Page 29: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/29.jpg)
FREQUENCY HOPPING
![Page 30: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/30.jpg)
Frequency-Hopping Spread SpectrumFHSS
Data
Frequency
Modulator
FH-SS
Frequencyhopping
generator
2FSK:01
Time
![Page 31: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/31.jpg)
Frequency-Hopping Spread SpectrumFHSS
Transmitter 1Frequency Transmitter 2
Users/channelsare separatedby using differenthopping patterns.
Time
Collision
![Page 32: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/32.jpg)
FH codes (1)
![Page 33: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/33.jpg)
FH codes (2)
![Page 34: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/34.jpg)
DIRECT SEQUENCESPREAD SPECTRUM
![Page 35: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/35.jpg)
Direct-Sequence Spread SpectrumDSSS (1)
Information signal
1:
0:
1
Spreading
1:
0:
DSSS signal
Users/channelsare separated
by using differentspreading codes.
1BW ∝T
BW ∝T
Tb
b Tc
Spreadingc code
Length of one
chip in the code.
![Page 36: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/36.jpg)
Direct-Sequence Spread SpectrumDSSS (2)
DSSS signal Information signal
Despreading
1: 1:
0: 0:
Spreadingcode
![Page 37: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/37.jpg)
Code-division multiple access (CDMA)
Despread
Code 1
f
Code 2
(Code 1)
Despread(Code 2)
Despread(Code N)
f
f
f
We want codes with low cross-correlationbetween the codes since the cross-talk between“users” is determined by it.
Code N
![Page 38: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/38.jpg)
Impact of delay dispersion
• CDMA spreads signals over larger bandwidth -> delaydispersion has bigger impact.
• Two effects:- Intersymbol interference: independent of spreading; needs to be
combatted by equalizer
- Output of despreader is not impulse, but rather an approximation tothe impulse response
• Needs Rake receiver to collect all energy
![Page 39: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/39.jpg)
Rake receivers
Despreading becomes a bit more complicated
... but we gain frequency diversity.Copyright: Prentice-Hall
![Page 40: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/40.jpg)
Code families (1)
• Ideal goals:- Autocorrelation function is delta impulse
MC for i 0ACFi
0 otherwise
– Crosscorrelation function should be zero
CCFj,kt 0 for j k
– CCF properties should be (approx.) independent of relative shiftbetween users
![Page 41: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/41.jpg)
Code families (2)
Copyright: Ericsson
![Page 42: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/42.jpg)
Code families (3)
• Kasami-codes:- Larger family of codes that trades of number of codes vs. ACF and
CCF properties
• Gold sequences• Overview of results (for length 255):
Sequence Number of codes Maximum CCF
PN-Sequence 2Nreg 1 255
Gold 2Nreg 1 257 3Nreg/2 1.5 10. 5dB
S-Kasami 2Nreg/2 16 3Nreg/2 12dB
L-Kasami 2Nreg/22Nreg 1 4112 3Nreg/2 3 9dB
VL-Kasami 2Nreg/22Nreg 12 106 3Nreg/2 6 6dB
![Page 43: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/43.jpg)
Orthogonal codes
• Codes with perfect orthogonality are possible, but only forperfectly synchronized users
• Walsh-Hadamard codes:- Size 2x2
1H
1 1
11
– Larger sizes: recursion
nHn Hhad hadHn 1 n nH Hhad
![Page 44: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/44.jpg)
Orthogonal Variable Spreading Factor (OVSF)codes
• When different spreading factors are needed
…these codesIf this code is cannot be used
used… receiver.
![Page 45: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/45.jpg)
MULTIUSER DETECTION
![Page 46: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/46.jpg)
Principle of multiuser detection
• Conventional approach: treat interference like noise
• However: interference has structure that can be exploited
![Page 47: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/47.jpg)
Linear MUD
• Receiver structure
• Zero-forcing: T R1
- Drawback: noise enhancement• MMSE: T R1 N0 I1
![Page 48: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/48.jpg)
Nonlinear MUD (1)
• Multiuser MLSE:- optimally detect transmit sequences of all users
- Number of states in trellis grow exponentially with number of users
- Too complex for practical implementation
• Serial Interference cancellation:- Detect strongest user first; subtract its impact from signal, then
detect second strongest,…
- Drawback: error propagation
![Page 49: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/49.jpg)
Nonlinear MUD (2)
• Parallel interference cancellation:- Detect all users at once; subtract part of their impact from signal,
then repeat this
![Page 50: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/50.jpg)
TIME HOPPING IMPULSE RADIO
![Page 51: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/51.jpg)
Time Hopping
• Train of pulses
Tf
• TPul ~ Tf/100
• PN sequence {cj}, NP code = Np pulses, Tc: dither time
Tf
Cj.Tc Cj+1.Tc Cj+2.Tc
![Page 52: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/52.jpg)
Interference Suppression
• Other impulse radio sources:- Relative delay of users cannot be influenced
- Different users use different hopping codes
- No “catastrophic collision” possible
User 1
User 2
1 pulse collides1 symbol = 8 pulses• Narrowband interference
- Receiver “sees” it only for duration of pulse
- Suppression by factor Tf/Tp
![Page 53: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/53.jpg)
Summary
• The available radio resource is shared among users in amultiple access scheme.
• When we apply a cellular structure, we can reuse the samechannel again after a certain distance.
• In cellular systems the limiting factor is interference.
• For FDMA and TDMA the tolerance against interferencedetermines the possible cluster size and thereby theamount of resources available in each cell.
• For CDMA systems, we use cluster size one, and thenumber of users depends on code properties and thecapacity to perform interference cancellation (multi-userdetection).
![Page 54: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/54.jpg)
Orthogonal FrequencyDomain Multiplexing
![Page 55: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/55.jpg)
Contents
• Principle and motivation
• Analogue and digital implementation
• Frequency-selective channels: cyclic prefix
• Channel estimation
• Peak-to-average ratio
• Inter-channel interference
• Adaptive modulation
• Multi-carrier CDMA
![Page 56: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/56.jpg)
PRINCIPLE, MOTIVATIONAND BASIC IMPLEMENTATION
![Page 57: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/57.jpg)
Principle (1)
• For very high data rates, equalization and Rake receptionbecomes difficult
- Important quantity: product of maximum excess delay and systembandwidth
- Especially critical for wireless LANs and PANs
• Solution:- transmit multiple data streams with lower rates on several carriers
- Have carriers multiplexed in the most efficient possible way:
- Signals on the carriers can overlap and stay orthogonal
![Page 58: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/58.jpg)
Principle (2)
• How close can we space the carriers?
fn nW/N W N/TS
• Carriers are still orthogonalcnck i1TS expj2fntexpj2fktdt cncknk
iTS
![Page 59: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/59.jpg)
Analogue vs. digital implementation
• Analogue implementation
• Digital implementation
![Page 60: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/60.jpg)
Why can we use an IFFT?
• Transmit signal is N1
st sit i i n0
• With basis pulse1
cn,ignt iTS
expj2nt for 0 t TSTS TSgnt
0 otherwise
• Transmit signal sampled at tk kTS/N
N11sk stk TS
cn,0 expj2n k.N
n0
• This is the definition of an IFFT
![Page 61: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/61.jpg)
Frequency-selective channels
• Cyclic prefix, i.e., repeat last samples at beginning ofsymbol
• Converts linear to circular convolution
![Page 62: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/62.jpg)
Performance in frequency-selective channels(1)
![Page 63: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/63.jpg)
Performance in frequency-selective channels(2)
![Page 64: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/64.jpg)
Performance in frequency-selective channels(3)
• How to improve performance?- adaptive modulation (different signal alphabets in different
subcarriers)
- spreading the signal over all tones (multicarrier CDMA)
- Coding across different tones
![Page 65: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/65.jpg)
ADVANCED IMPLEMENTATIONISSUES
![Page 66: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/66.jpg)
Channel estimation (1)
• Easiest approach: dedicated pilot symbols
• Estimated channel gain on subchannel n
S rn,i/cn,i
where r is the received signal and c the transmit signal
• Performance improvement:- Channels on subcarriers are correlated
- Exploit that knowledge for noise averaging
hiLMMSE RhhLSR1S
LShihLS
RhhLS :covariance matrix between channelgains and least-squares estimate ofchannelgains,
RhLShLS : autocovarance matrix of least-squares estimates
![Page 67: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/67.jpg)
Channel estimation (2)
• Reduction of overhead by scatterered pilots
![Page 68: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/68.jpg)
Effect of PAR problem
• Increases BER
Copyright: Wiley
![Page 69: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/69.jpg)
Remedies for the PAR problem (1)
• Backoff
Copyright: Wiley
![Page 70: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/70.jpg)
Remedies for the PAR problem (2)
- Residual cutoff results in spectral regrowth
Copyright: Wiley
![Page 71: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/71.jpg)
Remedies for the PAR problem (3)
• Coding for PAR reduction
• Phase adjustments• Cannot guarantee certain PAR
![Page 72: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/72.jpg)
Remedies for PAR problem (4)
• Correction by multiplicative factor- Simplest case: clipping
- More gentle: Gaussian functions
st st 1 n max 0, |sk|A0 expt2|sk | 2
• Correction by additive factor
2t
![Page 73: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/73.jpg)
Intercarrier interference (ICI)
• Intercarrier interference occurs when subcarriers are notorthogonal anymore
![Page 74: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/74.jpg)
Remedies for ICI (1)
• Optimize the carrier spacing and symbol duration- Larger subcarrier spacing leads to smaller ICI
- Larger spacing leads to shorter symbol duration: more sensitive toICI; cyclic prefix makes it less spectral efficient
- Maximize ES N
SINR N0 PsigNcpN
ES N PISIPICI
N0 Psig N1cpN Psig
• Optimum choice of OFDM basis signals
![Page 75: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/75.jpg)
Remedies for ICI (2)
• Self-interference cancellation
• Frequency-domain equalizers
![Page 76: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/76.jpg)
Waterfilling
• To optimize capacity, different powers should be allocatedto the subcarriers
• Waterfilling:2
Pn max 0, nwith P N1 Pn|n|2
![Page 77: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/77.jpg)
MUTLICARRIER CDMA (MC-CDMA)AND
SINGLE-CARRIER FREQUENCY-DOMAIN EQUALIZATION (SC-FDE)
![Page 78: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/78.jpg)
And now for the mathematics…
• A code symbol c is mapped onto a transmit vector, bymultiplication with spreading code p.
• For parallel transmission of symbols: a vector of transmitsymbols c is mapped by multiplication with a spreadingmatrix P that consists of the spreading codes for thedifferent symbols
c Pc P p1 p2 pN
• Symbol spreading is undone at the receiver
r Hcn
PH1r PH1HPc PH1n
cn
![Page 79: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/79.jpg)
Transceiver structure for MC-CDMA
![Page 80: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/80.jpg)
SC-FDE Principle
• Move the IFFT from the TX to the RX
![Page 81: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/81.jpg)
Multiple antenna systems
![Page 82: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/82.jpg)
Definitions
• What are smart antennas and MIMO systems?
A MIMO system consists of several antenna elements, plus adaptivesignal processing, at both transmitter and receiver, the combination ofwhich exploits the spatial dimension of the mobile radio channel. Asmart antenna system is a system that has multiple antenna elementsonly at one link end.
Transmitter Channel
H1,1
Antenna 1 H2,1H
Receiver
Antenna 1
Antenna 2
Signal
Data source
Signalprocessing
nŢ1
Antenna 2
H1,
processing Data sink
nR
H2,nR
HnŢ nR
Antenna nT
Antenna nR
![Page 83: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/83.jpg)
TDMA System with SFIR (1)
InterferenceInterference
transient
Interference transients
transient
BS
User cell
Interfering cell
1
Interfering cell 2
![Page 84: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/84.jpg)
TDMA System with SFIR (2)
![Page 85: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/85.jpg)
TDMA System with SDMA
Pair ofSDMA users
Powerclass
Pair ofSDMA users
BS
![Page 86: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/86.jpg)
2G (single rate) CDMA System
K McNrSIRthreshold
BS
![Page 87: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/87.jpg)
3G (Multirate) CDMA System
Desired user
Speech interferer
High data-rate interferer
BS
![Page 88: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/88.jpg)
Temporal reference (TR) algorithms
Basic idea:
• Choose antenna weights so that deviation of array outputfrom transmit signal is minimized
• Needs training sequence
![Page 89: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/89.jpg)
Spatial reference (SR) algorithms
• Determine DOAs, then do beamforming• A priori information for DOA estimation: array structure
• Algorithms for DOA estimation:- Fourier analysis
- Spectrum-based estimators- Parametric estimators
DOA-Estimation
user
Azimuth
Weightdetermination
interferer
Beamforming
Azimuth
![Page 90: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/90.jpg)
SR classification
DOA estimationSR algorithms
parametric spectral-based
subspace-based maximum subspace-based beamformingmethods likelihood methods
ESPRIT SAGE MUSIC MVM
![Page 91: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/91.jpg)
Blind Algorithms - Definition (1)
• Blind Estimation =
Identification of the system parameters h(t) orinput s(t) using only the output information
(i.e. without access to the input sequence).
• Applications:- equalisation
- speech processing
- image processing
– etc.
n(t)
s(t)h(t) + x(t)
![Page 92: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/92.jpg)
Blind Algorithms - Definition (2)
• Blind:
no training sequencesno known array properties
(DOAs)• but
structural signal properties
• Semi-blind:
bothstructural signal properties
andknown bit fields
![Page 93: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/93.jpg)
Blind Algorithms - Identification problem
Array outputdta
X=HS
Unknownchannel impulse
response
Unknowntransmitted
dta
� SIMO, MIMO problem(single or multiple inputs)
� separate or joint estimation ofH and S :
- space(-time) filter orspace-time detector
![Page 94: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/94.jpg)
Why downlink processing ?
UPLINK(reverse link)
DOWNLINK(forward link)
![Page 95: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/95.jpg)
Mobile Feedback based Beamforming
closed loop control:feed hDL or wDLback
UL
DL
Estimate:hDL
• MS estimates hDL
• Feedback of DL channelparameters (hDL or wDL)
![Page 96: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/96.jpg)
MIMO SYSTMES
![Page 97: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/97.jpg)
MIMO Transmission - Generic Structure
PowerAllocation
Bits ST/MatrixModulation
S
P
P1
P2
PQ
LinearPrecoding
V
1
nT
![Page 98: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/98.jpg)
MIMO Transmission - System Model
• Basic system model
Y= H X+ N= H V P S+ N
– S… ST modulation matrix containing the transmitted signalsof Q transmission streams during T symbol periods
- P… power allocation matrix P=diag(P11/2,...,PQ1/2) for Qstreams
- V… linear precoding matrix (e.g. for beamforming purpose)
- H… MIMO channel matrix (nR ×nT) - assumed to be constantduring T symbol periods
- Y… received signal from nR antennas during T symbols
- X… TX signal from nT antennas during T symbol periods
- N… receiver noise at nR antennas during T symbols
![Page 99: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/99.jpg)
MIMO SYSTMESWITH CSI AT TRANSMITTER
![Page 100: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/100.jpg)
Decomposing the instantaneous channel
• Deterministic instantaneous channel can be decomposedvia SVD:
H =UΛV H
min(nR n, T)
= λu Hv∑i=1
i i i
• Equivalent to min(nR,nT) independent parallel channelswith powers λi.
![Page 101: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/101.jpg)
Transmitting on eigenmodes
• Transmit precoding is matched to Tx eigenmodes:
y=H V P sprecoding power signal
• The modulation matrix is just a serial to parallel conversion
s 1
s
s=
2
#
s
min(nR,nT)
![Page 102: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/102.jpg)
Waterfilling
• Capacity formula for unequal power distribution
γC=logdet I +
HHPH bits /s / Hz2 nR nT
![Page 103: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/103.jpg)
Performance
Many TX antennas: for unknown channel, TX power “wasted”
![Page 104: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/104.jpg)
Diversity gain
• Write channel matrix asH
(2/2) array0
H =U ΛV• Excite channel with Vi, receive
Hwith Ui
2• Received power is λi
• Full benefit only for uncorrelated
0.1
no diversityλmin+λmax
0.01
contributions
• nT·nR diversity
• But: beamforming gain limitedUpper bound: (nT
1/2+nR1/2)2
-20 -15
0
0.1
0.01-20 -15
Copyright: IEEE
-10 -5 0 5 10
Power / dB
(4/4) array
Σλ
-10 -5 0 5 10 15
Power / dB
![Page 105: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/105.jpg)
MIMO SYSTMESWITHOUT CSI AT THE TRANSMITTER
![Page 106: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/106.jpg)
Capacity formula
• Instantaneous channel characterized by matrix H
• Shannon’s formula (for two-dimensional symbols):
C =log
• Foschini’s formula:
2 (1+γ| H |2)bits/s/ Hz
γC=logdet I +
HHH bits /s / Hz2 nR nT
![Page 107: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/107.jpg)
Capacity for fading channel (I)
• Rayleigh fading channel.
• Capacity becomes random variable.
• Channel not known at transmitter.
• χ22k...random variable; chi-square with 2k degrees of freedom
• Transmit diversityC=log2(1+(γ/n)⋅χ2n2)
• Receive diversityC=log2(1+γ⋅χ2n2)
• Comb. transmit/receive diversity: linear with n for fixed outage
C>
• Spatial cycling
n
∑k=1
1
log
n
2[1+(γ/ n)χ 2
2k
2
]
C=n∑k=1
log 2[1+(γ)χ2kn ]
![Page 108: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/108.jpg)
Capacity for fading channel (II)
γ= 21dB
1
.8
(1,1)
.6
.4
.2
0010 20 30 40 50
Capacity [bits/s/Hz]
![Page 109: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/109.jpg)
Capacity with correlation
![Page 110: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/110.jpg)
Measured capacities (LOS and NLOS)
Copyright: IEEE
![Page 111: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/111.jpg)
Limited number of scatterers
Copyright: IEEE
![Page 112: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/112.jpg)
Performance when one interfererdominates
010
T-BLAST(PIC)+1 IC SIR=0dBT-BLAST(PIC)+1 IC SIR=5dBT-BLAST(PIC)+1 IC SIR=10dBT-BLAST(PIC)+1 IC SIR=20dBT-BLAST(PIC)+1 IC No Int.single link Capacity LBsingle link Capacity
-110
-210
Copyright: IEEE-5 0 5 10 15 20 25 30
![Page 113: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/113.jpg)
Performance when two interferersdominate
010
-110
-210
-5 0 5
N = 4, 4QAM
T-BLAST(PIC)+MMSE SIR=0dBT-BLAST(PIC)+MMSE SIR=5dBT-BLAST(PIC)+MMSE SIR=10dBT-BLAST(PIC)+MMSE SIR=20dBT-BLAST(PIC)+MMSE No Int.
single link Capacity LBsingle link Capacity
10 15 20 25 30SNR (dB) Copyright: IEEE
![Page 114: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/114.jpg)
Frequency-selective environments
• Channel gives more diversity
• Equalizers: very complicated
• OFDM:- Subdivision into many frequency channels,
- Flat-fading MIMO system on each tone
- Efficient signal processing by using FFT
- But: coding across tones required to exploit frequency diversity
![Page 115: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/115.jpg)
Capacity in frequency-selective channels
Copyright: IEEE
Frequency diversity leads to smaller capacity fluctuations
![Page 116: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/116.jpg)
BLAST TRANSCEIVERS
![Page 117: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/117.jpg)
Spatial Multiplexing (H-BLAST)
s s s s 1
5 9 13
s s s s
S = 2 6 10 14 VBLAST s s s s
3 7 11 15
s s ss4 8 12 16
• Outer coding over T symbols (block length)
• Outer coding is independent for all streamsÆ no spatial diversity
• No coding over the streams - is sometimes also called“vector modulation”
S=[ s s s s ]T1 2 3 4
![Page 118: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/118.jpg)
H-BLAST - principle
![Page 119: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/119.jpg)
Spatial Multiplexing (D-BLAST)
• Diagonal BLAST
• Modulation matrix for the example nR=nT=Q=T=4
s s s s 1
8 11 14
s s s s
S = 2 5 12 15 VBLAST s s s s
Y =H V P S
3 6 9 16
s s ss4 7 10 13
• Data streams are cycled through antennas
• Achieves spatial multiplexing gain (rate=4) andspatial diversity
![Page 120: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/120.jpg)
SPACE-TIME CODING
![Page 121: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/121.jpg)
Design rules for ST-coding
• Probability of picking wrong code symbol with ST-codes:−n rnR r
λ
R 4N 0
r rank of A
∏i=1
i
Es
λ...eigenvalues of A
A = (c (t)−c '(t))(c (t)−c '(t))ik
∑ i i k kt
• Design rule:
- for achieving full diversity effect, A must have full rank
diversity order not decreased by frequency selectivity
- for optimizing coding gain (with full diversity),det( A)]min[
ci c,k 'must be maximized
![Page 122: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/122.jpg)
Space Time Block Codes
• Example: Alamouti code (nT=Q=T=2)
s −s 1SAlamouti
• Linear reception:s =h
=s2
r+hr
2
s1
+
n
Y =H V P S
1 1 1
s =hr *
2 2 1
−hr +n2 2 2 1 1 2
• Two symbols are transmitted during two symbol periods (rate 1 -no spatial multiplexing)
• Coding over the streams - achieves 2nd order TX diversity
• Reaches capacity only for nR=1
![Page 123: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/123.jpg)
GSM
![Page 124: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/124.jpg)
Simplified system overview
BTS
BTS
BTS
BTS
BTS
BSCVLR
BSS MSC
BSC
MSCBSS VLR
Copyright: Hewlett Packard
EIR
AUC
HLR
Interface toother networks
BTS Base Transceiver Station VLR Visitor Location RegisterBSC Base Station Controller EIR Equipment Identity RegisterBSS Base Station Sub-system AUC AUthentication CenterMSC Mobile Switching Center HLR Home Location Register
![Page 125: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/125.jpg)
Simplified block diagram
Speech Channel Burstcoder encoder formatting
bits
Speech Viterbi Viterbidecoder decoder equalizer
quality info.
(Encryption not included in figure)
Modulator/transmitter
Receiver
![Page 126: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/126.jpg)
Some specification parameters
![Page 127: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/127.jpg)
GMSK modulation
![Page 128: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/128.jpg)
Power spectrum
![Page 129: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/129.jpg)
TDMA/FDMA structure
TDMA/FDMA
A physical channeltimeis denoted by time slotindex and ARFCN
Amplitude
2
1
0
7
1 2 3 4 5 6
ARFCN
7
6
5
4
3
Frequency
Copyright: Hewlett Packard
ARFCN Absolute Radio Frequency Channel Numberchannels spaced 200 kHz apart
![Page 130: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/130.jpg)
Up/down-link time slots
Time slot index2345670123456701
ARFCN
ARFCN0123456701
Time slot index FrameCopyright: Hewlett Packard
![Page 131: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/131.jpg)
Some of the time slots
Normal3 start 58 data bits 26 training 58 data bits 3 stop 8.25 bits
bits (encrypted) bits (encrypted) bits guard period
FCCH burst3 start
bits 142 zeros3 stop 8.25 bitsbits guard period
SCH burst3 start 39 data bits 64 training 39 data bits 3 stop 8.25 bits
bits (encrypted) bits (encrypted) bits guard period
RACH burst8 start 41 synchronization 36 data bits 3 stop 68.25 bits extended
bits bits (encrypted) bits guard period
Copyright: IEEE
FCCH Frequency Correction CHannelSCH Synchronization CHannelRACH Random Access CHannel
![Page 132: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/132.jpg)
Frames and multiframes
Super frame 51 Multiframes
Multiframe 0 26 Frames
615Frame 8 Timeslots
576.92 µs
Timeslot 156.25 Bits
Copyright: Hewlett Packard
![Page 133: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/133.jpg)
Mapping of logical channels to physicalchannels
• Logical channels transmitted in differentframes/superframes/…
![Page 134: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/134.jpg)
Vocoder
Copyright: Wiley
![Page 135: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/135.jpg)
Channel coding of speech
The speech code bits are in three categories, with different levelsof protection against channel errors.
Block code
Parity check
Typ Ia Typ Ib50 Bits 132 Bits
50 3 132
Typ II78 Bits
4 Uncoded
convolutional code rate 1/2constraint length 5
378 78
456 Bits per 20ms speech frameCopyright: IEEE
![Page 136: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/136.jpg)
Interleaving and frequency hopping
• Bits interleaved over different frames
Copyright: IEEE
• Optional: frequency hopping, so that each frames seesdifferent channel and interference
![Page 137: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/137.jpg)
Encryption
![Page 138: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/138.jpg)
Viterbi equalizer
![Page 139: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/139.jpg)
Example for handover
• Handover between BTSs controlled by same MSC butdifferent BSCs
![Page 140: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/140.jpg)
GPRS and EDGE
GSM has evolved into a high-speed packet radio system in two steps
GPRS General Packet Radio Serviceswhere empty time slots can be usedto transmit data packets.Four new coding schemes are used(CS-1, ..., CS-4) with different levelsof protection.
EDGE Enhanced Data-rate for GSM Evolutionwhere, in addition to GPRS, a new
8PSK modulation is introduced.
Up to 115 kbit/sec
Up to 384 kbit/sec
Eight new modulation and coding schemesare used (MCS-1, ..., MCS-8) withdifferent levels of protection.
![Page 141: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/141.jpg)
GPRS network
SGSN Serving GPRS Support NodeGGSN Gateway GPRS Support Node
ISP Internet Service Provider
![Page 142: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/142.jpg)
EDGE 8PSK modulation
Linear 8-PSK ... but with rotation of signal constellation for each symbol
We avoid transitionsclose to origin, thus
getting a lower amplitudevariation!
3π 2×
8
3π
8 3×3π
8
![Page 143: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/143.jpg)
IS-95 and CDMA 2000
![Page 144: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/144.jpg)
Speech coding
• Original speech codec: IS-96A- 8.6 kbit/s
– Bad speech quality
• Enhanced speech codec: CDG-13- 13 kbit/s
– Code excited linear prediction (CELP) principle
- Much better speech quality
• Further enhancement: Enhanced Variable Rate CoderEVRC- Uses fewer number of bits both during speech pauses and during
active period
- 8.6 kbit/s
![Page 145: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/145.jpg)
Spreading and modulation for uplink
![Page 146: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/146.jpg)
Spreading and modulation for downlink
![Page 147: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/147.jpg)
Logical channels (1)
• Traffic channels:- for transmission of user data
- Depending on speech codec, use of rate set 1 or rate set 2
• Access channel:- Only in uplink
- Allows MS that does not have current connection to transmit controlmessages: security messages, page response, origination, andregistration
![Page 148: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/148.jpg)
Logical channels (2)
• Pilot channel
• Synchronization channel- Transmits system details that allow MS to synchronize itself to the
networks
• Paging channel
• Power control subchannel
• Mapping of logical channels to physical channels:- Assignment of different Walsh codes for different channels
![Page 149: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/149.jpg)
Improvements in CDMA 2000
• Enhanced supplemental channels that can transmit datawith higher rates
• Dedicated and common channels for packet data
• Walsh codes with variable length (OVSF codes)
• Faster power control for downlink
• Pilot for each uplink channel
• Enabling of smart antennas and transmit diversity
![Page 150: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/150.jpg)
Chapter 23
Wideband Code-DivisionMultiple Access (WCDMA)
![Page 151: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/151.jpg)
Third-generation systems
• IMT-2000 established by International TelecommunicationsUnion
• 3GPP and 3GPP2 are two organizations developingstandards for IMT-2000
• 3GPP allows several “modes”- Wideband CDMA
- C-TDMA
- DECT
- EDGE
- S-CDMA (China)
• Goals
} UMTS
- Higher spectral efficiency
– More flexibility, better suited for data transmission
![Page 152: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/152.jpg)
UMTS simplified system overview
![Page 153: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/153.jpg)
WCDMA - some parameters
Carrier spacing 5 MHzChip rate 3.84 Mchips/secUplink spreading factor 4 to 256Downlink spreading factor 4 to 512
All cells use the same frequency band!
![Page 154: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/154.jpg)
RF aspects
• Frequency bands
- USA: uplink 1850-1910 MHz; downlink 1930-1990 Copyright: 3GPP
• Transmit power- MS: 33, 27, 24, 21 dBm
– BS: not specified in standard; typically 40-46 dBm
![Page 155: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/155.jpg)
Spectrum mask
Frequency offset ∆f from carrier (in MHz)
2.5 2.7 3.5 7.5 ∆fmax
-15 0
-20 P= 43 dBm -5
-25P = 39 dBm -10
-30 -15
-35 -20
-40P = 31 dBm -25
Copyright: 3GPP
![Page 156: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/156.jpg)
Mapping of logical to physical channels
• Some physical channels have no equivalent logical channel
![Page 157: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/157.jpg)
Multiplexing
Copyright: 3GPP
![Page 158: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/158.jpg)
Coding
• CRC added for error detection
• Convolutional codes:- Rate ½ for common channels
- Rate 1/3 for dedicated channels
• Turbo codes- Code rate 1/3
- Mainly for high-data-rate applications
![Page 159: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/159.jpg)
Channelization and scrambling
data spread spectrum signal
channelization scramblingcode
![Page 160: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/160.jpg)
Orthogonal Variable Spreading Factor
The OVSF codes used for variable rate spreading can be viewedas a code tree.
Copyright: 3GPP
We can create several orthogonal channels by picking spreading codesfrom different branches of the tree.
![Page 161: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/161.jpg)
Downlink
![Page 162: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/162.jpg)
Structure of downlink packet
Copyright: 3GPP
![Page 163: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/163.jpg)
Uplink
![Page 164: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/164.jpg)
Structure of uplink packet
Copyright: 3GPP
![Page 165: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/165.jpg)
Data rate and spreading factor
Data rate
TimeSpreading factor
Time
Transmit power
Time
Independent ofdata rate, we
spread to the full
bandwidth.
Transmit powerand generatedinterference to
others varyaccordingly.
![Page 166: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/166.jpg)
Data rate and interference
In simple words, with a limited interference allowed, we can havemany low data-rate channels or a few high data-rate channels.
Interference
MS 3
MS 2
MS 1
Time
![Page 167: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/167.jpg)
Soft handover
Since all base stations used the same frequency band, a terminalclose to the cell boundary can receive “the same” signal from more thanone base station and increase the quality of the received signal.
BS 1 BS 2
![Page 168: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/168.jpg)
Chapter 24
Wireless LANsIEEE 802.11
![Page 169: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/169.jpg)
History
• Wireless LANs became of interest in late 1990s- For laptops
- For desktops when costs for laying cables should be saved
• Two competing standards- IEEE 802.11 and HIPERLAN
- IEEE standard now dominates the marketplace
• The IEEE 802.11 family of standards- Original standard: 1 Mbit/s
- 802.11b (WiFi, widespread after 2001): 11 Mbit/s
– 802.11a (widespread after 2004): 54 Mbit/s
– 802.11e: new MAC with quality of service
– 802.11n: > 100 Mbit/s
![Page 170: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/170.jpg)
802.11a PHY layer
• Transceiver block diagram
Copyright: IEEE
![Page 171: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/171.jpg)
802.11a PHY layer
• The following data rates are supported:
Data rate (Mbit/s) Modulation coding rate coded bits per subcarrier coded bits per OFDM symbol data bits per OFDM symbol
6 BPSK 1/2 1 48 24
9 BPSK 3/4 1 48 36
12 QPSK 1/2 2 96 48
18 QPSK 3/4 2 96 72
24 16-QAM 1/2 4 192 96
36 16-QAM 3/4 4 192 144
48 64-QAM 2/3 6 288 192
54 64-QAM 3/4 6 288 216
![Page 172: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/172.jpg)
11a header and preamble
• Header conveys information about data rate, length of thedata packet, and initialization of the scrambler
Copyright: IEEE
![Page 173: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/173.jpg)
11a header and preamble
• PLCP preamble: for synchronization and channelestimation
Copyright: IEEE
![Page 174: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/174.jpg)
802.11b air interface
• Key air interface parameters- Frequency range: 5.40-2.48 GHz
- Carrier spacing: 20-25 MHz
- Data rates: 1, 2, 5.5, 11 Mbps
• Modulation and multiple access:- for low data rates, as well as for header and preamble (1 Mbit/s):
• Direct-sequence spreading with Barker sequence
• Differential phase shift keying modulation
- For high data rates: complementary code keying (CCK)
- Multiple access by FDMA and packet radio access
• Channel coding:- Convolutional coding with rate ½ is option
![Page 175: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/175.jpg)
Transceiver structure for 802.11b
Copyright: IEEE
![Page 176: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/176.jpg)
MAC and multiple access
• Frame structure:- Contains payload data, address, and frame control into
• Multiple access: both contention-free and contention-basedaccess
Copyright: IEEE
![Page 177: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/177.jpg)
Contention-based access
• CSMA (carrier-sense multiple access):
Copyright: IEEE
![Page 178: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/178.jpg)
Contention-free access
• Polling:
Copyright: IEEE
![Page 179: UNIT V ADVANCED TRANSCEIVER SCHEMES Ref.: Wireless Communication, Molisch](https://reader033.vdocuments.us/reader033/viewer/2022061522/56649e9f5503460f94ba1121/html5/thumbnails/179.jpg)
Further improvements
• 802.11e: improvements in the MAC; provides quality ofservice
- CSMA/CA-based Enhanced Distributed Channel Access (EDCA)manages medium access during CP.
- Polling-based HCF (Hybrid Coordination Function) ControlledChannel Access (HCCA) handles medium access during CFP.
- BlockACK and delayed blockACK reduce overhead
- Contention Free Burst (CFB) and Direct Link Protocol (DLP)improve channel efficiency.
• 802.11n: higher throughput by using multiple antennaelements