1H0.1SSI.
`Infoml-at:ion_ Technology: Tmnsni
`
`Pr
`
`‘essmg, and Storage
`
`VT/aeory and
`Applications of
`
`Ahmad R. S
`
`. Bahai
`
`and
`
`Burton R. Saltzberg
`
`SPRINT 1020
`
`SPRINT 1020
`
`

`
`Mu1ti—Carrier
`
`Digital Communications
`
`Theory and Applications of OFDM
`
`

`
`lnformation Technology: Transmission, Processing, and Storage
`
`Series Editor".
`
`Jack Keil Wolf
`
`Uiziversir_i' of California at San Diego
`La Jolla, California
`
`Editorial Board:
`
`James E. Mazo
`
`Bell Laboratories, Lucent Technologies
`Murray Hill, New Jersey
`
`John Proakis
`
`Northeastern Unz‘versit_i-’
`Boston, Massachusetts
`
`William H. Tranter
`
`Virginia Po/_).=teC/mic Institute and State Um'versit_v
`Blacksburg, Virginia
`
`Mulli—Camer Digital Communications: Theory and Applications of OFDM
`Ahmad R. S. Bahai and Burton R. Saltzberg
`
`Piinciples of Digital Transmission: With Wireless Applications
`Sergio Benedetto and Ezio Biglieri
`
`Simulation of Communication Systems, 2nd Edition: Methodology, Modeling,
`and Techniques
`Michel C. Jeruchim, Philip Balaban, and K. Sam Shanmugan
`
`A Continuation Order Plan is available for this series. A continuation order will bring delivery of each new volume
`immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact
`the publisher.
`
`iii
`
`

`
`Multi—Carrier
`
`Digital Communications
`
`Theory and Applications of OFDM
`
`Ahmad R. S. Bahai and
`
`Burton R. Saltzberg
`Algarex, Inc.
`Iseiin, New Jersey
`
`Kluwer Academic Publishers
`
`New York, Boston, Dordrecht, London, Moscow
`
`iv
`
`

`
`eBook ISBN:
`Print ISBN:
`
`O-306—45974—X
`0-306-46296-6
`
`©2002 Kiuwer Academic Publishers
`New York, Boston, Dordrecht, London, Moscow
`
`Print ©1999 Kiuwer Academic/ Plenum Publishers
`New York
`
`All rights reserved
`
`No part of this eBook may be reproduced or transmitted in any form or by any means, electronic,
`mechanicai, recording, or otherwise, without written consent from the Publisher
`
`Created in the United States of America
`
`Visit Kiuwer Oniine at:
`and K|uwer’s eBooi<store at:
`
`http://kiuweroniine_com
`http://ebooks.k|uweronlinecom
`
`

`
`This page intentionally left blank
`
`Vi
`
`

`
`Contents
`
`CHAPTER 1 INTRODUCTION TO DIGITAL COMMUNICATIONS ............................2
`
`1.1
`1.2
`
`.....................................................2
`BACKGROUND ..........................................................
`EVOLUTIOIN‘ OF OFDM ..............................................................................................................7
`
`CHAPTER 2 SYSTEM ARCHITECTURE ................................................................................17
`
`MULTI-CARRIER SYSTEM FUNDAMENTALS .........................................................................17
`
`
`
`2.1
`2.2
`
`PARTIAL FFT.............................................................................................................. 25
`2.3
`CYCLIC EXTENSION ...........
`.......................................................................................27
`2.4
`CHANNEL ESTIMATION ......................
`...........................29
`2.5
`APPENDIX —— MATHEMATICAL MODELLING OF OFDM FOR TIME-VARm’G
`2.6
`RANDOM CI-IAZ\";\’EL ...............................................................................
`.....
`
`.......
`
`...........32
`
`CHAPTER 3 PERFORMANCE OVER TIME-INVARIANT CHANNELS .................41
`
`3.1
`3.2
`3.3
`3.4
`
`TIME-I.\'VARIA;\'T NON-FLAT CHANNEL WITH COLORED NOISE ........................................4I
`ERROR PROBABILITY ........................................................................................................42
`BIT ALLOCATION ...................................................................
`
`BIT AND POWER ALLOCATION ALGORITHMS FOR FIXED BIT RATE .....................................53
`
`CHAPTER 4 CLIPPING IN MULTI-CARRIER SYSTEMS ........................................ ..57
`
`INTRODUCTION .............................................................................................................. 57
`4.1
`POWER AIIPLIEIER NON-LINEARITY
`....
`................................................................. 59
`4.2
`BER ANALYSIS ............................................................................................................63
`4.3
` 4.4 BANDWIDTH REGROWIH
`
`
`ix
`
`

`
`x
`
`Contents
`
`CHAPTER 5 SYNC HRONIZATION ...............
`
`...........
`
`..................83
`
`TIMING AND FREQUENCY OFFSET IN OFDM.....
`SYNCHRONIZATION AND SYSTEM ARCHITECTURE
`TIMING AND FRAJIIE S\".\‘CHRO:\'IZATIO:\'
`
`....... 83
`......88
`..
`
`
`.....
`...........
`
`.........
`.......
`
`5.1
`5.2
`5.3
`
`5.4
`5.5
`
`FREQUENCY OFFSET ESTIMATION
`PHASE NOISE
`
`93
`
`CHAPTER 6 E UALIZATION
`
`......................................103
`
`6.1
`
`6.2
`63
`6.4
`6.5
`6.6
`
`INTRODUCTION....................
`
`.........103
`
`TIME DOMAIN EQUALIZATION
`EQL*ALIz.AIIo.\' l:\' DMT ..........
`FREQUENCY D0.\IAI.\' EQUALIZATION....
`tlouuolonooIonvouoluuuoon
`
`ECHO CANCELLATION
`
`APPE:\’DIX——JOI;=‘\'T IZ\':‘{0\'ATl0;\' REPRESENTATION OF ARMAMODELS
`
`..........116
`
`..........
`
`CHAPTER 7 CHANNEL CODING
`
`..135
`
`7.1
`7.2
`7.3
`7.4
`7.5
`7.6
`
`NEED FOR CODING ....
`BLOCK CODING I.\' OFDM
`CONV'0LL’TIO:VAL ENCODING
`CONCATENATED CODING
`TRELLIS CODING IN OFDM .. ..................................................
`TLRRO CODING IN OFDM
`
`
`
`CHAPTER 8 ADSL.................
`
`........
`
`............................159
`
`8.1
`8.2
`8.3
`
`WIRED ACCESS TO HIGH RATE DIGITAL SERVICES......................159
`PROPERTIES OF THE WIRE-PAIR CHANNEL
`...................160
`ADSL SYSTEMS .......
`
`CHAPTER 9 WIRELESS LAN ..........
`
`................................................
`
`9.1
`
`9.2
`9.3
`9.4
`
`INTRODUCTION
`
`PHYSICAL LAYER TECHNIQUES FOR WIRELESS LAN
`OFDM FOR WIRELESS LAN
`
`RECEIVER STRUCTURE ......
`
`181
`182
`
`

`
`Comems
`
`xi
`
`
`CHAPTERIODKHTALBROADCASHNG.....................................“B1
`
`10.1
`10.2
`10.3
`10.4
`
`BROADCASTING OF DIGITAL AI;DIO SIGNALS .................................................................191
`SIGNAL FORMAT ......................................................................................................194
`OTHER DIGITAL BROADCASTING SYsTI:.\I
`
`DIGITAL VIDI:0 BROADCASTING ..................................................................................198
`
`CHAPTER 11 FUTURE TRENDS...................................................................................203
`
`COMPARIS():\’ WITH SINGLE CARRIER i\'IODL7LATI0.\' ...........................................................203
`MITIGATION or CLIPPING EFFECTS ..........................
`....205
`OVERLAPPED TRANSFORMS .............................................................................. ..206
`COMBHEDCDDLAANDOFDR4"
`ADVANCES IN I_V1PLE.VIENTATION ..............................................................................213
`
`
`
`11.1
`11.2
`113
`11A
`11.5
`
`INDEX...
`
`...............................................................................................................................217
`
`

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`xii
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`Mu1ti—Carrier
`
`Digital Communications
`
`Theory and Applications of OFDM
`
`xiii
`
`

`
`System Arc/4iz‘ecture
`
`29
`
`symbol experience considerable distortion, and with longer delay spread,
`
`more samples will be affected. Using cyclic extension,
`
`the convolution
`
`changes to a circular operation. Circular convolution of two signals of length
`
`N is a sequence of length N so the inter-block interference issue is
`resolved.
`
`Proper windowing of OFDM blocks, as shown later,
`
`is important to
`
`mitigate the effect of frequency offset and to control
`
`transmitted signal
`
`spectrum.
`
`However, windowing should be
`
`implemented after cyclic
`
`extension of the frame,
`
`so that
`
`the windowed frame is not cyclically
`
`extended. A solution to this problem is to extend each frame to 2N points at
`
`the receiver and implement a 2N FFT. Practically,
`
`it requires a 2N IFFT
`
`block at the transmitter, and 2N FFT at the receiver. However, by using
`
`partial FFT techniques, we can reduce the computation by calculating only
`
`the required frequency bins.
`
`Ifwindowing was not required, we could have simply used zero padded
`
`pre/postfix, and before the DFT at the receiver copy the beginning and end
`
`of frame as prefix and postfix.
`
`This creates the same effect of cyclic
`
`extension with the advantage of reducing transmit power and causing less
`ISI.
`
`The relative length of cyclic extension depends on the ratio of the
`
`channel delay spread to the OFDM symbol duration.
`
`2.5 Channel Estimation
`
`Channel estimation inverts the effect of non—selective fading on each sub-
`
`carrier. Usually, OFDM systems provide pilot signals for channel estimation.
`
`in the case of time—varying channels the pilot signal should be repeated
`
`frequently. The spacing between pilot signals in time and frequency depends
`
`

`
`3 0
`
`System Architecture
`
`on coherence time and bandwidth of the channel. We can reduce the pilot
`
`signal overhead by using a pilot signal with a maximum distance of less than
`
`the time and coherence bandwidths. Then, by using time and frequency
`
`the impulse response and frequency response of the channel
`interpolation,
`can be calculated.
`
` i
`
`3 4...........................2‘,........___.)._V__% ...........My
`Coiieteet Time
`
`Q
`
`Figure 2.7. Pilot positioning in time and frequency.
`
`Let
`
`h,=(h,,h2,---,hM)T
`
`2.21
`
`represent the overall impulse response of the channel, including transmitter
`
`and receiver filters, with length M [6]. The N —element training sequence is
`
`represented by
`
`X=[X,j], 1SisM+N—1, 1sj.<_M
`
`X ={x,_j.+,,
`
`0,
`
`lsi-—j+1sN.
`
`elsewhere
`
`The noise samples are
`
`n=(n,,rz2,-~-,nM+N_,)T,
`
`2.22
`
`2.23
`
`

`
`Svstem Architecture
`
`with
`
`3‘
`
`*
`
`Rn = E{nn }= LL ,
`
`31
`
`2.24
`
`in which L is a lower triangular matrix, which can be calculated by the
`
`Cholesky method. The received signal is then
`
`r = X/zt +rz.
`
`2.25
`
`After correlation or matched filtering,
`
`the estimate of the impulse
`
`2.25
`
`A h
`
`, = X*r=X*Xh, +X*n.
`
`response is:
`
`If the additive noise is white, the matched filter is the best estimator in
`
`tenns of maximizing signal—to—noise ratio. However, the receiver filter colors
`
`the noise. With a whitening filter the estimate is given in [5]. An unbiased
`
`estimator, which removes the effect of sidelobes, is [5]
`
`lit =(X*R,j‘x)“ X*R,_"r=h+(X*R;‘X)“‘ x*R;'n.
`
`2.27
`
`In the dual system architecture, circular convolution is replaced by
`
`multiplication. The repetition of the training sequence results in circular
`
`convolution. Therefore, Equation 2.26 is replaced by:
`
`I}'”=X"iX‘°‘H“’+X“’*N“,
`
`2.28
`
`where superscript 0.) shows Fourier Transform and all products are scalar.
`
`The same procedure can be applied to Equation 2.27. This procedure is also
`
`called frequency equalization.