Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

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10 Introductionprocessing gain P G is multi-carrier modulated in the way that the chips of a spreaddata symbol are transmitted in parallel and the assigned data symbol is simultaneouslytransmitted on each sub-carrier (see Figure 4). As for DS-CDMA, a user may occupythe total bandwidth for the transmission of a single data symbol. Separation of the usersignals is performed in the code domain. Each data symbol is copied on the sub-streamsbefore multiplying it with a chip of the spreading code assigned to the specific user. Thisshows that an MC-CDMA system performs the spreading in the frequency direction and,thus, has an additional degree of freedom compared to a DS-CDMA system. Mappingof the chips in the frequency direction allows for simple methods of signal detection.This concept was proposed with OFDM for optimum use of the available bandwidth.The realization of this concept implies a guard time between adjacent OFDM symbolsto prevent ISI or to assume that the symbol duration is significantly larger than the timedispersion of the channel. The number of sub-carriers N c has to be chosen sufficientlylarge to guarantee frequency nonselective fading on each sub-channel. The applicationof orthogonal codes, such as Walsh–Hadamard codes for a synchronous system, e.g. thedownlink of a cellular system, guarantees the absence of multiple access interference inan ideal channel and a minimum multiple access interference in a fading channel. For signaldetection, single-user detection techniques such as maximum ratio combining (MRC),equal gain combining (EGC), zero forcing (ZF), or minimum mean square error (MMSE)equalization, as well as multi-user detection techniques like interference cancellation (IC)or maximum likelihood detection (MLD), can be applied.As depicted in Figure 4, MC-DS-CDMA modulates sub-streams on sub-carriers with acarrier spacing proportional to the inverse of the chip rate. This will guarantee orthogonalitybetween the spectra of the sub-streams [44]. If the spreading code length is smalleror equal to the number of sub-carriers N c , a single data symbol is not spread in the frequencydirection, instead it is spread in the time direction. Spread spectrum is obtained bymodulating N c time spread data symbols on parallel sub-carriers. By using high numbersof sub-carriers, this concept benefits from time diversity. However, due to the frequencynonselective fading per sub-channel, frequency diversity can only be exploited if channelcoding with interleaving or sub-carrier hopping is employed, or if the same informationis transmitted on several sub-carriers in parallel. Furthermore, higher frequency diversitycould be achieved if the sub-carrier spacing is chosen larger than the chip rate. Thisconcept was investigated for an asynchronous uplink scenario. For data detection, N ccoherent receivers can be used.It can be noted that both schemes have a generic architecture. In the case where thenumber of sub-carriers N c = 1, the classical DS-CDMA transmission scheme is obtained,whereas without spreading (P G = 1) it results in a pure OFDM system.By using a variable spreading factor in frequency and/or time and a variable sub-carrierallocation, the system can easily be adapted to different environments such as multi-celland single-cell topologies, each with different coverage areas.Today, in parallel with multi-carrier transmission, the field of multi-carrier spread spectrumcommunications is considered to be an independent and important research topic(see References [21] to [25], [28], and [38]). Several deep system analysis and comparisonsof MC-CDMA and MC-DS-CDMA with DS-CDMA have been performed thatshow the superiority of MC-SS [26, 31, 34–36]. In addition, new application fields havebeen proposed such as high rate cellular mobile (4G), high rate wireless indoor, and fixed
Introduction 11and broadband wireless access (F/BWA). In addition to system-level analysis, a multitudeof research activities have been addressed to develop appropriate strategies for detection,interference cancellation, channel coding, modulation, synchronization (especially uplink),and low cost implementation design.The Aim of This BookThe interest in multi-carrier transmission and in multi-carrier spread spectrum is stillgrowing. Many researchers and system designers are involved in system aspects and theimplementation of these new techniques. However, a comprehensive collection of theirwork is still missing.The aim of this book is first to describe and analyze the basic concepts of multi-carriertransmission and its combination with spread spectrum, where the different architecturesand the different detection strategies are detailed. Concrete examples of its applicationsfor future cellular mobile communications systems are given. Then, we examine otherderivatives of MC-SS (e.g. OFDMA, SS-MC-MA, and DFT-spread OFDM/interleavedFDMA) and other variants of the combination of OFDM with TDMA, which are todaypart of LTE, WiMAX, WLAN, and DVB-RCT systems. Basic OFDM implementationissues, valid for most of these combinations, such as channel coding, modulation, digitalI/Q generation, synchronization, channel estimation, and effects of phase noise andnonlinearity are further analyzed.Chapter 1 covers the fundamentals of today’s wireless communications. First a detailedanalysis of the radio channel (outdoor and indoor) and its modeling are presented. Thenthe principle of OFDM multi-carrier transmission is introduced. In addition, a generaloverview of the spread spectrum technique, especially of DS-CDMA, is given. Examplesof applications of OFDM and DS-CDMA for broadcast, WLAN, and cellular systems(IS-95, CDMA-2000, WCDMA/UMTS, HSPA) are briefly presented.Chapter 2 describes the combinations of multi-carrier transmission with the spread spectrumtechnique, namely MC-CDMA and MC-DS-CDMA. It includes a detailed descriptionof the different detection strategies (single-user and multi-user) and presents their performancein terms of the bit error rate (BER), spectral efficiency, and complexity. Here acellular system with a point to multi-point topology is considered. Both downlink anduplink architectures are examined.Hybrid multiple access schemes based on OFDM, MC-SS, or spread spectrum areanalyzed in Chapter 3. This chapter covers OFDMA, being a derivative of MC-CDMA,OFDM-TDMA, SS-MC-MA, DFT-spread OFDM/interleaved FDMA, and ultra wideband(UWB) schemes. All these multiple access schemes have recently received wide interest.Their concrete application fields are detailed in Chapter 5.The issues of digital implementation of multi-carrier transmission systems, essentialespecially for system and hardware designers, are addressed in Chapter 4. Here, thedifferent functions such as digital I/Q generation, analogue/digital conversion, digitalmulti-carrier modulation/demodulation, synchronization (time, frequency), channel estimation,coding/decoding, and other related RF issues such as nonlinearities, phase noise,and narrowband interference rejection are analyzed.In Chapter 5, concrete application fields of OFDMA, OFDM-TDMA, and MC-SS forB3G cellular mobile (LTE and WiMAX), 4G (IMT-Advanced), wireless indoor (WLAN),
Page 2: Multi-Carrier andSpread SpectrumSys
Page 6 and 7: This edition first published 2008©
Page 11 and 12: Contentsix4.3.2 One-Dimensional Cha
Page 13: ForewordThis book discusses multi-c
Page 17 and 18: Preface (First Edition)Nowadays, mu
Page 19: AcknowledgementsThe authors would l
Page 22 and 23: 2 Introductionambitious technologic
Page 24 and 25: 4 IntroductionTables 1 and 2 summar
Page 26 and 27: 6 IntroductionPower densityTimeFreq
Page 28 and 29: 8 Introductiona high immunity again
Page 32 and 33: 12 Introductionand interactive mult
Page 34 and 35: 14 Introduction[43] Saltzberg, B. R
Page 36 and 37: 16 FundamentalsBSTSFigure 1-1Time-v
Page 38 and 39: 18 Fundamentalswhere p =|a p | 2 (1
Page 40 and 41: 20 Fundamentalssuch that the effect
Page 42 and 43: 22 FundamentalsTable 1-2 Delay powe
Page 44 and 45: 24 Fundamentals(i) Fixed Positioned
Page 46 and 47: 26 Fundamentalson sub-channel n of
Page 48 and 49: 28 Fundamentals10 010 −1OFDM (OFD
Page 50 and 51: 30 Fundamentalsin order to achieve
Page 52 and 53: 32 FundamentalsThe discrete length
Page 54 and 55: 34 FundamentalsThe following matrix
Page 56 and 57: 36 FundamentalsTable 1-11Wireless l
Page 58 and 59: 38 FundamentalsFrequency hopping (F
Page 60 and 61: 40 FundamentalsFinally, a threshold
Page 62 and 63: 42 Fundamentals1.3.3 Applications o
Page 64 and 65: 44 FundamentalsTable 1-12Radio link
Page 66 and 67: 46 FundamentalsOrthogonalV-SF codeF
Page 68 and 69: {{48 Fundamentalsdata symbolsspread
Page 70 and 71: 50 FundamentalsCellular Mobile Radi
Page 72 and 73: 52 Fundamentals[27] Haindl B., “M
Page 75 and 76: 2MC-CDMA and MC-DS-CDMAIn this chap
Page 77 and 78: MC-CDMA 57whered = (d (0) ,d (1) ,.
Page 79 and 80: MC-CDMA 59i.e. the spreading is per
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MC-CDMA 61Table 2-1 PAPR bounds of
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MC-CDMA 632.1.4.4 Rotated Constella
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MC-CDMA 65After inverse OFDM the re
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MC-CDMA 67and requires only informa
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MC-CDMA 69hard interference evaluat
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MC-CDMA 71Thedataofthedesireduserk
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MC-CDMA 73L corresponds to the spre
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MC-CDMA 752.1.7 Combined Equalizati
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MC-CDMA 77broadcasting, WLAN, and W
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MC-CDMA 792.1.8.1 Log-Likelihood Ra
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MC-CDMA 81For coded MC-CDMA systems
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MC-CDMA 83where Q different user gr
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MC-CDMA 85Table 2-2MC-CDMA system p
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MC-CDMA 87first iteration. The opti
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MC-CDMA 8910 010 −110 −2BER10
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MC-CDMA 9110 010 −1BER10 −210
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MC-CDMA 9310 010 −110 −2BER10
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MC-DS-CDMA 95c (k) (t)f 00d (k)S/P+
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MC-DS-CDMA 97The user-specific dela
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MC-DS-CDMA 9910 010 −1BER10 −21
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References 101[7] Brüninghaus K. a
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References 103[49] Steiner B., “U
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106 Hybrid Multiple Access SchemesI
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108 Hybrid Multiple Access Schemesw
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110 Hybrid Multiple Access Schemest
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112 Hybrid Multiple Access SchemesO
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114 Hybrid Multiple Access SchemesT
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116 Hybrid Multiple Access SchemesA
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120 Hybrid Multiple Access Schemest
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122 Hybrid Multiple Access SchemesA
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126 Hybrid Multiple Access Schemes[
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4Implementation IssuesA general PHY
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Multi-Carrier Modulation and Demodu
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Synchronization 139The performance
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Synchronization 141null symbol as a
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Synchronization 143resulting SNR ca
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Synchronization 145SNR Degradation
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Synchronization 147FFTr(k)estimated
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Synchronization 149the timing error
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Synchronization 151A first simple s
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Synchronization 153Transmitted 2 re
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Channel Estimation 155Special cases
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Channel Estimation 157The mean squa
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Channel Estimation 159by the second
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Channel Estimation 161Given the nor
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Channel Estimation 163and f D, filt
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Channel Estimation 16510 010 −110
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Channel Estimation 16710 010 −13
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Channel Estimation 169in order to r
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Channel Estimation 17110 010 −1BU
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Channel Estimation 173timefreq. 00
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Channel Coding and Decoding 1754.4.
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Channel Coding and Decoding 177Tabl
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Channel Coding and Decoding 179a (k
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Channel Coding and Decoding 181n rk
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Channel Coding and Decoding 183Bit
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Channel Coding and Decoding 185Bit
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Signal Constellation, Mapping, De-M
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Signal Constellation, Mapping, De-M
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Adaptive Techniques in Multi-Carrie
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RF Issues 193hence reduce, for inst
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RF Issues 195s(t)r(t)e jf(t)White n
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RF Issues 197receivedsignalto detec
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RF Issues 1994.7.2.1 Effects of Non
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RF Issues 2011e−011e−02UplinkDo
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RF Issues 203of data pre-distortion
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RF Issues 205Table 4-8Minimum total
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RF Issues 207Detection strategyIn t
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RF Issues 209above formula becomes(
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References 211[21] Fazel K., “Nar
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References 213[66] Nobilet S., Hela
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5Applications5.1 IntroductionThe de
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Introduction 217high speed as well
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3GPP Long Term Evolution (LTE) 219H
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3GPP Long Term Evolution (LTE) 221U
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3GPP Long Term Evolution (LTE) 2231
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3GPP Long Term Evolution (LTE) 227T
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3GPP Long Term Evolution (LTE) 229C
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WiMAX 237Table 5-12 Downlink LTE sp
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WiMAX 239Wi-FiBusinessTSWiMAX BSTSM
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WiMAX 241Table 5-16Summary of the I
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WiMAX 243WiMAXInteroperabilityInter
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WiMAX 245UNIAirinterfaceSNITerminal
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WiMAX 247Radio ResourceControlIniti
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WiMAX 249Frame n−1 Frame n Frame
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WiMAX 251Read RF-Channel ListScan F
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WiMAX 253NormaloperationTS measures
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WiMAX 255Table 5-18Example of some
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WiMAX 257Total bandwidth (between 1
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WiMAX 259Sub-carriers (frequency)n0
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ApplicationsWiMAX 261Table 5-23 Gen
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WiMAX 263Table 5-27(OFDMA)FEC codin
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WiMAX 265M-QAMMappingSTC withSpatia
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WiMAX 267Frame n−1 Frame n Frame
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WiMAX 269Table 5-29WirelessMAN-OFDM
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WiMAX 2710Power density in dB−25
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WiMAX 273Table 5-37diversityPeak da
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WiMAX 275Table 5-41DL link budget e
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Future Mobile Communications Concep
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Wireless Local Area Networks 283MTB
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Wireless Local Area Networks 285fre
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Interaction Channel for DVB-T: DVB-
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References 297Table 5-58Parameters
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References 299[32] Taoka H., Higuch
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302 Additional Techniques for Capac
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340 Definitions, Abbreviations, and
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350 SymbolsG l,lGG [j]h(t)h(τ,t)H(
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Index3GPP 218Adaptive techniques 19
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Index 355Forward error correction (
Page 377 and 378:
Index 357Multi-carrier modulation a
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Index 359Maximum likelihood paramet
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