Multicarrier techniques for 4G mobile communications

e information bits so as to make the SNR per bit as equal as possible over different subcarriers (bit loading). In 2002, an MC-CDM system based on the Shannon’s Water Filling Theorem was proposed for a downlink. It is called ‘‘MC-CDM system with frequency scheduling’’ [13, 14]. Note that, unlike the case of a point-to-point data transmission, a multiplexing system needs to take into consideration the inter- and intracell interference power, as well as the noise power, because it suffers from multiple access interference and intercell interference. Figure 10.8 shows the concept of an MC-CDM system with frequency scheduling. First, a base station transmits a common pilot signal to all users [see Figure 10.8(a)], and each mobile user estimates its received signal to noise plus interference power ratio (SNIR) in block by block [see Figure 10.8(b)]. Then, each user notifies the signal qualities (SNIRs) to the base station in a piggyback manner [see Figure 10.8(c)]. Finally, based on the 210 Multicarrier Techniques for 4G Mobile Communications Figure 10.8 Concept of an MC-CDM system with frequency scheduling: (a) pilot signal transmission; (b) block-by-block SNIR estimation; (c) SNIR (block quality) notification; (d) data signal transmission; and (e) data signal reception. 211Future Research Directions SNIR table obtained from all the users, the base station determines which blocks should be used for an individual user [see Figure 10.8(d)]. The data transmission is made only in blocks with higher SNIRs for each user, so the frequency scheduling scheme can much improve the BER performance and enhance the system performance [see Figure 10.8(e)]. 10.4 OFDM Adaptive Array Antennas 10.4.1 Principle of Adaptive Array Antenna An adaptive array antenna is an antenna that controls its own pattern, by means of feed-back or feed-forward control [15, 16]. Here, we consider only receiving array antennas. Figure 10.9 shows the basic configuration of an adaptive array antenna and its antenna beam pattern. An adaptive array antenna changes its antenna pattern through optimization of the SNIR, by changing the values of array weights [see Figure 10.9(a)]. It does not need to know the arrival direction of interference or desired signal in advance, because an antenna pattern can automatically reject the interference direction by null and track the desired signal direction [see Figure 10.9(b)]. So far, adaptive array antennas have been discussed for the suppression of cochannel interferers, delayed signals beyond the guard interval, and Doppler shifted signals in an OFDM scheme [17–26]. As shown in Sections 10.4.2 and 10.4.3, there are four different types of adaptive array antennas considered applicable for the OFDM scheme. 10.4.2 Post-FFT and Pre-FFT Type OFDM Adaptive Array Antennas Figure 10.10 shows two types of adaptive array antennas applicable for the OFDM scheme. Figure 10.10(a) shows a post-FFT type OFDM adaptive array antenna [17], where there is one OFDM demodulator, including the FFT at each antenna element. Using this configuration, the weighted outputs are combined at each subcarrier, so it requires high computational complexity, although the attainable performance would be better. On the other hand, Figure 10.10(b) shows a pre-FFT type OFDM adaptive array antenna [18–26], where there is only one OFDM demodulator. Using this configuration, the weighted array outputs are combined just before the OFDM demodulator, so it can reduce computational complexity, although the attainable performance would be inferior to that of the post- FFT type adaptive array antenna. 212 Multicarrier Techniques for 4G Mobile Communications Figure 10.9 Principle of an adaptive array antenna: (a) basic configuration; and (b) antenna beam pattern. TE AM FL Y Team-Fly® 213Future Research Directions Figure 10.10 Two types of adaptive array antennas: (a) a post-FFT type; and (b) a pre-FFT type. 10.4.3 Weight-Per-User and Weight-Per-Path Type OFDM Adaptive Array Antennas Figure 10.11 shows two types of adaptive array antennas, which are workable in multipath environments. Figure 10.11(a) shows a weight-per-user type 214 Multicarrier Techniques for 4G Mobile Communications Received Signals from One User Path#1 Path#2 Path#3 (a) Weight per User-Type Adaptive Antenna Array (b) Weight per Path-Type Adaptive Antenna Array w (i)*1 w (i) * 2 w (i) * N Σ Path#1 Path#2 Path#3 w (i)1*1 w (i)1*2 w (i)1* N Σ w (i)2*1 w (i)2*2 w (i)2* N Σ w (i)3*1 w (i)3*2 w (i)3* N Σ Path#1 Path#2 Path#3 Path#1 Path#2 Path#3 Σ T im e D elay C o m p en satio n T im e D elay C o m p en satio n Figure 10.11 Two types of adaptive array antennas: (a) a weight-per-user type; and (b) a weight-per-path type. adaptive array antenna [17–26], which controls its own antenna beam pattern for incoming signals from a desired user with a set of array weights. On the other hand, Figure 10.11(b) shows a weight-per-path type adaptive array antenna, which controls its own antenna beam pattern for 215Future Research Directions each incoming signal through a different path from the same desired user with a set of array weights. It is very clear that the weight-per-user type array antenna is much simpler than the weight per path-type array antenna. Note that the weight-per-path type array antennas are applicable for not only multicarrier transmission but also singlecarrier transmission, whereas the weight-per-user type arrays are applicable only for multicarrier transmission, including OFDM and SS-based transmission. This is because the OFDM and SS signals are inherently robust to multipath fading. 10.5 MIMO-OFDM When a transmitter and a receiver, with an appropriate channel coding/ decoding scheme, are equipped with multiple antennas, the presence of multipath fading can improve achievable transmission rates [27]. For such MIMO channels, several optimum space-time codes have been designed, assuming that the transmitter does not know the structure of the channel [28, 29]. Figure 10.12 shows a MIMO system, where the transmitter has M -element antennas and the receiver has N -element antennas. For the MIMO channel, we can define the channel matrix (M · N ) as H = {hij } (10.1) where hij means the path gain between the i th transmit antenna element and the j th receive antenna element. In general, the MIMO system requires a flat fading characteristic at each subchannel, in other words, hij should be Figure 10.12 A MIMO system. 216 Multicarrier Techniques for 4G Mobile Communications a complex value. Therefore, if the transmission rate is high enough to make the whole channel frequency selective, it requires an OFDM signaling to have a flat fading over each subchannel. In this sense, the OFDM scheme is suited for the MIMO system [30]. Field trial results on a 4G MIMO- OFDM system have been reported [31]. As shown, the design of space-time codes assumes no knowledge on the structure of the transmission channel at the transmit side. If the transmit- ter knows the channel structure, a joint transmitter/receiver optimization is furthermore possible for the multiple transmit/receive antennas scenario [32, 33]. The OFDM scheme can play an important role in such a situation. 10.6 Linear Amplification of OFDM Signal with Nonlinear Components As shown in Section 4.9, OFDM signals are much more sensitive to non- linear amplification than singlecarrier-modulated signals. Therefore, when amplifying the OFDM signals with a nonlinear power amplifier, a larger input back-off is required to reduce the spectrum spreading, and it results in a low-power efficiency. Nonlinear amplification has been considered to be unavoidable. Indeed, many techniques to reduce the spectrum spreading have been proposed for OFDM systems, such as deliberately clipping [34] and so on. However, almost all the techniques require complicated signal processing or show some performance degradation, so there has been no ‘‘killer’’ technique to make the OFDM signals robust against nonlinear amplification. In 2002, a semiconductor company was successful in a linear amplifica- tion of OFDM signals with nonlinear amplifiers [35], which was based on the linear amplification with nonlinear components (LINC) method. The LINC is an old technique [36], which dates back to 1935 [37], and is based on a fact that any bandpass signal can be represented by two constant-envelope phase-modulated signals. Figure 10.13 shows the principle of the LINC method. Define an input signal as Vin (t ) = a (t ) e jU(t ) (10.2) where a (t ) is an envelope and U(t ) is a phase. The input signal Vin (t ) can be represented by the following two signals, S1 (t ) and S2 (t ), with a constant envelope of Vm X ‡ |a (t ) | C: 217Future Research Directions Figure 10.13 Principle of the LINC method. Vin (t ) = S1 (t ) + S2 (t ) (10.3) S1 (t ) = Vm e j {u (t )+f (t )} (10.4) S2 (t ) = Vm e j {u (t ) - f (t )} (10.5) Substituting (10.4) and (10.5) into (10.3) leads to f (t ) = cos- 1Ha (t )2VmJ (10.6) Figure 10.14 shows a LINC signal separation. Even if an input signal has an arbitrary envelope and an arbitrary phase, there always exist two signals with the same constant envelope, the sum of which is equal to the input signal. S1 (t ) and S2 (t ) have the constant envelope, so they can be amplified with highly power-efficient and highly nonlinear power amplifiers. Defining the gain and phase of the two nonlinear amplifiers as G and w , the output signal is given by Vout (t ) = Ge jw {S1 (t ) e j2p fc t + S2 (t ) e j2p fc t } (10.7) = GVin (t ) e j (2p fc t + w ) 218 Multicarrier Techniques for 4G Mobile Communications Figure 10.14 A LINC signal separation. The LINC method can work quite well if the characteristics (AM/ AM, AM/PM, PM/AM and PM/PM conversion characteristics) of the two nonlinear amplifiers are all the same. However, it is practically impossible. If there is a mismatch between them, the LINC method not only cannot reduce the spectrum spreading but also generates some inband distortion in the amplified OFDM signals. Figure 10.15 shows a combination of a predistortion and the LINC to compensate for the gain/phase mismatch. In the figure, e is defined as the error between the input signal and the amplified output. The predistorter gives the input signal a predistortion so as to minimize the error. Several mismatch cancellation methods have been proposed [38, 39]. 10.7 Conclusions To show future research directions, we briefly presented several recent inter- esting research topics related to multicarrier techniques. We believe that multicarrier techniques will play important roles in 4G systems, however, to make the multicarrier a core physical layer technique in 4G systems, there are a lot of future research areas we should investigate further. For instance, there has been intensive research recently all over the world on variants based on the MC-CDMA scheme. However, few works 219Future Research Directions Figure 10.15 A combination of a predistortion and the LINC. have been dedicated to pure OFDM-based schemes aimed at 4G systems, with emphasis on the signal format to cope with the Doppler shift due to mobile motions. We think that one way to give the system a robust- ness against the Doppler shift is through the use of scattered pilots (see Section 8.2). In terms of access protocols, no one knows whether CDMA is really suited for the specification in 4G systems. OFDM-TDMA and OFDM- CSMA/CA, as well as MC-CDMA systems, are all candidates. The perfor- mance comparison of these systems in multiple and isolated cell environments will be required. Adaptive array antennas can enhance the transmission performance for OFDM-based systems. As shown in Section 10.4, there are many different ways to configure array antennas and OFDM demodulators. This has been a recent hot topic on 4G systems, however, further investigation, taking into 220 Multicarrier Techniques for 4G Mobile Communications consideration the trade-off between the receiver complexity and the attainable performance, will be required. For MIMO-OFDM, this has also been a recent hot topic in wireless communications in conjunction with adaptive array and diversity antennas. However, we have never seen the capacity analysis of a MIMO-OFDM system that can jointly suppress cochannel interference from other cells. Finally, for the LINC method, there are a lot of ways for gain/phase mismatch cancellation. Examining the trade-off between hardware complex- ity and attainable performance will be important. References [1] Ojanpera, T., and R. Prasad (eds), Wideband CDMA for Third Generation Mobile Communications, Norwood, MA: Artech House, 1998. [2] 3 GPP, 3G TR25.848, V.0.6.0, May 2000. [3] Atarashi, H., and M. Sawahashi, ‘‘Variable Spreading Factor Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM),’’ Proc. of 2001 Third International Workshop on Multicarrier Spread-Spectrum and Related Topics (MC-SS2001), September 2001, pp. 113–122. [4] IEEE Std. 802.11a, ‘‘Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications: High-Speed Physical Layer Extension in the 5-GHz Band,’’ IEEE, 1999. [5] ETSI TR 101 475, ‘‘Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Physical (PHY) Layer,’’ ETSI BRAN, 2000. [6] ARIB STD-T70, ‘‘Lower Power Data Communication Systems Broadband Mobile Access Communication System (CSMA),’’ ARIB, December 2000. [7] ARIB STD-T70, ‘‘Lower Power Data Communication Systems Broadband Mobile Access Communication System (HiSWANa),’’ ARIB, December 2000. [8] Abeta, S., et al., ‘‘Forward Link Capacity of Coherent Multicarrier/DS-CDMA and MC-CDMA Broadband Packet Wireless Access in a Multicell Environment,’’ Proc. of IEEE VTC2000-Fall, Boston, MA, September 2000, pp. 2213–2218. [9] Atarashi. H., S. Abeta, and M. Sawahashi, ‘‘Broadband Packet Wireless Access Appro- priate for High-speed and High-Capacity Throughput,’’ Proc. of IEEE VTC2001- Spring, Rhodes, Greece, May 2001, pp. 566–570. [10] Hanada, Y., K. Higuchi, and M. 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T., Adaptive Antennas Concepts and Performance, Englewood Cliffs, NJ: Prentice Hall, 1988. [16] Monzingo, R. A., and T. W. Miller, Introduction to Adaptive Arrays, New York: John Wiley & Sons, 1980. [17] Li, Y., and N. R. Sollenberger, ‘‘Adaptive Antenna Arrays for OFDM Systems with Cochannel Interference,’’ IEEE Trans. Commun., Vol. 47, No. 2, February 1999, pp. 217–229. [18] Nishikawa, A., Y. Hara, and S. Hara, ‘‘OFDM Adaptive Array for Doppler-Shifted Wave Suppression,’’ Technical Report of IEICE, RCS-2000-113, October 2000, pp. 57–62. [19] Nishikawa, A., Y. Hara, and S. Hara, ‘‘A Study on OFDM Adaptive Array in Mobile Communications,’’ Technical Report of IEICE, RCS-2000-232, March 2001, pp. 73–78. [20] Nishikawa, A., Y. Hara, and S. Hara, ‘‘An OFDM Adaptive Array for Doppler-Shifted Wave Suppression,’’ Proc. 2001 IEICE General Conference, B-5-151, March 2001, p. 549. [21] Hara, S., A. Nishikawa, and Y. Hara, ‘‘A Novel OFDM Adaptive Antenna Array for Delayed Signal and Doppler-Shifted Signal Suppression,’’ Proc. IEEE International Conference on Communications (ICC) 2001, Helsinki, Finland, June 11–14, 2001, pp. 2302–2306. [22] Hara, S., S. Hane, and Y. Hara, ‘‘Adaptive Antenna Array for Reliable OFDM Transmission,’’ Proc. 6th International OFDM Workshop, Hamburg, Germany, September 18–19, 2001, pp. 1.1–1.4. [23] Hane, S., Y. Hara, and S. Hara, ‘‘Selective Signal Reception for OFDM Adaptive Array Antenna,’’ Technical Report of IEICE, AP-2001-69, August 2001, pp. 35–41. [24] Hara, S., S. Hane, and Y. Hara, ‘‘Does OFDM Really Prefer Frequency Selective Fading Channels,’’ Proc. 2001 Third International Workshop on Multicarrier Spread- Spectrum (MCSS2001) and Related Topics, Oberpfaffenhofen, Germany, September 26–28, 2001, pp. 1–4. [25] Hane, S., et al., ‘‘OFDM Null Steering Array Antenna (in Japanese),’’ Technical Report of IEICE, RCS2002-124, July 2002, pp. 31–36. [26] Budsabathon, M., et al., ‘‘On Pre-FFT OFDM Adaptive Antenna Array for Delayed Signal Suppression,’’ Technical Report of IEICE, RCS2002-125, July 2002, pp. 37–42. [27] Raleigh, G. G., and J. M. Cioffi, ‘‘Spatio-Temporal Coding for Wireless Communica- tion, ‘‘IEEE Trans. Commun., Vol. 46, No. 3, March 1998, pp. 357–366. 222 Multicarrier Techniques for 4G Mobile Communications [28] Tarokh, V., N. Seshadri, and A. R. Calderbank, ‘‘Space-Time Codes for High Data Rate Wireless Communication: Performance Criterion and Code Construction,’’ IEEE Trans. Inform. Theory, Vol. 44, No. 2, March 1998, pp. 744–765. [29] Tarokh, V., H. Jafarkhani, and A. R. Calderbank, ‘‘Space-Time Codes from Orthogo- nal Designs,’’ IEEE Trans. Commun., Vol. 45, July 1999, No. 5, pp. 1456–1467. [30] Li, Y., N. Seshadri, and S. Ariyavisitakul, ‘‘Channel Estimation for OFDM Systems with Transmit Diversity in Mobile Wireless Channels,’’ IEEE J. Select. Areas Commun., Vol. 17, No. 3, March 1999, pp. 461–471. 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TE AM FL Y Team-Fly® List of Acronyms 1G first generation 2G second generation 3G third generation 3GPP Third Generation Partnership Project 4G fourth generation ACI adjacent channel interference A/D analog to digital ADSL asymmetric digital subscriber lines AM amplitude modulation ARIBE Association of Radio Industries and Businesses AWGN additive white Gaussian noise BDMA band division multiple access BER bit error rate BPSK binary phase shift keying BRAN broadband radio access network BWA broadband wireless access CDM code division multiplexing CDMA code division multiple access CPSK phase shift keying/coherent detection CSMA/CA carrier sense multiple access with collision avoidance CW continuous wave D/A digital to analog DAB digital audio broadcasting DFS dynamic frequency selection 223 224 Multicarrier Techniques for 4G Mobile Communications DPSK phase shift keying/differential detection DS direct sequence DSL digital subscriber line DVB-T terrestrial digital video broadcasting DFT discrete Fourier transform Eb /N0 ratio of energy per bit to power spectral density of noise EGC equal gain combining ETSI European Telecommunications Standards Institute FDP frequency domain pilot FEC forward error correction FFT fast Fourier transform FH frequency hopping FM frequency modulation GSM global systems for mobile telecommunications GSN generalized shot noise HDR high data rate HF high frequency Hi-Fi high fidelity HIPERLAN/2 High Performance Radio Local Area Network Type Two HSDPA high-speed downlink packet access IDFT inverse discrete Fourier transform IFFT inverse fast Fourier transform IEEE The Institute of Electrical and Electronic Engineers, Inc. i.i.d. independent and identically distributed IMT international mobile telecommunications IS interim standard ISDB-T terrestrial integrated services digital broadcasting ISI intersymbol interference ISM industrial, scientific and medical ITU International Telecommunication Union ITU-R International Telecommunication Union-Radiocom- munication Standardization Sector LAN local area network LINC linear amplification with nonlinear components LMS least mean square MAC medium access control MAN metropolitan area network 225List of Acronyms MC-CDM multicarrier code division multiplexing MC-CDMA multicarrier code division multiple access MCM multicarrier modulation MFN multifrequency network m.g.f. moment generating function MIMO multiple input and multiple output MMAC multimedia mobile access communication MMSEC minimum mean square error combining MRC maximum ratio combining MUI multiple user interference OFDM orthogonal frequency division multiplexing OFCDM orthogonal frequency and code division multiplexing OFDMA orthogonal frequency division multiple access ORC orthogonality restoring combining PAN private area network PAPR peak to average power ratio PDC personal digital cellular p.d.f. probability density function PDNR preliminary draft of new recommendation PHY physical layer PM phase modulation PN pseudo noise QAM quadrature amplitude modulation QPSK quadrature phase shift keying RMS root mean square SCM singlecarrier modulation SF spreading factor SIC serial interference cancellation SNIR signal to noise plus interference power ratio SNR signal to noise (power) ratio SS spread spectrum SSPA solid state high power amplifier TDMA time division multiple access TDMA/DSA time division multiple access with dynamic slot assignment TDP time domain pilot TPC transmission power control US uncorrelated scattering VSF variable spreading factor 226 Multicarrier Techniques for 4G Mobile Communications WSS wide sense stationary WSSUS wide sense stationary uncorrelated scattering About the Authors Shinsuke Hara was born in Osaka, Japan, on January 22, 1962. He received his B.A., M.A., and Ph.D. degrees from Osaka University in Osaka, Japan, in 1985, 1987, and 1990, respectively. From April 1990 to September 1997, he was an assistant professor at the Department of Communications Engineering, Faculty of Engineering, at Osaka University. Since October 1997, he has been an associate professor with the Department of Electronic, Information System, and Energy Engi- neering at the Graduate School of Engineering at Osaka University. From 1995–1996, he was a visiting scientist with the Telecommunications and Traffic-Control Systems Group at Delft University of Technology in Delft, the Netherlands. Dr. Hara’s research interests include the application of digital signal processing techniques for high-speed and high-reliable wireless communica- tions systems. He was the technical program cochairman of the PIMRC’99 International Symposium in Osaka, Japan, as well as the technical pro- gram cochairman of the WPMC’01 International Symposium in Aalborg, Denmark. Ramjee Prasad was born in Babhnaur (Gaya), India, on July 1, 1946. He is now a Dutch citizen. He received his B.A. in engineering from the Bihar Institute of Technology in Sindri, India, in 1968, and his M.A. in engineering and Ph.D. from Birla Institute of Technology (BIT) in Ranchi, India, in 1970 and 1979, respectively. 227 228 Multicarrier Techniques for 4G Mobile Communications He joined BIT as a senior research fellow in 1970 and became an associate professor in 1980. While at BIT, Dr. Prasad supervised a number of research projects in the area of microwave and plasma engineering. From 1983–1988, he was with the University of Dar es Salaam (UDSM), in Tanzania, where he became a professor of telecommunications in the Depart- ment of Electrical Engineering in 1986. At UDSM, Dr. Prasad was responsi- ble for the collaborative project Satellite Communications for Rural Zones with Eindhoven University of Technology in the Netherlands. From Febru- ary 1988–May 1999, he was with the Telecommunications and Traffic Control Systems Group at Delft University of Technology (DUT), where he was actively involved in the area of wireless personal and multimedia communications (WPMC). He was the founding head and program director of the Center for Wireless and Personal Communications (CEWPC) of International Research Center for Telecommunications–Transmission and Radar (IRCTR). Since June 1999, Dr. Prasad has been with Aalborg University as the research director of the Department of Communication Technology and holds the chair of wireless information and multimedia communications. He was involved in the European ACTS project Future Radio Wideband Multiple Access Systems (FRAMES) as a DUT project leader. He is currently the project leader of several international, industrially funded projects. Dr. Prasad has published more than 300 technical papers, contributed to several books, and has authored, coauthored, and edited 12 books. These books, all published by Artech House, are: CDMA for Wireless Personal Communications; Universal Wireless Personal Communications; Wideband CDMA for Third Generation Mobile Communications; OFDM for Wireless Multimedia Communications; Third Generation Mobile Communication Sys- tems; WCDMA: Towards IP Mobility and Mobile Internet; Towards a Global 3G System: Advanced Mobile Communications in Europe, Volumes 1 & 2; IP/ATM Mobile Satellite Networks; Simulation and Software Radio for Mobile Communications; Wireless IP and Building the Mobile Internet; and WLANs and WPANs towards 4G Wireless. His current research interests lie in wireless networks, packet communications, multiple-access protocols, advanced radio techniques, and multimedia communications. Dr. Prasad has served as a member of the advisory and program commit- tees for several Institute of Electrical and Electronic Engineers, Inc. (IEEE) international conferences. He has also presented keynote speeches and deliv- ered papers and tutorials on WPMC at various universities, technical institu- tions, and IEEE conferences. In addition, he was a member of the European cooperation in the scientific and technical research (COST-231) project 229About the Authors dealing with the evolution of land mobile radio (including personal) commu- nications as an expert for the Netherlands, and he was a member of the COST-259 project. He was the founder and chairman of the IEEE Vehicular Technology/Communications Society Joint Chapter, Benelux Section, and is now the honorary chairman. In addition, Dr. Prasad is the founder of the IEEE Symposium on Communications and Vehicular Technology (SCVT) in the Benelux. He was the symposium chairman of SCVT’93. Dr. Prasad is the coordinating editor and editor-in-chief of the Kluwer International Journal on Wireless Personal Communications and a member of the editorial board of other international journals, including the IEEE Communications Magazine and the IEE Electronics Communication Engi- neering Journal. He was the technical program chairman of the PIMRC’94 International Symposium, held in The Hague, the Netherlands, from Sep- tember 19–23, 1994, and also of the Third Communication Theory Mini- Conference in Conjunction with GLOBECOM’94, held in San Francisco from November 27–30, 1994. He was the conference chairman of the 50th IEEE Vehicular Technology Conference and the steering committee chairman of the second International Symposium WPMC, both held in Amsterdam, the Netherlands, from September 19–23, 1999. He was the general chairman of WPMC’01, held in Aalborg, Denmark, from September 9–12, 2001. Dr. Prasad is the founding chairman of the European Center of Excel- lence in Telecommunications, known as HERMES. He is a fellow of IEE, a fellow of IETE, a senior member of IEEE, a member of the Netherlands Electronics and Radio Society (NERG), and a member of IDA (Engineering Society in Denmark). Index 2G systems, 1 Applications, 159–67 conclusions, 1673G systems, 1 4G systems digital broadcasting, 159–62 wireless LANs, 162–65available/evolving access technology, 6 capabilities, 4 See also Orthogonal frequency division multiplexing (OFDM)layered structure, 5 MC-CDMA as candidate for, 200 Asymmetrical digital subscriber lines (ADSL), 63multicarrier technique advantages for, 9 multicarrier techniques for, 7–8 Autocorrelation function, 87, 130 of generated pilot symbol, 125possible paths towards, 204 seamless network, 4 of input OFDM signal, 79 of output OFDM signal, 80source, 204 toward, 2–7 of transmitted signal, 130 AWGN channelsAdaptive array antennas. See OFDM BER in, 46–49, 137adaptive array antennas defined, 45Adaptive subcarrier recovery, 197 DFT window timing error in, 135Additive white Gaussian noise (AWGN), DFT window width error in, 13643 RMS frequency error in, 136nonlinear channel with, 90 TDP BER in, 117power spectral density, 128 timing metric for, 103with two-sided power spectral density, See also Additive white Gaussian noise45 (AWGN)See also AWGN channels Adjacent channel interference (ACI), 79 Band division multiple access (BDMA), 7 BandwidthA/D resolution definition of, 91 coherence, 20 OFDM signal, 38quantization ranges and, 87–88 sensitivity to, 86–88 roll-off factor, 112 231 232 Multicarrier Techniques for 4G Mobile Communications BDPSK-based OFDM system, 63 QDPSK-based OFDM systems, 61 RMS delay spread vs., 120, 121BER, 43 against number of subcarriers, 72, 73 sliding DFT-based carrier recovery, 199attainable, by multicarrierization, 60 in AWGN channels, 46–49, 137 symbol/bit interleaved coded OFDM scheme comparison, 155, 158bit interleaved coded OFDM scheme (3-path i.i.d.), 153 symbol interleaved coded OFDM scheme (3-path i.i.d.), 152bit interleaved coded OFDM scheme (4-path i.i.d.), 156 symbol interleaved coded OFDM scheme (4-path i.i.d.), 155bit interleaved coded OFDM scheme (interleaving depth), 154, 157 symbol interleaved coded OFDM scheme (interleaving depth),CPSK-based OFDM systems in Rayleigh fading channels, 49 154, 157 TDP/FDP transmission parameters,DPSK-based OFDM system, 47 DPSK-based OFDM systems in 116 TDP method in AWGN channel, 117Rayleigh fading channels, 49–61 DS-CDMA, analysis, 175–76 in time selective channels, 52–56 in time selective channel withDS-CDMA in downlink, 195 DS-CDMA system in uplink, 197 frequency offset, 74–77 Binary PSK (BPSK), 44, 47evaluation in GSN channel parameters, 70 Bit error rate. See BER Bit interleaved coded OFDM scheme,in frequency nonselective channel, 55, 150, 151 146–49 BER (3-path i.i.d.), 153in frequency selection channel, 52–56 in frequency selective channel with BER (4-path i.i.d.), 156 BER comparison, 155, 158frequency offset, 74–77 in frequency selective Rayleigh fading BER (interleaving depth), 154, 157 block diagram, 147channel, 139 lower bound, 71, 73 branch metric, 148, 149 Euclidean distance calculation, 149maximum Doppler frequency vs., 122 MC-CDMA, analysis, 183–86 maximum likelihood decoding, 147 transition p.d.f., 148MC-CDMA system, 191–94 MC-CDMA system in downlink, 194 uniform input distribution, 148 See also Coded OFDM schemeMC-CDMA system in uplink, 196 modulation/demodulation scheme Branch metric, 148, 149 Broadband wireless access (BWA), 166performance, 45 in nonlinear channel with AWGN, 90 Carrier frequency offset synchronization,in nonlinear channel with noise free, 9989 Channel model, 170–71for nonlinear characteristics, 90 Chaotic pilot symbol generation, 121–23OFCDM, 208 autocorrelation property, 125OFDM in GSN channel, 67–69 illustrated, 124OFDM system performance, 45 PN sequence generation, 124path selection threshold vs. (TDP in time domain, 124method), 117, 118 Code division multiple access (CDMA), 1for peak-to-peak quantization range, 91, 92 adoption, 7 TE AM FL Y Team-Fly® 233Index downlink, 170 DFT window timing estimation, 101–6 block diagram, 106DS-CDMA, 169, 170, 171–76 MC-CDMA, 169, 176–200 performance, 107–10 principle, 101–6OFDM with, 8 Code division multiplexing (CDM), 1 DFT window timing synchronization parts, 99Coded OFDM scheme, 141–58 BER in frequency nonselective pilot-assisted, 100 Differential PSK (DPSK), 43Rayleigh fading channel, 151, 152 binary (BDPSK), 50, 63 phase transition, 51bit interleaved, 146–49 conclusions, 156–58 quadrature (QDPSK), 50, 61, 62 See also DPSK-based OFDM systemsnumerical results, 149–56 subcarrier arrangement, 150 Digital audio broadcasting (DAB), 159–60 defined, 160symbol interleaved, 143–46 transmission parameters, 150 parameters, 160 Digital broadcasting, 63, 159–62Coherent PSK (CPSK), 43 Column vectors, defining, 95 audio, 159–60 terrestrial integrated services, 161–62Convolutional codes design, 143 terrestrial video, 160–61 Dirac’s Delta function, 18transfer function of, 151 Convolutional encoding, 142–43 Direct sequence CDMA. See DS-CDMA Discrete Fourier transform (DFT)defined, 142 illustrated, 142 GSN suppression, 71 inverse (IDFT), 32Correlation function spaced-frequency, 170 matrix, 33 rectangular window, 33spaced-time, 20–21 Covariance matrix, 95 use of, 30–33 window width, 128CPSK-based OFDM systems, 46–48 AWGN channel BER, 47 window width error, 134, 135, 136 See also DFT window timingin Rayleigh fading channels, 49 transmission diagram, 46 Distorted spreading codes, 182–83 Doppler power spectrum, 23–24Cyclostationary signal, 127, 129–34 defined, 20–21 D/A resolution density, 23 definition of, 91 illustrated, 24 quantization ranges and, 87–88 Doppler shift, 23 sensitivity to, 86–88 DPSK-based OFDM systems, 47–48 Deinterleaving, 144, 145 BER, 47 DFT window timing, 113 in Rayleigh fading channels, 49–61 error evaluation, 134 theoretical bit error rate analysis, error in AWGN channel, 135 50–52 error in frequency selective Rayleigh transmission diagram, 48 fading channel, 137 DS-CDMA, 169, 170, 171–76 measuring, 102–3 BER analysis, 175–76 metric for AWGN channel, 103 BER lower bound, 186 metric in static 20-path channel, 104 decision variable, 181 downlink, BER performance, 195transmission parameters, 104 234 Multicarrier Techniques for 4G Mobile Communications DS-CDMA (continued) Frequency nonselective channels BER, 55, 150, 151I -finger Rake receiver illustration, 172 MC-CDMA performance comparison, defined, 20 Rayleigh, 25170 power spectrum, 172 Ricean, 26 Frequency offsetRake combiner, 174, 175, 176 receiver, 173–75 compensation methods, 78–79 fading channels, transmissionSIC scheme, 174 simulation parameters, 193 parameters, 78 frequency selective channel with,for symbol decision, 181 system illustration, 172 74–77 introduction, 74transmitter, 171–73 uplink, BER performance, 197 phase shift caused by, 106 QDPSK-based OFDM system against,See also Code division multiple access (CDMA) 78 sensitivity in, 72–79Dynamic frequency selection (DFS), 165 time selective channel with, 74–77 Estimators Frequency offset estimation optimum, 133 block diagram, 106 suboptimum, 133, 134 performance, 110–11 performance illustration, 111Fading channels. See Multipath fading channels principle, 105–6 Frequency offset synchronization, 99, 100Fast Fourier transform (FFT), 33 inverse (IFFT), 149 Frequency selective channels BER in, 52–56, 139replacing DFT by, 33 Fifth-order intermodulation, 81 defined, 20 with frequency offset, BER, 74–77First generation (1G) systems, 1 Fourier transform QDPSK-based OFDM system, 61 Rayleigh, 25–26for convolution of two-time domain functions, 181, 182 RMS DFT window timing error in, 137fast (FFT), 33 inverse, 95–96 RMS DFT window width error in, 138Frequency diversity effect, 141–58 Frequency domain RMS frequency error in, 138 Frequency selective fadingcovariance matrix, 183, 185 interpolation in, 116 BDPSK-based OFDM system in, 63 QDPSK-based OFDM system in, 62PN sequence generation in, 124 PN sequence in, 122 robustness against, 61–63 Frequency selectivityFrequency domain pilot (FDP) BER vs. RMS delay spread, 120 guard interval and, 58 number of subcarriers and, 57error variance vs. RMS delay spread for, 118, 119 Future research, 203–20 conclusions, 218–20OFDM transmitter model, 115 performance, 116 introduction, 203–4 linear amplification with nonlinearsymbols, 100 Frequency hopping (FH) spread spectrum components, 216–18 MC-CDMA variants, 204–11(SS), 167 235Index MIMO-OFDM, 215–16 IEEE 802.11, 162 OFCDM, 204–9 IEEE 802.11a, 162, 163 OFDM adaptive array antennas, parameters, 164 211–15 time-frequency structure, 163, 166 IEEE 802.11g, 165Gaussian noise, 89 IEEE 802.11h, 165–66Gaussian random variables, 109, 110 IEEE 802.16a, 166–67complex-valued, 108 defined, 166real-valued, 109, 110 specifications, 167Gaussian stochastic process, 15, 17 Impulse response, 114complex-valued, 15, 17 equivalent baseband, 15WSSUS, 19 estimated, 114Generalized shot noise (GSN), 64–69 IMT-2000, 2BER of OFDM, 67–69 evolution, 3BER of SCM, 65–67 system capabilities beyond, 3channel, 64–65 terrestrial radio interfaces, 3complex-valued, 64 timelines, 7DFT suppression of, 71 Inhomogeneous traffic, 6effect of, 65 Interleaving, 144, 145Laplacian channel, 73 deinterleaving and, 144, 145lognormal channel, 71, 72, 73 depth, 153, 154, 157power spectrum, 64 Intermodulation power, 88Global Systems for Mobile Telecommunications (GSM), 1 Interpolation Guard interval insertion cubic spline, 120 with cyclic prefix, 35, 36 in frequency domain, 116 head/tail, 188–91 Intersymbol interference (ISI) received signals, 36 elimination with head/tail guard transmitted signals, 35 interval insertion, 191 with, 35, 36 from neighboring signals, 112 without, 34, 35 Inverse DFT (IDFT) Guard intervals fast (IFFT), 149 energy efficiency and, 58 matrix, 32 frequency selectivity and, 58 use of, 33 optimum length of, 56–59 See also Discrete Fourier transform (DFT)Head/tail guard interval insertion, 188–91 Inverse Fourier transform, 95–96effectiveness, 191 illustrated, 190 Jakes’ model, 23ISI/MUI elimination, 191 illustrated, 23See also MC-CDMA with omnidirectional antenna, 97Heavy-tailed distribution functions, 65 Hermitian transpose, 95 Laplace distribution, 70, 73High data rate (HDR), 1 GSN channel, 73High-performance radio LAN type two saddle-point method, 70(HIPERLAN/2), 2, 165 See also Lognormal distributionHigh-speed downlink packet access (HSDPA), 1–2 Least mean square (LMS), 196 236 Multicarrier Techniques for 4G Mobile Communications Likelihood function, 129–30 simulation parameters, 186, 193 for symbol decision, 181calculating, 132 system design, 186–88obtaining, 132–33 system illustration, 178redefining, 132 transmitter, 176–79LINC, 216, 216–18 transmitter illustration, 178benefits, 218 transmitter structure, 177for gain/phase mismatch, 218 uplink, BER performance, 196predistortion combination and, 218, uplink, nonminimum phase response,219 192principle, 217 variants, 204–11signal separation, 217, 218 See also Code division multiple accessLinear multiuser detection scheme, 182 (CDMA)Lognormal distribution, 69–70 Mean square error (MSE), 183GSN channel, 71, 72, 73 minimization of, 181See also Laplace distribution minimum, combining (MMSEC), 98, 181, 183, 199Man-made noises, robustness against, Metropolitan area networks (MANs), 16663–72 MIMO-OFDM, 203–4, 215–16, 220Maximum likelihood decoding, 145, 147 field trial results, 216Maximum likelihood parameter estimation illustrated, 215blind, 127–39 Minimum mean square error combiningconclusions, 135 (MMSEC), 181for cyclostationary signal, 129–34 multiuser detection scheme, 183Maximum ratio combining (MRC), 181 sliding DFT-based parameters, 199MC-CDM, 209–11 subcarrier recovery method for, 198with frequency scheduling, 209, 210 Multicarrier modulation (MCM), 27illustrated, 210 defined, 27SNIR, 209, 211 first systems employing, 29 MC-CDMA, 169, 176–200 frequency spectra, 28 as 4G mobile communication nonoverlapped band-limited orthogonal candidate, 200 signals, 32 BER, 191–94 SCM comparison, 28 BER analysis, 183–86 transmitted waveform comparison, 31 BER lower bound, 186 in wireless channels, 29 decision variable, 181 See also Orthogonal frequency division downlink, BER performance, 194 multiplexing (OFDM) DS-CDMA performance comparison, Multifrequency network (MFN), 160 170 Multimedia mobile access communication head/tail guard interval insertion (MMAC), 2, 162 method, 188–91 parameters, 164, 165 MC-CDM, 209–11 support, 163 multipath delay profile, 184 Multipath delay profiles, 18–19 power spectrum, 178 in channel model, 171 quasi-synchronous uplink, 182 examples of, 22 received wave, 180 exponentially decaying, 22 receiver, 179–83 i.i.d., 22 MC-CDMA, 184receiver illustration, 178 237Index Multipath fading, 13 basic configuration, 212 post-FFT, 211–13Multipath fading channels, 13–26 bandwidth, 20 pre-FFT, 211–13 principle, 211characteristics of, 13–26 equivalent baseband impulse response, weight-per-path, 213–15 weight-per-user, 213–1515 example illustration, 14 OFDM signals, 67 autocorrelation function, 79, 80examples, 22–26 frequency nonselective, 19–20, 25, 26 bandwidth, 38 cyclical extension, 43frequency selective, 19–20, 25–26 Rayleigh, 14–18 cyclostationary property, 127 frequency selective fading channel, 113received signal, 14 Ricean, 14–18 frequency spectrum, 38 input, to nonlinear amplifier, 79time nonselective, 21 time selective, 21 as narrowband Gaussian noise, 87 output, of nonlinear amplifier, 80Multipath propagation model, 17 Multiple input and multiple output power spectra, 39, 40, 84, 85, 87 total symbol transmission rate, 37(MIMO), 203–4, 215–16 Multiple user interface (MUI), 170, 191 See also Orthogonal frequency division multiplexing (OFDM)Multiplicative noise, 45 OFDM symbol, 37 Noise cyclical extension, 127 Gaussian, 89 period, 37 generalized shot (GSN), 64–69 width, 128 impulsive, 66, 69 Optimum estimator, 133 multiplicative, 45 Organization, this book, 8–10 Nonlinear amplification, 216 Orthogonal frequency and code division power spectrum evaluation by, 84 multiplexing. See OFCDM unavoidable, 216 Orthogonal frequency division Nonlinear channels multiplexing (OFDM), 27–40 with AWGN, BER, 90 advantage, 33 intermodulation power, 88 applications, 159–67 with noise free, BER, 89 bandwidth, 38 Nyquist filter, 112 BER, in GSN channel, 67–69 with CDMA, 8, 169–200OFCDM, 203, 204–9 advantage, 205 characteristics, 43–92 coded system, 141–58BER, 208 code/time division multiplexing, 206 conclusions, 39 CPSK-based, 46–48concept, 206 frequency division multiplexing in, 207 current form of, 38 DPSK-based, 47–48scalability, 205 transmission parameters, 209 maturation, 8 origin, 27–30variable spreading factor (VSF), 207, 208 QDPSK-based, 61–62, 78 reasons to use, 27See also MC-CDMA OFDM adaptive array antennas, 211–15 receiver, 34, 100 receiver model, 101antenna beam pattern, 212 238 Multicarrier Techniques for 4G Mobile Communications Orthogonal frequency division in frequency selective fading channel, multiplexing (OFDM) 61 (continued) See also Orthogonal frequency division synchronization, 99 multiplexing (OFDM) transmitter, 34, 100 Quadrature amplitude modulation uncoded system, 141 (QAM), 119–20 waveform, 37 Quadrature PSK (QPSK), 44 See also Multicarrier modulation employing, 47 (MCM); OFDM signals signal constellations, 122, 146 Orthogonality restoring combining (ORC), 180 Radio channels model, 44–45 Peak-to-average power ratio (PAPR), 123 transmitted signals in, 44–45 Peak-to-peak quantization range, 91–92 Rake combiner, 174, 175, 176 Personal area networks (PANs), 3 Rayleigh distribution Personal Digital Cellular (PDC), 1 defined, 17 Phase offset, 74 illustrated, 17 Phase shift keying (PSK) uses, 17–18 binary (BPSK), 44, 47 Rayleigh fading channels, 14–18 coherent (CPSK), 43 CPSK-based OFDM system BER, 49 differential (DPSK), 43 DPSK-based OFDM system BER, quadrature (QPSK), 44, 47 49–61 Pilot-assisted DFT window timing frequency nonselective, 25, 150, 151 synchronization/subcarrier frequency selective, 25–26, 137–39, recovery method, 111–21 152–53 frequency domain, 115–16 transmission parameters for BER numerical results, 116–21 evaluation, 60 time domain, 111–15 Ricean fadingPilot symbols, 105 channels, 14–18, 26baseband component vector, 196 Rayleigh fading vs., 18chaotic generation method, 121–23 Ricean K factor, 17discontinuous, 194, 197 Rice distributiongeneration, 112 defined, 16ISDB-T insertion method, 161 degeneration, 18N -point DFT of, 106, 107 illustrated, 17spectral property, 106–7 RMS delay spread, 20subcarrier insertion, 115 BER vs. (2-path i.i.d.), 120Pseudo noise (PN) sequence BER vs. (8-path exponentiallyin frequency domain, 122 decaying), 121generation method, 121 error variance vs., 119pulse-shaped, 111–12 See also Root mean square (RMS) RobustnessQDPSK-based OFDM systems frequency selective fading and, 61–63against frequency offset, 78 man-made noises and, 63–72BER of, 61, 62 OFDM system, 69in frequency nonselective fading channel, 62 Roll-off factor, 112 239Index Root mean square (RMS) OFCDM and, 207 variable (VSF), 207, 208DFT window timing error, 134, 135 DFT window timing error (frequency Subcarrier recovery, 99 adaptive, 197selective Rayleigh fading channel), 137 with DFT, 198 frequency domain pilot-assisted,DFT window width error, 134, 135, 136 115–16 for MMSEC, 198DFT window width error (frequency selective Rayleigh fading sliding DFT-based, 194–200 weights for, 114channel), 136 frequency error, 134, 135, 136 Subcarriers number, in lognormal GSN channel,frequency error (frequency selective Rayleigh fading channel), 138 72 optimum number of, 56–61See also RMS delay spread Suboptimum estimator, 133, 134 Saddle-point method, 69, 70 Symbol interleaved coded OFDM scheme, Schmidl’s method, 101–2 143–46 Sensitivity BER (3-path i.i.d.), 152 to A/D and D/A resolutions, 86–88 BER (4-path i.i.d.), 155 in frequency offset, 72–79 BER comparison, 155, 158 to nonlinear amplification, 79–86 BER (interleaving depth), 154, 157 Serial interference cancellation (SIC) block diagram, 145 scheme, 174 Euclidean distance calculation, 147 Signal to noise plus interference power interleaving/deinterleaving, 144, 145 ratio (SNIR), 209, 211 See also Coded OFDM scheme Simbo’s method, 79–82 Synchronization Singlecarrier modulation (SCM) carrier frequency offset, 99 BER, in GSN channel, 65–67 DFT window timing, 99 frequency spectra, 28 elements, 99 MCM comparison, 28 as functionality, 99 time-limited signal, 32 in OFDM system, 99 Sliding DFT-based subcarrier recovery, System model, 128–29 194–200 BER performance, 199 Taylor series, 129 Terrestrial digital video broadcastingillustrated, 198 phase rotation, 197 (DVB-T), 160–61 adoption, 160simulation parameters, 199 sliding width, 197 coherent demodulation, 161 defined, 160Solid state high power amplifier (SSPA), 82 parameters, 162 subcarriers, 161AM/PM conversion characteristic, 82, 83 See also Digital broadcasting Terrestrial integrated services digitalBER deterioration and, 88 for input OFDM signal, 82 broadcasting (ISDB-T), 161–62 defined, 161Spaced-time correlation function, 20–21 Spreading factor (SF) demodulation schemes, 161 parameters (audio), 164change, according to cell layouts, 208 240 Multicarrier Techniques for 4G Mobile Communications Terrestrial integrated services digital performance, 116 symbols, 100broadcasting (ISDB-T) Time nonselective fading channels, 21(continued) Time selective fading channels, 21parameters (television), 162 BER in, 52–56pilot symbol insertion, 161 with frequency offset, BER, 74–77time-frequency structure, 161, 163 Transmission power control (TPC), 165See also Digital broadcasting Third-order intermodulation, 81 Uncorrelated scattering (US), 18 Time division multiple access (TDMA), 7 Viterbi decoding, 142–43Time domain pilot (TDP) defined, 143BER in AWGN channel, 117 trellis diagram, 144BER vs. path selection threshold, 117, 118 Wide sense stationary (WSS), 18 data frame structure, 112 Wireless LANs, 63 WirelessMANTM, 166method block diagram, 113