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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 20, NO. 2, FEBRUARY 2002

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Guest Editorial Multiuser Detection Techniques With Application to Wired and Wireless Communications Systems II

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ULTIUSER detection (MUD) techniques hold the promise that future multiple-access communications systems will be able to use all the dormant capacity that is potentially available in existing communications networks. This second issue devoted to the topic of MUD techniques1 features 22 contributions that address key areas for the development of the field. In wireless transmission systems, MUD often must be performed in the presence of possible rapid variations of the channel. In such situations, receiver complexity is an issue, and this is the focus of the first group of papers in this issue. In “Reduced and Differential Parallel Interference Cancellation for CDMA Systems,” Nahler et al. investigate various parallel architectures for interference cancellation. The paper, “A Low-Complexity Combined Antenna Array and Interference Cancellation DS-CDMA Receiver in Multipath Fading Channels,” by Mohamed and Dunham combines beamforming to reduce co-channel interference with parallel interference cancellation to mitigate in-beam multiple-access interference, to result in a low-complexity system for multiuser reception in frequency-selective channels. Lee and Kim consider the gambit of choosing a very simple detector that exploits the characteristics of CDMA signals in “A One-Shot LDD With Pre-SDC/Post-MRC for Random CDMA Over Asynchronous Rayleigh Channels.” Two suboptimal multiuser detectors based on the maximum-likelihood criterion are presented in “Reduced State Maximum-Likelihood Multiuser Detection for Down-link TD-CDMA Systems,” by Benvenuto et al. It is shown that these detectors perform much better than the zero-forcing and the minimum-mean-square-error detectors, while maintaining a complexity that is proportional to the number of users. Castoldi and Kobayashi investigate linear interference cancellation for the downlink in “Co-Channel Interference Mitigation Detectors for Multirate Transmission in TD-CDMA Systems.” The proposed receivers employ tunable-complexity structures that cancel intracell interference, and treat intercell interference differently, depending on the operating environment. A unifying framework for a new class of receivers that employ linearly constrained interference cancellation is presented in “Interference Subspace Rejection: A Framework

Publisher Item Identifier S 0733-8716(02)00988-5. 1The reference for the first issue is “Multiuser detection techniques with application to wired and wireless communications systems I,” IEEE J. Select. Areas Commun., vol. 19, Aug. 2001.

for Multiuser Detection in Wideband CDMA” by Affes et al. These detectors operate in various modes, ranging from linear receivers to interference cancellers. In addition to interference rejection, they perform space and time diversity combining, array processing, and synchronization and can operate in multiple mixed-traffic scenarios. Fan and Siu discuss linear detectors and the mutual effect of code orthogonality and adaptive implementation in “A Dual-Mode Multiuser Detector for DS-CDMA Systems.” The paper, “Blind Adaptive Multiuser Detection for Cellular Systems Using Stochastic Approximation With Averaging,” by Das and Varanasi provides a common framework for stochastic-approximation-based blind adaptive algorithms for linear minimum mean square error (MMSE) MUD, and shows how the performance of such algorithms can be improved by averaging. Multiuser detection for bandwidth-efficient transmission systems represents a broad area that is addressed by the second group of papers. The paper, “On Bandwidth-Efficient Multiuser-Space-Time Signal Design and Detection,” by Ng and Sousa proposes a concept known as interference-resistant modulation, in which multiple users coordinate transmissions to produce diversity effects akin to those of space-time coding. Janssen and Slimane conduct an analysis of the error probability for the particularly difficult successive cancellation situation in “Symbol Error Probability Analysis of a Multiuser Detector for -PSK Signals Based on Successive Cancellation.” In “A Novel Iterative Multiuser Detector for Complex Modulation Schemes,” Lampe et al. show that significant performance gains are achieved by taking into account that the multiuser interference becomes rotationally variant in the course of the iterations of a soft-decision interference canceller. The possible applications to the area of MUD of the iterative algorithms that have been successfully used for the decoding of turbo codes and low-density parity-check codes have generated enormous interest. In interference rejection for digital subscriber line technologies, which is the topic of the third group of papers, the interference itself becomes like one of the codes in a system. Then the likelihood of all symbols may be estimated if the channel is known accurately. This can lead to large gains in the performance of a detection system as long as fundamental bounds of multiuser communications are not compromised. Indeed, maximum a posteriori or maximum-likelihood detectors are often approximated by detectors with lower complexity. The papers “Turbo Multiuser Detection for Coded DMT VDSL Systems,” by Dai and Poor, “Multiuser Soft Interference Canceler via Iterative Decoding for DSL Applications,” by

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 20, NO. 2, FEBRUARY 2002

Cheong et al., and “A Novel Tunable-Complexity Turbo-Soft Detector for High-Throughput HDSL Applications Over ISI Channels with Crosstalk,” by Baccarelli et al., address methods by which iterative decoding can be used to remove crosstalk generated by signals that are transmitted over phone lines sharing a common binder. These papers investigate various approximations to the optimum decoder through the recursive construction of likelihoods. In the papers of the fourth group, various aspects of MUD for code division multiple access (CDMA) systems are considered. The paper, “Signature Sequence Adaptation for DS-CDMA with Multipath,” by Rajappan and Honig considers the joint adaptation of transmitter and receiver for CDMA uplink channels. In one implementation, appropriate transmitter waveforms are determined at the base station and communicated via a feedback channel to mobile transmitters. Distributed algorithms are also considered for the modulation adaptation. In “The Coding–Spreading Tradeoff in CDMA Systems,” Veeravalli and Mantravadi use general definitions of coding and spreading to show that every bandwidth redundancy scheme can be expressed as a concatenation of coding followed by spreading. This observation is then used to examine coding–spreading tradeoffs in CDMA systems employing MUD followed by single-user decoding. In “Performance Analysis of Linear Multiuser Detectors for Randomly Spread CDMA Using Gaussian Approximation,” Yoon and Bar-Ness analyze the performance of linear decorrelating detectors and MMSE detectors, and derive approximate expressions of the probability density function of the near-far resistance as well as of the bit-error rate for random spreading sequences. “Multipath Interference Canceller for High-Speed Packet Transmission With Adaptive Modulation and Coding Scheme in W-CDMA Forward Link,” by Higuchi et al. proposes a multistage multipath interference canceller for orthogonal code-multiplexing on the downlink that provides significant performance gain relative to a chip equalizer and conventional techniques. The proposed method is combined with adaptive modulation to achieve superior throughput. “Experiments on Pilot Symbol-Assisted Coherent Multistage Interference Canceller for DS-CDMA Mobile Radio,” by Sawahashi et al., investigates a three-stage coherent multistage interference canceller in the presence of frequency-selective multipath fading. A fast transmission power control (TPC) method suitable for this detector is also proposed. The combination of the proposed interference canceller and fast TPC significantly decreases the transmission power of a mobile station compared to the matched filter-based RAKE receiver. The use of pilot signals is explored, and the case of a nonflat-fading channel is specifically investigated in “MCI Cancellation for Multicode Wideband CDMA Systems,” by Chen et al.

Genetically modified codes for the same case are investigated by Abedi and Tafazolli in “Genetically Modified Multiuser Detection for Code Division Multiple Access Systems.” The topic of receiver synchronization in multiple-access systems is addressed in the final paper, “Channel-Independent Synchronization of Orthogonal Frequency Division Multiple Access Systems,” by Barbarossa et al. In particular, synchronization algorithms for the downlink and uplink of orthogonal frequency-division multiple-access systems are proposed that do not require training sequences, and exhibit a performance that does not depend on the location of zeros of the channel transfer function. ACKNOWLEDGMENT We gratefully acknowledge the persons who have made possible the realization of this double issue. Our thanks go to the members of the J-SAC Editorial Board, in particular to Bill Tranter, the Editor-in-Chief, and Sue McDonald, the Executive Editor, for their advice during the course of the project; to Jeff Cichocki, Managing Editor, IEEE Publishing Services, and the members of his staff, for their help during the production of the issue; to Charlotte Bolliger, IBM Zurich Research Laboratory, and to Joice DeBolt, Stanford University, for their gracious assistance in administering the project. Special thanks go to the reviewers, whose timely efforts were essential for the selection of the papers that appear in this double issue, and above all to the authors, who effectively described with their contributions the impressive developments that are taking place in the field of multiuser detection. GIOVANNI CHERUBINI, Guest Editor IBM Zurich Research Lab CH-8803 Rüschlikon Switzerland JOHN M. CIOFFI, Guest Editor Stanford University Department of Electrical Engineering Stanford, CA 94305-9515 USA ALEXANDRA DUEL-HALLEN, Guest Editor North Carolina State University Department of Electrical and Computer Engineering Raleigh, NC 27695-7914 USA H. VINCENT POOR, Guest Editor Princeton University Department of Electrical Engineering Princeton, NJ 08544-5263 USA WILLIAM H. TRANTER, J-SAC Board Representative

IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 20, NO. 2, FEBRUARY 2002

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Giovanni Cherubini (S’80–M’82–SM’94) received the Dr.Ing. degree in electrical engineering (summa cum laude) from the University of Padova, Italy, in 1981, and M.S. and Ph.D. degrees in electrical engineering from the University of California, San Diego, in 1984 and 1986, respectively. In 1984, he received a scholarship from M/A-COM Linkabit, San Diego, for his work on the synchronization of spread-spectrum systems. Since 1987, he has been with the IBM Zurich Research Laboratory, Rüschlikon, Switzerland. His research interests include the study of transceiver architectures for high-speed data transmission and signal processing for bandwidth-efficient communications. In 1995, Dr. Cherubini served as Guest Editor for the Special Issue of the IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS on Copper Wire Access Technologies for High-Performance Networks. From 1995 to 1996, he was co-editor of the IEEE Standard 100BASE-T2 for Fast Ethernet transmission over voice-grade cables. Since 1999, he has been Editor for CDMA Systems for the IEEE TRANSACTIONS ON COMMUNICATIONS.

John M. Cioffi (S’77–M’78–SM’90–F’96) received the B.S.E.E. degree from the University of Illinois, Urbana-Champaign, in 1978 and the Ph.D.E.E. degree from Stanford University, Stanford, CA, in 1984. He was with Bell Laboratories, Holmdel, NJ, from 1978 to 1984 and IBM Research, San Jose, CA, from 1984 to 1986. He has been with Stanford University as an electrical engineering Professor from 1986 to present. He founded Amati Communications Corporation, Palo Alto, CA, in 1991 (it was purchased by Texas Instruments in 1997) and was officer/director from 1991 to 1997. He currently is on the boards or advisory boards of BigBand Networks, Coppercom, GoDigital, Ikanos, Ionospan, Ishoni, IteX, Marvell, Kestrel, Charter Ventures, and Portview Ventures, and is a Member of the US National Research Council’s CSTB. His specific interests are in the area of high-performance digital transmission. Dr. Cioffi received the following awards: IEEE Kobayashi Medal in 2001, IEEE Millennium Medal in 2000, IEE JJ Tomson Medal in 2000, 1999 University of Illinois Outstanding Alumnus, 1991 IEEE COMMUNICATIONS MAGAZINE best paper, 1995 ANSI T1 Outstanding Achievement Award, and NSF Presidential Investigator from 1987 to 1992. He became a member of the National Academy of Engineering in 2001. He has published over 200 papers and holds over 40 patents, most of which are widely licensed, including basic patents on DMT, VDSL, and V-OFDM.

Alexandra Duel-Hallen received the B.S. degree in mathematics from Case Western Reserve University, Cleveland, OH, in 1982, the M.S. degree in computer, information and control engineering from the University of Michigan, Ann Arbor, in 1983, and the Ph.D. degree in electrical engineering from Cornell University, Ithaca, NY in 1987. From 1987 to 1990, she was a Visiting Assistant Professor with the School of Electrical Engineering, Cornell University. From 1990 to 1992, she was with the Mathematical Sciences Research Center, AT&T Bell Laboratories, Murray Hill, NJ. She is an Associate Professor with the Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, which she joined in January 1993. Her current research interests are in equalization, wireless communications, and multiuser detection. From 1990 to 1996, Dr. Duel-Hallen was Editor for Communication Theory for the IEEE TRANSACTIONS ON COMMUNICATIONS.

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H. Vincent Poor (S’72–M’77–SM’82–F’87) received the Ph.D. degree in electrical engineering and computer science in 1977 from Princeton University, Princeton, NJ. He is currently a Professor with the Department of Electrical Engineering, Princeton University. He is also affiliated with Princeton’s Department of Operations Research and Financial Engineering, and with its Program in Applied and Computational Mathematics. From 1977 until 1990, he was a Faculty Member with the University of Illinois, Urbana-Champaign. He has also held visiting and summer appointments at several universities and research organizations in the United States, Britain, and Australia. His research interests are in the area of statistical signal processing and its applications, primarily in wireless multiple-access communication networks. His publications in this area include the book, Wireless Communications: Signal Processing Perspectives. Dr. Poor is a member of the National Academy of Engineering, and is a Fellow of the Acoustical Society of America, the American Association for the Advancement of Science, the Institute of Mathematical Statistics, and the Optical Society of America.. He has been involved in a number of IEEE activities, including serving as President of the IEEE Information Theory Society in 1990, and as a member of the IEEE Board of Directors in 1991 and 1992. Among his other honors are the Frederick E. Terman Award of the American Society for Engineering Education (1992), the Distinguished Member Award from the IEEE Control Systems Society (1994), the IEEE Third Millennium Medal (2000), the IEEE Graduate Teaching Award (2001), and the Joint Paper Award of the IEEE Communications Society and Information Theory Society (2002).