Guest editorial multiuser detection techniques with application to wired and wireless communications systems II

M 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 techniques 1 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. 1 The reference for the first issue is " Multiuser detection techniques with application to wired and wireless communications systems I, " IEEE J. Select. 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. …