NEAR-OPTIMUM TREE-SEARCH DETECTION SCHEMES FOR BIT-SYNCHRONOUS MULTIUSER CDMA SYSTEMS OVER GAUSSIAN AND 2-PATH RAYLEIGH-FADING CHANNELS

In this paper, simple reduced tree-search detection schemes of the bre adth-first type are applied to suboptimal joint multiuser detection in bit-synchronous code-division multiple access (CDMA) systems over bot h Gaussian and two-path Rayleigh-fading channels, It is pointed out th at in contrast to the case of the optimal multiuser detector, the choi ce of the receiver filter severely influences the performance of subop timal multiuser detectors. Simulation results supported by analysis sh ow that breadth-first tree search algorithms using a decorrelating noi se whitening receiver filter perform better than similar receivers, wh ich solely use a matched filter (MF) for virtually all nonsingular spr eading code sets studied in this paper, Most of the code sets are rand omly generated, The M- and T-algorithm detectors based on decorrelatin g noise whitening filter (WF) outputs can achieve near optimum perform ance at a very low complexity compared to the optimal detector, althou gh the proposed detectors are more complex than some known suboptimum detectors. Furthermore, the use of combining techniques is considered for a two-path Rayleigh-fading channel, and a semi-synchronous CDMA st ructure is proposed, It is shown that if maximum ratio combining (MRC) is employed, the decorrelating noise WF still exists, The correspondi ng suboptimal combining detector with a decorrelating noise WF outperf orms a similar noncombining detector.