Achieving Single-User Performance in a FEC-coded DS-CDMA system using the Low-Complexity Soft-Output M-Algorithm

This paper presents a soft-output version of the Malgorithm (SOMA) to reduce the complexity of a turbo multiuser detector in a DS-CDMA system employing a forward error correction code. The SOMA reduces the complexity by pruning an equivalent tree that represents all possible transmit signalvectors. It utilizes paths that are traversed but discarded in a pruned tree to reduce the total number of paths that need to be visited. We show a simple and effective method of using these discarded paths without having to store them. BER performance is presented for convolutional-coded CDMA system employing both random spreading sequences and Gold spreading sequences. Both the AWGN and Rayleigh fading channels are considered.