An iterative multiuser receiver for FEC coded CDMA

The powerful iterative algorithm of turbo code is employed in the proposed iterative multiuser receiver for the downlink of a forward error correction (EEC) coded direct-sequence code-division multiple access (DS-CDMA) environment. The receiver iterates between the 2 coding dimensions, namely the spreading codes and the FEC codes. The optimum iterative multiuser receiver uses the optimum decentralised single-user detector to generate the single-user extrinsic information for the single-user decoders. This paper suggests a sub-optimum detector using a folded trellis preselection stage for the multiuser signal detection, in order to reduce the dominating complexity of the optimum decentralised detector. Simulation results show that performance is close to optimum. The effect of the single-user decoders' extrinsic information on the signal detection stage is also investigated and it is found that extrinsic information improves performance.