An iterative multiuser receiver using groupwise MLSE and interference cancellation in an MC-CDMA system

In this paper, a low-complexity iterative multiuser receiver using groupwise maximum-likelihood sequence estimation (MLSE) combined with interference cancellation for a turbo-coded multicarrier code-division multiple access (MC-CDMA) system is proposed. The approach is based on grouping the active users according to their signal strengths and computing the log-likelihood ratios by using MLSE in each group at the first iteration. For subsequent iterations, a modified interference cancellation scheme that can benefit from code extrinsic information available through decoding is used. Simulation results are presented in a Rayleigh multipath fading environment for a data transmission scheme. Comparisons are made with iterative receivers using the maximum a posteriori (MAP) criterion and soft interference cancellation. Performance very close to that of an MAP-based iterative receiver is achieved by this novel scheme within a few iterations, with much lower computational requirements. This scheme also performs significantly well under the near-far conditions.