Efficient groupwise multiuser detection with iterative soft interference cancellation for multi-rate MC-CDMA

This paper presents an effective multiuser detector (MUD) for the uplink of multi-rate multi-carrier code division multiple access (MC-CDMA) systems. The MUD considered is an iterative receiver which utilizes the soft information to refine the estimation of the interference to enhance the interference cancellation capability. More specifically, users are first classified into separate groups according to their transmission rates. In each iteration, these groups of users are detected sequentially based on a set of group detectors with the removal of multiple access interferences (MAI) group by group, where the estimated interferences in each group, incurred from the users either in the same rate group or in the other rate groups, are refined successively with the assistance of the soft information in the symbol detection process. Moreover, for practical low-complexity implementations, the users in each group are further partitioned into smaller subgroups based on their effective channel correlations and then detected in parallel by a bank of minimum mean-squared error (MMSE) soft detectors to further reduce the computational load. Conducted simulations show that the proposed MUD can effectively suppress the MAI to render superior performance but with reduced computations compared to previous works.