Multi-carrier CDMA with iterative decoding and soft-interference cancellation

A novel multi-user detection scheme applying iterative soft-interference cancellation in multi-carrier code division multiple access (MC-CDMA) systems is proposed and investigated. The novel detection scheme cancels the interference from the other users by taking into account reliability information about the detected interference. For this purpose, we do not use the decisions from the inner decoder (despreader) but the more reliable soft-values from the outer soft-in/soft-out decoder to reduce error propagation. It can be shown that the iterative soft-interference cancellation scheme clearly outperforms an MC-CDMA system with inner joint detection based on maximum likelihood sequence estimation (MLSE) which is followed by an outer channel decoder. Furthermore, the bit error rate (BER) obtained with the proposed scheme closely approaches the single-user bound. Hence, iterative soft-interference cancellation is able to eliminate almost all multiple access interference.