Soft interference cancellation and channel estimation in uncoded asynchronous DS-CDMA system

The conventional interference cancellation receiver is subject to performance degradation due to incorrect decisions on interference subtracted from the received signal. This paper aims at deriving algorithms to improve the performance of interference cancellation and channel estimation in an uncoded asynchronous DS-CDMA system with orthogonal modulation. Two soft cancellation schemes, one based on the maximum a posterior (MAP), the other based on the nonlinear minimum mean square error (MMSE) criterion are presented and proved to be superior to the conventional PIC scheme with minor increase in complexity. Furthermore, the best system performance (2dB gain in a 21-user system) is observed when the derived soft information is also used for channel estimation.