A Low-Complexity Multi-User CDMA Receiver with Blind Channel Estimation and Partially Adaptive MAI Suppression

A low complexity multi-user receiver with blind channel estimation and multiple access interference (MAI) suppression is proposed for a CDMA system under multipath fading and frequency offset. The design of the receiver involves the following procedure. First, a method of joint MAI suppression and channel estimation is developed based on the generalized sidelobe canceller (GSC) technique. In particular, channel estimates are obtained blindly in the form of the effective composite signature vectors (CSV) of the users. Second, a low-complexity partially adaptive (PA) realization of the receiver is proposed which incorporates reduced-rank processing based on the information of multi-user CSV's. By a judiciously designed decorrelating procedure, a new PA receiver is obtained with a much lower complexity. Finally, pilot symbols assisted frequency offset estimation and channel gain compensation give the estimate of users' symbols. Further performance enhancement is achieved by a decision aided scheme in which the signal is reconstructed and subtracted from the receiver input data, leading to significantly faster convergence. The proposed receiver is shown to be robust to multipath fading and frequency offset, and achieves nearly the same performance of the optimal maximum SINR and MMSE receivers with a much lower overhead for pilot symbols.