Performance analysis of minimum variance CDMA receivers

Constrained optimization of the receiver's output variance has previously been proposed as a relatively simple method for designing blind multiuser detectors for DS-CDMA systems. A single constraint is sufficient for the AWGN case, whereas multiple constraints should be used in a multipath environment. It is shown in this paper that the choice of the constraint parameters in the multipath case can have a significant effect on the system performance. A max/min approach for optimizing the constraint is proposed, resulting in blind solutions with improved performance. It is shown that the performance of the proposed method tends to be close to that of the MMSE receiver at high SNR, whereas the constraint parameters converge to the multipath channel parameters. The proposed method does not require knowledge of the interfering users' codes and timing. Simulation results support those performance claims.