Abstract:In long-code used DS/CDMA communication systems, the convergence of perfor-mance is limited by the number of users in multi-stage Linear Soft Decision Parallel Interference Cancellation (LSD-PIC) multiuser detectors. In this paper, the precondition method in matrix computation is proposed to be applied to improve the convergence of iteration and overcome the convergence breakdown in the case of high load for the LSD-PIC multiuser detectors. Further-more, the polynomial preconditioner which could be obtained by low computational complexity is proposed, and the optimal coefficients for zero-order and first order polynomial preconditioner are deduced.