Efficient multi-rate multi-user detection for the asynchronous WCDMA uplink

Sub-optimal multi-user joint-detection (JD) is an effective technique for combating the effects of multiple-access interference in CDMA communication systems. Its implementation, however, is accompanied by a prohibitive computational complexity when supporting large numbers of asynchronous users and channels with long impulse responses. Two approaches for the reduction of this complexity are compared. The first is based on an approximate Cholesky factorization. The second is based on iterative schemes such as the method of conjugate gradients or the Jacobi algorithm and its derivatives. The two approaches result in significant reductions in complexity at the expense of little or no degradation in performance. Results are presented for the asynchronous multi-rate environment of the WCDMA uplink with exact and realistic channel estimates.