Minimum joint probability of error based adaptive multiuser detection for multipath DS-CDMA channels

DS-CDMA is a popular multiple access technology for wireless communications. However, its performance is limited by multiple access interference and multipath distortion. Multiuser detection and space time processing are two signal processing techniques employed to improve the performance of DS-CDMA. We propose a blind adaptive space-time multiuser detection algorithm in this paper, based on the criterion of minimum joint probability of error (MJPOE). The optimal filter weights are computed adaptively using a gradient descent approach. The algorithm is blind and offers a BER performance better than the non-adaptive MMSE algorithm, at the cost of higher computational complexity. An approach for reducing the computational overheads of MJPOE using Gram-Schmidt orthogonalization is suggested. The convergence rate of MJPOE is much faster than earlier known adaptive implementations of the MMSE detector, viz. LMS and RLS. Simulation results are presented for asynchronous multipath channels, with multiple antennas employed at the receiver.