Adaptive iterative CDMA multiuser detection in unknown multipath channels

Abstract

This paper presents an adaptive iterative (turbo) receiver for coded asynchronous CDMA systems. This receiver consists of a soft-input soft-output (SISO) multiuser detector, which is implemented in the weighted least squares (WLS) sense with the BCJR algorithm, and a bank of SISO channel decoders. All parameters needed for the receiver are estimated or adaptively obtained. Simulation results show that in a multicellular environment the proposed adaptive turbo receiver outperforms the matched filtered turbo receiver in terms of bit error rate (BER) performance. It is observed that the turbo principle allows significant reduction in training overhead. As the SNR increases, the adaptive receiver's BER performance is found to approach the optimal WLS receiver's performance.