Space-time coded soft-iterative multiuser receivers for WCDMA

This paper proposes a soft-iterative multiuser receiver of low complexity, based on the principle of turbo decoding. A serially concatenated system is used, where every user employs a convolutional code, interleaver, space-time block code (STBC) and the spreading operation. The proposed receiver uses a soft-input soft-output (SISO) multiuser detector-decoder, which is basically a soft interference canceller for the space-time coded wideband code division multiple access (WCDMA) signal. In each iteration, extrinsic information is interchanged between the different SISO blocks giving asymptotically unbiased estimates. The introduction of STBC adds decorrelation between the different user signals, relaxing the interleaver design and less iterations are needed for the system to converge. The receiver allows the use of a less complex soft matched filter instead of a minimum mean square error (MMSE) filter. It achieves nearly single-user performance, and gives an excellent trade-off between implementation complexity and performance for advanced WCDMA multiuser receivers.