A low-complexity iterative multiuser receiver for turbo-codedDS-CDMA systems

Optimal joint multiuser detection and decoding for direct-sequence code-division multiple-access (DS-CDMA) systems with forward error correction normally requires prohibitively high computational complexity. A suboptimal solution with low complexity is therefore appealing for use in practical applications. We propose a low-complexity iterative multiuser receiver for turbo-coded DS-CDMA systems. The proposed approach consists of a modified decorrelating decision-feedback detector (MDDFD) and K single-user turbo decoders, where K is the number of users in the DS-CDMA system. The MDDFD is derived on the basis of maximizing a likelihood probability and has a feature that it can use the reliability information from the turbo decoders' output. In addition, the MDDFD can deliver interference-cancelled soft outputs to the turbo decoders where the calculation of transition metrics is modified appropriately. Both performance analysis and computer simulation results have indicated that the reliability information from the turbo decoders' output can enhance the multiuser detection capability of the MDDFD. Computer simulations have also shown that the proposed iterative multiuser receiver outperforms the conventional DDFD-based multiuser receiver in terms of the bit-error probability