Weighted extrinsic feedback in the iterative multiuser decoding of coded CDMA

In iterative decoding it is well accepted that extrinsic information is to be exchanged between full-complexity soft-input, soft-output constituent decoder components. It is, however, still an open problem to determine the optimal information for exchange between reduced complexity decoder components that are only approximating posterior probabilities. In this paper we investigate the use of weighted extrinsic feedback in iterative multiuser decoding for coded code-division multiple-access (CDMA) systems. The case of no extrinsic feedback corresponds to the conventional approach of exchanging extrinsic information, while full extrinsic feedback corresponds to exchanging a posteriori information. Weighted extrinsic feedback offers a trade-off between the two extreme cases, which can provide significant improvements. These improvements are demonstrated through simulation of an iterative multiuser decoder using parallel interference cancellation as the soft-input, soft-output multiuser detector