Convergence behavior of iterative turbo multiuser detection algorithms

Mutual information transfer characteristics of soft-in/soft-out decoders have been used recently for studying the convergence behavior of iterative decoding algorithms. The swapping function of the extrinsic information is pictured as a decoding trajectory in the extrinsic information transfer (EXIT) chart. EXIT chart is a powerful tool for estimating the convergence and bit error rate of iterative decoding algorithms. We study the convergence behavior of turbo multiuser detection, and also of the group blind multiuser detection algorithm proposed recently, using the EXIT chart method. The influence of the different code memory lengths, code polynomials and cross correlation matrixes on the convergence behavior of the turbo multiuser detection algorithm are studied as well. Finally, the sensitivity of the turbo multiuser decoding algorithm to the signal-to-noise ratio mismatch at the receiver, is investigated by means of the EXIT chart.