EXIT chart analysis of turbo multiuser detection

We study the mutual information transfer characteristics of the soft interference cancellation (SIC) multiuser detectors (MUD) for coded code-division multiple-access (CDMA) systems in synchronous additive white Gaussian noise (AWGN) and asynchronous multipath fading channels. Based on the extrinsic information transfer (EXIT) chart technique, we compare the asymptotic (as the block length goes to infinity) performance and the convergence behavior of different joint detection schemes which are highly dependent upon different system parameters and channel conditions. A framework of using the EXIT chart to analyze the coding-spreading tradeoff is also addressed for turbo multiuser detection. Results show that the SIC-minimum mean square error (MMSE) MUD generally provides a higher spectral efficiency than the SIC-match filter (MF) MUD. Moreover, the impact of finite block length on the convergence behavior of turbo MUD is also analyzed using a consistent Gaussian approximation on the distribution of the output extrinsic information.