Analysis of iterative multi-user detection schemes with EXIT charts

CDMA has been established as a standard multiple access scheme in mobile radio communications. However, high spectral efficiency can only be achieved by applying multi-user detection schemes combatting the inherent multi-user interference. Since the optimum maximum likelihood approach is far too complex for practical implementations, suboptimum iterative strategies are applied. These iterative strategies follow the turbo principle well-known from coding theory and can be analyzed by means of extrinsic information transfer (EXIT) charts. This paper analyzes the performance of iterative multi-user detection schemes by EXIT charts. For simplicity, an AWGN channel and a synchronous transmission are assumed. Starting with optimum APP components, we show that the performance of the iterative scheme is well predictable by the EXIT chart technique. Results for different signal to noise ratios are presented. For non-ideal components like the parallel interference cancellation, the prediction becomes less accurate but is still possible.