Convergence thresholds analysis of iterative multi-user detection

In this paper, we analyze the convergence behavior of an iterative (turbo) multi-user detection turbo-coded CDMA system. A recently proposed method to analyze the convergence behavior of turbo architectures is Variance Exchange Graph which uses the error variances of bits as a parameter to visualize the convergence behavior of iterative structures. It provides helpful design guidelines for iterative multi-user detection systems. In this paper, using the Variance Exchange Graph, the possibility of convergence to the single-user performance in terms of two parameters, signal to noise ratio and number of users, is predicted and analyzed. The predicted results are validated by simulations.