Fidelity Charts and Stopping/Termination Criteria for Iterative Multiuser Detection

An iterative multiuser detection (IMUD) receiver is considered for a code-division multiple-access (CDMA) system with turbo codes. Fidelity is considered as a metric for convergence analysis and an approximation of fidelity as a function of variance of the log-likelihood ratios is introduced. Fidelity charts are compared with extrinsic information transfer (EXIT) charts as tools for convergence analysis and a close approximation of the relationship between fidelity and mutual information is proposed. We then use this function to approximate a closed form expression for the EXIT function of an interference canceller. Further, we propose a new stopping criterion for the turbo decoder and the IMUD receiver which achieves complexity saving of up to 50% over conventional designs.