ASYMPTOTIC ANALYSIS OF ITERATIVE CHANNEL ESTIMATION AND MULTIUSER DETECTIONWITH SOFT FEEDBACK IN MULTIPATH CHANNELS

Large system analysis of a randomly spread direct-sequence code-division multiple-access system in a frequency-selective chan-nel is considered. The receiver uses iterative channel estimation and multiuser detection (MUD) with soft feedback from single-user decoders to refine both the decisions of the linear minimum mean square error (LMMSE) MUD, and the initial pilot-based estimates of the LMMSE channel estimator. Replica method, a tool from statistical physics, and density evolution with Gaussian approxima-tion are used to obtain the asymptotic performance of the LMMSE MUD with soft parallel interference cancellation. The results indi-cate that as the channel coherence time grows, the performance of corresponding single-user system having perfect channel state in-formation can be approached even in an overloaded multiuser sys-tem using channel estimation and vanishing pilot overhead. 1