Improved Multistage Detector by Mean-Field Annealing in Multi-User CDMA

We propose a multistage multi-user detector for Code Division Multiple Access that implements Mean-Field Annealing. Annealing is a well known technique to avoid local minima in detection and optimisation problems. Local minima certainly occurs in CDMA multi-user detection leading to anomalous Bit Error Rate curves. Annealing is implemented as a standard multi-user detector implementing interference cancellation, but with a control parameter determining the slope of the squashing/mapping function. We derive a bound on the control parameter for the first stage of the detector. We also propose an annealing scheme. We show empirically the performance of the proposed detector, which follows closely the optimum detector implemented by exhaustive search, i.e. has gains of several dB’s compared to standard multiuser detectors like linear-MMSE, linear-MMSE first stage followed by interference cancellation, and multi-stage interference cancellation with clipped soft decision, the last being the closest to our proposed detector. The proposed detector gains up to dB compared to the Clipped Soft Decision Multistage detector at no added complexity. Keywords— CDMA, Multistage Multi-User Detection, Interference Cancellation, Anomalous -curves.