A variational free energy minimization interpretation of multiuser detection in CDMA

We propose a unified approach for deriving and studying multiuser detection algorithms using the concept of variational free energy minimization. Under this generalized framework, we readily arrive at many popular multiuser detection schemes. In addition to its systematic appeal, there are several other advantages of this viewpoint. First of all, by condensing the design of multiuser detectors into the selection of a few key probability distributions, namely p(b), p(r|b) and Q(b), we provide rigorous justifications for numerous detectors that were proposed on heuristic grounds and recommend new and improved designs. Furthermore, the free energy formulation facilitates convenient joint detection and decoding (utilizing the turbo principle) when error-control codes are incorporated, as well as efficient parameter estimation via the variational expectation maximization (EM) algorithm.