Multi-User Detection Based on Expectation Propagation for the Non-Coherent SIMO Multiple Access Channel
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We consider the non-coherent single-input multiple-output (SIMO) multiple access channel with Grassmannian signaling under Rayleigh block fading. We propose a novel soft-output multi-user detector that computes the marginalized posterior of each transmitted signal using only the knowledge about the channel distribution. Our detector is based on expectation propagation (EP) approximate inference and has polynomial complexity in the number of users. A simplification of this detector, with reduced complexity, coincides with soft minimum-mean-square-error (MMSE) estimation and successive interference cancellation (SIC). Both detectors produce accurate approximates of the true posterior which lead to a high mismatched sum-rate of the system that uses the approximate posterior as the decoding metric. The proposed detectors also outperform, in terms of symbol error rate, a conventional coherent pilot-based detector and a state-of-the-art detector based on projecting the received signal onto the subspace orthogonal to the interference. The gain of our EP and MMSE-SIC detectors are further observed in terms of the bit error rate when using their soft outputs for a turbo channel decoder.
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