Non-Coherent Multi-User Detection Based on Expectation Propagation

In this paper, we propose a novel soft-output multi-user detector for non-coherent multiple access with Grassmannian signaling under Rayleigh block fading. Our detector is based on expectation propagation (EP) approximate inference and has polynomial complexity in the number of users. A simplified version of this scheme coincides with a scheme based on soft minimum-mean-square-error (MMSE) estimation and successive interference cancellation (SIC). Both schemes, especially EP, produce accurate approximates of the true posterior. They outperform a baseline decoder based on projecting the received signal onto the subspace orthogonal to the interference in terms of both hard-detected symbol error rate and coded bit error rate.