# Multi-User Detection Based on Expectation Propagation for the Non-Coherent SIMO Multiple Access Channel

## TL;DR

This paper introduces a novel expectation propagation-based multi-user detector for non-coherent SIMO multiple access channels, achieving improved performance over existing methods in symbol error rate and sum-rate, with polynomial complexity.

## Contribution

It develops a new EP-based detector for non-coherent SIMO channels that outperforms state-of-the-art methods and simplifies complexity with two variants.

## Key findings

- Outperforms projection-based interference mitigation methods.
- Achieves lower symbol error rates than conventional coherent detectors.
- Provides high achievable sum-rates and improved BER with turbo decoding.

## Abstract

We consider the non-coherent single-input multiple-output (SIMO) multiple access channel with general signaling under spatially correlated Rayleigh block fading. We propose a novel soft-output multi-user detector that computes an approximate marginal 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, the number of receive antennas, and channel coherence time. We also propose two simplifications of this detector with reduced complexity. With Grassmannian signaling, the proposed detectors outperform a state-of-the-art non-coherent detector with projection-based interference mitigation. With pilot-assisted signaling, the EP detector outperforms, in terms of symbol error rate, some conventional coherent pilot-based detectors, including a sphere decoder and a joint channel estimation-data detection scheme. Our EP-based detectors produce accurate approximates of the true posterior leading to high achievable sum-rates. The gains of these detectors are further observed in terms of the bit error rate when using their soft outputs for a turbo channel decoder.