An Improved EPA based Receiver Design for Uplink LDPC Coded SCMA System

TL;DR

This paper proposes an EPA-based joint detection and decoding receiver for uplink LDPC-coded SCMA systems, significantly reducing complexity and latency while maintaining error rate performance.

Contribution

It introduces a novel EPA-based receiver design that integrates joint detection and decoding on an aggregated factor graph, improving over traditional message passing algorithms.

Findings

EPA-based receiver reduces computational complexity.

Faster convergence compared to Turbo receiver.

Maintains comparable error rate performance.

Abstract

Sparse code multiple access (SCMA) is an emerging paradigm for efficient enabling of massive connectivity in future machine-type communications (MTC). In this letter, we conceive the uplink transmissions of the low-density parity check (LDPC) coded SCMA system. Traditional receiver design of LDPC-SCMA system, which is based on message passing algorithm (MPA) for multiuser detection followed by individual LDPC decoding, may suffer from the drawback of the high complexity and large decoding latency, especially when the system has large codebook size and/or high overloading factor. To address this problem, we introduce a novel receiver design by applying the expectation propagation algorithm (EPA) to the joint detection and decoding (JDD) involving an aggregated factor graph of LDPC code and sparse codebooks. Our numerical results demonstrate the superiority of the proposed EPA based JDD receiver over the conventional Turbo receiver in terms of both significantly lower complexity and faster convergence rate without noticeable error rate performance degradation.