Multi-User SR-LDPC Codes

TL;DR

This paper proposes Multi-User SR-LDPC coding for uplink NOMA, enabling multiple users to transmit efficiently with joint decoding, outperforming traditional schemes at finite blocklengths and matching MAP performance in some regimes.

Contribution

It introduces MU-SR-LDPC coding, extending SR-LDPC to multi-user scenarios with a low-complexity joint decoding algorithm, achieving higher spectral efficiency.

Findings

MU-SR-LDPC achieves higher spectral efficiency than OMA and NOMA at finite blocklengths.

Decoding performance approaches MAP decoding in certain regimes.

Numerical simulations support the theoretical advantages of MU-SR-LDPC.

Abstract

This article introduces a novel non-orthogonal multiple access (NOMA) scheme for coordinated uplink channels. The scheme builds on the recently proposed sparse-regression low-density parity-check (SR-LDPC) code, and extends the underlying notions to scenarios with many concurrent users. The resulting scheme, called Multi-User SR-LDPC (MU-SR-LDPC) coding, consists of each user transmitting its own SR-LDPC codeword using a unique sensing matrix in conjunction with a characteristic outer LDPC code. To recover the sent information, the decoder jointly processes the received signals using a low-complexity and highly-parallelizable AMP-BP algorithm. At finite blocklengths (FBL), MU-SR-LDPC codes are shown to achieve a target BER at a higher spectral efficiency than baseline orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA) schemes with similar computational complexity. Furthermore, MU-SR-LDPC codes are shown to match the performance of maximum a posteriori (MAP) decoding in certain regimes. For certain blocklengths and a sufficiently high number of users, MU-SR-LDPC codes may achieve a higher spectral efficiency than the approximate FBL capacity of the effective single-user Gaussian channel seen by each user in a comparable OMA scheme. Results are supported by numerical simulations.