Rate-Diverse Gaussian Multiple Access: Efficient Encoder and Decoder Designs

TL;DR

This paper introduces a novel rate-diverse encoding and decoding scheme for two-user Gaussian multiple access channels, enabling simultaneous decoding with improved performance over existing methods.

Contribution

It proposes practical LDPC code design methods and a joint decoding algorithm that outperform traditional schemes by decoding both user messages simultaneously.

Findings

Achieves up to 1.0 dB gain over existing schemes

Develops practical LDPC code design methods for rate-diverse GMAC

Identifies optimal rate allocation for best decoding performance

Abstract

In this work, we develop a pair of rate-diverse encoder and decoder for a two-user Gaussian multiple access channel (GMAC). The proposed scheme enables the users to transmit with the same codeword length but different coding rates under diverse user channel conditions. First, we propose the row-combining (RC) method and row-extending (RE) method to design practical low-density parity-check (LDPC) channel codes for rate-diverse GMAC. Second, we develop an iterative rate-diverse joint user messages decoding (RDJD) algorithm for GMAC, where all user messages are decoded with a single parity-check matrix. In contrast to the conventional network-coded multiple access (NCMA) and compute-forward multiple access (CFMA) schemes that first recover a linear combination of the transmitted codewords and then decode both user messages, this work can decode both the user messages simultaneously. Extrinsic information transfer (EXIT) chart analysis and simulation results indicate that RDJD can achieve gains up to 1.0 dB over NCMA and CFMA in the two-user GMAC. In particular, we show that there exists an optimal rate allocation for the two users to achieve the best decoding performance given the channel conditions and sum rate.