LDPC Codes with Soft Interference Cancellation for Uncoordinated Unsourced Multiple Access

TL;DR

This paper introduces an improved unsourced multiple access coding scheme using LDPC codes with soft interference cancellation, significantly enhancing performance over previous methods by enabling effective soft information exchange.

Contribution

It replaces the polar code with an LDPC code and employs a soft-input soft-output MMSE estimator, enabling better iterative decoding in unsourced multiple access channels.

Findings

Significant performance improvements over previous schemes.

Effective soft information passing between MMSE estimator and LDPC decoder.

State-of-the-art results across various system parameters.

Abstract

This article presents a novel enhancement to the random spreading based coding scheme developed by Pradhan et al.\ for the unsourced multiple access channel. The original coding scheme features a polar outer code in conjunction with a successive cancellation list decoder (SCLD) and a hard-input soft-output MMSE estimator. In contrast, the proposed scheme employs a soft-input soft-output MMSE estimator for multi-user detection. This is accomplished by replacing the SCLD based polar code with an LDPC code amenable to belief propagation decoding. This novel framework is leveraged to successfully pass pertinent soft information between the MMSE estimator and the outer code. LDPC codes are carefully designed using density evolution techniques to match the iterative process. This enhanced architecture exhibits significant performance improvements and represents the state-of-the-art over a wide range of system parameters.