On the Design of Multi-Dimensional Irregular Repeat-Accumulate Lattice Codes

TL;DR

This paper introduces a novel method for designing multi-dimensional lattice codes using non-binary IRA codes, enabling efficient decoding and near-Shannon-limit performance by leveraging permutation-invariance and Gaussian approximation.

Contribution

It proposes a new encoding structure for multi-dimensional IRA lattice codes that ensures symmetry and permutation-invariance, facilitating analysis and optimization.

Findings

Codes approach Shannon limit within 0.46 dB

Outperform existing lattice coding schemes

Enable Gaussian approximation for iterative decoding

Abstract

Most multi-dimensional (more than two dimensions) lattice partitions only form additive quotient groups and lack multiplication operations. This prevents us from constructing lattice codes based on multi-dimensional lattice partitions directly from non-binary linear codes over finite fields. In this paper, we design lattice codes from Construction A lattices where the underlying linear codes are non-binary irregular repeat-accumulate (IRA) codes. Most importantly, our codes are based on multi-dimensional lattice partitions with finite constellations. We propose a novel encoding structure that adds randomly generated lattice sequences to the encoder's messages, instead of multiplying lattice sequences to the encoder's messages. We prove that our approach can ensure that the decoder's messages exhibit permutation-invariance and symmetry properties. With these two properties, the densities of the messages in the iterative decoder can be modeled by Gaussian distributions described by a single parameter. With Gaussian approximation, extrinsic information transfer (EXIT) charts for our multi-dimensional IRA lattice codes are developed and used for analyzing the convergence behavior and optimizing the decoding thresholds. Simulation results show that our codes can approach the unrestricted Shannon limit within 0.46 dB and outperform the previously designed lattice codes with two-dimensional lattice partitions and existing lattice coding schemes for large codeword length.