Protograph-Based LDPC Code Design for Bit-Metric Decoding

TL;DR

This paper introduces a protograph-based LDPC code design method optimized for bandwidth-efficient coded modulation, achieving near-capacity performance for high-order ASK with probabilistic shaping.

Contribution

It presents a joint optimization technique for LDPC node degrees and bit-channel mapping tailored for BICM with uniform and shaped inputs, matching multi-edge type code performance.

Findings

Codes operate within 0.69 dB of capacity at 4.2 bits/channel use

Constructed codes perform as well as existing multi-edge type codes

Achieves reliable communication at low error rates with high spectral efficiency

Abstract

A protograph-based low-density parity-check (LDPC) code design technique for bandwidth-efficient coded modulation is presented. The approach jointly optimizes the LDPC code node degrees and the mapping of the coded bits to the bit-interleaved coded modulation (BICM) bit-channels. For BICM with uniform input and for BICM with probabilistic shaping, binary-input symmetric-output surrogate channels are constructed and used for code design. The constructed codes perform as good as multi-edge type codes of Zhang and Kschischang (2013). For 64-ASK with probabilistic shaping, a blocklength 64800 code is constructed that operates within 0.69 dB of 0.5log(1+SNR) at a spectral efficiency of 4.2 bits/channel use and a frame error rate of 1e-3.