Protograph-Based LDPC Code Design for Shaped 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 shaped and uniform inputs in high-order ASK schemes.

Contribution

It presents a joint optimization technique for LDPC node degrees and bit-to-channel mappings tailored for shaped and uniform BICM, improving code performance close to theoretical limits.

Findings

Codes operate within 0.63dB and 0.69dB of capacity.

Designed codes achieve target error rates at high spectral efficiencies.

Performance matches or exceeds prior multi-edge type codes.

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 for the code design are used. The constructed codes for uniform inputs perform as good as the multi-edge type codes of Zhang and Kschischang (2013). For 8-ASK and 64-ASK with probabilistic shaping, codes of rates 2/3 and 5/6 with blocklength 64800 are designed, which operate within 0.63dB and 0.69dB of continuous AWGN capacity for a target frame error rate of 1e-3 at spectral efficiencies of 1.38 and 4.25 bits/channel use, respectively.