Bandwidth Efficient and Rate-Matched Low-Density Parity-Check Coded Modulation

TL;DR

This paper introduces a bandwidth-efficient coded modulation scheme combining probabilistic shaping with LDPC codes, achieving near-capacity performance across various spectral efficiencies without iterative demapping.

Contribution

It proposes a novel low-complexity coded modulation scheme using distribution matching and LDPC codes, applicable to ASK and QAM, with rate adaptation and near-capacity performance.

Findings

Operates within 1 dB of AWGN capacity at 1e-3 FER

Supports spectral efficiencies from 1 to 5 bits/s/Hz

Uses only 5 modulation modes for flexible rate adaptation

Abstract

A new coded modulation scheme is proposed. At the transmitter, the concatenation of a distribution matcher and a systematic binary encoder performs probabilistic signal shaping and channel coding. At the receiver, the output of a bitwise demapper is fed to a binary decoder. No iterative demapping is performed. Rate adaption is achieved by adjusting the input distribution and the transmission power. The scheme is applied to bipolar amplitude shift keying (ASK) constellations with equidistant signal points and it is directly applicable to two-dimensional quadrature amplitude modulation (QAM). The scheme is implemented by using the DVB-S2 low-density parity-check (LDPC) codes. At a frame error rate of 1e-3, the new scheme operates within less than 1 dB of the AWGN capacity 0.5log2(1+SNR) at any spectral efficiency between 1 and 5 bits/s/Hz by using only 5 modes, i.e., 4-ASK with code rate 2/3, 8-ASK with 3/4, 16-ASK and 32-ASK with 5/6 and 64-ASK with 9/10.