Design of Low-Density Parity-Check Codes for Modulation and Detection

TLDR

The study examines a coding‑modulation scheme that feeds irregular LDPC coded bits directly into a modulator. The authors implement iterative decoding by linking LDPC variable nodes to detector nodes, optimize the code through curve fitting of extrinsic information transfer charts, and provide design examples for AWGN and MIMO fading channels with receiver‑side channel knowledge. On MIMO fading channels, the scheme achieves performance within 1.25 dB of capacity and surpasses a parallel‑concatenated turbo code by wide margins when transmit antennas exceed receive antennas.

Abstract

A coding and modulation technique is studied where the coded bits of an irregular low-density parity-check (LDPC) code are passed directly to a modulator. At the receiver, the variable nodes of the LDPC decoder graph are connected to detector nodes, and iterative decoding is accomplished by viewing the variable and detector nodes as one decoder. The code is optimized by performing a curve fitting on extrinsic information transfer charts. Design examples are given for additive white Gaussian noise channels, as well as multiple-input, multiple-output (MIMO) fading channels where the receiver, but not the transmitter, knows the channel. For the MIMO channels, the technique operates within 1.25 dB of capacity for various antenna configurations, and thereby outperforms a scheme employing a parallel concatenated (turbo) code by wide margins when there are more transmit than receive antennas.