LDPC Code Design for Noncoherent Physical Layer Network Coding

TL;DR

This paper presents an optimization of LDPC codes for noncoherent physical-layer network coding in two-way relay channels, improving error-rate performance through EXIT-based Tanner graph design while maintaining standard code complexity.

Contribution

It introduces a novel EXIT-based Tanner graph optimization method for LDPC codes tailored to noncoherent PNC, enhancing relay decoding performance for specific modulation schemes.

Findings

Error rate improvements up to 1.2 dB demonstrated

Optimized codes tailored for M=4 and M=8 modulation orders

Performance gains achieved without increasing computational complexity

Abstract

This work considers optimizing LDPC codes in the physical-layer network coded two-way relay channel using noncoherent FSK modulation. The error-rate performance of channel decoding at the relay node during the multiple-access phase was improved through EXIT-based optimization of Tanner graph variable node degree distributions. Codes drawn from the DVB-S2 and WiMAX standards were used as a basis for design and performance comparison. The computational complexity characteristics of the standard codes were preserved in the optimized codes by maintaining the extended irregular repeat-accumulate (eIRA). The relay receiver performance was optimized considering two modulation orders M = {4, 8} using iterative decoding in which the decoder and demodulator refine channel estimates by exchanging information. The code optimization procedure yielded unique optimized codes for each case of modulation order and available channel state information. Performance of the standard and optimized codes were measured using Monte Carlo simulation in the flat Rayleigh fading channel, and error rate improvements up to 1.2 dB are demonstrated depending on system parameters.