Noncoherent LDPC-Coded Physical-Layer Network Coding using Multitone FSK

TL;DR

This paper presents a noncoherent LDPC-coded physical-layer network coding scheme using multitone FSK that improves throughput and energy efficiency in fading channels through novel demodulation, iterative decoding, and optimized LDPC codes.

Contribution

It introduces a novel soft-output demodulator and optimized LDPC codes for noncoherent physical-layer network coding with multitone FSK, enhancing performance and energy efficiency.

Findings

Bit-error rate improved by up to 1.1 dB with optimized LDPC codes.

Performance approaches the theoretical achievable rate.

Energy efficiency gains are more significant with higher modulation orders.

Abstract

A noncoherent two-way relaying system is developed using physical-layer network coding for improved throughput over conventional relaying in a fading channel. Energy-efficient noncoherent operation is achieved using multitone frequency shift keying (FSK). A novel soft-output demodulator is developed for the relay, and corresponding achievable exchange rates are found for Rayleigh fading and AWGN channels. Bit-error rate performance approaching the achievable rate is realized using a capacity-approaching channel code and a receiver architecture that iterates between demodulation and channel decoding. Iterative decoding is performed feeding information back from the channel decoder to the demodulator. Additionally, error-rate performance is made to approach the achievable rate more closely by optimizing LDPC codes for this system. The energy efficiency improvement obtained by increasing the modulation order is more dramatic for the proposed physical-layer network coding scheme than it is for a conventional point-to-point system. Using optimized LDPC codes, the bit-error rate performance is improved by as much as 1.1 dB over a widely known standardized LDPC code, and comes to within 0.7 dB of the limit corresponding to the achievable rate. Throughout this work, performance for physical-layer network coding is compared to conventional network coding. When noncoherent FSK is used, physical-layer network coding enables higher achievable rates, and conventional network coding exhibits better energy efficiency at low rates.