Iterative Receiver Processing at Relays in PNC-Enabled Multi-Hop Underwater Acoustic Networks

TL;DR

This paper introduces an iterative detection and decoding strategy for relay nodes in PNC-enabled multi-hop underwater acoustic networks, improving reliability and reducing error rates in challenging multipath and Doppler conditions.

Contribution

It proposes a novel adaptive detection framework combining three algorithms to enhance BER performance in time-varying UWA channels with practical validation.

Findings

Achieves BERs around 10^{-5} at 8 dB SNR and 1.5 m/s velocity.

Outperforms baseline schemes in lake experiments and sea trials.

Demonstrates robustness of the proposed algorithms in real multi-hop UWA deployments.

Abstract

Physical-layer network coding (PNC) can increase end-to-end throughput in bi-directional multi-hop underwater acoustic (UWA) networks. However, multipath delay spread and Doppler-induced inter-carrier interference (ICI) in UWA channels can degrade the reliability of PNC transmission in a three-node relay configuration. More critically, error accumulation across multiple relay nodes leads to a pronounced increase in the end-to-end bit error rate (BER) in multi-hop networks. To address this issue, we develop an iterative detection and decoding processing strategy for relay nodes within a PNC-enabled multi-hop UWA network based on orthogonal frequency division multiplexing (OFDM) modulation. The proposed design integrates three key algorithms: (i) an adaptive channel-aware factor graph detection algorithm that is suited for time-varying UWA channels; (ii) a parity-check-constrained soft-information refinement algorithm that improves the accuracy of the information feedback from the decoder to the detector; and (iii) a linear minimum mean square error (LMMSE) detection algorithm based on a superimposed model, which offers low computational complexity as an alternative scheme. Extensive simulation results demonstrate that the adaptive detection algorithm achieves BERs on the order of $10^{-5}$ at a relative velocity of 1.5 m/s UWA channel and a signal-to-noise (SNR) of 8~dB. Both lake experiments and sea trials in the Taiwan Strait confirm that the proposed iterative receiver algorithms outperform baseline schemes in terms of BER performance under practical UWA channel conditions, showing their robustness and applicability in real multi-hop deployments.