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

2026-04-23

AI Summary

This work addresses the severe degradation of physical-layer network coding (PNC) reliability in multi-hop underwater acoustic networks, caused by multipath delay spread, inter-carrier interference from Doppler shifts, and error accumulation at relays. To mitigate these challenges, the paper proposes an OFDM-based iterative receiver architecture that integrates adaptive channel-aware factor-graph detection, a parity-constrained soft information refinement mechanism, and low-complexity superimposed LMMSE detection to enable efficient soft information exchange between detector and decoder. This design effectively suppresses error propagation and significantly enhances decoding accuracy over time-varying underwater acoustic channels. Simulations demonstrate a bit error rate on the order of 10⁻⁵ at 8 dB SNR with a relative node speed of 1.5 m/s. Both lake and sea trials confirm the scheme’s substantial performance gains over existing baseline methods in real-world underwater environments.

Technology Category

• Planning, Routing, and Scheduling: Scheduling under Uncertainty
• Multiagent Systems: Multiagent Systems under Uncertainty
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

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.

Problem

• Physical-layer network coding
• Underwater acoustic networks
• Bit error rate
• Inter-carrier interference
• Multi-hop relaying

Innovation

• Physical-layer Network Coding
• Iterative Receiver
• Underwater Acoustic Networks
• OFDM
• Error Accumulation Mitigation