Enhanced SWIPT with Cooperative Relaying for Energy Efficient and Reliable NOMA based Underwater Acoustic Sensor Networks

Non-orthogonal multiple access (NOMA) based underwater acoustic sensor networks (UASNs) face several critical challenges, including limited bandwidth, energy constraints, and unreliable communication links. To address these issues, we propose an enhanced simultaneous wireless information and power transfer (ESWIPT) scheme with cooperative relaying (CR). Unlike terrestrial communication channels, underwater channels have distance-dependent bandwidth characteristics, where near users experience higher bandwidth than far users. Based on this, we propose enhanced power splitting (PS) and time switching (TS) SWIPT techniques combined with CR for NOMA-based UASNs. In the proposed scheme, the additional bandwidth available at the near user, by virtue of the lesser distance from the source, is utilized to harvest energy, and also the near user acts as a relay to forward messages to the far user. By combining enhanced SWIPT with CR, the proposed scheme achieves higher data rates, better energy efficiency, and lower outage probability. We derive closed-form expressions for the ergodic rate, energy efficiency, and outage probability for both enhanced PS-SWIPT (EPS-SWIPT) and enhanced TS-SWIPT (ETS-SWIPT) with CR. Analytical and simulation results show that the proposed scheme outperforms conventional CR and SWIPT methods in UASNs, making it a potential scheme for next-generation underwater sensor networks.