Optimized Resource Allocation for Delay-Tolerant ALOHA–NOMA for Enhancing the performance of Underwater Acoustic Sensor Networks

In this work, we introduce a propagation delay-tolerant ALOHA–NOMA-based cross-layer protocol for enhancing the performance of Underwater Acoustic Sensor Networks (UASNs). Various phenomena such as multi-path fading, Doppler spread, frequency as well as distance-dependent path loss, and limited available distance-dependent bandwidth have a significant impact on performance of UASNs. Due to these distinct characteristics, ALOHA is often considered a viable medium access control (MAC) protocol for UASNs, even though ALOHA is inefficient as far as channel utilization is concerned. Recently, non-orthogonal multiple access (NOMA) has been envisioned as a thriving enabling technology to meet the burgeoning demands of energy-constrained and bandwidth-constrained UASNs. As a result, we propose propagation delay-tolerant ALOHA-NOMA, where NOMA is employed in the physical layer with optimal utilization of distance-dependent bandwidth and transmission power, to improve the performance of ALOHA-based UASNs. We derive closed-form expressions for the MAC layer utilization factor, goodput, and energy consumption in UASNs by taking into account UASN channel characteristics. Results show that the proposed ALOHA-NOMA scheme significantly improves the performance of UASNs. Finally, we also derive mathematical expressions for the optimal channel attempt rate to maximize the MAC layer utilization factor. The analytical results are validated through extensive ns-3 simulations.