T-Lohi: A New Class of MAC Protocols for Underwater Acoustic Sensor Networks

TLDR

Underwater acoustic sensor networks require MAC protocols that cope with extreme latencies and high collision risk, making conventional CSMA designs inefficient. This work proposes T‑Lohi, a distributed, energy‑efficient MAC protocol tailored for underwater acoustic sensor networks. T‑Lohi uses a tone‑based contention resolution that leverages space‑time uncertainty and a low‑power wake‑up receiver to detect collisions and count contenders, achieving high throughput across all loads. Simulations show T‑Lohi’s energy cost is only 3–9 % above optimal, its channel utilization reaches up to 30 % of the theoretical maximum, and it remains stable and fair across all load levels.

Abstract

This paper introduces T-Lohi, a new class of distributed and energy-efficient media-access protocols (MAC) for underwater acoustic sensor networks (UWSN). MAC design for UWSN faces significant challenges. For example, acoustic communication suffers from latencies five orders-of-magnitude larger than radio communication, so a naive CSMA MAC would require very long listen time resulting in low throughput and poor energy efficiency. In this paper, we first identify unique characteristics in underwater networking that may affect all MACs, such as space-time uncertainty and deafness conditions. We then develop T-Lohi employing a novel tone-based contention resolution mechanism that exploits space-time uncertainty and high latency to detect collisions and count contenders, achieving good throughput across all offered loads. Lohi uses our low-power wake-up receiver to significantly reduce energy consumption. Finally, we evaluate design choices and protocol performance through extensive simulation. The results show that the energy cost of packet transmission is within 3-9 % of optimal, and that Lohi achieves good channel utilization, within 30% utilization of the theoretical maximum. We also show that Lohi is stable and fair under both low and very high offered loads.