An energy-conserving depth-based layering MAC protocol for underwater sensor networks

Underwater sensor networks (UWSNs) are effective tools for discovering and observing the underwater environment. Due to the unique characteristics of its acoustic channels such as long propagation delay, limited bandwidth, and high bit error rate, most contention-based Media Access Control (MAC) protocols are usually costly. As a result, both contention-based MAC protocols with and without RTS/CTS schemes do not perform as efficiently as their achieved performance in terrestrial networks. A collision-free approach is increasingly considered to more likely achieve a better performance by preventing any possibility of collisions in order to improve the energy efficiency and throughput across the network. In this paper, we propose a novel energy-conserving and collision-free depth-based layering MAC protocol, called DL-MAC, for UWSNs. Through multiple layers and distributed clustering approach, DL-MAC successfully schedules reception and transmission periods according to nodes priority in the network. It also addresses the spatial-temporal uncertainty, near-far, and hidden/exposed terminal problems. Our extensive simulation study shows that DL-MAC outperforms previously reported protocols in terms of throughput, packet delivery ratio, energy consumption, and fairness under varying offered loads.