Dynamic Countdown Scheduling MAC Protocol in Underwater Acoustic Sensor Networks

Underwater acoustic sensor networks (UASNs) are highly sensitive to collisions due to the unique characteristics of underwater acoustic signal propagation. Thus, developing medium access control (MAC) protocols that can effectively avoid collisions has become particularly important. This paper proposes a dynamic countdown scheduling MAC protocol (DCS-MAC) to achieve collision-free transmission for UASNs. First, transmission schedules of nodes are integrated directly into data frames, eliminating the need for control frames, thereby reducing latency and energy consumption. Second, considering defined collision constraint, a dynamic countdown strategy is introduced where the transmission schedule of each node dynamically adjusts according to collected collision constraints, reducing the probability of data frame collisions. Then, interval trees are used to dynamically update collision constraints, maximizing the coverage of collision time periods and selecting the optimal transmission schedule. Finally, simulation results show that DCS-MAC excels in data frame delivery rate, network throughput, throughput fairness, and energy consumption.