TARS: A Traffic-Adaptive Receiver-Synchronized MAC Protocol for Underwater Sensor Networks

Efficient medium access control (MAC) is desirable for underwater sensor networks (UWSNs). However, designing an efficient underwater MAC protocol is challenging due to the long propagation delay of the underwater acoustic channel and the spatial-temporal uncertainty. In this paper, we propose a novel Traffic-Adaptive Receiver-Synchronized underwater MAC protocol, TARS, a stochastic light-weight channel access scheme that addresses the spatial-temporal uncertainty for maximizing the network throughput. We adjust the packet transmission time (phase) in a slot, which is dependent on the sender-receiver distance, to align packet receptions for collision reduction. Both the sound propagation speed variation and the node mobility are considered in setting the optimal transmission phase and the slot size. We employ a queue-aware utility-optimization framework to determine the optimal traffic-adaptive transmission strategies dynamically, taking into account both the packet interference and the data queue status. Extensive simulation results show that compared to the existing representative underwater MAC protocols, TARS achieves better performance with higher network throughput and lower packet end-to-end delay.