Fair MAC Protocol Based on Adaptive DIFS for Underwater Acoustic Sensor Networks

Abstract: Underwater acoustic sensor networks (UASNs) have become a very active research area in recent years. Compared with wireless networks, UASNs have long propagation delay of acoustic signals, which pose challenges to the design of medium access control (MAC) protocol. There is a spatial unfairness problem caused by spatial-temporal uncertainty. The packet arrival time at the receiver depends on both the distance between the sender and receiver and the sender’s transmission time. Therefore, it is hard to provide the fairness to channel access among senders in UASNs. In this paper, we propose a fair MAC protocol based on adaptive DIFS (DCF inter-frame space) to solve the unfairness problem. In CSMA based MAC protocols, if the channel is idle for a fixed DIFS period of time, then a sender starts its own backoff process. In the proposed protocol, the DIFS value is dynamically set according to the distance between the sender and the receiver. Senders with close distances from the receiver have large DIFS values, and distant senders have small DIFS values. The proposed protocol addresses the unfairness problem by equalizing channel access probabilities of all nodes regardless of the distance.