FDCA: A Full-Duplex Collision Avoidance MAC Protocol for Underwater Acoustic Networks

Unlike terrestrial radio frequency communication, acoustic waves are major communication means in underwater networks. Unfortunately, acoustic waves incur long propagation delays that must be considered in the media access control (MAC) design to achieve a high throughput. Another major reason for low throughput is that almost all the acoustic modems operate under half-duplex mode. For increasing communication throughput, several full-duplex acoustic modems are proposed. However, most current MAC protocols are designed for half-duplex modems that are not suited for full-duplex modems. Toward a proper approach, this paper models and analyzes the impact of full-duplex modem characteristics on the Aloha protocol. We propose a full-duplex collision avoidance (FDCA) MAC protocol for underwater acoustic networks. It is a hand-shaking based protocol that designed for full-duplex modems to maximize network throughput. Collision avoidance schedule algorithm avoids the collisions at both the receiver and the sender by passively acquired local information (neighboring nodes' propagation delay and expected transmission schedules). Moreover, to cope with the channel's long propagation delay, it launches multiple simultaneous handshaking processes with neighbors to concurrently propagate multiple packets in the underwater channel. Our extensive simulation results have confirmed that the FDCA protocol outperforms the existing full-duplex MAC protocols in representative long propagation delay scenarios.