R-MAC: An Energy-Efficient MAC Protocol for Underwater Sensor Networks

Underwater sensor networks are significantly different from terrestrial sensor networks in that sound is mainly used as the communication medium. The long propagation delay and limited bandwidth of acoustic channels make the existing MAC protocols designed for radio networks either unpractical or not energy efficient for underwater sensor networks. In this paper, we propose a reservation-based MAC protocol, called R-MAC. The major design goals of R-MAC are energy efficiency and fairness. R-MAC schedules the transmissions of control packets and data packets to avoid data packet collision completely. The scheduling algorithms not only save energy but also solve the exposed terminal problem inherited in RTS/CTS-based protocols. Furthermore, the scheduling algorithms allow nodes in the network to select their own schedules, thus loosening the synchronization requirement the protocol. Additionally, R-MAC supports fairness. By simulations, we show that R-MAC is an energy efficient and fair MAC solution for underwater sensor networks.