Design of a Propagation-Delay-Tolerant MAC Protocol for Underwater Acoustic Sensor Networks
Underwater acoustic sensor networks (UASNs) can be employed in a vast range of applications, retrieving accurate and up-to-date information from underneath the ocean's surface. Although widely used by terrestrial sensor networks, radio frequencies (RFs) do not propagate well underwater. Therefore, acoustic channels are employed as an alternative to support long-distance and low-power communication in underwater sensor networks even though acoustic signals suffer from long propagation delay and have very limited bandwidth. In this paper, we introduce an adaptive propagation-delay-tolerant collision-avoidance protocol (APCAP) for the media access control (MAC) sublayer of UASN. The protocol includes an improved handshaking mechanism that improves efficiency and throughput in UASN where there is a large propagation delay. The mechanism guarantees nodes that can potentially interfere with a forthcoming transmission are properly informed. It also allows a node to utilize its idle time while waiting for messages to propagate, which is otherwise wasted by most existing MAC protocols. The simulation results indicate that where employed by UASN, APCAP exhibits good performance and outperforms the other MAC protocols examined in this paper.