Medium Access Control in Underwater Sensor Networks: a comparison between the standard JANUS and ad-hoc energy efficient MAC protocols

One of the most relevant requirements for Underwater Wireless Sensor Networks (UWSNs) is energy saving and, because of the dense network deployment and the shared communication medium, an efficient MAC protocol is considered a key point to satisfy the rigid energy constraints. The development of MAC protocols for UWSNs is a challenging task due to energy limitations, long propagation delays and low data rates. For example, acoustic communication suffers from latencies five orders of magnitude larger than radio communication, so a naive code division multiple access (CSMA) MAC would require a very long listen time resulting in low throughput and poor energy efficiency. Efforts have been made to define MAC protocols based on both contention-free and contention-based techniques. The JANUS protocol defines a MAC protocol that has been proven to be effective in multiple conditions but few studies exist about its energy efficiency with respect to other underwater MAC protocols. To this end, the aim of this research is to provide a comparative study of several types of MAC protocols, including the one defined in the JANUS standard, in terms of energy efficiency and throughput. Furthermore, open research issues will be summarized.