State-of-the-Art Medium Access Control (MAC) Protocols for Underwater Acoustic Networks: A Survey Based on a MAC Reference Model

Similar to radio-frequency-based wireless networks (RWNs) used in terrestrial environments, the medium access control (MAC) protocol is a key element for underwater acoustic networks (UWANs). However, due to peculiar features of underwater acoustic channels such as long propagation delay, very small channel capacity, low channel reliability, and high dynamics of channel quality, not only MAC protocols but also MAC design strategies originally developed for RWNs cannot work well in UWANs. A large number of UWAN MAC protocols have been investigated in the literature, and most of them have not been reviewed in the available surveys. To allow the reader to have an overview on the state-of-the-art UWAN MAC protocols, this paper reviews these proposals with an enhanced MAC reference model. This model decomposes an MAC protocol into a couple of components that make up a common structure for various MAC protocols so that they can be more easily understood. The major remaining issues and possible research directions are also discussed.