Contention free MAC protocol based on priority in underwater acoustic communication

Underwater acoustic sensor network technology can be applied in underwater environment such as the sea or rivers. It can be mainly used for data acquisition, underwater exploration, prevention of natural disasters, unattended environmental monitoring systems, and military for underwater surveillance. Despite of this promising outlook, underwater sensor network has so many limitations in communicating, due to a harsh environment like the water. Radio frequency is used mainly in the terrestrial sensor network, but this cannot be used in the underwater environment because of serious attenuation phenomenon in the water and limited bandwidth such as 30 ~ 300Hz. Optical wavelength is also not a solution in water due to light dispersion. Underwater sensor network can provides enhanced communication environment by using acoustic communication, which has an excellent transport characteristics in water. In spite of this advantage, acoustic communication in underwater environment has some limitations such as long propagation delay, low transfer rates and very limited bandwidth when compared to the ground. In addition, the underwater sensors can malfunction due to corrosion and limited battery capacity. Battery cannot be recharged easily due to the lack of energy source such as solar energy and limited reach ability in the water. Due to the different nature of the underwater environment and applications, there are several drawbacks with respect to the suitability of the existing terrestrial MAC solutions in the underwater environment. In fact, channel access control in UW-ASNs poses additional challenges due to the peculiarities of the underwater channel, in particular limited bandwidth, very high and variable delay, channel asymmetry, and heavy multipath and fading phenomena. Therefore, considering the above characteristics, a suitable MAC protocol with energy efficiency for underwater acoustic sensor network has to be developed.