The Research Of MAC Protocol Based On TDMA For Underwater Acoustic Sensor Networks

With the fast development of underwater acoustic communication techniques, underwater acoustic sensor network (UAN) is being more and more used in the marine environment monitoring, development of mineral resources, navigation aid, natural disaster prevention, strategic command, and other aspects of the wide range of applications. Compared to the mature terrestrial radio communications, underwater acoustic sensor network has distinct characteristics, such as narrow available bandwidth, long propagation delay, and strong signal attenuation. Therefore, MAC protocols originated from the terrestrial wireless communication can not be directly applied to underwater acoustic communication, and dedicated MAC protocols should be proposed.By reviewing a large number of domestic and foreign researches under UAN, we identify several key problems that need to be addressed for designing MAC of UAN: delay, power consumption and fairness. Traditional handshake mechanism will worsen the acoustic communication delays and decrease the network throughput; unordered data transmissions lead to collisions and serious waste of energy; delay-induced unfairness impairs the overall network performance; the network is required to extendible enough to handle frequent entrance of new node or expiration of old nodes.Regarding to the special characteristics of underwater acoustic channel, we propose a dedicated Underwater TDMA MAC protocol (UN-TD) for the many-to-one underwater monitoring sensor network. Its basic idea is that, by dynamically monitoring the delay from the node to itself, the gate node or AP node schedules the sending slot, sleeping slot and listening slot for each client node in a centralized way, so as to maximize the overall network throughput and energy efficiency in the premise of guaranteeing collision-free packet transmission.We also compare UN-TD's performance of throughput, energy efficiency, average delay, fairness against ALOHA and DACAP. Simulation results show that: UN-TD outperforms the other three protocols in throughput, energy efficiency and fairness, at the expense of inducing longer delay. It is suitable for delay-insensitive many-to-one underwater monitoring sensor network.