The Design And Analysis Of The MAC Protocol In Underwater Acoustic Sensor Networks

Unlike terrestrial networks that mainly rely on radio waves for communications, underwater networks utilize acoustic waves, which have comparatively lower loss and longer range in underwater environments. However, acoustic waves incurs long propagation delays that typically lead to low throughput. Besides, energy cost of transmission underwater is much higher than reception (almost 125:1). In addition, the adverse environmental conditions feature specific characteristics of underwater sensor networks, such as low communication bandwidth, large propagation delay, high error probability, and intermittent connectivity, and pose a range of challenges to underwater communication and networking.Based on the aforementioned observations, we explore from the following several aspects to provide reliable and efficient communication:(1) to predict and reduce collision and retransmission; (2) to use appropriate MAC scheduling schemes to enable efficient communication underwater sensor networks. This thesis firstly investigates DOTS protocol which uses passively obtained local information to increase the chances of concurrent transmissions while reducing the likelihood of collisions. However, this protocol cannot well deal with the situation where several exposed terminals or hidden terminals compete the chances of concurrent transmission. Therefore, this paper adopts simple but efficient listening period assignment scheme to reduce the concurrent competition collisions of exposed terminals or hidden terminals.Secondly, we propose an underwater practical MAC protocol, called UPMAC. The main objective of UPMAC is to adapt to the network load conditions by providing two modes (high and low load modes) and switching between them based on different offered load. Turn-around time overhead is reduced and it is less vulnerable to control packet corruption, since we reduce the use of control packets by the technique of piggyback. UPMAC provides a low data collision rate in both one-hop and multi-hop situations because we use Receiver-based approach in high load mode.Finally, we implement UPMAC, ADOTS and many other existing underwater acoustic MAC protocols on the simulator Aqua-Sim. We set many scenarios to compare and analyze the performance of these protocols. Extensive simulations show that our approach can achieve significantly better performance in both general and Sea Swarm topologies.