A study on the MAC protocol for dynamic underwater acoustic sensor networks

The design of the media access control protocol (MAC) is one of the key challenges during the developing of underwater acoustic sensor networks (USN). In contention-based MAC protocols, packet collisions can be reduced by exchanging control packets. And if a packet is lost, the sender usually retransmit it. But all the above are much more difficult to be adopted in USN because the propagation delay and the transmission energy consumption are pretty large. The contention-free MAC protocols such as TDMA are usually used in USN to overcome the difficulties led by contention based protocols. However, the channel efficiency is still very low when the classical TDMA and its variants with fixed timeslots are applied directly in dynamic USN. Aiming at this problem, a new guard time setting method is presented in this paper. It uses some prior information, such as the maximum propagation delay of the networks and the maximum relative speed of the sensor nodes with respect to the center node and the mechanism of the packet transmission for the sensor nodes. Analysis and simulations show that the proposed method can reduce the time interval of the data packets received at the center node, which can improve the channel efficiency and the performance of the dynamic USN effectively.