A Sequence-Scheduled and Query-Based MAC Protocol for Underwater Acoustic Networks with a Mobile Node

摘要

Since mobile nodes such as autonomous underwater vehicles can effectively expand network coverage, underwater acoustic networks with mobile nodes have attracted more and more attention in recent years. To ensure the timely access of a mobile node without disturbing the normal transmission of data packets from static nodes, a sequence-scheduled and query-based medium access control protocol is proposed in this paper. The underwater nodes with data packets to be transmitted reply with a control packet for channel reservation after receiving the broadcast control packet of the buoy, then the reserved nodes transmit their data packets as the order calculated by the buoy. We develop a mechanism to adjust the transmission order of the control packets sent by the underwater nodes in the handshake phase to reduce the collision and guarantee the success rate of reservation, and a query is initiated when the reserved control packet of the mobile node is not received by the buoy in the handshake to respond to the data transmission request of the mobile node in time. Simulations show that the maximum nodal throughput of the proposed MAC protocol increases by at least 20% and the access delay of the mobile node decreases by about 90%, compared to the two reference protocols. Besides, the average access probability of the mobile node in the proposed protocol is more than 90%.