Medium Access Control Protocols In Underwater Acoustic Sensor Networks

Underwater acoustic sensor network(UWASN)has tremendous application prospect in the marine environmental monitoring and resource explorations.There has'been a growing interest in the research and development of UWASN.Due to the high bit error rate,the low transmission rate and the limited available bandwidth of the underwater acoustic channel,UWASN has characteristics of high packet error rate,long packet transmission delay and spatial-temporal network delay time uncertainty.Therefore,designing effective networking techniques in underwater acoustic sensor network is of great importance.In this paper,we study the medium access control(MAC)technique in the UWASN.According to the long propagation delay in UWASN,we analyze the "efficiency"and "transmission" problems in the handshake-based MAC protocol,and propose waiting resource usage MAC(WRUMAC)protocol,aiming at reusing the idle resources.In the WRUMAC protocol,when a node receives a control packet,it waits for a period of time,and then sends a response packet.The waiting time is used to ensure that all the neighboring nodes of the control packet's sender have received that control packets in order to avoid the potential collisions.Using this method,we can solve the "transmission" problem caused by the asynchronous packet transmission in the UWASN with long propagation delay.The idle waiting time of a pair of nodes can be exploited by its neighboring nodes for extra data transmission.With this method,we can solve the problem of "efficiency" caused by idle resources waste in the UWASN.Theoretical analysis and simulation results show that the proposed MAC protocol can improve the network throughput,reduce the end-to-end delay and the energy consumption of the network.Considering the problems of long propagation delay,high packet error rate and multi-user transmission interference,we study the error control mechanism and efficient transmission scheme for the underwater acoustic communication,and propose an on-demand TDMA MAC protocol integrating continuous transmission and error control.In this protocol,we use on-demand TDMA to schedule multiple users to use the channel resources,a continuous ARQ scheme for packet transmission,and the hybrid ARQ(HARQ)mechanism to deal with the data packet error.Moreover,the time slots are assigned according to the traffic of the node,the error control mechanism and the state of the node.Simulation results show that the proposed on-demand TDMA MAC protocol has a higher network throughput and a lower end-to-end delay.In addition,the proposed protocol can adapt to the different network environment well.