Research On MAC Design And Implementation Of Underwater Mobile Node Networking

With the rapid development of marine affairs,underwater acoustic network technology has developed rapidly in recent decades.Media access control(MAC)protocol is an important part of underwater acoustic network,which divides the underwater acoustic channel resources to each node and guarantees the reliable communication between the nodes.The underwater acoustic channel is complex and changeable,the long time delay and the narrow band width make the design of underwater MAC protocol face higher packet loss rate and longer network delay than that of MAC protocol which is used on the land.No MAC protocol is suitable for all networks.The goal of this paper is to solve the problems of long network delay and high packet loss caused by long and varying transmission delay when MAC protocol is used in underwater mobile network,so as to improve the throughput of underwater mobile network and to improve the network performance.This paper has done the following works.Firstly,the common network simulation software is introduced,OPNET is selected as the network simulation software,and then to solve the problems existing in OPNET wireless communication model when used in the underwater acoustic network,the pipeline file parameters in the OPNET wireless communication model are modified,so that it can adapt to the underwater acoustic channel.The physical layer of underwater acoustic channel is analyzed,and the bit-error rate curve obtained by simulation of the physical layer is taken into OPNET to simulate the behavior of the physical layer,after these the entire underwater acoustic network simulation platform is built.To solve the problems existing in the MAC protocols based on TDMA protocol when used for underwater mobile network,the DTSHL protocol is improved,to allow the underwater mobile network synchronous more accurately and efficiently,the improved protocol synchronization time is about one-half of the original protocol,and the synchronous precision is basically identical with the original protocol.The traditional TDMA protocol has the problem of low channel utilization in underwater environment,to solve this problem,the TDMA protocol based on delay time is studied,and the protection time is added to the mobile nodes to ensure the reliability of packet transmission and improve the throughput.Simulation results show that the improved protocol has higher throughput,lower network delay and packet loss rate when applied in the underwater mobile network under balanced load,the results also show that when the node speed is faster,the network has better performance.Finally,an adaptive MAC protocol is designed for the defects of the improved TDMA protocol and ALOHA protocol,such as long network delay at low network load which the improved TDMA protocol has and high packet loss rate at high network load which exists in ALOHA protocol.The simulation results show that the adaptive MAC protocol both have the characteristics of the improved TDMA protocol which has low packet loss rate and ALOHA protocol which has low time delay under the condition of unbalanced network load,and the throughput is always kept at a high level.