Research On MAC Protocol For Underwater Acoustic Networks Based On CW-MAC

In recent years,military and civilian demand for marine resource exploitation has continued to grow,and underwater acoustic communication networks play a very important role in marine resource exploration,natural disaster warning,military intelligence collection and maritime military defence.However,unlike terrestrial wireless networks,which make extensive use of electromagnetic waves for communication,underwater acoustic communication networks are usually deployed in harsh environments with long propagation delay,narrow effective bandwidth,variable topologies and restricted node energy,so they cannot directly adopt the media access control（MAC）protocols applicable to terrestrial wireless communication networks.To address these issues,it is vital to study MAC protocols suitable for use in underwater acoustic communication networks.To address the problem of poor network performance caused by randomly selected node contention window（CW）of the traditional contention window MAC（CW-MAC）protocol,this thesis builds a model of a underwater acoustic sensor network with the help of NS-3 simulation software and uses the control variable method to adjust the number of nodes in the network,packet size,communication rate,node distribution range and simulation time to simulate the CW-MAC protocol and study the parameters affecting the average throughput of the CW-MAC protocol.This thesis proposes a congestion based contention window MAC（CCW-MAC）protocol to address the problems of poor channel fairness and large delay caused by the fixed CW in the traditional CW-MAC protocol.The CCW backoff mechanism adopted in this protocol divides the contention level of network nodes for channels into two stages:intense and moderate according to CW_basic,and adopts different uuadratic curves to calculate non-linear multiplication and division factors to adjust the CW of nodes in these two stages.Combining theoretical research and simulation analysis,it is clear that the CCW-MAC protocol effectively improves node access channel fairness,increases network throughput and reduces average end-to-end delay.To address the problem of empty window periods caused by large underwater propagation delays,this thesis proposes an adaptive varying contention window MAC（AVCW-MAC）protocol based on propagation delays.The AVCW backoff mechanism used in the protocol differentiates the CW of each node based on the propagation delay from each sensor node to the cluster and the two variables₁ and₂,which are the backoff factors.Simulation results show that the AVCW-MAC protocol has higher network throughput and lower average end-to-end delay than the traditional CW-MAC protocol with the same number of sensor nodes.