Research On Congestion Control Based On MAC Layer Auto Rate Protocol In Ad Hoc Networks

Ad Hoc network is a centerless network which is composed of several wireless data transmission devices and does not need fixed communication facilities.The network node is not only a communication terminal,but also can be used as a router to forward data for other nodes.Media access control protocol is an important part of the Ad hoc network protocol architecture.It is mainly used to coordinate nodes access to shared channels,which directly affects the network congestion response speed.The MAC protocol can effectively use limited wireless resources to play a decisive role in the performance of Ad hoc network.Therefore,it is significant to study the MAC protocol and related technologies of Ad hoc network and improve the performance of MAC protocol.Channel competition is a way to solve the wireless channel conflict,and the research of channel competition algorithm is of great significance to improve the total throughput of the network.In this paper,the effect of channel transmission rate on network throughput is analyzed.In view of the problem of network performance anomaly in multi rate network,and with the increase of node number,the node causes too much collision and frequent backoff because the node still uses the original initial competitive window to access the channel,and proposes a competitive window Control algorithm.Set initialization of the contention window,for each node according to the different transmission rate,so as to improve the fairness of the time.The improvement measure increase the chance of the high rate nodes competition to getting into the channel and solve the performance anomaly in the network so as to achieve the basic fairness.On the basis of realizing the fairness of multi rate time,the corresponding optimal competitive window value can be selected according to the change of the number of nodes to reduce the collision probability and avoid too many backoff.In the NS2 network simulation experiment,the improved competitive window control algorithm of rate adaptive MAC protocol is combined with rate adjustment algorithm of RBAR,so that the network performance is greatly improved,and the throughput and fairness are better.The rate adaptive MAC protocol only chooses the transmission rate according to the quality of the channel only according to the transmission quality of the channel,but does not take into account the possible node congestion in the network.Therefore,a congestion control method based on RBAR protocol is proposed in this paper.In the congestion control method based on RBAR protocol,the congestion detection method is used in the MAC layer,and the queue length congestion detection method is adopted.When congestion occurs,by adjusting the window and using the packet transmission mechanism,multiple packets can be transmitted continuously after an access channel to speed up the rate of data transmission in the congestion area.When the node is not congested,the node adjusts the competitive window according to the competitive window control algorithm optimized in this paper,in order to solve the problem of network performance anomaly and embody the advantages of the multi rate network.In the NS2 network simulation experiment,a congestion control mechanism based on RBAR protocol is implemented through TCL language and C++ language.The results of NS2 simulation show that the excellent performance of this congestion control method in network throughput,packet success rate and buffer overflow ratio proves that it can alleviate node congestion and improve network performance in the case of network congestion.