Research On Backoff Algorithm And Rate Control For MAC Protocol In Vehicle Networking

This paper optimizes the networks performances of Binary Exponential Backoff algorithm and Rate Control algorithm in IEEE802.11 p after deeply studying the MAC protocol of vehicle network.A vehicle density based backoff algorithm is proposed for the problem that Binary Exponential Backoff algorithm is not suitable to vehicle network.The basic idea of the proposed algorithm is that the vehicle nodes obtain the number of vehicles in the communication range and calculate the vehicle density by broadcasting beacons regularly,and dynamically adjust the contention window value according to the size of the density.Therefore,it is more suitable for the vehicle network environment where the topology changes rapidly.The simulation results show that compared with the Binary Exponential Backoff algorithm,the proposed algorithm can achieve improvement by 30.7% in terms of throughout,and the average end-to-end delay is reduced by 20 ms.The network performance of vehicle networking is improved effectively.The rate control algorithm in IEEE802.11 p cannot respond to the change of channel state in real time,lead to the reduction of date transmission efficiency and the lower network performance.In order to solve the above problem,this paper proposed a rate control algorithm based on contention window.At first,the Sample Rate algorithm is used to estimate the channel,then the contention window value is introduced to adjust the channel estimation that make it more real-time and accurate,while the reasons for the transmission failure can be accurately obtained.The algorithm can effectively avoid unnecessary speed reduction and increase speed blindly by introducing contention window value to adjust channel estimation,thus improving data transmission efficiency and network performance.The simulation results show that the rate control algorithm based on contention window value can improve the network throughput compared with the sample rate algorithm and ARF algorithm in IEEE802.11 p,and further improve the network performance of vehicle network.