Research On Optimization Of Channel Access Mechanism For Internet Of Vehicles Based On DSRC

Frequent traffic accidents and increasingly congested traffic have become issues that cannot be ignored in modern society.In order to ensure traffic safety and improve traffic efficiency,the concept of intelligent transportation system came into being.As a key part of the realization of the intelligent transportation system,the Internet of vehicles based on Dedicated Short Range Communication(DSRC)provides information interaction between vehicles and between vehicles and roadside devices,which has become a hotspot in the field of modern transportation research.However,the DSRC developed from the traditional wireless network standard can not adapt well to the rapidly changing vehicle environment,and the transmission performance is greatly reduced when the number of vehicles increases.Therefore,this paper analyzes the factors that affect the transmission efficiency,and focuses on the research of channel access mechanism optimization method of DSRC.The specific contents and achievements are as follows:(1)To solve the problems of high node collision probability and high packet loss rate in the tranditional backoff algorithm,the hybrid backoff algorithm(HBA)is proposed.During the back-off phase,the nodes adjust the competition window by linear/exponential growth and linear decrease.A two-dimensional Markov chain model is established to analyze the relationship between collision probability and the size of contention window and the number of nodes,and the calculation formula of system performance index is given.The simulation results show that the collision probability and packet loss rate of this method are smaller than the traditional backoff algorithm,the throughput is improved,and the transmission performance is significantly improved.(2)Aiming at the problem of unfair channel access caused by the mobility difference of vehicle nodes,an adaptive control algorithm based on vehicle speed is proposed.In the process of backoff,the nodes dynamically adjusts the size of contention window according to the speed difference with its neighbors,thereby adjusting its channel access priority.The simulation results show that compared with the traditional channel access method,the fairness of channel access is significantly improved.(3)To solve the problem that the fixed priority mechanism can not meet the requirements of quality of service(QoS)of different businesses,an adaptive control algorithm based on differential QoS is proposed.The service is divided into three QoS levels,and different backoff algorithms are implemented in different levels;the emergency safety message with the highest QoS requirements will send a busy signal while transmitting to ensure the absolute priority of its transmission.The simulation results show that this method can effectively reduce the transmission delay and packet loss rate of QoS services,and ensure the timely transmission of emergency and safety messages.It is a reliable access algorithm.