Research On Channel Allocation Mechanism And Message Transmission Method Of MAC Layer In VANET

Vehicular Ad-hoc Network(VANET)is developed from traditional Mobile Ad-hoc Network(MANET),which is an important part of Intelligent Transportation Systems(ITS).VANET is also core technology for improving traffic efficiency and reducing traffic accidents.VANET has the characteristics of dynamic topology,high-speed movement of vehicles and extremely unstable channel quality.VANET needs frequent information exchange,while the transmission performance of message depends on Medium Access Control(MAC)protocol.Therefore,many scholars and experts conduct in-depth research on MAC protocol,the purpose of which is to improve network performance,adapt to different communication scenarios and satisfy service requirement.This paper makes in-depth research on relevant mechanisms of MAC layer in VANET.The main research work is as follows:This paper summarizes overall architecture,characteristics and related protocol standards of VANET systematically,and deeply analyzes relevant mechanisms of MAC protocols for VANET.It also elaborates on the problems and challenges faced by MAC protocols for VANET.This paper deeply studies channel allocation mechanism of MAC layer in VANET.Considering the characteristics of vehicular uneven distribution,fast density change in real vehicular network scenario and existing MAC protocol cannot adapt well to changing network scenarios,this paper proposes an adaptive TDMA scheduling strategy based on beacon messages(BMA strategy).It uses adaptive algorithm to allocate time slots dynamically,which effectively reduces the rate of access collisions and merge collisions when vehicles acquire time slots.At the same time,the simulation environment is built and BMA strategy compared network performance with existing protocols ADHOC and VeMAC.The simulation results show that BMA strategy proposed in this paper has higher channel access probability,lower collision rate and lower time delay.Aiming at the problem of low retransmission efficiency after failure of message transmission in traditional TDMA protocol,this paper proposes a message communication method of MAC layer based on cooperative communication of neighbor nodes(RC-TDMA).It mainly introduces cooperative nodes to retransmit failed messages by cooperative communication.And it makes full use of idle time slot under current time frame for message transmission,which effectively improves channel utilization rate and reduces time delay.Meanwhile,this paper compares network performance of RC-TDMA with traditional TDMA mechanism and C-TDMA mechanism on the simulation platform.Simulation results show that the RC-TDMA mechanism proposed in this paper has better performance on indexes like average number of time slots for successful message transmission per frame,transmission delay and throughput.So the RC-TDMA mechanism is suitable for scenarios with poor channel quality and low reliability of message transmission.