Research On Congestion Control In Vehicle Ad Hoc Network

The Internet of Vehicles plays an important role in the ITS.As the key technology of vehicle communication,VANET is mainly aimed at achieving vehicle safety.Applications in VANET are mainly divided into security applications and non-secure applications.Security applications support vehicles which equipped with VANET communication modules can send periodic safety messages and event-driven messages to ensure that surrounding neighboring vehicles can understand the situation immediately and avoid danger.Specific environments of VANET such as wireless broadcast communications,limited bandwidth,high-speed movement of vehicles,etc.,may all result in obstructing the exchange of secure messages between vehicles.Periodic safety message is the most basic and important message in safety applications.However,due to the capacity limitation of VANET,especially when vehicles are becoming denser,only sending periodic safety messages may result in channel saturation and even channel congestion.Not only periodic safety messages cannot be transmitted normally,but also severely affecting the transmission of event-driven messages which are often critical and important for the safety of vehicles and drivers.Therefore,it is very important to analyze the impact of V2 V single-hop broadcasting periodic safety messages on VANET performance.More and more researchers are focusing on the study of channel saturation caused by security information,and propose various congestion control solutions.These solutions also provide strategies for periodic security messages,mainly aim to limit the allocation of resources to it.To a certain extent,it guarantees the reliable and efficient delivery of secure messages.However,these congestion control schemes often reduce the network load with a single factor,making it unavailable in a changed environment.In the conceptual scheme of reactive congestion control scheme conceived in this paper,the effects of various factors such as transmission range,transmission interval,and vehicle density on the performance of the VANET network are comprehensively considered.The size of the transmission range determines the number of vehicle nodes sharing the channel within the communication range.Enlarging the transmission range will reduce the spatial multiplexing rate of the wireless channel,causing an increase in collisions,and a large transmission range requires a large transmission power whichwould influence nearby nodes to receives messages correctly.Transmission interval determines the number of messages generated by the vehicle.Although a short transmission interval can improve the accuracy of the message,it will result in a higher channel load.Vehicle density is the most influential factor on the channel load among various factors of vehicle movement and the data transmitted in the channel increases linearly with the number of vehicles accessing the network.Each factor has its own impact on the network load,and the combination of different factors also generates new influence.In this paper we conducted a simulation experiment in NCTUns software to analyze the influence of various factors on the performance of VANET network.The simulation scene is straight road,and three kinds of vehicle density referenced the traffic flow theory are set.The vehicle transmits the periodic safety message transmission through the two-ray ground model in different road environments.The transmission range is gradually expanded from 100 m to 300 m.The transmission interval between messages is increased from 100 ms to 500 ms.By evaluating QoS such as throughput,packet loss rate,and transmission delay,etc,to analysis the reception performance of periodic safety messages.The relationship between network load C and transmission range r,transmission interval t,and vehicle density d,can be expressed as C=f(r,t,d).The simulation results show that when the vehicle density is high,adjusting the transmission range and transmission interval has a more significant effect on the network performance.And the adjustment of the transmission range can continue to affect the network performance,but adjusting a step size after the transmission interval reaches 200 milliseconds has less impact on the net work performance.Therefore,when designing a congestion control scheme,in the case of a vehicle with a large density,the vehicle within the communication range should be effectively reduced by shortening the transmission range first,and then the transmission interval should be adjusted according to the requirements of the vehicle on the accuracy of the message.The experimental results in this paper provide a basis for awareness of channel congestion and will be used as the precondition for the next step in implementing a congestion control algorithm.