The Utility Maximization Based VANET Congestion Control Strategies

Cooperative Vehicle Safety Systems(CVSSs)is one of the vehicle safety applicationswhich faces most challenges in VANET.CVSSs rely on periodically-broadcast single-hop beacons to track neighboring vehicles accurately and avoid traffic accidents by sending warning messages in potentially dangerous traffic scenarios.But being different from tradition ad-hoc networks,VANET features high-speed mobility of vehicles,frequently-changing traffic density,channel attenuation caused by surroundings on roads and hidden nodes,which will severely damage the performance of wireless communication.Due to these characteristics,wireless communication of vehicles to vehicles and vehicles to roadside units will face serious challenges,the performance of CVSSs will be seriously influenced because of the increase of transmission delay and decrease of package delivery rate.So congestion control strategies must be designed to prevent channel congestion,thus fairly allocating channel resources and satisfying safety requirements of vehicles.Existing congestion control strategies aim to ensure the performance in network layer,without considering the safety requirements of vehicles in different driving contexts,so channel resources cannot be allocated fairly.To realize fair allocation of channel resources while preventing channel congestion,according to network utility maximization(NUM),two congestion control strategies considering vehicles' safety requirements was proposed.(1)A congestion control strategy based on vehicles' collision time was proposed.First of all,the NUM model for channel resource allocation was introduced.A utility function reflecting vehicle's safety requirements was proposed in the model.Then under the condition of fixed transmit powers,a optimization problem of channel resource allocation was proposed.Lastly,to solve the optimization problem,a distributed congestion control algorithm named Utility-Based Rate Congestion Control algorithm(UBRCC)was designed,the algorithm works out the optimal beaconing rate by updating vehicle's congestion price,realizing the resource allocation according to vehicle's safety requirements.(2)Based on NUM theory,a congestion control strategy considering vehicle's collision probability was proposed.Firstly,the mobility model of vehicle's collision scenario was built,then based on the mobility model,the method to calculate the collision probability of two vehicles was introduced.Based on thecollision probability,the utility function reflecting vehicle's safety requirements was proposed,then the optimization problem of channel resource allocation was proposed.Lastly,to solve the optimization problem,a distributed congestion control algorithm named Collision Probability-Based Rate Control(CPBRC)was designed.The performance of both congestion control strategies are validated via simulation experiments in NS-3,simulation results show that both algorithms not only prevent channel congestion,but keep low transmission delay,high package delivery rate and low tracking errors in traffic density changing scenarios,thus satisfying vehicles' safety requirements.