Research On Access Technonology In Vehicular Ad Hoc Networks

With the explosive growth of automobile and the development of automobile industry,road safety and traffic efficiency have attracted more and more concerns and attentions.Vehicular ad hoc network(VANET)is an enabling technology to improve road safety and traffic efficiency by establishing vehicle communications.In VANET,vehicles will transmit status related messages to enhance the environments perception in safety applications.The related information could also be collected to support traffic control to improve the traffic efficiency.Compared with traditional wireless networks,VANET shows unique characters in terms of high mobility,periodic-broadcast service,high-reliability and low-delay requirements,and self-organizing access.These features bring significant challenges to the system design in VANET,especially in high-density and high-load scenarios,where it is hard to meet the requirements of the supported applications.Therefore,aiming at these challenges,the main research contents of this paper focus on the mobility model,service model,access issue in high-density scenarios,and the resource allocation overheads.The systematical research is conducted from different perspectives to solve the access congestion and collision issues and to meet the high-reliability and low-delay requirements.First,the mobility feature of VANET is analyzed.In VANET,the high mobility and rapid changing states of motion will impact the stability of topology and degrade the performance of the safety applications.Based on the study of the existing works on mobility of VANET,the changing of mobility and human factors in realistic scenarios are neglected.Therefore,the mobility of vehicles in different state(following,approaching,deceleration)is analyzed based the car-following model,considering the environments and human factors.Based on the analysis model,a differentiated safety message broadcasting rate control algorithm is proposed,which can meet the requirements of safety applications,meanwhile the redundant information is reduced.Simulation results show that the proposed algorithm can alleviate the channel congestion by reducing redundant information to improve the system performance.Second,the service model of VANET is analyzed is this paper.The research focuses on the next generation vehicular network technology:sensor data sharing.Vehicles can obtain global views of surrounding environments by exchange data collected by equipped sensors.Based on the analysis model and simulation results,it can be found that the extra messages introduced by the sharing process and forwarding will greatly increase the channel load and degrade the system performance.Therefore,a location-based sensor sharing algorithm is proposed,where the sharing range is divided in to segments,and the sharing process in controlled according to the location information.Simulation results show that the proposed algorithm can make sure that nodes can get timely perception of environments in the sharing range,meanwhile the system performance is improved by reducing redundant information.Third,the performance of VANET in high-density scenarios is analyzed in this paper.Due to the self-organizing method of access in VANET,the high collision probability of access in high-density scenarios will increase the delay and packet loss rate,which is a prominent problem.Therefore,a self-sorting based access algorithm is proposed in this paper.Nodes will form a queue via self-sorting process,and the queue can occupy the channel for transmission only if its length reaches a threshold.Thus,the massive unordered random access will turn into the access of queues,which are differentiated by the completion time of the self-sorting process.Analysis and simulation results show that the proposed algorithm has outstanding performance advantages in high-density scenarios.Last,the resource allocation overhead in VANET is analyzed.In VANET,the resource allocation is conducted in a self-organizing way through control messages,which will introduce a lot of overheads.Seldom works have been done to investigate the general resource allocation process and its overheads.A permutation-based analysis model is proposed in this paper,where the resource allocation pattern is treated as a permutation.Based on the model,the minimum bits required to represent a non-collision resource allocation pattern is derived.The node distribution,resource reuse and the dynamicity of service are considered.The analysis model provides new insight in the algorithm design and overcome control.