Research On High Speed Data Distribution Protocol For VANET Based On Digital Fountain Code

With the fact that more and more vehicles are equipped with electronic devices,VANET has become the main communication way between OBU(On Board unit)and the Internet or data center.The cooperative downloading method is able to offer high speed data transmission with the help of vehicle to vehicle and vehicle to AP(Access Point)links.However the position shift of vehicles may cause the change of transmission channel,thus it can improve the PLR(Package Lost Rate),and decrease the amount of downloaded data.To solve these problems,this paper has studied the network environments based on express way,and is aimed at the theory of cooperative downloading method.Firstly,this paper focuses on the key technologies and theories of VANETs,including network structure,the channel fading model and the establishment of vehicle motion model,in addition with several classic cooperative downloading methods.Quite apart from that,we studies the cooperative vehicle select strategy and establish the technological process of cooperative downloading in VANETs.Secondly,this paper discusses the information gathering-and-analysis method,and the realization of distributed fountain code.The dynamic update of vehicle information and the designed timer in APs improve efficiency and the construction of Markov Chain is able to predict vehicle's trajectory in advance.Based on above studies,we design the distributed fountain code on the base of three-point communication model and digital LT code,and workout the calculation method of degree distribution function.Last but not least,this paper designs the simulation experiment by using VanetMobiSim and NS-2 platform.The VanetMobiSim platform is used to describe traffic conditions and NS-2 platform is used to simulate network status.The simulation result indicates that the proposed strategy could keep the PLR below 5%,meanwhile improve the throughput by about 20% with vehicle speed from 60km/h to 120km/h.