Research And System Implementation Of Vehicle Ad-hoc Network Access Mechanism Based On SDN

With the development of the research on vehicular ad-hoc network(VANET),there are two problems that will seriously affect the communication performance of VANET: one is that the existing network architecture and node functions can not meet the needs of the rapid iteration of the current vehicle network functions;the other is that the current control channel access mechanism can not guarantee the reliable communication between wireless nodes.Aiming at the above problems,this thesis designs a VANET network architecture based on Software Defined Network(SDN)technology to improve the existing network architecture.Based on the above architecture,a control channel access mechanism is designed to ensure wireless nodes Reliable and efficient communication,and finally implement the network architecture proposed in the article based on open source software.The main work of the thesis is as follows:(1)Aiming at the problem that there is no centralized control architecture,closed node function and high coupling between software and hardware in current VANET,a kind of VANET system based on SDN is designed.By reconstructing the wireless node,the network function control mode is abstracted from the bottom driver to the top programmable interface,which improves the node programmability.Based on the North-South interface and other control channels,the application layer can realize the flexible deployment of business strategy without caring about the specific implementation of the lower nodes.(2)Aiming at the problems of high collision rate and low channel utilization of existing CSMA/CA,TDMA and other control channel access mechanisms,a centralized control channel access scheme is designed.TDMA is used to transmit fixed frequency information and CSMA/CA is used to transmit random data,which reduces the access conflict rate.Combining collision detection and slot allocation are carried out according to the moving state of the vehicle.The slot collision prediction algorithm can reduce the probability of collision and improve the channel utilization.The simulation results show that the performance of the proposed access mechanism is better than that of the packet loss rate and throughput.(3)Based on the open source software such as ath9 k and Openwrt,the prototype system of VANET based on SDN is developed.After testing,the system performance conforms to the WAVE protocol standard.Based on the prototype system,the proposed access mechanism is verified and tested.The test results show that the prototype system has good programmability and access mechanism performance.