Research On Key Technology Of Video Transmission In Vehicular Ad Hoc Network

VANET (Vehicular Ad Hoc Network) is the foundation of remote traffic accident earlywarning, real-time traffic information query, highway electronic toll collectiontechnology, etc. In the practical road environment, the high speed will lead to thedynamic topology changes, at the same time, the wireless signal is also affected byterrain which would degrade communication quality or even interrupt the process.Therefore, efficient video transmission has been a difficult problem. In this paper, areal-time video transmission network demonstration system based on embeddedtechnology is studied, which might provide a reference for intelligent transportation.In this paper, demonstration video transmission system in VANET is designed andimplemented. Devkit8500development board based on DM3730processor is selected asthe hardware platform and the DWA125wireless network adapter is configured.802.11g protocol is used in the physical layer of the network protocol stack and UDPprotocol is used in the transport layer. We focus on improving AODV protocol innetwork layer, designing and implementing the video capture and transmission programbased on V4L2, the module of network routing protocol, auto-startup program and themodule of the wireless network card driver, and testing the demonstration system inoutdoor.The main contents and contributions are as follows:(1) The overall scheme of the demonstration system is designed and software andhardware platform of embedded system is built. Devkit8500D development boardand USB camera8100-U are the main components of the hardware platform andDWA125wireless network card is configured. The CPU is DM3730, and the guiding fileof USB driver is also configured. Thus the hardware platform drive work is completed.The Fedora12system is the core of the software platform based on the Linux2.6.31kernel. The whole platform is divided into four parts: Bootloader, Linux kernel, Linuxroot file and application layer. The software system is programmed into the NANDFLASH of development board by cross compilation. After the hardware and software platform has been completed, gcc and glibc program and function etc arecompiled and installed and a complete set of cross compiler tool chain is established,which pave the way for the cross compilation of the application layer;(2) The AODV routing protocol in network layer is improved and implemented. Theoverall structure of the network protocol stack is studied, the insufficient considerationof the risk of link break of the AODV network is pointed out, the function of Workflowand the establishment and maintenance of the routing table in the AODV routingprotocol are analyzed and the maintenance of the routing table in AODV is optimized.The main methods are as follows: several control function is added in the Hellomessage, the energy consumption and the signal intensity of the adjacent nodes isdetected and threshold formula of energy and signal strength is introduced, whichwould help to control the maintenance of the routing table. The performance of themodified protocol is simulated and analyzed using NS2simulation software. Theresults show that the average end-to-end delay and packet loss rate are improved by theoptimized AODV protocol(3)The key modules and programs of the demonstration system is designed andimplemented, which includes: the program of video capture, the module of the wirelesstransmission and the module of network routing protocol. The program of video captureand transmission is designed based on the V4L2function in Linux, the UDP transportprotocol is used, the data is segmented marked and stored in the buffer for transmissionand the received data is restored according to the marked function at receiving end; Thecompilation of wireless transmission module is divided into two steps: Firstly the kernelparameters of RT3070source code of DWA125network card is modified, and themodified source code is cross compiled. The built files of STA driver and SoftAP driverfiles are compiled into the kernel. The compilation step of network routing protocolmodule is as follows: The source code parameter of improved protocol is modified, thenit is cross compiled to built aodv module and aodv executive files. The aodv module iscomplied into the kernel and program is transplanted into the restore devices ofdevelopment board. Finally, the complied module and program of applied layer iswritten into the system. The system is started successfully with power supply and boththe module and program work well.(4) Demonstration system has been tested in outdoor. Because of lack of cost, weused three development board to simulate the real-time video transmission in the environment of vehicular ad hoc network. The system parameters are as follows：Themaximum radius of video communication is93meters. The maximum radius of routingcommunication is61meters. The maximum speed of the node-movement is5m/s.