Multi-mode Wireless LAN Switching Control Algorithm

VANET (Vehicular Ad Hoc Network) is provided with wide foreground about safety drivingand dynamic traffic information distribution, which constitutes an autonomous system betweenvehicles based on wireless communication technology. Improvement of the handoff algorithm asseamless connection and the handoff delay reduction as the purpose is a hot topic in the field.The improvement of handoff algorithm has encountered a great challenge due to frequentlychanging network structure.The thesis presents a handoff algorithm by using multi-mode wireless NIC to avoid themaximum delay used by scanning process in the handoff process via analyzing the characteristicof existing handoff algorithms and summarizing their shortcomings. According to the demand ofthe vehicle communication in VANET, a FPGA-based vehicular wireless platform is proposed inthis paper. In the platform, flexibility of FPGA is used to achieve efficient media access controlalgorithms, RF module and SOPC is connected by serial peripheral interface (SPI), and thecontrol logic in complex network protocols is implemented in uClinux kernel. On the platformexpands the two different frequency wireless module, witch can switch freely in the coordination of thecontrol module. The driver development of the key communication interface SPI in the uClinuxmakes the interaction between upper application of the system and underlying hardware good.The software controls the two channels in alternate communication for sharing the work of datacommunications and pre-scan through the multi-threaded application program, and builds aneighbor table to prepare for the handoff. The algorithm solves scanning latency problem withtwo RF modules in dual-frequency. The integration of FPGA and embedded operating system inthe platform brings efficient and flexible control, simple unified and extensible interface.Experimental results show that the platform has good application prospects with simple andflexible structure and low cost.In order to verify the correctness and effectiveness of the algorithm design, we implementdual-RF wireless platform on the DE2board, the SPI driver program in uClinux, neighbor tablewith maintenance procedures and multi-threaded control program. The real experiments on theactual platform prove its correctness and validity in the actual scene and show that the algorithm can reduce the handoff latency effectively.