Research On Vehicle Positioning System Design And Positioning Method Based On RFID

With the rapid development of vehicular ad hoc network(VANET) technology, VANET applications such as safe driving and emergency rescue demand high position accuracy, but traditional GPS(Global Positioning System) and wireless positioning method are difficult to meet new position requirement. So there is an urgent need for a kind of high-precise vehicle positioning method. RFID(Radio Frequency Identification, referred to as RFID) is the core technology of VANETs, which can be used to position vehicle. RFID reader of base station can read the information saved in RFID tag of license plate. The position of vehicle can be calculated by means of characteristic parameters disseminated from RFID readers to tags. In this case, there is no need for vehicle to be equipped with onboard devices, which is easier to achieve.In urban signal interference among vehicles and shield of dense buildings lead to the noise-signal ratio decreases of the signal transmission, which reduce the vehicle positioning accuracy. The layout of the base stations also has an influence on the positioning accuracy. So two kinds of vehicle positioning methods are presented in this paper, which are double base stations vehicle positioning method based on RFID and multiply base stations vehicle positioning method based on RFID respectively. The first method is used for base stations arranged in more intensive environment, the second applies to relatively sparse environment.The main contents of this paper are as follows:(1) A vehicle positioning system based on RFID is designed. This system is suitable for the conditions that base stations are relatively dense or relatively sparse. Aiming at the influencing factors and key problems of vehicle positioning system, this paper puts forward the system frame of the vehicle positioning system, and then the overall scheme of the vehicle positioning system based on RFID is proposed.(2) A double base stations vehicle positing method based on RFID technology is proposed, which is suitable for the case in which the RFID base stations are relatively dense. The vehicle positioning accuracy decreases along with the increase of distance from the base station to the vehicle. In this dissertation, Kalman filter is used to optimize and update the vehicle position continuously, and the final output is the optimal value of the vehicle position. The inputs of the algorithm are the fixed distance between two successive base stations and the distance from vehicle to base station. Simulation results show that this method can effectively reduce the positioning errors.(3) A multiply base stations vehicle location method based on RFID is proposed. This method takes advantage of fuzzy entropy principle of fuzzy technology to divide RFID base stations into three categories first. Then Chan algorithm is used to position vehicle. Finally, three vehicles’ position is weighted to obtain vehicles’ precise position. This method can effectively overcome the problem of low positioning accuracy using Chan algorithm, which is cased by the environmental noise and the distribution of the base stations. The experimental results show that this method is superior to the traditional Chan algorithm and the 2-step algorithm based on averaging method, which can meet the requirements of vehicle positioning accuracy in VANETs.