Research Of Vehicle Positioning Based On Phase Method Of RFID

In recent years, due to the surge in the number of vehicles throughout the world, the necessity of establishing a system for both localization and management of cars is becoming an agreement. Traditional vehicle localization and information collection techniques such as Global Localization System(GPS), image method, dead reckoning et al. have short backs in application scenarios, system complexity, implementing cost or localization accuracy. The RFID technique becomes an excellent candidate as its superiority in low-cost, high location accuracy and automatic identification. Besides, RFID technique has a good combination with the existed traffic base equipments, which can form a completed system of management and localization. Hence, high accuracy RFID localization technique has shown its promising application in the field of vehicle localization.In this paper, a positioning approach based on phase method of RFID is presented. Firstly the structure of RFID vehicle localization system is introduced. The working frequency and signal form in the system is discussed. Then Sub-sampling scheme and Zero-IF scheme are adopted to deal with received signal and extract the signal's phase information. A backscatter path is introduced in the simulation and a Multi-Tag method is proposed to improve the accuracy of lane recognition. In non-line of sight(NLOS) environment, RF signal's propagation path will beyond of the actual distance between reader and tag, which will cause a decline in accuracy. In order to solve this problem, an algorithm based on convex optimization and distance inverse compensation is proposed. The algorithm first turn the localization problem into an optimization problem combined with several constrained terms. Then get its Lagrange dual function so the optimal solution for the dual function is also the optimal solution for the original function. The distance inverse compensation is used in an iterative way to decrease the impact of NLOS for the distance measurement.Simulation result showed that, phase based algorithm for RFID localization system can complete vehicle localization and lane recognition. The algorithm based on convex optimization and distance inverse compensation improved the localization accuracy in NLOS environment.