| In the 21st century, Intelligent Transportation System (ITS) has become the inevitable trend of city traffics, which is the key to many traffic problems. Intelligent vehicle location system is the central part of ITS. This paper puts emphasis on search and location of vehicle, which is a sub-system of wireless and infrared dual-mode ITS proposed by Dr. Mu and others.A total solution of search and location of vehicle is designed based on RFID and wireless location. The implementation is divided into 2 steps: First, estimate the TDOA (Time Difference of Arrival) of signals received by base stations; second, estimate the coordinates of the vehicle by solve the hyperbolic equations with Chan algorithm. The main work of this paper is as follows:(1) Design a total solution of vehicle search and location based on RFID: location method based on TDOA. A modified LMSTDE is applied to estimate TDOA, and then Chan algorithm is applied to estimate the coordinates of the vehicle.(2) Sub-sample time delay estimation is taken into account in order to get high resolution TDOA. Interpolation of GCC (Generalized Cross Correlation), time delay estimation based on cubic spline and adaptive time delay estimation are discussed. A modified LMSTDE is chosen to give better TDOA estimation.(3) With active RFID, the sequence and modulation of the vehicle answer signal are known to the base station. So, it is possible to estimate the TOA (Time of Arrival) first. 2 TOAs give a TDOA. Simulation results show that this way can achieve better performance than those ways receiving TDOA directly, which is the superiority of RFID. The answer sequence is in the form of an almost perfect autocorrelation sequence to receive better TDOA estimation.(4) Simulations show good performance of the proposed solution, even under multipath environment. When the signal to noise ratio (SNR) is -18dB, the mean location error is less than 9 meters; even when SNR=-20dB, the mean location error is still less than 15 meters.
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