Kalman Filter based RFID tag velocity estimation in the presence of frequency hopping

This paper compares different techniques for estimating the velocity of UHF RFID tags within practical applications. We use COTS RFID equipment complying with ISO18000-6C standards, including the use of frequency hopping, to capture tag identification, phase angle and signal strength data. A Phase-Difference-of-Arrival technique is applied to calculate tag velocity. Different signal estimation techniques, including Kalman filtering and Exponential Smoothing, are used to improve the accuracy of the estimated velocity in noisy conditions. These techniques are evaluated and compared within different scenarios, including cases with a fixed speed, acceleration and deceleration. Shortcomings of the RFID backscatter signal parameters are shown, and the effects of the number of tags present and number of samples taken within one frequency hop cycle are investigated. Finally, the potential to use such techniques within practical applications and required improvements are discussed.