A Phase and RSSI-Based Method for Indoor Localization Using Passive RFID System With Mobile Platform

In this paper, a phase and RSSI-based method for indoor localization of UHF RFID tags is proposed and demonstrated. The proposed method exploits the received phase and RSSI profile combined with the location of the moving antenna to locate target tags. The phase and RSSI measurements are collected by a mobile robot carrying a RFID reader and antennas. By analyzing the received RSSI, of which the strength can indicate whether the signal is stable or not, a valid phase profile can be obtained. After obtaining valid phase profile according to the received RSSI, the location of the target along the antenna trajectory is calculated from the stationary point of the phase curve. The location orthogonal to the antenna trajectory distance is estimated by finding the integer number of wavelengths at the point of closest approach which fits the phase profile. 2D localization requires only one straight-line trajectory while 3D localization requires an L-shape trajectory. After estimating the x and y coordinate using the stationary point on each trajectory, the height of the target can be calculated by considering the integer number of wavelengths at the point of the closest approach. A 12 cm 2D localization error and 14 cm 3D localization error are demonstrated.