Robot-based Indoor Positioning of UHF-RFID Tags: the SAR Method with Multiple Trajectories

This paper presents the application of the Synthetic Aperture Radar (SAR) localization method for indoor positioning of UHF-RFIDtags when the robot-mounted reader antenna moves along multiple trajectories. By properly combining the phase data associated to a set of multiple paths, the whole length of the combined synthetic aperturesenlargesand then the localization accuracy may improve. Besides, duringconsecutive inventory rounds, several tag position estimates are available and they can be profitably combined to minimize the localization uncertainty. Different combination approaches are investigated to determine the best choiceto improve the localization performance. The method capabilities are discussed through a numerical analysis,by considering different configurations of the multiple apertures and different measurement uncertaintysources. Finally, the proposed localization method is validated through an experimental analysis carried out with commercial RFID hardware and a robotic wheeled walker,in an indoor scenario, by employing different types of tags. The knowledge of the reader/robot trajectoryrequired by the SAR methodis here achieved with an optical system.