Phase-based Ranging of RFID Tags with Applications to Shopping Cart Localization

Abstract

In this work, we investigate the problem of localizing RFID tags using a ranging method used in frequency-modulated radars. The idea is to exploit the phase change of the tag response due to frequency changes that normally happen as the RFID reader frequency hops. We demonstrate the general feasibility of this technique in ranging standard RFID tags using commodity readers. We then use it for a localization application - localizing shopping carts in supermarket aisles. We show that the ranging and localization accuracies are very good (median errors 5cm and 10cm respectively) even at distances over 4m making the technique competitive with existing techniques that require more complex set up.