UHF RFID Localization Based on Evaluation of Backscattered Tag Signals

Abstract

This paper introduces a 2-D position measurement system for passive ultra-high frequency (UHF) radio frequency identification (RFID) tags based on evaluation of backscattered transponder signals. The main application of the system is the localization of stationary objects tagged with RFID transponders. By combining phase and amplitude evaluation, the accuracy and the robustness of the position estimates are significantly improved compared with either approach alone. A multiple input multiple output system in which, sequentially, each frontend is configured to work as a transmitter while the remaining frontends serve as receivers is used to enable position estimation. For proof of concept, a local position measurement system demonstrator was built comprising conventional passive EPCglobal Class-1 Gen-2 UHF RFID tags, a commercial off-the-shelf RFID reader, eight transceiver frontends, baseband hardware, and signal processing. Measurements were carried out in an indoor office environment where the $3.5~{\mathrm{ m}} \times 2.5$ m measurement zone was surrounded by drywalls and concrete floor and ceiling. The experimental results showed accurate localization with a root-mean-square error of 0.020 m and a median error of 0.011 m. To determine the limits of the system, accuracy simulations were performed, which confirm the experimental results.