UHF RFID Localization Based on a Frequency-Stepped Continuous-Wave Approach

This paper introduces a 2-D position measurement system for passive UHF RFID tags based on a frequency-stepped continuous-wave approach. The main application is the localization of objects tagged with RFID transponders. Using this method, no system calibration is required, and phase-ambiguity can be avoided by evaluating the backscattered transponder signals using multiple transmit frequencies of the interrogator signal. To prove the localization method, a local position measurement system demonstrator was used 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 a measurement zone of 5.0 m × 3.5 m was surrounded by drywalls, concrete floor and ceiling. The experimental results showed accurate localization with a root-mean-square error of 22.2 cm and a median absolute error of 17.0 cm.