Performance evaluation and verification of spread-spectrum based UHF RFID ranging

This paper presents measurement results of a recently introduced time of flight (ToF) ranging method for backscattering RFID tags. The measurements are done with off the-shelf EPC Class1 Gen2 tags, an automated tag positioner, a modified software defined radio (SDR) platform as the RFID reader, and a PC post-processing the ranging results. The ranging error and its variance is measured and discussed at tag distances of 0.1–4m for different tags, operating frequencies, and ranging signal power levels. The underlying ranging principle is successfully verified, and its practical performance limitations due to multipath propagation is shown. Furthermore, the paper shows that by a smart choice of the localization sequence, measurement errors stemming from nonlinear distortion of the power amplifier can be reduced.