Phase of arrival ranging method for UHF RFID tags using instantaneous frequency measurement

The paper gives an overview of the phase of arrival (PoA) and time of arrival (ToA) techniques for distance measurement of UHF RFID tags. It introduces a new method based on the evaluation of received signal phase change during a linear frequency modulation (LFM) chirp. The phase of signal arrival is converted to the instantaneous frequency of a FMCW beat using a delay-multiply FSK demodulator with signal level normalization. Range estimation is afterwards calculated from the averaged instantaneous frequency. The mathematical description is verified by the simulation of the ranging process in MATLAB. The final part describes the techniques for commercial EPC Class-1 Generation-2 RFID tags which allow the backscattering of defined harmonic frequency for a known time.