A hybrid algorithm for range estimation in RFID systems

The deployment of RFID technology will gain a significant boost if indoor location positioning is incorporated into RFID systems. Recent development in range estimation indicates that phase difference of arrival (PDOA) shows a promising performance. PDOA technique suffers from an inherited limitation of phase difference which is restricted to the maximum of 2p radians. In this paper a robust algorithm to overcome this limitation and unwrap the phase is presented. A theoretical model has been developed to accurately unwrap the phase using the round trip time of flight. Simulation results show that the proposed method can be used to estimate the range even under significant Round Trip Time of Flight (RTTF) measurement error. It is shown that a wide range of time measurement errors can converge to actual distance if the frequency difference of the transmitted waves is properly selected.