Abstract: Radio frequency identification (RFID) technology has been widely concerned and applied in the field of indoor positioning. Range estimation is the important basis to realize RIFD indoor positioning. In this paper, the fusion method based on multi-frequency phase difference and Chinese remainder theorem (CRT) is applied in surface acoustic wave (SAW) RFID technology for the first time. The unambiguous range estimation is realized. The main error sources and corresponding correction methods of the method to realize range estimation in the SAW RIFD system are analyzed. Through simulation experiments, it is found that the ambiguous phase measurement error of the SAW RFID reader system should not exceed the system index requirement of 3° in theory to achieve high stability and high precision range estimation. Finally, the realization of the method in the SAW RFID system is verified by experiments, and the results show that the root mean square error of range estimation of the current system is 16.7 cm.

Key words: surface acoustic wave (SAW), multi-frequency phase difference, Chinese remainder theorem (CRT), radio frequency identification (RFID) tag, range estimation