FFT Based Rate Estimation for UHF RFID Systems

This paper focuses on the rate estimation in radio frequency identification (RFID) reader receivers, which plays a significant role for the stability and the efficiency of RFID systems. RFID readers have to estimate the rate of the tag reply, i.e. the so-called backscatter link frequency (BLF). According to the focused EPCglobal Class-1 Gen-2 standard, the BLF can have a variation of up to +/- 22%. Most literature uses time domain algorithms to estimate this BLF. However, the proposed techniques are not suitable to estimate the rate when multiple tags reply simultaneously to the reader. In case of such tag collision we utilized the frequency domain representation of the replies to estimate the BLF. The performance is tested with different rates and the both supported modulation techniques, i.e. FM0 and Miller. Simulation results show the high performance of utilizing the FFT for estimating the BLF. This especially holds in case of collisions that cannot be easily estimated by means of time domain algorithms.