UHF-RFID backscatter channel analysis for accurate wideband ranging

Positioning and ranging within UHF RFID are highly dependent on the channel characteristics. The accuracy of time-of-flight based ranging systems is fundamentally limited by the available bandwidth. This paper first analyzes the UHF RFID backscatter channel formed by convolution of the individual constituent channels. For this purpose, we present comprehensive wideband channel measurements in two representative scenarios and an analysis with respect to the Rician K-factor for the line-of-sight component, the root-mean-square delay spread, and the coherence distance, which all influence the potential positioning performance. Based on these measurements, we validate the Cramér Rao lower bound for time-of-flight based ranging under the influence of dense multipath and present two types of range estimators, a maximum likelihood and a matched filter approach. The resulting range estimates highlight the need for an increased bandwidth for UHF RFID systems with respect to time-of-flight based ranging.