Range estimation for passive RFID systems that use power-optimized waveforms

This work investigates three major phenomena of range estimation performance for a passive RFID system that transmits power-optimized waveforms (POWs). The shape of the POW, nonlinear charge pump reflections, and frequency-flat multipath environments are investigated. A maximum-likelihood (ML) range estimator analyzes the backscattered signal from a passive RFID tag that includes the POW as a carrier of tag data. The interferers in a linear-reflection system are multipath components and noise. However, the charge pump of the tag may also induce nonlinear distortion on the reflected POW. It is shown in this paper that each of these sources of interference may be accounted for in theoretical models of the uncertainty and bias of the ML estimator.