The estimation of tag read and no-read zones is the most important preliminary planning step in radio-frequency identification (RFID) system installations. Today, in the ultra-high frequency band (UHF: 860–960 MHz), this estimation is based on either a free-space or a simplified multipath channel model for the signal propagation in the wireless link between the interrogator and the tag. Using measurements in a standard multipath indoor environment, this paper proves that recent approaches are not able to estimate tag read regions in a given passive UHF RFID system setup with high reliability. A modified multipath channel model is presented, that considers environmental and setup specific properties as well as an arbitrary number of signal paths to achieve a more accurate estimation. It includes the orientation of the tag antenna and the interrogator antenna, their polarizations and their three-dimensional gain patterns, as well as complex reflection coefficients for the reflected signal paths. The presented model equations are ready to use and are implemented into a flexible, easy-to-use, and easy-to-setup simulation environment with low computing times. It predicts the tag read regions separately for the downlink and the uplink and then combines the results for an overall estimation. The comparison of read region simulations and tag readability measurements shows that the our model delivers a 87.2 % reliability in the prediction of the tag read regions. The results of the estimation can be used to optimize RFID system setups in a way that read regions are maximized.
['Markus Cremer', 'Uwe Dettmar', 'Rainer Kronberger', 'Anjum Pervez']
Modeling of the Passive UHF RFID Multipath Channel for Tag Read Region Estimation