Modeling of the Passive UHF RFID Multipath Channel for Tag Read Region Estimation

Abstract

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 threedimensional 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.

Study about the Influence of Tag Collision over the Identified RFID tag signals

“…Passive UHF RFID systems have a vast application to identify dense populations of tags (such as asset tracking, automated inventory, supply chain management, etc.) and, therefore, they are almost found exclusively for indoor use [10]. In these places, the multipath effect is even more pronounced due to the passive nature of the tag operation and the inherently low signal to noise ratio (SNR) of the weak backscatter tag signal [11].…”

RFID Technology for Management and Tracking: e-Health Applications

“…It is important to avoid coverage areas overlapping to ensure that RFID tags are detected by just one antenna. Another source of error is the presence of multipath [23,24], especially in indoor scenarios like the one illustrated in Figure 1. Under normal operation conditions, only those items within the coverage area of the RFID antenna are detected.…”

“…The effect of multipath can be clearly observed in the measurements (Figure 3a): signal strength does not monotonically decay with distance. Of course, more accurate methodologies for coverage evaluation (such as the proposed in [24]) can be considered depending on the system requirements.…”