Item-Level RFID Tag Location Sensing Utilizing Reader Antenna Spatial Diversity

A robust estimation procedure for sensing the locations of passive UHF radio frequency identification (RFID) tags is introduced based on spatial deployment of the reader antennas for maximum signal diversity. A signal model is developed for the received signal strength indicator seen by each reader antenna and incorporated into a mean-square error testing function. The error function is minimized at each test point in the interrogation zone to find the point with the minimum mean-square error. The minimization is independent of the tag type and orientation, making the proposed method very robust compared with other methods that are based on reference tags and radio maps. Experimental results are presented for a realistic retail scenario with multiple tagged items achieving an estimation accuracy of 35 cm. The location sensing system uses conventional UHF RFID readers, antennas, and passive tags, providing additional capability to existing item-level RFID systems. This added value will help to offset the high cost of large-scale RFID infrastructure development.