Reducing localization ambiguity of immobile passive UHF RFID tagged physical objects

Location sensing of physical objects is one of critical issues in many applications. Passive UHF Radio Frequency Identification (RFID) technique provides an efficient solution because of its low cost for installation and easy identification of the tagged physical objects. In this paper, we research on the localization problem using passive UHF RFID systems. We discuss theoretical and practical characteristics of a passive UHF RFID system. We propose novel algorithm to minimize the number of ambiguous tag points against a single RSSI value from a target tag and increase accuracy of location estimation in 2D grid space. Because of a single Received Signal Strength Indicator (RSSI) can be related to multiple points in the monitoring area due to signal propagation when we use the RSSI based localization technique. According to the analysis of our experiment results, our proposed approach shows over 50% improvement compared with the conventional k-Nearest Neighbor algorithm in a test frame, and 23.24cm of estimation error with a high granularity for localization of box level items with 4 different positions in the immobile applied application such as a smart shelf.