Robust passive UHF RFID tag localisation by intersecting RSSI indexed antenna sensitivity regions

The localisation of parts, tools and other equipment in manufacturing production is important to reduce search times and analyze time consuming transportation on the shop floor. The use of passive RFID UHF tags is beneficial because these are relatively low cost, detectable from a few meters, battery-free and can withstand extreme conditions, including high-temperature cleaning processes. This paper proposes a method to estimate the location of passive UHF RFID tags based on several RSSI measurements obtained at various antenna locations and orientations, i.e. various antenna poses, that can be achieved e.g. by an antenna mounted on a mobile robot. The method accounts for the antenna’s directional sensitivity and the unknown location and orientation of the tag. From the RSSI readings obtained at each antenna pose and the antenna sensitivity function, a region is derived the tag can be in. Then the tag location is estimated as the center of the intersection of the regions obtained at various antenna poses. By incorporating uncertainty into the model, the method is robust to environmental variations and changes in measurement conditions. Experimental results demonstrate tag localisation accuracy well below 15 cm in 95% of the experiments.