Localization of passive UHF RFID label with Unscented Kalman Filter based on angle-dependent RSSI measurements

For indoor localization systems Radio Frequency Identification (RFID) is an often chosen technique. This paper uses Received Signal Strength Indicator (RSSI) values from passive UHF RFID labels for the localization process. Based on the measurements of these RSSI values a formula is derived to describe the relation between distance from tag to antenna as well as its dependency on the angle between tag and antenna. Two different methods how to incorporate the angle-dependency into the localization process are introduced. Applying these methods an Unscented Kalman Filter (UKF) is used for localization. In our demonstration environment localization accuracy is improved by roughly a factor two when three antennae are used.