Study the estimated distance error in indoor localization using UHF-RFID

Distance estimation is the fundamental step in indoor localization. In RSS (Received Signal Strength)-based localization, the radio propagation model of a RFID (Radio Frequency IDentification) tag based on the RSSI (Received Signal Strength Indicator) measurements is used to convert the signal strength into distance. However, the propagation model for a single tag in one direction is not too accurate due to large deviations in the measured RSSI values. In this paper, an approach using a single RFID tag is presented. Performances of a single active UHF-RFID tag operating at 433 MHz are examined. Distance estimations are determined using the One-Slope Model (OSM). Improvements in distance estimations for different angles are based on an averaging algorithm which allows detecting the attenuation of the signal in a series of positions of the reader antenna. In addition, the Path Loss Exponent 'n' is also determined in different positions. Further, Experimental validations show the evolution of the Power when the distance (tag-reader) increases. Then, the Path loss contours, for measured distances, are plotted.