Accurate Localization and Tracking of a Passive RFID Reader Based on RSSI Measurements

Real-time locating systems require high localization accuracy in the order of a few centimeters. Conventional methods for radio frequency identification (RFID) localization fail to achieve such accuracy, particularly in complex radio frequency propagation environments. In this paper, we propose a method for locating and tracking an RFID reader that can achieve such accuracy in a complex propagation environment by exploiting received signal strength indicator (RSSI) measurements as the only form of observation obtained from multiple spatially distributed passive tags. There are three key contributions of this paper. First, we analyze the effect of propagation impairments, non-isotropic radiation pattern of the tag antennas and multipath propagation, on RSSI measurements and the overall localization and tracking performance. Next, we compensate for the artifacts of multipath propagation and non-isotropic antenna pattern and obtain a maximum likelihood (ML) estimate of the RFID reader in a 2-D Cartesian space. The ML estimates of the reader position, together with its velocity, are then used as inputs to the Kalman filter for dynamical estimation of its trajectory. Finally, we present experimental results to demonstrate that the proposed method substantially improves the localization accuracy compared to other state-of-the-art methods for a given tag density.