Two-Dimensional Position and Orientation Estimation Using a 5.8 GHz RFID System

Precise estimation of object position and orientation using RF tags is an emerging application of RFID technology. In this work, we present a novel wireless two-dimensional position and orientation estimation and tracking technique that illustrates the concept of sensor fusion-using multiple, disparate sensor measurements to synthesize a single, superior estimate of position and orientation. The technique is implemented using a 5.8 GHz RFID system that consists of three readers and a customized tag equipped with a 3-axis accelerometer, 3-axis gyroscope and 3-axis magnetometer. Received signal strengths and packet-to-packet phase differences at the reader are used to measure radial tag positions and radial tag velocities, and backscattered data packets provide measurements of the tag's linear accelerations, angular velocities and orientations. A hybrid inertial microwave reflectometry (HIMR) algorithm is used to produce motion-capture grade estimates of tag position and orientation; in experiments, a two-dimensional position accuracy of less than 13 mm was achieved. The HIMR algorithm is designed using physics-based modeling equations, modifications are proposed to accommodate temporary link loss, and observability analyses clarify the foundations of the estimator design method.