A tag-free solution to unobtrusive indoor tracking using wall-mounted ultrasonic transducers

Methods for indoor tracking typically require a person to carry some type of a body worn tag. A novel tag-free solution is presented that utilizes low cost wall-mounted ultrasonic transducers. The active ultrasonic transducers capture analog echoes, which are then digitized and analyzed in order to calculate the 1-D range of the moving person. The tracking algorithm utilizes a number of signal processing techniques including band-pass filtering, Hilbert transformation, and background subtraction to remove interference from other objects in the room. The range data from multiple sensors are treated as observations in a Bayesian framework using the sigma-point Kalman smoother (SPKS) to determine a person´s 2-D position and velocity. The SPKS also performs “self-calibration” or simultaneous localization and mapping (SLAM) to determine the location of the wall-mounted transducers. The indoor tracking accuracy of the tag-free system is better than 0.5 meters.