Camera-Based Positioning System for Battery-Less Retroreflective Tags

This article proposes a novel indoor positioning system (IPS) that can simultaneously track multiple battery-free tags with centimeter accuracy. Our system uses a camera located near a light source to track tags with special designs. Our tags have unique fiducial markers printed on prismatic retroreflective material instead of paper used in traditional systems. Our system has achieved average position errors of less than 2.9 and 7.1 cm for perpendicular distances between the camera and tags of 3.28 to 7.48 m, respectively. When the tags move at a speed of 1.12 m/s, our system remains unaffected in terms of positioning accuracy. Our tags are more robust to changes in lighting conditions than traditional paper tags because our tags can be located in five different scenarios, including a dark environment where traditional paper tags cannot be detected. Experimental results show that the working range of our tag is approximately twice that of paper tags, and the position error is not significantly affected by the ambient lighting conditions. Our system can be implemented using smartphones without any expensive add-on equipment.