3D Passive Positioning Based on RFID Tag Array

RFID-based passive positioning is essential for many Internet-of-Things applications. However, existing RFID-based passive positioning systems either have low precision or require multiple antenna arrays, which are bulky and expensive. In this paper, a 3D passive positioning scheme is developed based on RFID tag arrays. One of the tags can harvest the energy of the surrounding electromagnetic waves to power the embedded orientation sensors (an accelerometer and a magnetometer) and then send the orientation information of an object to an RFID reader. When an object is equipped with such RFID tag arrays, its direction can be estimated by exploring the phases of the signals reflected by the tags and the orientation of the object. Furthermore, based on the triangulation principle, the 3D location of an object can be determined by using multiple RFID tags on the object and two antennas at the RFID reader. Thus, compared with existing schemes, the required number of RFID antennas for 3D passive positioning is greatly reduced. The proposed scheme is implemented based on a COTS RFID platform. The experimental results show that the 90-percentile accuracy of the proposed system is within 9 centimeters.