A Real-Time Multi-Antenna SAR-Based Method for 3D Localization of RFID Tags by a Moving Robot

In this paper, we present a prototype method for 3D localization of UHF RFID tags by a moving robot. The proposed method represents an extension of Phase ReLock, in 3D space. Phase measurements are collected by at least two antennas, thus a multi-antenna synthetic aperture is created. We propose a new optimization problem, which involves measurements from all different antennas. Thanks to phase-unwrapping, the new multi-antenna optimization problem preserves its convex-like properties. Consequently, it is solved rapidly by standard optimization techniques. Furthermore, we introduce a confidence metric that can identify measured data, which deteriorate the accuracy of the estimations. These can be removed from the measurements' dataset. We have conducted extensive measurements, employing four antennas on top of a SLAM-enabled robot; i.e., the robot is able to create a map of the unknown environment and continuously estimate its pose inside the map. The proposed method outperforms prior art with respect to accuracy and computation time. It achieves mean 3D error less than 20cm with an estimation-time of only 0.17s per tag on an average laptop.