TDE-Loc: Unambiguous RFID Localization Using Trajectory Deformation Error

Radio frequency identification (RFID) technology has become a powerful tool across industries, yet reliable RFID localization remains a significant challenge due to phase ambiguity. When RF signals complete multiple $2\pi $ phase cycles, they create multiple possible distance measurements, making it difficult to determine a tag’s precise location. Existing works either deploy more antennas or impose additional constraints to mitigate the ambiguity effect. Addressing this critical obstacle, this article proposes the TDE-Loc, an innovative 2-D RFID localization system that overcomes phase ambiguity with minimal deployment requirements and no extra constraints, thus enhancing the reliability and precision of RFID-based applications. We propose a novel tracking algorithm, synthetic aperture radar (SAR) hologram of displacement (HD), which leverages synthesized displacements to achieve accurate and robust trajectories using only two antennas. Moreover, we designed a global unimodal metric, named the trajectory deformation error (TDE), to evaluate the trajectory deformation caused by wrong initial positions and find the actual initial position without ambiguity. We build a prototype of TDE-Loc and evaluate it across various environments. It outperforms existing systems in both tracking and localization with fewer antennas and deployment requirements. TDE-Loc can track the tag with only two antennas and achieves 1.69 and 6.35 cm in median and 90th percentile error, respectively. When enhanced with a third antenna, the system delivers precise localization, with median and 90th percentile errors of 3.63 and 5.37 cm.