Hybrid RFID-GNSS Circuit for Robust Vehicular Navigation in Signal-Degraded Environments

This work presents the design and implementation of a novel hybrid GNSS–RFID circuit architecture aimed at enhancing positioning accuracy in environments where satellite navigation performance is degraded by signal obstruction and multipath effects. The RFID subsystem enhances global GNSS positioning by leveraging a network of local passive resonant circuits, i.e., UHF RFID tags, which act as local anchors. These RFID tags provide position refinement information that is used by the control circuit to improve localization performance. The theoretical model and the circuit-level implementation for the adaptive and dynamic power control over the RFID interface are presented, enabling the estimation of distance from local tags based on backscattered signal strength and controlled RF excitation levels. The circuit provides RFID-assisted dynamic reconfiguration of GNSS receiver parameters, including carrier-to-noise ratio thresholds (CN0), satellite angle-of-arrival filtering, and elevation-based 2D/3D mode switching. To validate the proposed circuit, experimental tests were conducted in three obstructed agricultural and forestry environments using U-blox Zed-F9P GNSS modules as the hardware platform. Positioning performance was compared between a standalone GNSS configuration and the same module augmented with the RFID-assisted circuit. A third Zed-F9P receiver, operating in real-time kinematic (RTK) fix mode, served as a ground-truth reference for accuracy evaluation. Positioning errors were evaluated using metrics such as mean error, median error, and error variance. Results demonstrate that the RFID-assisted architecture enables up to 43% reduction in positioning error and a significant decrease in error variance, confirming the robustness and adaptability of the proposed circuit under challenging conditions.