Fusion of UWB and Magnetic Ranging Systems for Robust Positioning
Valerio Brunacci, Alessio De Angelis
Abstract
Measuring the position of robots or other devices in challenging environments, with tight accuracy requirements and insufficient coverage from satellite navigation systems, is crucial for improving existing applications and enabling novel solutions. In this article, two of the most commonly used positioning technologies are ultrawide band (UWB) ranging systems (RSs) and magnetic RS. These technologies present limitations that can be overcome by combining them and exploiting their complementary features. Specifically, the UWB RSs provide long-range accuracy and the standard deviation in the line-of-sight (LOS) condition is distance invariant, but the accuracy degrades in short-range and non-LOS (NLOS) conditions. Contrastingly, a magnetic RS exhibits robustness to NLOS scenarios and provides high accuracy over short distances, yet does not perform as well as UWB RSs over long distances. In this article, the compatibility and complementary characteristics of these two RSs are experimentally proven for the first time. The robustness in NLOS conditions of the magnetic RS and the low dispersion with increasing distance of the UWB RS represent the complementary characteristics. This complementarity is leveraged by the proposed fusion method: the adaptive tightly coupled extended Kalman filter (ATCEKF). The proposed fusion method is experimentally characterized in mixed LOS and NLOS conditions, resulting in 6.9 cm of error in an outdoor environment. The positioning error decreased by 55% with respect to the UWB standalone positioning system and 32% with respect to the magnetic standalone positioning system. Therefore, the proposed fusion method improves the robustness and accuracy of position estimation. These results are also confirmed by an additional experiment. In it, the new small-sized and battery-powered mobile node are implemented using a Raspberry Pi 4 Model B.