Characteristics of Experimental VDE-SAT Ranging Signals and System Performance Analysis for Critical Navigation ^†

Traditional Global Navigation Satellite Systems (GNSSs) are subject to intentional or unintentional disturbances in the northern regions of Norway, leading to loss of critical infrastructure. The VHF Data Exchange System (VDES) has been suggested as an alternative source of positioning, navigation and timing (PNT), based on statistical estimates. However, an empirical investigation into the feasibility of such a contingency-system has only recently become possible after the launch of the NorSat-TD satellite with purpose-designed VDES ranging capabilities. This paper presents an analysis of the characteristics of empirical VDE-SAT range measurements and a system-level performance analysis of a single-satellite system. In total, 1121 VDE-SAT pseudorange observations obtained from 54 satellite passes, recorded from July to October 2023, are analyzed. Residual analysis shows that these observations have a large and constant mean error of about 416 km, with a standard deviation of 335.2 m. The previously neglected atmospheric propagation effects on a VDE-SAT range measurement are shown to be significant, and the largest effect is likely to be the time-delay due to the ionosphere. The system performance analysis shows that VDE-SAT as a PNT-source has potential to be a navigation backup system, with a target metric positioning accuracy of 1000 m. This project was funded by the ESA NAVISP program.