Analysis of the Occurrence of Critical Satellites in GAST-D+ Processing

Michael Nietlispach, Michael Felux

Abstract: This paper investigates the conditions under which critical satellites can occur in the potential future GAST-D+, which processes ranging signals from one frequency and uses satellites from the GPS and the Galileo constellations. For this purpose, VPLs are simulated using GAST-D+ and GAST-D processing for 612 locations organized in a grid for latitudes from -80° to +80° and longitudes from -170° to +180°, containing cells spaced by 10° in each direction. The simulations are conducted over 24 hours and are based on broadcast ephemerides for the GPS and Galileo satellites. Throughout the simulations, varying numbers of highest-weighted satellites are deselected in every second of the simulation and at each location. This is done to account for unhealthy highest-weighted satellites in the constellations due to failure or maintenance as well as to simulate the sudden loss of a highest-weighted satellite. Occurrences of critical satellites are identified based on the simulated VPLs. Detailed analyses of the grid and VPLs are carried out for cases in which three and four highest-weighted satellites are deselected. The results show that critical satellites can occur in GAST-D+ processing when one highest-weighted satellite of each constellation is unhealthy, and a further highest-weighted satellite is lost. Increasing the number of unavailable satellites in the constellations increased the number of occurrences of critical satellites. Therefore, it cannot be ruled out that critical satellites occur in GAST-D+ processing at latitudes relevant for GBAS users when one highest-weighted satellite of each constellation is unhealthy, and a further highest-weighted satellite is lost.
Published in: Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023)
September 11 - 15, 2023
Hyatt Regency Denver
Denver, Colorado
Pages: 1842 - 1854
Cite this article: Nietlispach, Michael, Felux, Michael, "Analysis of the Occurrence of Critical Satellites in GAST-D+ Processing," Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023), Denver, Colorado, September 2023, pp. 1842-1854. https://doi.org/10.33012/2023.19299
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