Global Implications of GPS and Galileo RAAN Drifts on GNSS Performance

H. Krag, A. Leonard, P. Ranaudo, E. Blomenhofer

Abstract:	With the launch of the GALILEO constellation, two autonomous GNSS systems will be available for users world-wide. The GNSS performance achieved when both constellations are used will depend very much on the geometry of the overall constellation which is determined by the number and spacing of orbital planes and the orbital parameters altitude and inclination. These are well known for both constellations. However, as far as the orientation of the planes is concerned, no requirement for the right ascension of ascending node (RAAN) exists for Galileo. The choice of this parameter defines the initial phase angle between the GPS and Galileo constellation and is a potential driver for the performance of the overall system. Since natural orbit perturbation mechanisms cause an altitude dependent drift of this parameter, this phase angle is also subject to continuous changes throughout the mission. In past studies, no respect to the phase angle has been given so far and constellation drifts have been neglected. This paper provides first assessments on the impact of the phase angle between the two constellations on the parameters characterizing the performance of the combined system mainly based on aeronautical requirements. The analysis has been conducted using the AVIGA 2.4 Pro GNSS service volume simulator. The results have been cross-checked with the help of another two independent simulators. The results show that the overall performance tends to be higher when the Galileo planes are in between two GPS planes in contrast to the cases where GPS and Galileo planes are coplanar. This tendency is enhanced for higher user masking angles. This analysis has been repeated for different states of the GPS constellation (nominal constellation and constellation of week 187) and another design variant for GPS III. It turns out that for all scenarios, the alternating GPS and Galileo planes yield best results.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2467 - 2477
Cite this article:	Krag, H., Leonard, A., Ranaudo, P., Blomenhofer, E., "Global Implications of GPS and Galileo RAAN Drifts on GNSS Performance," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2467-2477.
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