Novel Composite Clock Algorithm for the Generation of Galileo Robust Timescale

P. Roldan, S. Trilles, X. Serena, A. Tajdine

Abstract:	The synchronization of satellite clocks is one of the key functions for the satellite geolocation provided by the navigation systems. This time synchronization is carried out with respect to a system time, which must meet very demanding criteria. Among these criteria, the reference time is usually required to be tightly linked to a physical timescale, such as the International Atomic Time (TAI), to allow its use in timing and metrological applications. It must be also stable enough to allow an accurate predictability of the offsets between satellite clocks and the system time, a key factor for ensuring a good level of performance in the user positioning. In addition, the system time must be always available, since any interruption of its generation or dissemination to the end-users could lead to the unavailability of the system. Finally, this timescale must be resilient to any event that could jeopardize its availability and stability. Generally two techniques are possible for the generation of a system time: either this timescale is given by a single physical clock, and then we speak of a master clock, or it is given as a well-made average of a set of physical clocks, and then we speak of a composite clock or paper time. This paper presents a novel composite clock algorithm designed by Thales Alenia Space, based on the IGS algorithm but modified to maximize the robustness to the typical operational conditions found in the generation of GNSS system times. The integration of this algorithm within the orbit and clock estimation and the navigation message generation functions is also considered, to fully analyze the use case of GNSS system time generation. The performance of the algorithm is finally presented, as well as its behavior in presence of feared events like clock jumps, degraded stability or removal of clocks.
Published in:	Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022) September 19 - 23, 2022 Hyatt Regency Denver Denver, Colorado
Pages:	2790 - 2799
Cite this article:	Roldan, P., Trilles, S., Serena, X., Tajdine, A., "Novel Composite Clock Algorithm for the Generation of Galileo Robust Timescale," Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), Denver, Colorado, September 2022, pp. 2790-2799. https://doi.org/10.33012/2022.18521
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