Orbit Determination and Time Synchronization Using Navigation Ground Nodes for GNSS-Independent LEO PNT

Masaya Murata, Elena Galletti, Kyohei Akiyama, and Satoshi Kogure

Peer Reviewed

Abstract:	In this paper, the Orbit Determination and Time Synchronization (ODTS) aspect of the GNSS-independent LEO PNT system is addressed and the ODTS accuracy is scrutinized through a series of simulation evaluation. We assume the ODTS performed onboard the LEO PNT satellite using one-way navigation signals (pseudo-range type measurements) broadcasted from globally distributed ground nodes and obtained via the Inter-Satellite Links (ISL). The ground nodes are called the Navigation Ground Nodes (NGN) that are pseudolites on ground, and their measurements together with two ISL measurements obtained from the closest LEO PNT satellites flying in the adjacent orbital planes are assumed and processed by the continuous-discrete extended Kalman filter in our simulation. Our simulation results based on this setting showed that when the number of the NGN was 35 and the Chip Scale Atomic Clock (CSAC)-level clock was assumed for the LEO PNT satellite, the sub-meter level Signal-In-Space-Error (SISE) was achievable after the onboard navigation filter convergence and during epochs when larger than or equal to 2 NGN were visible from the LEO PNT satellite. When the smaller number of the NGN was visible from the LEO PNT satellite, the onboard clock estimation error was rapidly increased and our target SISE that was sub-meter-level could not be achieved. When the number of the NGN was larger than 100 such as 124, the faster convergence of about one day and lower SISE were both observed. The SISE improvement by the ISL measurements from our simulation configuration was minor, such as about 10 centimeters, however, there is a further potential for the ISL to synchronize time in space such that while the LEO PNT satellite could not receive enough signals from the NGN, by connecting to the other LEO PNT satellites that were receiving enough signals from the NGN, the onboard clock estimation accuracy may be significantly improved. The GNSS-independent LEO PNT could address the GNSS vulnerabilities such as the severe jamming currently ongoing and the spoofing too by using secure signal design while maintaining the GNSS-level PNT accuracy. The results presented in this paper are expected to provide the architecture implication for the design of the GNSS-independent LEO PNT system using the NGN and ISL.
Published in:	Proceedings of the 2026 International Technical Meeting of The Institute of Navigation January 26 - 29, 2026 Hyatt Regency Orange County Anaheim, California
Pages:	96 - 107
Cite this article:	Murata, Masaya, Galletti, Elena, Akiyama, Kyohei, Kogure, Satoshi, "Orbit Determination and Time Synchronization Using Navigation Ground Nodes for GNSS-Independent LEO PNT," Proceedings of the 2026 International Technical Meeting of The Institute of Navigation, Anaheim, California, January 2026, pp. 96-107. https://doi.org/10.33012/2026.20531
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