Overbounding Time-Correlated Clock & Ephemeris Errors for Precise Point Positioning

Rebecca Wang, Juan Blanch, and Todd Walter

Abstract:	Safe navigation in Global Navigation Satellite System (GNSS) standalone positioning has historically relied on Receiver Autonomous Integrity Monitoring (RAIM) and Advanced RAIM (ARAIM). These frameworks are built on well-characterized error models for broadcast signals, providing integrity parameters such as user range accuracy (URA) and satellite fault probabilities. However, extending such methods to high-precision positioning techniques, including Precise Point Positioning (PPP) and Real-Time Kinematic (RTK), presents new challenges. Unlike standalone GNSS, PPP relies on frequent correction updates that mitigate slowly varying broadcast errors but introduce vulnerability to latency and fast faults. The emergence of rapid satellite clock faults since early 2023 underscores the need for refined integrity monitoring strategies, which requires characterization of the set of nominal errors (Wang et al., 2024). Therefore, this work builds on prior efforts in modeling and overbounding correlated GNSS errors for PPP services through focusing on the nominal errors. We propose a methodology for handling multiple covariance matrices that represent different uncertainty sources within the PPP filter, enabling tighter and more realistic overbounding of correlated error processes. Using a chi-square–based criterion, we establish appropriate overbounding values for parameters critical to PPP integrity services, demonstrate their application in a simplified filter implementation, and validate them in the user error bound. Results show that our approach achieves reduced conservatism while maintaining integrity, improving vertical protection levels. This work provides a practical, computationally efficient, and simple methodology for implementing integrity monitoring in high-accuracy positioning services, with direct relevance to applications such as autonomous driving, delivery, and safety-critical robotics.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	239 - 249
Cite this article:	Wang, Rebecca, Blanch, Juan, Walter, Todd, "Overbounding Time-Correlated Clock & Ephemeris Errors for Precise Point Positioning," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 239-249. https://doi.org/10.33012/2025.20473
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