On the Compatibility of GNSS User Segment with Emerging LEO-PNT Systems and Signals

M. Paonni, O. M. Picchi, A. Piccolo, L. Cucchi, F. Menzione, S. Wallner, M. Anghileri, C. Vazquez Alocén, P. Giordano, O. Julien

Abstract:	This paper investigates the topic of Radio Frequency compatibility among LEO-PNT and classic GNSS, focusing on the impact at user level, and ways to ensure that existing and future GNSS receivers will be able to operate reliably in the presence of multiple signals transmitted by LEO-PNT systems. To ensure compatibility with existing classic GNSS systems, LEO-PNT signals shall not cause harmful interference that degrades the performance of GNSS receivers, typically measured by the effective C/N0 level. Specific attention is paid to RFC in L-band RNSS allocations, which is already densely populated by many regional and global PNT systems. At first, the paper provides a discussion on the concept of compatibility, reviewing how the concept has been dealt over the last 20 years within the GNSS community, and how the GNSS providers have prioritized compatibility to ensure their coexistence. It is discussed how the assessment of RFC over the last 20 years has focused on GNSS systems transmitting their signals from MEO, which is commonly adopted by all global and regional systems, and from GEO, used by Satellite-based Augmentation Systems (SBAS), and how it is essential to make sure that methodologies, standard assumptions and typical use cases used to assess RFC are adequate once new systems transmitting from LEO are to be considered as well. The paper then examines the technical characteristics of LEO-PNT systems, their implications for spectrum compatibility, and the critical scenarios requiring attention to mitigate interference risks, assessing in particular the impact of the transmission of high power signals and of the specific orbital characteristics of LEO-PNT. It is also discussed how spectral separation is a key tool to ensure compatibility, explaining however how a good spectral separation does not guarantee perfect signal isolation. A long section is dedicated to high power systems, discussing how this can affect compatibility, efficiency and sustainability of the spectrum, and also how self-interference can heavily affect the ultimate C/N0 at user level. At last, the paper discusses the specific use case of space users, and how those could be heavily affected by LEO-PNT emissions. First, the overall power variation received by a ground user and different space users from a hypothetical interference LEO constellation. Then, an analysis is presented to evaluate the number of LEO-PNT satellites simultaneously visible to space receivers, potentially interfering with legacy GNSS signals, and the duration for which a significant number of LEO-PNT satellites remain visible, assessing the associated temporal impact. The analysis is performed for some EU Copernicus Sentinel satellites, orbiting at different altitude. An example of how a Sentinel satellite is affected by RF interference is also provided, demonstrating how impactful RFI can be on the satellite operations. The paper is concluded with specific recommendations and recalling how it is essential for the providers to comply with existing regulatory elements in order to ensure a sustainable access to the very limited spectrum resources available to the satellite navigation community.
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:	915 - 928
Cite this article:	Paonni, M., Picchi, O. M., Piccolo, A., Cucchi, L., Menzione, F., Wallner, S., Anghileri, M., Alocén, C. Vazquez, Giordano, P., Julien, O., "On the Compatibility of GNSS User Segment with Emerging LEO-PNT Systems and Signals," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 915-928. https://doi.org/10.33012/2025.20406
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