Assessment of Potential System Interference through Radio Frequency Compatibility Analysis by Emerging LEO Constellations using L5 Frequency

Himanshu Sharma, Dominik Dötterböck, Thomas Pany

Abstract:	Current trends in the space industry are shifting from Medium Earth Orbit (MEO) to Low Earth Orbit (LEO) constellations due to the cost-efficient launching capabilities and the feasibility of using COTS-based HW resources. This paper investigates the design and compatibility of signals for a proposed Low Earth Orbit Positioning, Navigation, and Timing (LEO-PNT) constellation operating in the L5 frequency band. A reference constellation of 338 satellites at an altitude of 1200 km and inclination of 60° was selected based on dilution of precision (DOP) analysis, representing a conservative “worst-case” standalone scenario. For the receiver, an elevation cut-off angle of 10° was assumed, yielding the most favorable DOP performance and satellite visibility at mid-latitudes. From a signal design perspective, candidate modulation schemes, including BPSK, QPSK, and BOC variants, were evaluated to identify optimal trade-offs between robustness and compatibility. Two representative signals were selected for detailed study: a BPSK(5) waveform, and a BOCsin(12,2) waveform at 1196 MMHz center frequency. Using an in-house compatibility analysis tool, the mutual interference between these LEO signals and GPS L5 and Galileo E5 signals was assessed. The results show that LEO-BPSK(5) introduces negligible interference, with C/No degradations ? 0.32 dB, confirming its potential as a safe baseline design. In contrast, LEO-BOCsin(12,2) produces higher interference levels, with C/No degradations up to 0.77 dB on Galileo E5, reflecting its greater spectral overlap. These findings highlight the trade-offs between advanced modulation formats and coexistence with legacy systems. Overall, the study demonstrates that LEO-PNT signal design must carefully balance spectral efficiency, robustness, and interoperability, and provides quantitative insights to guide future development of LEO-based navigation services. This paper also analyzes ITU Methodology 1639 within the framework of Resolution 609 and demonstrates that the inclusion of a new LEO-PNT signal does not lead to any degradation in the effective power flux-density (EPFD) levels. Furthermore, the study highlights several limitations of Resolution 609 when applied to the context of LEO satellite constellations.
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:	2444 - 2455
Cite this article:	Sharma, Himanshu, Dötterböck, Dominik, Pany, Thomas, "Assessment of Potential System Interference through Radio Frequency Compatibility Analysis by Emerging LEO Constellations using L5 Frequency," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 2444-2455. https://doi.org/10.33012/2025.20332
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