Galileo OSNMA as a Contribution to Resilient PNT

Cillian O’Driscoll, Ignacio Fernandez-Hernandez, Jon Winkel, Tom Willems, Sophie Damy, Javier Simon

Peer Reviewed

Abstract:	The GNSS spoofing threat has become a reality in recent years, with the number of reported cases increasing on a daily basis. Receiver resilience against such attacks is therefore becoming ever more important. A large body of work exists describing receiver-based techniques for detecting and mitigating spoofing attacks, including the use of Controlled Radiation Pattern Antennas (CRPAs), Automatic Gain Control (AGC) and ??/??? monitoring, Receiver Autonomous Integrity Monitoring (RAIM) based approaches, etc. However, the GNSS service provider can also contribute to this task, by the introduction of unpredictable but verifiable elements in the navigation signals. These elements can be introduced in the navigation message, via Navigation Message Authentication (NMA), or directly into the chips of the ranging codes, via Spreading Code Protection (SCP). In either case, the introduction of these elements makes it impossible for the attacker to spoof the GNSS signal, without first observing the signal. Galileo’s Open Service NMA (OSNMA) is the first global open implementation of NMA, and as such is well positioned to help in tackling the receiver resilience issue. Naturally, as the use of OSNMA increases, a number of experiments have been conducted to determine how well OSNMA-enabled receivers perform under real world spoofing conditions. In this paper, we address some recently published works describing such experiments, and evaluate the performance both of the OSNMA protocol and the receiver implementation thereof. We find a number of common issues that can arise, some perceptual (mis-construing an authenticated navigation message as directly implying an authentic navigation solution) and some implementational (particularly relating to achieving the secure time synchronization required by OSNMA). Based on the results obtained from these published works, we make some recommendations on increasing the resilience of OSNMA-enabled GNSS receivers.
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:	1465 - 1477
Cite this article:	O’Driscoll, Cillian, Fernandez-Hernandez, Ignacio, Winkel, Jon, Willems, Tom, Damy, Sophie, Simon, Javier, "Galileo OSNMA as a Contribution to Resilient PNT," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 1465-1477. https://doi.org/10.33012/2025.20471
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