Geometrical Constraints of Spoofing Unpredictable Signals and Application to Galileo OSNMA

Ignacio Fernandez-Hernandez, Cillian O’Driscoll, Jon Winkel, Tom Willems, Aleix Galan-Figueras

Peer Reviewed

Abstract:	This work proposes a model that combines signal unpredictability and a receiver time bound and defines a “spoofable” region, out of which a receiver cannot be spoofed without noticing, and a plausible region in which a potentially spoofed receiver must be located. The method is combined with a height constraint to further reduce these regions. When the receiver time bound is small enough, the region can be projected into the horizontal plane and approximated by a polygon, facilitating receiver computation. The model is evaluated with real data including real Galileo OSNMA unpredictable signals and NTS synchronization. While most anti-spoofing methods assume an initial state in which the receiver is tracking authentic signals, this method can be applied at startup, when the receiver is most vulnerable.
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:	469 - 481
Cite this article:	Fernandez-Hernandez, Ignacio, O’Driscoll, Cillian, Winkel, Jon, Willems, Tom, Galan-Figueras, Aleix, "Geometrical Constraints of Spoofing Unpredictable Signals and Application to Galileo OSNMA," Proceedings of the 2026 International Technical Meeting of The Institute of Navigation, Anaheim, California, January 2026, pp. 469-481. https://doi.org/10.33012/2026.20521
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