Detecting GNSS Spoofing using Temporal Behavior of Spoofed Signals

Birendra Kujur, Samer Khanafseh, and Boris Pervan

Abstract:	In this paper, we propose a novel method to detect Global Navigation Satellite System (GNSS) spoofing using Inertial Navigation Systems (INS) based on inherent noise of spoofed signals. We showed in prior work [21] that a solution separation-based monitor provides detection capability for slowly growing faults. We also demonstrated how the monitor can enable fault exclusion by utilizing an INS-only solution that is not corrupted by prior calibration using spoofed GNSS signals. We proposed utilizing sequence of solution separation monitor windows which allow us to maintain continuous bounded protection level while switching from one window to the next. However, for very slowly growing faults that may be present longer than the run time of a solution separation monitor window, spoofing can go undetected thereby invalidating the fault free assumption required to switch from one window to another. To mount an effective attack of this type, a spoofer would need to closely track the motion of the target to generate the appropriate GNSS signal. It is undeniable, however, that the spoofer would not be able to precisely replicate an authentic GNSS signal because of inherent error in the tracking device, latency of tracking and spoofed signal broadcast, and external environment factors such as wind gusts. In this work, we evaluate the worst-case scenario from missed detection aspect, where a spoofer replicates the authentic GNSS signal with only additive errors due to uncertainty and latency of user’s position. We model these tracking errors as additive white noise to the spoofed signal. We observe the changes in the stochastic nature of the Kalman filter position errors over time—i.e., prior to and after a spoofing onset. We propose a cumulative position domain innovation monitor, which accumulates these tracking errors over time to detect the anomalous temporal structure of the spoofed measurements. We analytically show that accumulated errors result in spectral change of the test statistic with a shift in mean and increased variance. We provide an analytical method to determine the length of the monitor window that would ensure detection of a minimum tracking error with given probability of missed detection requirement. This allows us to choose the length of solution separation monitor windows where detection is ensured to maintain the fault free assumption required to switch from one window to another.
Published in:	Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021) September 20 - 24, 2021 Union Station Hotel St. Louis, Missouri
Pages:	3668 - 3682
Cite this article:	Kujur, Birendra, Khanafseh, Samer, Pervan, Boris, "Detecting GNSS Spoofing using Temporal Behavior of Spoofed Signals," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 3668-3682. https://doi.org/10.33012/2021.17967
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