Autonomous Spoofing Detection and Mitigation in a GNSS Receiver with an Adaptive Antenna Array

A. Konovaltsev, M. Cuntz, C. Haettich, M. Meurer

Abstract:	The positioning and timing services provided by global satellite navigation systems (GNSSs) to the users are strongly affected by possible perturbations of the navigation signals in the radio propagation channel on their way from orbit to the Earth. Because of their extremely low power, the navigation signals can be easily jammed, on purpose or unintentionally, which poses the problem of radio frequency interference. Moreover, since the structure of the ranging signals and navigation data are open to public, it is not only possible to distort the GNSS signals in a brute-force way but to counterfeit them with the purpose to make the user’s receiver generating false position and/or time. This kind of interference is commonly referenced in the literature as spoofing. Because of its intentional nature, the spoofing threat was until recently considered as relevant only for military users. However, the number of GNSS applications in our everyday life grows continuously. It turns out that nowadays also many strategically important infrastructures, such as electric power grids or mobile communications networks, are becoming increasingly dependent on the GNSS services. Spoofing will definitely be a challenging problem for upcoming safety-of-life applications like airplane landing or ship navigation at a harbor. As a result, the attitude toward the spoofing threat in the civil user community is also changing. A great deal of research has been performed on finding solutions to the problem of GNSS spoofing. The most exhaustive ones based on the cryptographic authentication of GNSS signals were proposed on the system level and might be introduced in the future as a part of the modernization programs of existing GNSSs. The solutions at the receiver level are easier to introduce in a short time frame in order to protect the most critical applications. The authentic and spoofing signals can be discriminated by examining their amplitudes, frequency offsets and times-of-arrival. If the GNSS receiver uses multiple antennas, the desired and interfering signal can be additionally discriminated by utilizing information about spatial angles of arrival. The main advantage of this approach is that it can be effectively used with all possible kinds of spoofing, including so called meaconing where the GNSS signals are not manipulated in a sophisticated way but just received and re-transmitted in order to force a victim receiver to report the position of the meaconer receiving antenna. A technique for spoofing detection that makes use of estimated angles of arrival has been proposed by authors in [1]. The technique was used with an antenna array system where the main goal of the direction of arrival (DOAs) estimation is to provide aiding to the adaptive beamforming and nulling in order to improve GNSS signals reception and mitigate radio frequency interference. Because, for the sake of generality, the attitude of the antenna array was assumed to be unknown, the spoofing detection was treated as a joint detection (i.e. of spoofing) and estimation (i.e. of attitude) problem. The performance of the developed technique has been first evaluated by means of numerical simulations [1] and later by processing the data collected in field trials where a GNSS repeater was used to emulate the meaconing attack [2]. The results reported in [2] indicate good meaconing/spoofing detection performance in a static user scenario, while the performance in a dynamic case suffers noticeably from the instability of the signal tracking and, consequently, low availability of the DOA estimation and attitude determination. The current paper reports the results of investigations focused on resolving the identified problems by taking the following actions: (i) More than a single replica of the satellite signal is adopted in the underlying signal model that is used with the DOA estimation. This offers a substantial improvement of the spoofing detection probability, especially in the important phase of a spoofing attack where the spoofer tries to capture the receiver’s tracking loops. (ii) A sequential approach is applied to the estimation of the antenna array attitude. This massively improves the estimation accuracy by exploiting physical limitations of the dynamics of the antenna platform. Good knowledge about the statistical properties of the DOA estimation error is desired here. Since this error depends strongly on the used algorithms and antenna hardware, the DOA error statistics is assessed by processing extensive data which are collected using the DLR’s GALANT receiver [3]. (iii) Digital beamforming is utilized for the mitigation of the spoofing signals by placing spatial nulls in the reception pattern of the antenna array. This helps to significantly avoid the loss of tracking of the authentic signals during a spoofing attack. This also helps to maintain the continuity of the DOA estimation that is carried out in the post-correlation mode. Due to more stable signal tracking, a larger number of the range and DOA measurements are available for the PVT solution and attitude estimation, correspondingly, improving their performance. Further, the beamforming with the spatial nulls can be also used for protecting the receiver against spoofing already while (re)acquiring the GNSS signals. An improved joint spoofing detection and attitude estimation algorithm is proposed which encompasses the aforementioned approaches for improvements. The new algorithm is derived and analyzed in detail. In order to obtain realistic results, the performance of the spoofing detection and mitigation with the proposed improvements is not only assessed by simulations but also by post-processing of raw signal data collected during field trials in representative spoofing/meaconing scenarios. [1] M. Meurer, A. Konovaltsev, M. Cuntz, and C. Hättich, “Robust Joint Multi-Antenna Spoofing Detection and Attitude Estimation using Direction Assisted Multiple Hypotheses RAIM,” in Proc. ION GNSS 2012, 2012. [2] A. Konovaltsev, M. Cuntz, C. Hättich, and M. Meurer, “Performance Analysis of Joint Multi-Antenna Spoofing Detection and Attitude Estimation,” in Proc. of ION International Technical Meeting 2013 (ION ITM 2013), 2013. [3] M. Cuntz, A. Konovaltsev, M. Heckler, A. Hornbostel, L. Kurz, G. Kappen, and T. Noll, “Lessons Learnt: The Development of a Robust Multi-Antenna GNSS Receiver,” in ION GNSS 2010, 2010.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2937 - 2948
Cite this article:	Konovaltsev, A., Cuntz, M., Haettich, C., Meurer, M., "Autonomous Spoofing Detection and Mitigation in a GNSS Receiver with an Adaptive Antenna Array," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 2937-2948.
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