GNSS Secured Signals for Critical Air Traffic Management Applications and Specific Airspace Users

Pascal Barret and Dominique Colin

Abstract:	The Galileo satellite navigation system is now a reality and will take another step forward offering early services. The European Commission has planned to evaluate early services starting end of 2013 with some Pilot Member States (Italy and France for the time being). Some trials have been conducted with Eurocontrol and ESA in 2013 and 2014. The objectives were to evaluate the performances of the Galileo PRS and some combinations with other signals over Europe (GPS SPS, GPS PPS, Galileo OS, and EGNOS). This may have interoperability consequences, impact on concept of operations and, of course, industrial impact. In the case of aviation, the European Commission and EUROCONTROL created a GNSS Task Force in 2014 which focused on different items. One of them is the capability/potential offered by available GNSS secured signals for critical Air Traffic Management applications and some specific users. In Europe, the 2020+ Navigation baseline, as described in the Single European Sky Master Plan for ATM and in the European Organization for the Safety of Air Navigation (EUROCONTROL) GNSS policy for the civil aviation community, foresees that aircraft positioning means will become more and more satellite-based for all flight phases and that positioning will rely in the future on a minimum of two dual frequency satellite constellations and augmentations as required. It is expected that Galileo and GPS will be the targeted complementary constellations. This has been an essential element for the design of the Galileo's signals. In particular, they have been designed to be user friendly for an a current GPS user due to overlays of signals. The strategic importance of GNSS technology for the future of ATM infrastructure and operations is at the basis of the cooperation between EUROCONTROL and the European GNSS Agency (GSA). It is foreseen that this cooperation will include work in relation to the Public Regulated Service (PRS), an encrypted and robust signal by contrast to the open GNSS signal that can be subject to malicious interference. Considering the global ATM environment, one cannot fail to notice that numerous applications intended for navigation solutions purposes or for time-based solutions are relying on GNSS open signals. The US ‘Volpe Report’ of 2001 and 2010 highlighted the very high risks entailed by the dependence of American critical infrastructures vis-à-vis GPS as an open signal. These conclusions are also valid for European critical infrastructures relying on GPS or Galileo open signals. It is therefore of the utmost importance to protect, when appropriate, these infrastructures by ensuring that they can rely on an encrypted signal, which guarantees integrity and continuity, including during crisis situations. Aviation and ATM infrastructure are part of these critical infrastructures that should be protected at European level. Dependence of ATM infrastructure on GNSS is foreseen to increase over the next years. For instance, time synchronisation through GNSS will likely be critical. It is essential to be able to rely on a protected signal like Galileo PRS, rather than the current GPS (or future Galileo) open signal, which could be subject to non-intentional jamming or intentional jamming and/or spoofing. GPS PPS being a protected signal solution essentially dedicated to military users and applications, and under United States Department of Defense control, it is therefore legitimate, for critical civil GNSS applications in Europe, to shift to a civil protected signal under European civil control. In this sense, and by European Parliament and Council’s Decision 1104/2011, the Galileo PRS intends “to offer a public regulated service restricted to government-authorised users for sensitive applications which require effective access control and a high level of service continuity”. Recent jamming and spoofing capability evolutions of GNSS open signals lead to assess those threats and find solutions to protect ATM applications and ensure safety to aviation users. PRS offers benefits to potential users, such as resilience to spoofing and guaranteed availability in time of crisis. A benefit for the civil aviation community could also be expected. This could cover many applications whose functions require higher level of resilience for positioning or timing data and capability to detect and mitigate the potential Radio Frequency Interferences ‘effects. Depending on the GNSS based criticality of these applications and the specificity of some users, the question to be asked then is how to use the potential benefits of Galileo PRS. That is the reason why EUROCONTROL has participated in the first in-flight pre-operational campaign of the Galileo PRS signal in 2013, and will continue its investigations through its partnership with the GSA and its commitment to the Single European Sky ATM Research 2020 work programme. As an utmost priority it could be envisaged that there will be three concrete domains of research: • ATM satellite-based navigation systems, where some activities have already been developed and delivered some results through: - specific preliminary simulations (GPS outage exercise in Budapest with simulation of GPS loss in TMA and En-Route in an Required Navigation Performance (RNP) environment) - settlement of reporting tools (EUROCONTROL Voluntary ATM Incident Reporting - www.eurocontrol.int/services/evair - where GPS outages are reported and stored in a data-base). • ATM “GNSS time-based” applications such as radar/network synchronisation applications; • Specific airspace users’ needs such as State Aircraft for guarantee of service or Remotely Piloted Aircraft Systems (RPAS) for trajectory predictability. In the specific case of RPAS, the emphasis has to be put on: • Certified time for potential investigations since the RPAS is split in two main subsystems which require permanent data exchanges. Such exchanges may be human-to-machine or machine-to-machine, the latter being invisible for the remote pilot. Those data exchanges might also be queued because of the performance of the Command and Control (C2) link. In case of accident, a certified accurate unique time reference will support any complicated investigation, • Guaranteed data exchange robustness where there is a need of accurate knowledge of timed out transactions in high demanding performance airspace or in collision avoidance actions to immediately respond to critical data exchanges, • Continuous high accuracy of the navigation solution, especially in contingency situations such as lost link. This being mostly valid when the link is lost due to causes external to the RPAS itself (radio frequency interferences in the C2 link bands) • The potential benefits of high accuracy and robustness in positioning to support an innovative RPAS to RPAS anti-collision system for very low level operations. The objectives of this exploratory undertaking aim to: • Develop, assess, test, demonstrate PRS pertinence and concepts for aviation and ATM, on the basis of its knowledge of ATM users requirements, in coordination with the European Union (EU) authorities (which own the PRS); • Potentially apply the solutions to its own functions/services. The present abstract summarizes a presentation that could be given as part of the ION 2015 GNSS + Track B: High Performance and Safety-Critical Applications / Aviation and Marine Applications, outlining the results of the already performed work and the one to come through the three aforementioned domains of exploratory research.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	915 - 931
Cite this article:	Barret, Pascal, Colin, Dominique, "GNSS Secured Signals for Critical Air Traffic Management Applications and Specific Airspace Users," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 915-931.
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