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Session A6: GNSS Integrity and Augmentation

GBAS use Cases Beyond Precision Approaches – Drone Navigation
Sophie Jochems, Michael Felux, Philipp Schnueriger, Luciano Sarperi, Michael Jaeger, Zurich University of Applied Sciences - ZHAW, Switzerland
Location: Beacon B

The Ground Based Augmentation System (GBAS) is a precision approach and landing system which provides corrections for GPS navigation signals to airborne users. The correction and integrity parameters are transmitted via a VHF data broadcast. The broadcast is freely accessible and can therefore be received and decoded by virtually everyone. A GBAS ground station is located within the security perimeter of an airport, uses high-quality equipment that allows to keep errors to a minimum and furthermore, provides guaranteed levels of performance by specification and continuously self-monitors the integrity of the information provided.
This augmentation system by design only serves for a very specific purpose: in civil aviation, aircraft equipped with the appropriate avionics can use the provided information to correct GPS signals, ensure that all integrity requirements are met, and use the information regarding the approach geometry in the GBAS message to fly precision approaches. However, GBAS to date is not very widely used because i) not many airports are equipped with a GBAS ground station and ii) depending on the airport, not much of the fleet operating in and out is equipped with the GBAS landing system GLS. The reason for this is a classic chicken/egg problem: On the one hand, the Air Navigation Service Provider (ANSP), or in some cases also the airport operator, is responsible for the installation, operation and maintenance of a GBAS ground station. As this is rather expensive, not many ANSPs and/or airports are willing to install such a ground station without a solid business case. Especially because often only a few aircraft operating at this airport are actually suitably equipped to fly a GLS approach, it is currently still very difficult to generate operational benefits from a GBAS. On the other hand, there are the aircraft operators. For them, it is also financially not very rewarding to equip their aircraft with the required receiver as there may be only a few destinations within their network where flying a GLS approach is actually possible and might bring operational benefits.
Against this background, this paper discusses whether GBAS can be used in another context, in order to provide potential benefit to more users and for different services. One possibility is the emerging field of UAV navigation. The concept explored in this work is to receive the corrections provided by a GBAS ground station, forward them to a drone via data link or the cell phone network and re-use the information for drone guidance. In that way, already available information could be re-used in a meaningful way without significant effort. However, the potential benefits of this procedure in comparison to a Satellite Based Augmentation System (SBAS), e.g. WAAS or EGNOS, have to be carefully investigated as SBAS corrections are freely available to all users and also provide corrections and integrity to potential users via geostationary satellites.
In this paper, we investigate the protection levels achievable on a UAV by using the relayed GBAS corrections and integrity parameters. Due to the fact that these are locally generated by the GBAS the achievable performance is usually better than with SBAS. However, the GNSS navigation errors decorrelate with distance, leading to an increase in the protection levels. The resulting performance is then compared to the protection levels of a purely SBAS-based navigation to identify areas of potential use of the proposed system.



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