Sophie Jochems, Michael Felux, Philipp Schnüriger, Zurich University of Applied Sciences, Center for Aviation; Michael Jäger, Luciano Sarperi, Zurich University of Applied Sciences, Institute of Signal Processing and Wireless Communications - ZHAW, Switzerland

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In this paper, we investigate the potential performance of the envisioned Differentially Corrected Positioning Service (DCPS) for the Ground Based Augmentation System (GBAS). For this purpose, we receive and decode the GBAS messages transmitted by the operational GBAS station providing GBAS Approach Service Type (GAST) C (i.e. a CAT-I service) at Zurich airport. Based on these parameters we calculate the respective protection levels for the GBAS DCPS and compare them with the SBAS protection levels. Due to the fact, that the GBAS corrections are locally generated, the achievable performance is usually better than with SBAS. However, the GNSS navigation errors decorrelate with distance, leading to an increase in the protection level. Both, the GBAS and SBAS protection levels, are dependent on a k-factor. This factor is derived from the allocated integrity risk to an integrity risk and equals 6.18 in the case of SBAS. For GBAS, the k-factor is 10. This is a very conservative value, which would be adapted in the future as the DCPS, its use-cases and the required level of integrity are developed further. To show a less conservative and more realistic scenario for comparing SBAS and GBAS protection levels, a GBAS protection level with a reduced k-factor of 6.18 was additionally calculated. The resulting performance of the regular GBAS and the GBAS with a reduced k-factor is then compared to the protection levels of a purely SBAS-based navigation to identify areas of potential use of the proposed system. Based on these evaluations we show that the GBAS DCPS yields better performance in an area of (on average) more than 50 km around the GBAS station.