Extended Range Eurofix: A Robust 2,000 km Range Data Link for EGNOS/WAAS Integrity Messages over the Polar Region

D. van Willigen, A.W.S. Helwig, G.W.A. Offermans, R. Kellenbach and W.J. Pelgrum

Abstract:	Eurofix is an integrated Navigation system, which combines GPS and Loran-C. The Loran-C signals are additionally modulated to broadcast differential GPS and especially integrity information. A Eurofix user can correct and validate GPS observations and calculate his position. The accurate GPS position is then used to calibrate the Loran-C ranges to determine the unknown Additional Secondary phase Factor (ASF). In case GPS becomes unavailable, for instance due to shadowing or interference, calibrated Loran can be used to continue positioning. The dissimilarity of the Loran and GPS signals decreases the probability that they both will be unavailable at the same time. This system, first developed by Delft University of Technology, has been implemented on 4 European Loran-C transmitters and has been operational for a few years. With a range of over 1,000 km, one station in France, another one in Germany and two in Norway cover the larger part of Northwestern Europe, stretching from the North Cape down to the Pyrenees. The system might be used for land, maritime as well as aeronautical applications. The Eurofix modulation neither interferes with nor noticeably degrades the normal Loran-C positioning functionality. This means that legacy users of Loran-C can continue to use their equipment while new applications and services can be introduced using the Eurofix data transmission capabilities. Recent Loran-C/Eurofix receiver technology developments have shown the capabilities to receive Eurofix corrections from the Norwegian station Bø at about 2,000 km from Reelektronika’s headquarters in the Netherlands under heavy cross-rate conditions. This performance opens the possibility to use the robust extended-range data link facility to fill the coverage holes of EGNOS and WAAS over the high-latitude regions and the North Pole. This way GPS integrity information can be delivered to aircraft flying outside the footprints of the geostationary satellites. Importantly, the integrity information can be delivered within the time to alarm requirements for en-route navigation based on GPS positioning. Furthermore, modern Loran-C receivers can successfully remodulate the Eurofix-modulated pulses, thereby restoring the maximum Loran-C navigation capabilities. In this case Loran is still available as a reliable navigation back-up system for GPS. This paper will show results of the newly developed Loran/Eurofix receiver and the associated performance of the data link. Further, based on these results the possibilities are investigated for a long-range data link system based on Eurofix technology to fill the coverage holes of WAAS and EGNOS at high latitudes. Special attention is paid to the required bit-rate for provision of GPS integrity. It will be shown that the system can still meet the time to alarm requirements for aeronautical en- route navigation systems based on EGNOS and WAAS augmented GPS.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1752 - 1758
Cite this article:	van Willigen, D., Helwig, A.W.S., Offermans, G.W.A., Kellenbach, R., Pelgrum, W.J., "Extended Range Eurofix: A Robust 2,000 km Range Data Link for EGNOS/WAAS Integrity Messages over the Polar Region," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1752-1758.
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