EGNOS SBAS Data Reduction to Match ITU-R Eurofix Specifications

D. van Willigen, A. Helwig, G. Offermans, J. Seybold, G. Abwerzger, A. Salonico

Abstract:	EGNOS and WAAS DO-229 SBAS messages are intended for transmission data rates of 250 bps. To make the data also available in urban and polar areas where SBAS signals are often not available, it is in the ESA EGNOS TRAN program investigated whether the data set can be reduced so it matches the ITU-R Loran-C data broadcast channel specifications while not deteriorating the SBAS accuracy and integrity performances. Two approaches have been investigated: a local-area and a wide-area concept. In both concepts the basic EGNOS data was received through an EGNOS receiver installed at the Loran-C station at Sylt, Germany. The local-area concept converted the EGNOS DO229 into correction data for the location of the transmitter station. These data are then broadcast by Eurofix in the same way as it is done today with the present DGPS service. The more advanced approach which offers good accuracy at large distances from the Loran-C station is a typical wide-area service. This required new data conversion algorithms to reduce the 250 bps EGNOS DO 229 SBAS data stream to a modest 30 bps data rate while maintaining good accuracy and integrity performance. New message types containing this wide-area information have been designed, and this system is also implemented at the Sylt station. Special receiver algorithms have been developed that can reconstruct from these special Eurofix message types a RTCM SC-104 DGPS message that can be applied by most commercial DGPS receivers. The large advantage of this approach is that it offers high position accuracy over a very large service area. The range of a Eurofix transmitter is up to 2,000 km. This means that such services may then become available in the Polar Region and in areas with restricted view to the SBAS satellites like in cities, forests and valleys. The paper discusses the background philosophies of the data reduction process and it describes the resulting new message types. Finally, real-life measured DGPS performances from the Eurofix station at Sylt will be shown. Telespazio has been the project manager of this ESA EGNOS TRAN project which successfully ended in June 2003. Reelektronika designed and implemented the system while TeleConsult Austria was in charge of all real-life measurements.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1320 - 1326
Cite this article:	van Willigen, D., Helwig, A., Offermans, G., Seybold, J., Abwerzger, G., Salonico, A., "EGNOS SBAS Data Reduction to Match ITU-R Eurofix Specifications," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1320-1326.
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