GPS and Galileo Orbit and Ephemeris Simulations

U. Rossbach, R. Wolf, R. Kaniuth

Abstract:	The accuracy of a satellite navigation system to a large extent depends on the quality of its orbit determination. It furthermore depends on the orbit dissemination and reconstruction. That means the way the satellite orbit information is coded into ephemeris data, broadcast to the user and there converted back into satellite position data has a major impact on the positioning accuracy. The achievable user positioning accuracy in turn may also affect the integrity of the navigation system. In order to assess the effects of orbit determination, dissemination and reconstruction on user positioning accuracy and integrity, simulations have been carried out. These simulations were also intended to possibly aid in the selection of an ephemeris format for Galileo. Different formats for the broadcast of ephemeris data have been tested. These ephemeris formats go along with associated fitting algorithms to determine the ephemeris data from the predicted satellite positions as well as with associated satellite position computation algorithms for the user. All these algorithms have been included in the simulations. The ephemeris formats used were the GPS ephemeris format, the conventional GLONASS ephemeris format and an extended GLONASS format with the same number of degrees of freedom as the GPS format. For each of the formats, additional experiments have been conducted, investigating the effects of parameter resolution on the positioning accuracy. Similarly, it was investigated how the length of the ephemeris fit interval affects the positioning accuracy for the different ephemeris formats. The different combinations of ephemeris formats, resolutions and fit interval lengths are assessed for their suitability in terms of achievable positioning accuracy. The positioning accuracy is measured in both the computed satellite positions compared to the true satellite positions and the computed user position compared to the true user position. Another criterion in the assessment is the maximum computation time necessary for the user to calculate a satellite position. Based on these results, an ephemeris format is suggested that seems to be worthwhile to be selected for the use together with the new European Global Navigation Satellite System Galileo.
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:	2431 - 2435
Cite this article:	Rossbach, U., Wolf, R., Kaniuth, R., "GPS and Galileo Orbit and Ephemeris Simulations," 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. 2431-2435.
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