Timing Aspects of GPS-Galileo Interoperability: Challenges and Solutions

A. Moudrak, A. Konovaltsev, J. Furthner, J. Hammesfahr, A. Bauch, P. Defraigne, S. Bedrich

Abstract:	Interoperability with GPS has been one of the drivers for Galileo definition and design. This paper is dedicated to the timing aspects of the interoperability, related challenges, and solutions. Here, we discuss mainly technical issues; organizational and legal matters have been addressed by US-EU working groups and have been mentioned in the agreement on GPS Galileo cooperation signed by the US and EU sides on 26 June 2004. The offset between GPS and Galileo system timescales (GGTO) will cause a bias between GPS and Galileo measurements in combined navigation equipment and, consequently, a bias in the user position & time solution. The first part of the paper reviews approaches to deal with this problem and presents simulations of positioning accuracy for users of the combined equipment. The Galileo baseline foresees determination of GGTO on system level and its dissemination to users in the Galileo navigation message. The second part of the paper discusses the basic options for the GGTO determination (e.g., using a GPS time receiver connected to the physical realization of GST or a time transfer link between the Galileo Precise Time Facility and the US Naval Observatory). Finally, the accuracy of GGTO determination and prediction is studied with both simulated and real measurement data.
Published in:	Proceedings of the 36th Annual Precise Time and Time Interval Systems and Applications Meeting December 7 - 9, 2004 Hyatt Regency Washington on Capitol Hill Washington, D.C.
Pages:	279 - 292
Cite this article:	Moudrak, A., Konovaltsev, A., Furthner, J., Hammesfahr, J., Bauch, A., Defraigne, P., Bedrich, S., "Timing Aspects of GPS-Galileo Interoperability: Challenges and Solutions," Proceedings of the 36th Annual Precise Time and Time Interval Systems and Applications Meeting, Washington, D.C., December 2004, pp. 279-292.
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