GPS/Galileo Interoperability: GGTO, Timing Biases, and GIOVE-A Experience

Ricardo Píriz, Marta Cueto, Virginia Fernández, Patrizia Tavella, Ilaria Sesia, Giancarlo Cerretto, Jörg Hahn

Abstract:	The future European radio navigation system Galileo will use its own timescale for the synchronization and dissemination of the predicted satellite clocks. Broadcast satellite clock predictions must be referred to a common and stable time reference in order for the user to be able to obtain an accurate positioning solution. The new Galileo timescale is called Galileo System Time (GST) and is the equivalent of the GPS Time (GPST) scale used in the Global Positioning System. For timing applications, both the GPS and Galileo systems broadcast as well the difference between their respective system times (GPST and GST) and the universal timescale (UTC), with a maximum deviation requirement of the order of 1 microsecond for GPS (although in practice the deviation is currently below 10 nanoseconds) and 50 nanoseconds for Galileo. Furthermore, for GPS/Galileo interoperability the Galileo and GPS systems are planning to transmit within their navigation messages the so-called GPS to Galileo Time Offset (GGTO), i.e. the predicted difference between the GPST and GST system times. This paper analyzes the different issues involved in GPS/Galileo interoperability for positioning and timing, including GGTO and timing biases, and presents practical experience and solutions from the data processing of GIOVE-A, the first experimental Galileo satellite.
Published in:	Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting December 7 - 9, 2006 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	49 - 68
Cite this article:	Píriz, Ricardo, Cueto, Marta, Fernández, Virginia, Tavella, Patrizia, Sesia, Ilaria, Cerretto, Giancarlo, Hahn, Jörg, "GPS/Galileo Interoperability: GGTO, Timing Biases, and GIOVE-A Experience," Proceedings of the 38th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2006, pp. 49-68.
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