Implementation of the GPS to Galileo time offset (GGTO)

Precise timing is an inherent part of Global Navigation Satellite Systems (GNSS) like GPS, Glonass and in the future Galileo. In the framework of the interoperability and compatibility discussions between the United States and European Union it was agreed that both GPS and Galileo systems will compute and broadcast the mutual time offset between both system´s time scales. This information once available in the signal-in-space (SIS) navigation message will enhance users´s interoperability achievable with a combined receiver. This paper outlines efforts to harmonize the underlying navigation time scales of both GPS and Galileo to better facilitate a combined navigation solution. It further discusses different implementation solutions for the GPS to Galileo time offset (GGTO) and the working scheme adapted by both sides.