The GPS Transponder Concept—Towards One-Way and Two-Way GNSS Frequency Transfer

Abstract

In this section we discuss alternative, geometry-free approaches for positioning and time/frequency transfer using one-way and two-way measurements. The transmitter and receiver clock parameters can be separated or removed from the tracking geometry by using two-way measurements or introducing one-way measurements into the geometry-free linear combination. Clocks on board GNSS have become so stable that it makes interesting to steer their frequency using a geometry-free approach as demonstrated here. Galileo satellite clock parameters can be modelled using just two parameters per day (time drift and offset) with the remaining residual clock parameters showing the standard deviation at the level of 15 mm, see Sect. 18. Therefore, frequency steering of the satellite clock could be performed far more infrequently, (e.g., once a day) using the two-way frequency transfer approach. This could also bring to the separation of the prediction of GNSS satellite clock parameters (based on frequency steering) from the orbit prediction. We also discuss an application of the one-way frequency transfer approach based on geometry-free linear combination between two satellites (e.g., between GNSS satellites in MEO or with GEO). On the development of the two-way microwave metrology links for atomic clocks of the ACES mission we refer to Cacciapuoti and Salomon (2009).