Time and frequency transfer combining GLONASS and GPS data

In order to allow the use of GLONASS data from geodetic type receivers providing only raw data in RINEX format, we updated the R2CGGTTS software developed initially at the Royal Observatory of Belgium (ROB) for GPS data. The GLONASS navigation files are used for the determination of satellite clocks and positions, and the computation procedure to get the CGGTTS data from the pseudorange measurements is applied similarly as for the GPS satellites. Using the satellite orbits and clock products provided by the IGS analysis center ESA, we combine GPS and GLONASS in All in view. Adding GLONASS decreases the noise of the clock solution with respect to the GPS-only solution by about 20% thanks to the increased number of satellite observations. We also quantify the added value of using GLONASS data in addition to GPS data for time and frequency transfer based on Precise Point Positioning (PPP). A particular attention is given to the determination of the frequency-dependent hardware delays in both approaches.