Time and Frequency Transfer Using GNSS

Abstract

Since several years, GPS is used at the Royal Observatory of Belgium (ROB) for time and frequency transfer applications. Software for code and/or carrier-phase data analysis has been developed and allowed to detect the sensitivities and limitations of the methods. We have also extended the analysis to GLONASS and demonstrated that the satellite-dependent hardware delays are the main factors degrading the accuracy of the time transfer links. Presently, we perform all-in-view time transfer and contribute to the TAI by applying our in-house developed RINEX-CGGTTS conversion software on the code data form our Ashtech Z-XII3T GPS receiver. We are also routinely using the Bernese to compute the time links between BRUS and all the EPN stations equipped with an Ashtech Z-XII3T receiver. In order to anticipate the renewal of the time transfer equipment, we started to test different geodetic GPS receivers (the PolaRx2, developed by Septentrio (Belgium), and the LegacyE from Topcon) to investigate their suitability for time transfer applications. In the light of these results, the perspectives and improvements we expect for time and frequency transfer with the upcoming GALILEO and modernized GPS signals and their combination will be presented. In particular, we assess - with the help of simulated GPS and Galileo observations - the satellite visibility and the accuracy of the Common View time transfer for selected links, and discuss possibilities of employing guaranteed Galileo services for time and frequency transfer. These results were obtained in cooperation with German Aerospace Center (DLR) which is involved into the work on Galileo design and has developed a GNSS simulation software.