BeiDou Time Transfer With the Standard CGGTTS

The R2CGGTTS software tool developed at the Royal Observatory of Belgium (ROB) to provide clock solutions in the standard Common GNSS Generic Time Transfer Standard (CGGTTS) has been extended to BeiDou Navigation Satellite System (BDS). The BDS includes satellites in three different orbits: 1) Medium Earth Orbit (MEO); 2) Inclined Geosynchronous Satellite Orbit (IGSO); and 3) Geostationary Earth Orbit (GEO). This paper presents first results obtained with this upgraded software, and a comparison between common view (CV) time transfer solutions obtained with either BDS, or GPS or Galileo. These preliminary results indicate that the BeiDou MEO satellites give time transfer results with a higher noise than the GPS results. This additional noise is shown to be due to some elevation-dependent delay in the BDS code measurements. Some biases were furthermore pointed out between the CV results obtained with the different BeiDou MEO satellites when the receivers used in the two stations are of different make. These biases may reach some nanoseconds, and find most probably their origin in the receiver hardware or firmware. It is shown additionally that using the BeiDou IGSO satellites and the GEO satellites, although increasing the number of observations, especially in the Asia-Pacific region, introduces a significant time transfer noise in the CV results.