Experimental and simulation study for commercial time transfer service over geostationary satellite

Time transfer over satellite links has been explored since the satellite era began. Currently, Two Way Satellite Time and Frequency Transfer (TWSTFT) is routinely used between national timing laboratories to align national timing standards, and the Global Positioning System (GPS) provides accurate timing signals in addition to its more familiar navigation solution. This paper reports on a method for transferring time from a reference clock over commercial geostationary satellite links with a specified low level of uncertainty at the receiving stations, using only the ephemeris information provided by the satellite operator. An initial experiment, reported here, showed that with one master station, measuring aggregate extraneous delays and transmitting positioning and delay data plus a correction factor to the slave stations, allowed transfer of a 1 pps (pulse per second) timing signal with a standard deviation of 72 to 98 ns and peak-to-peak variations of 500 to 600 ns, when measured against a GPS reference. Subsequent analysis of the experiment uncovered some issues with the implementation, suggesting that these results could be substantially improved upon. Furthermore, a simulation of the system that modeled the extraneous delays produced results similar to those obtained in the experiment.