Experimental and Simulation Study for Commercial Time Transfer Service over Geostationary Satellite

摘要

Time transfer over satellite links has been explored since the satellite era began. Currently, TWSTFT is routinely used between national timing laboratories to align national timing standards and the GPS provides precise timing signals in addition to its more familiar navigation solution. For many years, the possibility of a one-way timing service over satellite has been explored but apart from the GPS a commercial timing service product of this kind is not yet available. This paper reports on an approach to timing signal transfer from a precision reference clock over commercial satellite links with a specified low level of jitter at the receiving stations, making use only of the projected 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 PPS timing signal with jitter standard deviation of 72ns-98ns and peak-to-peak of around 500ns-600ns, measured against a GPS reference. Subsequent analysis of the experiment uncovered some issues with the implementation which suggested that these results could be substantially improved upon. Furthermore, simulation of the one master station system modeling the aggregate extraneous delays as random white noise plus wander can produce similar results to those obtained in the experiment. Finally, we report on the ongoing development and simulation of a system with three master stations with the desired goal of no more than 100ns of jitter peak-to-peak. Simulations show that obtaining such performance with three master stations for satellite positioning will be highly dependent on the statistics of the noise due to the aggregate extraneous delays.