Improving TWSTFT short-term stability by network time transfer

Two Way Satellite Time and Frequency Transfer (TWSTFT) is one of the major techniques to compare the atomic time scales between timing laboratories. As more and more TWSTFT measurements are performed, large numbers of point-to-point two-way time transfer links have grown to be a complex network. For a future improvement of the TWSTFT performance, it is getting important to reduce measurement noise of the TWSTFT results. One of the methods is using the TWSTFT network time transfer. The Asia-Pacific network is an exceptional case of simultaneous TWSTFT measurements. Some indirect links through relay stations show better short-term stability than the direct link because the measurement noise may be neutralized in a simultaneous measurement network. In this paper, the authors propose a practicable method to improve the short-term stability by combing the direct and indirect links in the network. Through the comparisons of time deviation (TDEV), the results of network time transfer show clear improved short-term stabilities. For the links based on H-maser, the average gain of TDEV at 1 h averaging times is 20%. As TWSTFT short-term stability can be improved by network time transfer, the network may allow larger number of simultaneously transmitting stations.