Analysis of the Asia-Pacific TWSTFT network

Two way satellite time and frequency transfer (TWSTFT) is an important method to compare the atomic time scales between time keeping laboratories. The aim of this paper is to analyze the Asia-Pacific TWSTFT network, in which the measurements are performed synchronously by using multi-channel modems. As a result of the synchronous measurements, the clock drift and the majority path instabilities could be neutralized in the calculation of the closure links. This paper discusses what kinds of noise could be cancelled and what kinds of noise would still be kept in the result of the closure links by taking all three stations at the same time into account. From the re-examination of TWSTFT equations, we deduced that the time difference between two laboratories could be obtained via relay stations without debasing the stability in the synchronous TWSTFT measurements. The results show that the noises of the closure links in the Asia-Pacific TWSTFT network are very low. The smallest standard deviation of triangle closure is only 121 ps for the data over four months. The closing errors are closed to zero after removing calibration values. The analysis of modified Allan deviation confirms that the stability of data via relay station is in competition with the direct TWSTFT link. This paper also shows that the stability of TWSTFT could be improved by the weighted mean of the redundant TWSTFT links.