2-GEO TWSTFT for BDS ground stations: Confidence interval of clock difference Allan variance
Abstract
Two-way satellite time and frequency transfer (TWSTFT) is important for time and frequency transfer between ground stations in Chinese BeiDou Navigation Satellite System (BDS). Different from ordinary TWSTFT links with single geostationary (GEO) satellite between each pair of ground stations, there are 2-GEO TWSTFT links between ground stations in BDS. Based on the 2-GEO TWSTFT links, we have proposed a separation method of estimating Allan variance of clock difference apart from the influence of Allan variance of noise measurement. This paper analyzes the confidence interval of the clock difference Allan variance obtained by this method with the condition that the noise measurement is white phase noise and the clock difference is affected by white frequency noise. The results applied to the BDS measurement data show that the obtained confidence interval upper bound of clock difference Allan deviation (the square root of Allan variance) is 3.248×10<sup>-12</sup> with 0.95 confidence. Compared with the single link TWSTFT with Allan deviation of (8.59-8.91)×10<sup>-11</sup>(<italic>τ</italic>=1 s), it proves further that the separation method has ability to weaken the influence of noise measurement on the evaluation of Allan deviation of clock difference measured by two independent TWSTFT links.
