Research On TWSTFT Calibration Based On Double Mobile Stations

Far from now, Double Mobile Stations in Two-way satellite time and frequency transfer(TWSTFT) is one of the most important methods to achieve long-distance and high-precision time transfer, and the contrast uncertainty can be 1ns in general.Study found that the TWSTFT test performance is mainly affected by the calibration uncertainty of the equipment time delay. ITU recommends three equipment time delay calibration methods, they are bistatic zero baseline method, satellite simulator method and a single mobile station calibration method. The bistatic zero baseline method is not applicable for the built system since it is complex to achieve; Absolute time delay can be calibrated by satellite simulator method, in currently, the calibration precision of some equipment can achieve hundreds of picoseconds, however, stations are required calibrated separately and is not strong adaptability to the environment; single mobile station calibration method is the most accurate and commonly used method,it’s calibration using a single mobile station with the ground station to be calibrated for zero baseline test respectively, and obtain the relative delay between each mobile station and a single calibration station, the relative time delay of the two stations can be obtained after subtracting the relative delay above.Test data shows that this method can achieve the uncertainty to1 nanosecond, but single mobile calibration station only supports the same type of calibration ground stations and need to be interrupted during normal measurement calibration test stations, or the calibrated ground stations have other test channel, it is not sensitive to other asymmetric factors in TWSTFT link.In order to solve the problem TWSTFT system error calibration, this paper presents a method of Two-way satellite time and frequency transfer system overall calibration error which based on double mobile calibration stations, the systematic errors can be calibrated to within 0.5ns, enhance the precision of comparison TWSTFT.The main research and originality of this paper are as follows:(1) Research on the sources of the error in two-way satellite time transfer, analysis of their impact, and proposed correction method, especially the delay devices affected by environmental temperature changes, the modem transmit delay accurate calibration and so on.(2) Proposed an overall frequency transmission system error calibration method based on two-way satellite time mobile alignment station, a two-way mobile calibration station installed with the two ground stations which would be calibrated.Test ground station equipment time delay and the sum of asymmetric component in signal transmission space.(3) We designed and implemented a number of testing laboratories, including Zero baseline self-calibration, the test to compare with two-way fiber optic system, system error found test to calibrate two-way satellite system. The aim of the test based on self-test zero baseline is test the feasibility of poor calibration system of double mobile calibration stations, the standard deviation of double mobile calibration stations had obtained which is 0.07 ns and it is batter than other laboratory’s results all over the world. Test the fiber bidirectional comparison system between Xi’an and Lintong in order to verify calibration double mobile station has the capability of high-precision time and frequency transferv. The test uncertainty is better than 0.2ns,test results show that double mobile calibration station has capability of time and frequency transfer can achieve nanosecond precision. Calibrate the two-way satellite calibration system between Kashi and Xi’an, baseline is about 3000 km, it aims to test the ability of calibrate double mobile station calibration actual bidirectional link, test uncertainty is better than 0.2ns. Test results reflect the use of dual mobile station to a fixed station calibration bidirectional link calibration is feasible.