Research On Calibration Method Of System Error In TWSTFT

The Coordinated Universal Time(UTC)is the only standard of different time around the world,which requires high-precision and long-distance time comparison technology as the support to ensure the unity of time.In addition,inside some large systems,the deep-space exploration,satellite navigation,etc.have quite wide range of scopes for observation;meanwhile,the internal systems must have a unified time system,so it is necessary to develop a variety of time and frequency transfer techniques to achieve long-range and high-precision time synchronization.Two-Way Satellite Time Frequency Transfer(TWSTFT)is one of the most accurate long-distance time transmission techniques.As the signals of the two stations are mutually sent and received,and the propagation path is approximately symmetrical,which can offset the common error,TWFTFT can achieve a higher comparison accuracy.After many years' development,the error correction of the link can reach nanosecond or even below the magnitude of nanosecond,in which the correction of the equipment delay has become a research hotspot.The calibration capability of the equipment delay is the main factor to limit the improvement of comparison accuracy of TWSTFT,so the key to further enhancing the accuracy of TWSTFT is to accurately measure and calibrate the equipment delay of the two-way satellite station.The research contents of this paper are as follows:(1)The error sources in TWSTFT are studied and analyzed,and the correction methods of errors are given;(2)The characteristics of several common system error calibration methods are compared and analyzed,and a method of step-by-step calibration to calibrate the system error is proposed.According to the different sources,this method divides the system errors into two parts: the equipment time delay and the spatial link time delay.Respectively,the calibration method for equipment delay by the single mobile calibration station,and the calibration method for spatial link time delay by the single mobile calibration station and measured station are given,achieving the calibration of system error;(3)It develops a single mobile calibration station and designs a test to assess the equipment delay stability of single mobile calibration station,including testing the influence of equipment switch machine on time delay,the test on time delay difference of Modem between different channels as well as the test on equipment delay of single mobile calibration station;(4)It designs capacity assessment test of calibration system error by step-by-step calibration method,and takes the system error measured by the double mobile calibration station as the true value to evaluate the actual calibration performance of the step-by-step calibration method.The measured data show that the uncertainty of calibration is superior to 3ns.