一种卫星双向时频传递设备时延差的标定方法

Calibration method of delay difference of TWSTFT equipments

利用卫星双向时间频率传递方法可以实现精度优于1 ns的远程时间同步。卫星双向设备时延差是影响双向比对结果的一项主要误差。目前,国际上通用的方法是利用一套可移动的双向校准设备实现对两套卫星双向设备时延差的校准。该方法存在设备成本高、占用通信卫星资源且对天气条件要求较高等问题。随着i GMAS站和其他监测站点的建设,越来越多站点的接收机监测数据资源可用。提出一种利用各站点监测数据实现对卫星双向设备时延差的校准方法。当卫星双向比对两地同时具有监测数据可用时,可以通过事后数据处理的方式校准两地卫星双向设备的时延差。校准的主要思路是利用精密星历、钟差和电离层产品,从每颗星的伪距测量值中扣除传播路径中的各项延迟,得到本地与导航系统时间的时差。通过对所有可见星的时差结果进行加权、滤波,并扣除接收机间的相对时延,得到比对两地的全视站间钟差。最后,通过与同时段的卫星双向结果进行比较,得到两地卫星双向设备的时延差,校准精度优于1 ns。虽然该方法无法实现亚纳秒量级的校准,但是可以较为简单地标定出两地卫星双向设备的时延差,可以满足纳秒级的时间同步应用需求。

Two-Way Satellite Time and Frequency Transfer is the major technique for time comparison, which can achieve the remote time synchronization with a precision better than one nanosecond. The delay difference of two TWSTFT equipments is the primary, error that affects the TWSTFT comparison result. As the primary error in the TWSTFT comparison result, the difference between the delays of two ground station two way equipments must be eliminated. Currently, in the world, a set of mobile TWSTFT equipment is commonly used to calibrate the delay difference between two TWSTFT equipments. However, this method faces the problems of high-cost, occupying communication satellite resource and highly depending on the weather condition. As more and more iGMAS stations and other monitor stations are built, the measurement data from more and more stations are available. In this paper, a new method is proposed, which utilizes the measurement data from various stations to calibrate the delay difference of satellite two way equipments. When two stations involved in a TWSTFY comparison link simultaneously have the measurement data used for time comparison, simple post data processing can be applied to calibrate the delay difference of satellite two way equipments. With the precise ephemeris, clock bias and ionosphere product resource, various time delays in the propagation path are deducted from the pseudo-range measurement value of each satellite, the time difference between the local time and the navigation system time is obtained. Then, the time difference results of all the visible satellites are weighted and filtered, the relative time delay between the receivers is deducted to obtain the final all-in-view clock time difference between two stations of TWSTF＇F link. Finally, compared with the two way results of the satellites in the same time period, the delay difference of two way equipments in two satellites is obtained, the time calibration precision is better than l ns. Although the method can＇ t achieve the calibration precision of sub-nanosecond, it can simply calibrate the time difference of two way equipments in two satellites, which can satisfy the application requirements of nanosecond time synchronization.