Research On The Method Of Remote Reproduction Of UTC(NTSC) And Its Realization

National time service center(NTSC) is responsible for the generation, maintenance and dissemination of national standard time. In recent years, it has established national standard time UTC(NTSC) synchronized with UTC, and kept the deviation between UTC(NTSC) and UTC less than 10 ns. As always, studying practical techniques and adopting diversified means to provide the high-performance national standard time to the users in various industries so as to serve the national economy development of our country is one of the core tasks of NTSC. The UTC(NTSC) remote reproduction method proposed in this paper can make up the defect that the current timing systems lack timing accuracy of 1~5ns order of magnitude, which can provide a real-time timing scheme with an accuracy of 2 ns.On the basis of studying the existing remote time comparison methods, this paper presents a time comparison method applicable for UTC(NTCS) remote reproduction, which can contribute to solve such problem as the standard satellite common-view method has discontinuity in its measurement and fails to output the measurement results in real-time. Furthermore, the time comparison method proposed herein has achieved UTC(NTSC) remote reproduction system in engineering, which makes the deviation between the user local reproduction time with UTC(NTSC) achieved less than 5ns.The main research contents of this paper are as follows:(1) A deeper analysis of the requirements of the national standard remote time reproduction.This paper has fully analyzed the current status of the existing timing means, conducted an investigation and study on the requirements in high-precision frequency signal, time traceability, etc. of various industries, and deeply analyzed the national standard remote time reproduction, including its functionality, performance and cost, etc..(2) A research on the existing remote time comparison technology.By studying and analyzing such time comparison technologies as satellite common-view, PPP time transfer, satellite whole-view method, two-way satellite time transfer, optical-fiber time transfer, etc., it is found that the existing methods have the following disadvantages: 1) the satellite common-view method is discontinuous, which may have dead time in its measurements; 2) satellite common-view method, PPP time transfer, satellite whole-view, have poor real-time performance in their comparison results, especially the PPP time transfer and satellite whole-view which depend on post-processing of precise orbit and clock error data; 3) two-way satellite time transfer, optical-fiber time transfer, etc. need specialized links, therefore, the cost is too high if use these methods in large scale.(3) The proposal of UTC(NTSC) remote reproduction method, through which the reproduction accuracy is improved in combination with theoretical and experimental study.On the basis of the concept of satellite common-view, this paper has proposed a remote time comparison method applicable for UTC(NTSC) remote reproduction, by designing flexible observation period and performing observations and data processing in parallel, the method proposed herein has the abilities to ensure a continuous and uninterrupted traceability comparison and solve the problems of data processing, error correction, unequal accuracy data fusion, etc.; it has also designed a data real-time exchange method, through which the problems of communication reliability, environment adaptability caused by real-time information transmission requirements can be solved; studied and solved the problem of the error calibration issues caused by multiple satellite navigation systems being shared; studied a clock control strategy, which makes the output synchronized with UTC(NTSC) while taking the performance requirement of the stability into account by using real-time comparison data to control the frequency resource.(4) The development of UTC(NTSC) remote reproduction system is achieved in engineering.Based on a thoroughly theoretical research on the UTC(NTSC) remote reproduction methods proposed herein, from the engineering point of view, this paper has further analyzed the requirements of the reliability, stability and high-degree integration of the UTC(NTSC) remote reproduction system, implemented UTC(NTSC) remote reproduction system in engineering.(5) A thorough test of the performance of the system.This paper has carried out a number of targeted testing experiments, including zero baseline, short and long baseline experiments used for verifying the uncertainty of the system tests; by installing the reproduction terminals using different types of atomic clocks at a position where the users reside and using satellite two-way mobile calibration stations as independent testing means, the performance of its UTC(NTSC) reproduction can be verified. The experimental results show that, in the case of a reproduction terminal using cesium atomic clock, the daily stability of reproducing frequency signal is 1.8e-14 and the frequency accuracy is 1.99e-14; and in the case of a reproduction terminal using rubidium atomic clock, the daily stability of reproducing frequency signal is 9.45e-14 and the frequency accuracy is 1.36e-13.In order to study and thus implement UTC(NTSC) reproduction system, the innovation works of this paper are as follows:(1) This paper presents a method for remote reproducing national standard time.With reference to national standard time, a uniform standard time signal can be provided directly to the users across the country or even throughout the would by means of remote time comparison and the controlling of clocks, and the traceability of reproduced signal to international standard time UTC is achieved based on the existing international comparison link. This paper provides a new timing scheme which has the following advantages when compared with satellite timing: a much better accuracy of 2ns, an equivalent cost and an unlimited number of users.(2) This paper presents a new real-time and continuous common-view comparison method.An observation period of standard satellite common-view method is 16 minutes, wherein the observation data can be obtained in 13 minutes thereof and the remaining 3 minutes are observation intervals. Since a post-exchange processing is performed on the common-view data, a serious lagging will be generated in the comparison results. In this regard, this paper presents a new real-time common-view comparison method. This method breaks the inherent concept of observation period and designs a structure that the observation period can be flexibly set, through which method the discontinuity exists in the observation period of standard common-view method and the post-exchange processing of data can be solved.(3) This paper enhances the usability of time reproduction by means of using various fusion methods.By studying the characteristics and laws of systematic deviation between different navigation systems, this paper presents a delay deviation correction method which solves the systematic problem caused by multi navigation systems being shared. Since the number of the visible satellites increases, the baseline length of remote comparison is greatly increased. Therefore, an effective integration between multi-satellite navigation systems is achieved. In order to analyze the characteristics of pseudo-range and carrier phase data, this paper presents a suitable carrier phase smoothed pseudo-range method, through which a fusion sharing of both data is achieved and the requirement of unequal accuracy of users is satisfied.The results of the researches presented in this paper have been applied to Beijing, Tianjin, Shanxi, etc., and they have a practical value in reproducing UTC(NTSC) signal across the country.