Combination Of Hydrogen-Cesium Time Scale Based On Vondrak-cepek Combined Filtering

High-precision time has become a crucial parameter in science,technology,economy,military and social life of a country.It is widely used in navigation,power,communications,aviation,national defense and other fields.As the most basic physical quantity,it also plays a fundamental role in supporting national scientific research.At present,most international time-keeping laboratories use Hydrogen masers or cesium clocks or both to produce stable time scales.Joint time keeping is an ideal time scale based on the short-term stability of hydrogen maser and the long-term stability of cesium atomic clock.At present,most of the time-keeping algorithms used in the world are using the short-term stability of the hydrogen maser to modify the short-term frequency jump of the cesium clock;using the cesium clock or cesium clock group as the measurement reference of the hydrogen maser to modify the frequency drift of the hydrogen clock;weighting the modified atomic clock data to generate the comprehensive time scale.When hydrogen maser is used as a reference to measure cesium atomic clock,the main noise is phase white noise.After filtering by mathematical method,the short-term stability of time scale will still be affected by cesium atomic clock noise.The characteristics of the two kinds of atomic clocks are different.The traditional joint method adopts the same way to take the weight of the two kinds of atomic clocks,which has some limitations for the best use of the two kinds of atomic clocks.In response to this problem,in this paper,the analysis of several classical time scale algorithms are done and based on the time scale performance of the ensemble of hydrogen masers and cesium clocks,Vondrak-Cepek filtering method is used to realize the fusion of Hydrogen maser and cesium atomic clock at the time scale level,and preliminary results are obtained.Aiming at improving the performance of time scale,this paper makes use of the atomic clock resources of the time reference UTC(NTSC)system maintained by the National Time Service Center of the Chinese Academy of Sciences.Firstly,the power-law spectrum noise model of atomic clock is studied and different kinds of simulation methods of atomic clock noise are analyzed.Secondly,several classical time-scale algorithms are analyzed,and the time-scale calculation of all-cesium clocks and all-hydrogen masers is realized based on exponential filtering algorithm.The frequency drift of hydrogen atomic clock is analyzed by using the minimum error theory.The optimal estimation of parameters effectively improves the time scale performance of all-hydrogen masers.Finally,the time scale fusion algorithm based on Vondrak-Cepek filtering is studied.The two types of time scales are successfully fused and the time scale performance is improved.The research contents and innovations of this paper are divided into the following four parts:1.The digital simulation of different types of atomic clock noise has been completed.For the digital simulation of atomic clock data,on the one hand,it is helpful to analyze the noise of different types of atomic clock and detect the effectiveness of noise reduction and time scale algorithm;on the other hand,it can avoid spending a lot of time measuring data,effectively save time and resources,realize multiple simulation experiments at the same time,and reduce the waste of resources.Therefore,the digital simulation method of atomic clock noise is studied,and the simulation experiment is designed.Based on the clock difference data of the National Time Service Center,the noise parameters of different types are estimated by the least square method to simulate the noise of different atomic clocks.At the same time,the effectiveness of the simulation method is verified by design experiments.The digital simulation of atomic clock noise is helpful to understand the characteristics of atomic clock in a deeper level,and lays a foundation for giving full play to the performance of atomic clock.2.Several classical time scale algorithms are compared,and the performance of cesium hydrogen joint time scale based on classical algorithm is studied and analyzed.Atomic clocks are developing rapidly,but there is the possibility of failure of long-running physical equipment.Therefore,in order to ensure the reliability of the time scale,time keeping uses the data of several atomic clocks to calculate the comprehensive time scale mathematically.Its performance is higher than that any of the clock in time keeping group.The basic concepts,main features and principles of time scale are introduced.Different time scale algorithms are designed for different application requirements.Therefore,three classical time scale algorithms,ALGOS,AT1 and Kalman,are studied and compared.The advantages and disadvantages of these three methods are summarized.At the same time,based on the same atomic clock data,three classical algorithms of hydrogen masers and cesium atomic clocks combination are realized,and three comprehensive time scale performances are discussed and analyzed.The optimal algorithm is to realize the time scale of a single atomic clock type clock group and lay the foundation for the time scale fusion of hydrogen masers and cesium atomic clocks.3.A method for dynamically estimating frequency drift of Hydrogen maser based on minimum error theory is proposed.The main goal of the hydrogen masers and cesium atomic clocks joint time keeping is to make full use of the advantages of the two kinds of atomic clocks,and to eliminate or weaken the defects of the two kinds of atomic clocks.For hydrogen clocks,the effect of frequency drift term on time scale should be weakened.The traditional method is to set a fixed frequency drift parameter within a month interval,and deduct the frequency drift from the clock difference data of hydrogen maser to participate in the calculation of time scale.But in practice,the frequency drift of hydrogen maser is not constant.Therefore,taking the hydrogen atomic clock as the research object,this paper explores the dynamic estimation of the frequency drift of the hydrogen maser by using the minimum error theory.This method can model the frequency drift parameters accurately,and can reflect the operation characteristics of the hydrogen maser.The estimated frequency drift parameters are substituted for exponential filtering algorithm to improve the time scale performance of the ensemble of hydrogen masers.4.A time scale fusion algorithm of Hydrogen maser and Cesium atomic clock based on Vondrak-Cepek filtering is proposed.Hydrogen maser and cesium atomic clock are the main precise frequency sources in the produce of international atomic time and national standard time.They have excellent short-term and long-term stability characteristics,respectively.Making full use of the short-term stability of Hydrogen maser and the long-term stability of Cesium atomic clock has become a key technology in the process of time scale generation.The traditional hydrogen cesium combination method uses the same way for weight two different types of atomic clocks,which has some limitations for the best use of the advantages of the two types of atomic clocks.Therefore,in order to improve the long-term and short-term stability of the time scale,a method for generating the fusion time scale of Hydrogen and Cesium using Vondrak-Cepek combined filtering is proposed.Firstly,the exponential filtering algorithm is used to generate a time scale for all-hydrogen and cesium clocks respectively.Then,the key parameters of Vondrak-Cepek combined filtering are selected according to the least square principle.Then,the performance of the time scale of all-Cesium atomic clocks is enhanced by the differential information of the time scale time series of all-hydrogen masers,so as to obtain the Fusion time scale.The fusion time scale is superior to those of all-Cesium or all-Hydrogen time scales.Therefore,Vondrak-Cepek combined filtering algorithm can not only effectively suppress the short-term noise of the time scale of all-Cesium atomic clocks by using the short-term stability of the time scale of all-hydrogen masers,but also maintain the excellent long-term stability of the time scale of ensemble of Cesium atomic clock itself,so that the generated time scale takes into account the long-term and short-term stability performance.