Study On The Fusion Method Of GNSS Time Transfer Measurement

GNSS(global navigation satellite system)time and frequency transfer technology is the most important time and frequency transfer method because of its relatively low operating cost and high accuracy.However,there are still some problems in GNSS time frequency transfer or comparison technology,such as large noise and obvious data jitter.For aerospace users who have high requirements for time synchronization,it is necessary to ensure that they can obtain and maintain a stable and reliable time standard for a long time.Therefore,this paper focuses on the noise suppression and reliability improvement of GNSS time transfer data.By means of GNSS time transfer measurement data fusion,the data noise can be reduced and the time stability can be improved.The main contents of this paper include:(1)Aiming at the waste of measurement data in CGGTTS(common generic GNSS time transfer standard),an improved algorithm is proposed.All the measured data in the data period are used to calculate the time differences to improve the utilization rate of the measured data.At the same time,the data cycle is shortened to improve the real-time performance.Experimental results show that the improved algorithm can reduce the noise of the comparison results,and the noise performance can be improved by up to 6%.By analyzing the real-time performance,standard deviation,data volume,and calculation volume of files at different intervals,the appropriate data period is determined.(2)In order to reduce the noise in GNSS time transfer data,the relationship between satellite observation elevation and data noise is analyzed.A data fusion scheme based on satellite observation elevation is designed,and the feasibility of the scheme is verified by experiments.By studying the federated Kalman fusion algorithm,a GNSS measurement fusion scheme based on multi GNSS observation codes and multi receivers is designed.The experimental results show that compared with the single measurement method for time and frequency transfer,the federated Kalman fusion algorithm can reduce the link noise by about 80%,and improve the short-term stability.(3)In order to solve the problem of data interruption or abnormal in the long-term operation of NIMDO(UTC(NIM)disciplined oscillator)in the current remote time traceability network,a comprehensive time scale algorithm and its implementation scheme of multi-NIMDO fusion are designed.Based on the RTTH(remote time traceability hierarchy)network,an experimental platform is built for testing.The results show that the integrated time scale of multi-NIMDO fusion can reduce the data noise and improve the short-term stability of the clock.The time scale is not easy to be affected by the data interruption or abnormality of a certain site,and can provide accurate and reliable time reference for users.Based on the study of GNSS time and frequency transfer technology,this paper conducts data fusion algorithm research from three aspects,and verifies the feasibility of the fusion schemes through actual experiments,which prove that the data fusion algorithm proposed in this paper can effectively reduce the data noise and improve the time stability.Figure 53,tables 10,52 references.