| GNSS common view time service is a satellite time service method that can realize high-precision time transmission between users far away from each other.In the GNSS common view time service system,multiple reference stations observe the same GNSS satellite at the same time,and the bias between the local time and the GNSS satellite clock is obtained by calculating the pseudo range.Data is exchanged between reference stations to complete time comparison.The biases between the local time of the stations and the satellite clock are called clock biases for short.In order to obtain a more accurate clock bias of each reference station,it is necessary to set multiple reference terminals at each reference station.They observe the same GNSS satellite at the same time and calculate and output a set of clock bias data.In fact,at the same time,due to different observation positions and angles,the number of satellites and satellites observed by different reference terminals at the same reference station are different.Even if the same satellite is observed,the calculated output satellite clock biases are also different.It is an important premise to ensure the accuracy of time service to fuse the clock biases observed by different reference terminals in the same reference station,so as to obtain more accurate clock bias data of the reference station.At the same time,in order to ensure the security of data exchanged between reference stations,it is also very important to encrypt and decrypt the fused clock bias data efficiently.To solve the above problems,this paper deeply studies the clock bias data processing method,and develops a software that can comprehensively process the clock bias data of each reference terminal and output the fusion results.The main work of this paper is as follows:(1)The data fusion methods are investigated systematically.Facing the data fusion requirements of discontinuous multi-source satellite clock bias in GNSS common view time service system,a data fusion method using centralized fusion structure is proposed.Among them,Hampel filtering algorithm is used to eliminate the singular values in the observation data,and fill in some missing values of clock bias data at the same time;The clock bias data fusion is realized by using the weighted average algorithm of dynamic weight distribution;Kalman filtering or α-β The filtering algorithm performs tracking filtering,generates the final value of clock bias fusion,and provides a reference value for threshold decision.(2)Aiming at the problem of information leakage when transmitting clock bias fusion results through the network,the principle of data encryption and common data encryption technologies are studied.Using Open SSL,a hybrid encryption method based on RSA,MD5 and Base64 is designed to realize the safe transmission of clock bias fusion data.(3)Using Lab Windows / CVI integrated programming environment,a satellite station clock bias fusion and remote transmission software is developed.The software receives the real-time satellite station clock bias data of each reference terminal through the network,then saves,monitors,classifies and fuses all the data in real time,saves and encrypts the fusion results,and finally sends the data packet safely through the network or serial port.The simulation results of the algorithm show that the proposed clock bias data fusion method can better eliminate the observation error and output a group of satellite station clock bias data close to the real value and with small overall fluctuation.It is suitable for the fusion processing of satellite station clock bias data,and also provides reference ideas for other discontinuous multi-source data fusion applications;The proposed hybrid encryption method ensures the security of network communication.The software test results show that the satellite station clock bias fusion and remote transmission software has completed the expected functional requirements of clock bias data processing,and achieved the performance indexes such as the error of clock bias fusion result is less than 5nanoseconds,stable operation for more than 5 days,and time delay is less than 1 second.The relevant research conclusions and software technology of this paper have been successfully applied to a domestic satellite ground station. |
