Research And Application On GNSS Multi-system Time Interoperability

Nowadays,satellite navigation has entered a stage of rapid development.Four global satellite navigation systems(GNSS)and many regional satellite navigation systems have been built around the world.Each navigation system operates independently to provide users with positioning,navigation and time services(PNT).With the development and upgrading of various navigation systems,more and more navigation satellite resources are available.If satellite resources can be shared among various navigation systems,and the navigation satellite resources can be used efficiently.The accuracy and stability of services can be improved.It requires compatibility and interoperability among navigation systems.Compared with the services provided by single satellite navigation system,multiple GNSSs compatibility and interoperability can share resource and complementation can be achieved under complex circumstances.The service of users can be improved in intelligent transportation,urban buildings,mountains,forests and canyons.In terms of PNT services in complex environments such as rescue and disaster relief,the compatibility and interoperability of various systems can greatly improve the accuracy and reliability of PNT services.Compatibility and interoperability of navigation systems involve several technologies.Compatibility includes signals,messages,coordinate frames,etc.,interoperability focuses on time interoperability research.Time interoperability is the basis for the compatibility and interoperability of GNSS systems.It is also one of the important research contents of international GNSS cooperation in recent years.The research on time interoperability is mainly at the system level,involving three aspects:one is the research on the time offset monitoring between systems,the second is the research on the system time offset predicting algorithm,and the third is the research on the method of transmitting predict results.The paper mainly analyzes the method of generating and maintaining the system time of the four major global satellite navigation systems,the monitoring method of the time offset between systems,the predicting method of the system time offset and the method of broadcasting the system time offset.The main research contents and innovations are as follows:(1)The basic content of system time offset monitoring technology of time interoperability is researched,and different monitoring methods are introduced,including single station method and time link method.The time delay of the receiver used for time difference monitoring is measured using laboratory conditions.(2)Various methods of time offset prediction have been studied,including least squares quadratic forecasting method,ARIMA method,and Koopman method based on neural network.Concentrated methods are compared.(3)Two methods of broadcasting are studied,namely,the direct broadcasting of prediction values through the network and the broadcasting parameter method of navigation messages,and the advantages and disadvantages of the two methods are analyzed.Time provides a unified reference for the various tasks of the navigation systems,and the service can be completed only by unifying the time of the multi-GNSS systems participating in compatibility and interoperability.