Research On Time Transfer Method Of Virtual Common-View Station Based On Communication Satellites

The satellite orbit determination measurement,precision measurement,and many other fields require nanosecond time synchronization.However,satellite navigation systems could only achieve ten seconds time service.It is extremely necessary to build a dedicated time comparison links such as common-view and satellite two-way time and frequency time transfer,etc.,and exchange the comparison data afterwards to achieve time synchronization on the order of nanoseconds.Aiming at the problems of high cost,user capacity limitation and poor real-time performance of the existing nanosecond time synchronization methods,with the help of China Area Positioning System(CAPS)resources,a time transfer method based on communication satellites with high accuracy and precision was studied and realized.The principle of the common-view time transfer method based on communication satellite was analyzed.The core of this method is the satellite virtual atomic clock technology(referred to as “virtual clock”)with pseudo-range difference function.Users could obtain the virtual clock correction amount through the navigation message to correct the time transfer result.The accuracy should be equivalent to as same as the common-view time transfer by receiving the signal from the CAPS master station transmitted by the satellites.The errors of this method were analyzed in detail,and the time transfer experiment based on communication satellite was carried out.This method can realize the time synchronization at the level of nanoseconds in area.What the problem is that the accuracy decreased with the increase of the baseline between the user and CAPS master station,especially during the period of satellite maneuvering,and the accuracy could exceed 100 ns.In order to reduce the baseline length impact on common view time transfer,a virtual common-view reference station(referred to as “VCVRS”)time transfer method was studied and implemented.Firstly,a time transfer method of virtual common-view reference station based on communication satellites is proposed.Three to four time transfer base stations have been built up in China.These stations could monitor the timing deviation of the communication satellites and send back to the central station.The central station analyze and forecast the timing deviation model and broadcast the deviation through the communication satellite to users.The user could obtain the timing deviation data of each station,then calculate the virtual common-view reference station nearby.Thus,the use should achieve common-view with the virtual common-view reference station of zero-baseline.Therefore,real-time common-view comparison can be achieved of this method and not affected by the limitation of the baseline between the user and the time transfer base stations.All users in the coverage area should achieve nanosecond time synchronization.Secondly,the main errors of VCVRS system based on communication satellites were analyzed in detail.There are eight aspects of errors including the receiver error,ephemeris error,ionosphere delivering delay error,time synchronization error among stations,traceability model forecast error,modeling error of time transfer bias data,quantization error of the model parameters in navigation message and the influence of satellite maneuvering.Finally,through the analysis of existing technology development,the time transfer uncertainty of VCVRS was evaluated in theoretical way.Thirdly,the VCVRS system was implemented from the engineering,and the platform of the time transfer performance experiment was designed and implemented.The VCVRS time transfer experiment was carried out at several experiment places.The performance of the method of VCVRS during the satellite in the period of normal cruise and maneuver were analyzed respectively.During the period of normal satellite cruising,the time transfer uncertainty of Beijing could achieve 1.9 ns,and Kunming could achieve 7.7 ns.In the case of satellite maneuvering,the time transfer uncertainty in each experiment places could better than 30 ns,which is far superior to the general time transfer methods at the level of 100 ns.Finally,based on the VCVRS time transfer method proposed in this paper,it compared with the commonly used time transfer methods with high accuracy and precision.The difference of the performance was compared between VCVRS method and common-view time comparison,PPP time comparison and fiber time comparison respectively in several locations of China.So the superiority of the method of VCVRS has been further analyzed.In general,VCVRS method takes the idea of common-view time comparison into one-way time transfer,the real-time nanosecond-level time transfer is achieved.In addition,zero-baseline common view is also achieved by using the method of virtual common-view reference station.The problem that the time performance is decreasing with the increase of the baseline length,users in the coverage area could achieve the uncertainty of time transfer in the order of nanoseconds.It is a kind of promising method which has been applied in engineering systems.