Study Of The Method Of Precise Common-View Time And Frequency Transfer Via BDS GEO Satellites

The technology of time and frequency transfer between stations via carrier phase observation has been studied for many years,and the problem of ambiguity has always been the research focus.The international GNSS Monitoring and Assessment System(iGMAS)provides BDS/GNSS products including precision satellite orbits,so the development of precise time trasfer based on BDS satellites has become a hot topic of international research.China's BDS is developing rapidly,whose basic system has been completed and is providing services now.BDS has a hybrid constellation with several GEO satellites.Based on the characteristic of BDS,namely the visibility of GEO satellites to large area,the time and frequency transfer between stations using carrier phase observation of BDS GEO satellites and iGMAS products were studied in this paper.This new method was named as the method of Precise Common-View Time and Frequency Transfer via BDS GEO satellites(PCVTFT).In this paper,the measurement model of PCVTFT was established,the PCVTFT experiments with single GEO satellite,and the experiments of receiver delay calibration were carried out.In addition,the influence of orbit error and ionosphere error were analyzed.The main research achievements and innovations are as followed:(1)The PCVTFT method was proposed based on the BDS characters,and the PCVTFT measurement model was established in case of a single GEO satellite.Two stations observe the same GEO satellite in the method,so the amount of ambiguity can be effectively reducded in time transfer,and frequency transfer can be carried out with any period.(2)PCVTFT experiments were carried out based on iGMAS and BDS GEO satellites.1)For the Xi'an-Lintong baseline(about 30km),the result of no cycle slip in half a month was given,which was compared with the result of Two-Way Optical Time and Frequency Transfer(TWOTFT),and the agreement degree(RMS)between them was 0.11ns;2)For the Xi'an-Changchun baseline with a length of 2000 km,the PCVTFT result of no cycle slip in half a month was given,which was compared with the TWSTFT result,and the agreement degree(RMS)was 0.44ns;the PCVTFT result with long arc segment and standard cycle slip fixing was also given,and the agreement degree(RMS)was 0.5ns;3)For the Xi'an-Kashi baseline with a length of 3000 km,the PCVTFT result was compared with the TWSTFT result,and the agreement degree(RMS)was 0.76 ns.(3)The method of relative calibration of receiver delay with BDS civil precise code was studied,and the experiment were carried out.In the measurement scheme,the same local atomic clock is used,and total time delay of the receiver and antenna may be calibrated relatively.The station coordinates were calculated using PPP in advance,and the post-precise orbit provided by iGMAS was adopted.The experiment of relative delay calibration between iGMAS receiver and another receiver was carried out in Lintong.The calibration accuracy of receiver time delay with civil precise code is 0.52 ns,and the calibration accuracy of receiver time delay with the smoothed pseudo-range by carrier-phase is 0.26 ns.(4)The influence of orbit error and ionospheric error of GEO satellites on PCVTFT was analyzed.For GEO satellites currently in orbit,and the baselines of Xi'an-Changchun,Xi'an-Sanya and Xi'an-Kashi,the influence of GEO orbit errors on PCVTFT was calculated and analyzed.The ionospheric products of GEO dual-frequency solution are compared with IGS TEC products.In addition,the second-order ionospheric term is calculated and the influence on PCVTFT is also analyzed.(5)The PCVTFT real-time application scheme was designed.The data source includes NTSC station,Changchun station,Kashi station,Urumqi station and Sanya station.The scheme of real-time time transfer were designed and the data processd center was setup.The rapid ephemeris provided by iGMAS is adopted in the real-time data processing,and the real PCVTFT result is provided in the data processd center.