| In order to ensure our political,economic and military security,China's Beidou satellite navigation system construction has achieved remarkable results,and has formed 5GEO+5IGSO+4MEO constellation configuration for open services to the Asia-Pacific region in 2012.But currently,Beidou system tracking station is limited to the domestic,navigation satellite tracking arc limited,tracking network geometric constraints are poor,this increase the difficulty to get high-precision navigation constellation orbit.Therefore,navigation constellation precision orbit determination and time synchronization based on the regional station is one of the key technologies of the construction and operation of satellite navigation system.Real-time high-precision positioning is the forefront of the current satellite navigation and positioning service system development direction.High-precision satellite orbit and clock product and the user side carrier phase ambiguity fast convergence are the basis to achieve real-time high-precision service.At present,high-precision positioning services mainly through CORS and network RTK to achieve,but there are some flaws in service accuracy,service scope and so.In recent years,with the upgrading of space technology,the use of Low Earth Orbit(LEO)satellites as a navigation satellite has gradually become a research hotspot.To sum up,it is very important to carry out the global real-time centimeter-level navigation system based on High Earth Orbit(HEO),Middle Earth Orbit(MEO),and LEO satellites,and realize the real-time centimeter-level positioning service of our country's satellite navigation system.This paper takes the construction of HEO,MEO,and LEO global real-time centimeter-level navigation system as the goal,and meticulous studys the mathematical theory model,key technologies and algorithms.Based on the PANDA platform,we independent develop the high,middle,low orbit global real-time centimeter-level navigation system simulation software system,and finally use the different constellation configuration to simulate the method and model testing and verification.The main research work and contribution are as follows:1)This paper summarizes the status of precision orbit synchronization,precision positioning enhancement system and broadcast ephemeris fitting theory of existing satellite navigation system,and points out the difficulties of China's satellite navigation system and high-precision real-time service.We clearly carried out the necessity and urgency of constrution of HEO,MEO,and LEO navigation system technology research.2)The basic theory of precision orbit determination based on satellite navigation system is given,which mainly includes coordinate system and time system,satellite motion equation and its numerical solution,geometric observation model and parameter estimation.3)Based on the actual demand of high and low orbit satellite navigation system construction in China,three key technologies,such as the combination of inter-satellite data,orbit,high-precision fast positioning,low-orbit satellite broadcasting ephemeris model,are studied in detail.The corresponding mathematical model and algorithm implementation are described.4)The design of the real-time centimeter-level navigation system of HEO,MEO,and LEO satellites is carried out,and the corresponding system design is established.The system configuration,process design and interface design are discussed in depth.5)Based on the PANDA platform,the algorithm and data flow of satellite ephemeris simulation,observation data simulation and interplanetary orbit determination are given for the analysis of the global real-time centimeter-level navigation system.6)Based on the software developed by ourselves and the method of determining the orbit determination between the star and the earth,the test data are verified by a large number of simulation data.The results show that if the data of 7 ground stations are used only,the average RMS of the orbit is about 1.5 m;the ground monitoring station + the inter-satellite link,the ground monitoring station + the low-orbit satellite monitoring station The accuracy of the track and the time synchronization are obviously improved,and the advantages and disadvantages of the two are compared.The results show that the two methods can achieve the same grade of orbit accuracy.7)Based on the self-developed software,the LEO satellites were tested for the enhancement performance of the Beidou(3GEO+3IGSO+24MEO)navigation and positioning service.The effects of ground coverage,PDOP,pseudorange single point positioning accuracy Positioning convergence speed,PPP positioning accuracy and so on and analysis.The results show that the average visual satellite number is increased from 10.7 to 16.3 and the increasement is 52%.The average PDOP decreases from 1.63 to 1.22 and the decreasement is 25%.The effect of single point positioning on the pseudorange.is not obvious.,N,U three-way component on the pseudorange single point positioning accuracy of the RMS value were increased by 4%,6%,11%;PPP positioning accuracy of 10 cm within the required time from 28 minutes 35 seconds to 1 minute 9 seconds;in E,N,U three components on the direction of the PPP positioning accuracy RMS value increased by 42%,20%,40%.8)Based on the self-developed broadcast ephemeris fitting software,the LEO satellite broadcast ephemeris model is analyzed,and a new set of broadcast ephemeris model suitable for LEO satellites is proposed.For the orbital dynamics of low-orbit satellites,which is influenced by the high-order term of the earth's gravity field,this paper solves the problem of large fitting error when tangent with the traditional 16-parameter broadcast ephemeris,and can realize the low-orbit satellite broadcast ephemeris fitting accuracy within 5 centimeters. |
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