| Navigation satellite system can provide real-time positioning service with precision of 5m to 15 m. Such an accuracy level cannot meet the requirements for air and other special users. Therefore, the wide-area differential positioning system was established to improve the positioning accuracy and integrity of the navigation satellite system. Relative positioning can offer millimeter-level precision but it needs post-processing. A variety of RTK technology can provide real-time positioning accuracy of centimeter, but it’s restricted within a few tens of kilometers. In order to solve the issue of real-time decimeter-level positioning on a large and even global scale, we need use wide-area real-time positioning technology. With the use of China’s Beidou navigation system(BDS), the establishment of the wide-area real-time precise positioning system based on BDS will be an important direction of the differential system construction in our country in the future. Therefore, in this thesis, the application demand of the technology, system composition and principle, the layout of the reference stations, central station information processing and users’ positioning algorithm were studied and verified using GPS and Bei Dou data, providing a reference for designing and constructing China’s BDS wide-area real-time differential positioning system. The main research work includes:(1) Differential technology development trend and research status are summarized. The existing various differential technologies are analyzed and compared. The data processing principle, differential information transmitting way and the application fields of different differential technologies are summarized. At the same time, the development trend of future differential technologies is analyzed and summarized.(2) Several key concepts of navigation ability demand are discussed. Based on this, the error factors that influences the navigation and positioning accuracy have been clearly addressed about the key technical problems of the wide-area real-time differential positioning technology. The basic principle and system composition of the wide-area real-time differential positioning system are stated.(3) In terms of reference station layout, basic reference station layout methods such as the multi-objective optimization method, the simulation test method, and evaluation index method in reference station optimization such as satellite coverage and satellite visibility are investigated and demonstrated by using the data of GPS and Bei Dou, in China. The study indicates that the 30 or so reference stations can meet the demand of wide-area real-time precise positioning.(4) Several major existing orbit determination schemes have been compared. The applicability of the long arc dynamic method, short arc sliding window method and the filtering method to the real-time precise orbit determination of wide-area real-time positioning technology are analyzed and compared. Based on this, the thesis puts forward to use the long arc dynamic method to determine orbit, perform short-term prediction scheme, and formulate the relevant data processing strategy. In order to improve the efficiency of precise data processing, ambiguity fix and parameters recovery techniques in long arc dynamic legal are deeply studied, which effectively reduces the data processing time. The orbit determination results based on six China regional Bei Dou stations in RTN direction error were 0.65 m, 0.38 m, 0.15 m. The errors in RTN directions using 27 GPS stations were 0.22 m, 0.14 m and 0.08 m.(5) The real-time precise clock error estimation has been studied. The thesis compares and analyzes the existing various satellite clock error estimation algorithms, based on non-differential and the epoch difference combined model and then proposes a real-time high-frequency satellite clock error estimation algorithm. On the basis of phase observation data based on epoch-differential to estimate the clock change, the introduction of pseudo-range observation data to estimate the initial time clock deviation of satellite clock error, and a detailed analysis of the accuracy and convergence rate of two types of products, the thesis proposes an effective clock error product comprehensive strategy to effectively improve the accuracy of satellite clock error product. The GPS and BDS experimental results show that the accuracy of real-time clock error processing is better than 0.2ns.(6) In order to improve the processing efficiency of clock errors, considering that in a short time the time change of tropospheric delay is very limited, the thesis puts forward a strategy in which the troposphere parameters and clock error parameters are processed, respectively. The low processing frequency to calculate the troposphere parameters is used and then the tropospheric parameters directly are substituted into the high frequency clock error processing, which can effectively improve the processing speed of the clock error. The 27 domestic stations processing results show that using the frequency of 30s-450 s to deal with tropospheric delay parameters, the mutual difference of the real-time precise clock error calculated by real-time clock error processing is less than 0.02 ns.(7) The basic theory of ionospheric grid model generation, ionospheric delay real-time precise determination algorithm, satellite and receiver clock error determination algorithm have been studied. "Two-step method" was adopted to realize the effective separation of receiver frequency deviation and satellite frequency deviation. The ionospheric grid model generation data processing strategy are formulated. Using GPS and BDS measured data proves that the accuracy of ionospheric grid model is better than 0.4m. At the same time, a downgrading effect analyse of the ionosphere differential information precision is made, the experimental results show that the updating frequency of the ionosphere differential information which is restricted within 5 min is more reasonable.(8) The real-time precision positioning method and model algorithm have been researched, puting forward the square root information filtering of variable parameter real-time differential positioning algorithm. Based on GPS measured dynamic data, the thesis uses IGS precise ephemeris simulated real-time positioning to verified the reliability of the model algorithm and results indicate that the horizontal and height direction positioning accuracy are better than 15 cm.(9) The thesis develops a wide-area real-time differential positioning data analysis software. Using the China regional GPS and BDS measured data to calculate the satellite orbit, clock errors and ionospheric differential information and using dynamic and static data to systematicaly verify the wide-area real-time positioning, the horizontal positioning accuracy is better than 20 cm and the vertical positioning accuracy is better than 30 cm. |
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