Theoretical Research And Program Implementation Of BeiDou Navigation Satellite System Precise Point Positioning

Precise Point Positioning(PPP)is a positioning technique processing the observations at solely a single receiver on a global scale by fixing precise satellite orbits and clocks.PPP has been widely used in many fields.At present,BDS provide regional navigation services for users throughout Asia and Australia,BDS PPP has became an important subject in GNSS.This paper systematically studys PPP theory based on BDS.New metheods are introduced in consideration of BDS constellation and triple-frequency observations.Finally,a BDS&GPS PPP software is developed.The main research contents and results are as follows:The constellation of BeiDou Navigation Satellite System is composed of Geostationary Earth Orbit(GEO)satellites and Non-Geostationary Earth Orbit(Non-GEO)satellites.In consideration of the huge difference between GEO satellites altitude and Non-GEO satellites altitude,the global nonlinear least squres algorithm(Bancroft algorithm)is applied for BDS single point positioning in this paper.The Bancroft algorithm based on the Lorentz inner product is mainly in four dimensional space.A new algorithm to get the BDS observation weight is introduced by transforming Lorentz inner product into error equation,and then weight of the error equation is deduced.In order to testify the method,a code-minus-phase combination(CC)of BDS measurements is used to determine the code noise of GEO and Non-GEO satellites,a multipath combination(MP)is introduced to extract the multipath of pseudorange and improve the accuracy of single point positioning.The result indicates that new algorithm can improve the accuracy of BDS single point positioning.The methods of triple-frequency cycle-slip detection and correction based on geometry-free phase combination,code-phase combination and LAMBDA algorithm have been introduced.Then the performance of geometry-free phase combinations and code-phase combinations is assessed under different intervals.The experiment result indicates that the geometry-free phase combinations achieve better detection sensitivity than code-phase combinations which are affected by code noise and multipath error.We compare the three repair methods from the two aspects of time consumption and the rate of success.The result indicates that the method based on geometry-free phase combination gets the worst performance which is mainly caused by the searching method depended on the empirical value.The method based on code-phase combination doesn't need searching step which makes itself the quickest one,but some of the cycle-slips aren't determined correctly because of the influence of code noise and multipath error.The method based on LAMBDA algorithm costs least time and has the highest rate of success because the LAMBDA technique can flat the n dimensional search space and control the impact of errors remained after between epoch difference.Considering the analysis above,we recommend using two selected geometry-free phase combinations to detect cycle-slip and the LAMBDA technique to determine the cycle-slip.The pseudorange multipath error are extracted by using triple frequency data broadcasted by BDS.The result indicates that the multipath of pseudorange are at meter level and present quickly changes.The multipath error remained after between epoch difference can affect cycle-slip detection and repair.A method for BDS triple-frequency cycle-slip detection and repair with multipath correction in considering is introduced.Experiments are carried out to test the performance of the method.The result shows that the method can control the impact of multipath error and improve the rate of success repaired.A software with functions of GPS and BDS precise point positioning is developed.Performance assessment of the software is presented by using observations from IGS,iGMAS and MGEX.Results indicate that the accuracy of GPS-PPP is 1-3cm level on a global scale while BDS-PPP is 5 cm level,kinematic prcise point positioning of GPS is 10 cm level while BDS is 10-20 cm level.Results also prove that algorithm of the software is correct and can get high precision.In order to process the rover and the reference stations GPS data with different sampling rates,a new method is introduced.Firstly,all the epochs of rover that have synchronous observations with reference station are adjusted together and treated as known points.Secondly,we treat the observations of rover between two adjacent known points as a whole,use differential data between epochs of roving stations as observations,and adjust all the coordinates of roving stations in the whole together.The new method takes the correlation between epochs into consideration and reduces the error accumulation of difference between epochs.An experiment was carried out.The result showed that new method is more rigorous and can improve the rover positioning precision.