Methodology Of Multi-GNSS Undifferenced And Uncombined Real-time Precise Point Positioning

GNSS PPP uses precision satellite orbit and clock products provided by the outside after various error items are corrected and Kalman filtering method is adopted,a GNSS receiver can carry out high-precision positioning of static centimeter level and dynamic decimeter level to centimeter level in the global range.Users can receive the real-time orbit and clock correction information through the network to realize real-time precise point positioning.The traditional dual frequency ionosphere-free combination PPP can eliminate the influence of the first-order ionospheric delay,but it reduces the number of equations and magnifies the observation noise by three times because of the need for linear combination of different frequency observations.And the undifferenced and uncombined precise point positioning is based on the GNSS original values without any linear combination.All the frequencies and all the systems can be set up according to the unified model.It is more suitable for the unified expression of the precise point positioning observation equation with multi-system and multi-frequency.Therefore,this paper study the theory and method of undifferenced and uncombined precise point positioning.The main work and research contents of this paper are as follows:(1)The mathematical models of ionosphere-free combination and Undifferenced and uncombined precise point positioning are studied and given.The main error sources and error correction methods are described.Based on the post precise orbit and clock products of GFZ,the experiment of ionosphere-free combination precise point positioning by GPS and GPS/Galileo is carried out.The results show that the convergence time of post GPS/Galileo combined precise positioning is 30.6%shorter than that of single GPS,and the positioning accuracy of combined positioning in N?E?U directions is 12.8%,36.2%and 10.5%higher than that of single GPS.(2)The GPS and GPS/Galileo fusion single frequency positioning results show that the convergence time of single frequency GPS/Galileo is 17.6%shorter than that of GPS.The positioning accuracy of single frequency GPS/Galileo fusion positioning in N?E?U directions is 34.8%,21.6%and 19.2%higher than that of single GPS positioning.(3)The experiment of BDS/GPS/Galileo/GLONASS four systems fusion positioning is carried out.The four systems fusion can provide about 30 satellites and improve the geometry of the satellite.About 40%of the results of GPS can converge in 30 minutes,about 65%of the results can converge in 40 minutes,and the four systems are 69%and 85%respectively.The convergence time of the four systems is 28.7%shorter than that of single GPS.The positioning accuracy of the four systems fusion is better than 5cm in N?E?U directions,and 37.7%,20.2%and 19.1%higher than that of single GPS respectively.