Research On GNSS Precise Point Positioning Based On RTKLIB

Precise Point Positioning(PPP)is a positioning method which uses the carrierphase observations of a single receiver,as well as precise satellite orbits and clocks,to obtain the receiver's precise coordinates by correcting various errors in GNSS signal propagation.Compared with traditional relative positioning method,PPP has the advantages of low cost,no need for reference stations,and no limitation on the length of baselines.In recent years,Galileo and BeiDou have been gradually developed,together with GPS and GLONASS,the GNSS(Global Navigation Satellite System)composed of the four systems has significantly increased the number of satellites and observations,which is expected to increase the potential of PPP,improve positioning accuracy,reduce convergence time,and promote the widespread use of PPP.RTKLIB is an open source algorithm library for GNSS navigation and positioning,which has been widely used in various scientific and engineering applications.This paper researched and improved the GNSS PPP algorithms based on RTKLIB,which had high practical value.This paper improved the PPP algorithm and realized GNSS multi-system PPP processing based on the PPP module of RTKLIB.The main contents of this paper are:(1)The research status of PPP float and fixed solutions,real-time PPP,multiGNSS PPP,etc.,as well as the development and application of RTKLIB's PPP module,were introduced.(2)This paper introduced the latest status of GNSS constellation and the basic principles of GNSS PPP,including the transformation of time references and coordinate systems,ionosphere-free combination model,various error correction models in PPP,and EKF(extended Kalman filter)parameter estimation method,etc.(3)This paper introduced the features of RTKLIB,including the structure of the RTKLIB open source library,the contents of each source code file,and the compilation method.The RTKLIB PPP processing flow was studied.The algorithm was improved,and new protocol formats such as SP3-d and RINEX 3.03 were supported.The receiver antenna phase center model considering azimuth factors and gravitational time delay effect model were introduced,and other auxiliary functions like batch processing of statistics were added.After the improvement,the vertical accuracy of GPS PPP increased by 21.3%.(4)Using the improved RTKLIB PPP algorithm,the accuracy of the MGEX products of the BeiDou GEO satellite was compared and analyzed,and the influence of GEO satellites on the performance of static PPP was evaluated.The results showed that the accuracy of the MGEX products of GEO satellites was low,and excluding GEO satellites could improve the horizontal accuracy by about 70% and the vertical accuracy by about 10% in BeiDou PPP.The existing BeiDou PCOs were summarized and the impact of each PCO on the performance of BeiDou PPP was evaluated.The results showed that the PPP with Chang'an University's BeiDou-2 PCO had the highest accuracy,and the 3D error was 57.9% higher than that of the MGEX recommendation.(5)Using the improved RTKLIB PPP algorithm and products of 4 MGEX analysis centers(ACs),PPP static and kinematic solutions were obtained with the observation data of MGEX network in modes of single system,dual system and four systems.The positioning performances of different ACs' products,as well as the positioning performances of multi-system combination modes,were analyzed.The PPP results showed that the WUM products had the highest precision among the MEGX products.In different system combination modes,the four-system combination PPP had the shortest convergence time and the highest precision of 5 mm in horizontal direction and 10 mm in vertical direction,and good positioning results could still be obtained at a high elevation cutoff angle.