Research And Implementation Of Real-time BDS/GPS Single-frequency Ionospheric Augmentation Precise Point Positioning Algorithm Based On Android Platform

Precise Point Positioning(PPP)is a high-precision positioning technique with the support of high precision satellite orbit and clock products based on the observation information of a single GNSS receiver.In PPP,the system errors such as relativistic effects and phase wind-up et al.can be corrected errors by accurate model,and The ionospheric delay is corrected with dual-frequency ionosphere-free combinations or the external ionospheric model.Moreover,tropospheric delay,receiver clock error and the station coordinates are all estimated together.PPP is economical,simple and conve-nient.The available of real-time product services such as IGS-RTS enables PPP to real-time solve positioning results for navigation users,which unravels the fetters of the application of real-time PPP.The opening of real-time product services such as IGS-RTS enables PPP technology to solve the location results in real time,and the real-time application of PPP unravelles Mobile terminals,such as smart phones,have the advantages of portable,easy to operate and so on.It is being popularized in people's daily life,especially the android intelligent terminal has occupied a large number of user markets because of its high cost performance.At the same time,the location service on mobile terminal is widely used in various fields,and its demand is increasing.Various mobile terminal applica-tion,including navigation,shopping,tourism,and takeout,are constantly emerging,but the positioning accuracy of location services in the mobile terminal needs to be improved.Compared to the expensive measuring receiver,the GNSS positioning chip module on the mobile terminal has a low cost,a wide application market.,low promo-tion difficulty,and easy acceptance by the user.In this paper,Wuhan Mengxin MXT903 is adopted as a positioning chip module in the mobile terminal,and the related issues in real-time PPP algorithms are deeply studied and implements the algorithms in mobile terminals.The main contents and work of this paper are as follows:(1)Analyze the influence of different ionospheric models on GNSS positioning.Since the mobile terminal can only provide single-frequency observations,it is not possible to correct the ionospheric delay by dual-frequency ionosphere-free combinations.This paper uses different ionospheric models to correct the ionosphere delay and analyze its impact on GNSS positioning performance,which provides a reference for the selection of suitable ionospheric model in real-time terminal positioning.Among them,the ionospheric delay in single frequency SPP is directly corrected by the ionosphere model.The results show that the precision of the Klobuchar model is the worst,the precision of the CODE prediction product clpg is slightly better,and the precision of the real-time spherical harmonic ionosphere product cosong and the CODE after-product codg is the most accurate and basically equivalent.The single-frequency PPP positioning was performed using different ionospheric models as a priori constraint to the ionospheric estimation.The results show that the adoption of the real-time spherical harmonic ionosphere product cosong as a priori constraint can speed up the single-frequency PPP convergence.(2)Present real-time BDS/GPS single-frequency ionospheric augmentation PPP model.In this paper,various error sources and methods for eliminating or reducing the er-rors in single-frequency PPP are introduced and analyzed in detail.The data quality control methods such as the detection and repair of the clock jumps and the cycle slips in the observed values are analyzed.Based on real-time orbital clock data streams SSR corrections and real-time spherical harmonic ionosphere enhancement products,a real-time BDS/GPS single-frequency ionospheric augmentation PPP model was established.(3)Transplant the algorithm on android platform.This paper introduces the basic flow of porting the algorithm based on C language to the android terminal plat-form.Based on C language,the real-time BDS/GPS single-frequency ionosphere augmentation PPP algorithm is implemented on the VS2015 development platform,and the algorithm is used on the QT platform.The android development environ-ment is ported and the algorithm is compiled into an APK that can be run in the android environment,and the user interface of the APK is designed based on the C++ language.(4)Test the APK on mobile terminal in real scene.With the support of real-time orbit and clock SSR strream corrections and real-time ionosphere enhancement product cosong broadcasted by the National Geographic Information Bureau,the real-time BDS/GPS single-frequency ionosphere augmentation PPP APK is installed on the android terminal to perform field scene test The usability of APK and the position-ing accuracy of the algorithm in APK are analyzed and evaluated.The test results show that the BDS/GPS combination system can improve the positioning accuracy of single BDS.When the observation environment is poor,the dual system can sig-nificantly reduce the number of "flying points" of the single BDS.The BDS/GPS combination system positioning accuracy in the three directions of north,east,and elevation is 0.7m,2.17m,and 2.26m,and when no external produt support is available,the user can still be provided a SPP result.