Research On Models And Methods Of Precise Point Positioning Based On Multi-GNSS

GNSS Precise Point Positioning (PPP) can obtain decimeter to centimeter-level positioning accuracy in real-time model and millimeter-level positioning accuracy in static model with a single receiver on a global scale. With the establishment and development of the four navigation satellite systems, PPP based on multi-navigation satellite system and its combination has become a research focus. The multi-GNSS PPP research can be carried out by learning from existing GNSS PPP models and methods for reducing convergence time and improving real-time positioning accuracy, which will further promote the development and application of GNSS high-precision navigation and positioning.Data processing theory, models, methods and key technologies of multi-GNSS PPP are studied systematically. The multi-GNSS PPP is carried out based on Position And Navigation Data Analyst (PANDA) software.(1) GNSS PPP basic theory related to space-time framework and its conversion, GNSS observations and its combinations, as well as the observation equation linearization is studied in depth.(2) The characteristics of different type’s errors and the errors correction methods in GNSS positioning are analyzed in detail. Single GNSS system PPP model is conducted in-depth research, as the characteristics of frequency-dependent hardware delay in GLONASS system, the observation model is established with considering hardware delay correction. Then the multi-GNSS combination PPP model is derived from the single GNSS PPP model.(3) The methods of data quality control and parameter estimation in GNSS PPP are studied systematically, including cycle slip detection, gross error elimination, least squares method and kalman filter algorithm.(4) The IGS stations observation data of GPS and GLONASS, and the corresponding precise ephemeris and clock products provided by ESA are used in PPP test of GPS, GPS/GLONASS combination and GLONASS. Each GNSS PPP test includes three modes of static, post-processing kinematic and simulated real-time kinematic.The repeatability positioning accuracy of GNSS PPP is as follows:in static mode, the positioning accuracy in horizontal direction can reach1to2mm, in vertical direction can reach2to3mm; in post-processing kinematic mode, the positioning accuracy in horizontal direction can reach1to2cm, in vertical direction can reach2to3cm; in simulated real-time kinematic mode, after the positioning results convergence, the positioning accuracy in horizontal direction can reach1to3cm, in vertical direction can reach3to5cm. Compared with single-system PPP, GPS/GLONASS combination can significantly improve positioning accuracy, especially in a short period of time positioning and kinematic positioning. When the IGS week solutions are as reference values, the GLONASS PPP results in vertical direction have obvious systematic bias.In the aspect of convergence time of real-time kinematic positioning, to obtain10cm positioning accuracy in the three directions, the convergence time of a single system is about50minutes; the convergence time of GPS/GLONASS combination is about20minutes. Therefore, compared with single-system PPP, GPS/GLONASS combination can significantly shorten the convergence time, and improve the real-time positioning accuracy.(5) Based on BDS precise ephemeris and clock products provided by GFZ, the measured BDS observational data are used in BDS PPP test.The repeatability positioning accuracy of BDS PPP is as follows:in static mode, the positioning accuracy in East, North and Up direction can reach5.9mm,1.2mm and4.5mm, respectively; in post-processing kinematic mode, the positioning accuracy in horizontal direction can reach1to2cm, in vertical direction can reach4to5cm; in simulated real-time kinematic mode, after the positioning result convergence, the positioning accuracy in horizontal direction can reach1to2cm, in vertical direction can reach5to6cm. To obtain10cm positioning accuracy in the three directions, the convergence time in East and Up direction is about100minutes, in North direction is about50minutes. When the GPS single day solutions are as reference values, the BDS PPP results in vertical direction have obvious systematic bias.