GPS Precise Point Positioning Algorithms: Implementation And Performances

Precise Point Positioning (PPP) is a positioning technique using dual-frequency pseudorange and carrier phase observations from a stand-alone GNSS receiver along with the precise orbit and clock solutions published by IGS, one can determine the position of anywhere in the global area with a high precision, decimeter even centimeter. Besides the position, the receive clock corrections, Zenith Troposphere Delays (ZTDs) and float ambiguity estimates could also be obtained with this technique, which broaden applications of PPP techniches in the field of high-precision navigation and positioning, atmosphere delays'determination, precise time and frequency transfer etc.PPP technique and some key problems are discussed in this paper, including parameter estimations, stochastic model determinations, quality control, etc. The main contents and conclusions of this paper are as follows:1. The observation equations of PPP technique and its systematic errorsBased on original dual-frequency GPS code and phase observations, the observation equations of ionosphere-free combination and uncombined PPP techniques are deduced. Several corrections to the systematic errors existing in the measurements, such as relativistic effects, phase wind-up etc, are also presented.2. Two PPP techniques, including parameter estimation strategy and result analysisTwo PPP techniques are introduced, including their math models, unknown parameter estimation strategy and stochastic models. The advantages and disadvantages of each PPP technique are also discussed. Under different conditions such as static, simulated kinematic, low-dynamic offshore and high-dynamic airborne data, the overall performances of PPP techniques are investigated and analyzed. The results show that for both static and kinematic positioning, a position accuracy of 1～3 cm and 6～10 cm could be achieved with the author's PPP software.The positioning performances of two PPP techniques are compared for the first time. The results show that the convergence behavior and repeatability of filtered solutions can be well improved by comparing the uncombined PPP technique with the traditional one.3. Real time quality control of PPP techniqueReal time quality control of GPS PPP technique is proposed, the recursive DIA-procedure is adopted as quality control strategy to guarantee the reliability of the estimators from PPP technique. The results show that convergence behavior and repeatability of filtered solutions can be well improved after DIA-procedure.4. Some other applications of GPS PPP techniqueThe receive clock corrections and ZTDs can also be obtained with PPP technique, their accuracy are analyzed by comparing with corresponding IGS products. The results show that, based on dual-frequency observations of single station, one can realize millimeter accuracy without systematic bias in ZTDs'determination and 0.1～0.3ns accuracy in time transfer, which demonstrate the wide applications of PPP implementation.