Trustworthy precise point positioning with global navigation satellite systems

Abstract

With the modernization of the Global Navigation Satellite System (GNSS), GNSS precise point positioning (PPP) technology becomes popular benefiting from its wide coverage and high accuracy. However, PPP technology still has many challenges in terms of continuity, fast convergence, and integrity monitoring, and these unsolved issues result in limitations of engineering applications. In this thesis, a reliable PPP technology with GNSS is investigated. The main contributions of the thesis are as follows: (1) A new cycle slip repair method that uses multiple epochs of time-differencing and geometry-based observations are proposed which has a significant improvement in the success rate of cycle slip repairs compared to existing methods. The positioning results also reflect that this method can reduce position errors and improve the continuity of PPP technology. (2) A systematic comparison of current interpolation methods used for high-accuracy regional ionospheric corrections is presented. It is found that each method has essentially the same accuracy in a small regional network with only a few stations, while the Kriging interpolation method can significantly improve the accuracy when the size of the network increases. Besides, a new method for predicting the uncertainty after broadcasting by grid point is also proposed. It has been validated that it is significantly closer to reality than other existing methods. In addition, different ionospheric correction implementation methods at the user end are also compared. (3) A integrity monitoring scheme for use in PPP based on real-time kinematic (RTK) positioning networks (PPP-RTK) with regional atmospheric corrections has been developed, which is based on the impacts of faults on the estimators considering possible faults in undifferenced and uncombined measurements. (4) Procedures for integrity monitoring considering the risks caused by incorrect ambiguity fixing are investigated. Two different methods for considering the probability of wrong ambiguity fixing including categorizing it into unmonitored fault and categorizing it as an individual type of fault are proposed and analyzed. (5) An integrity monitoring (IM) scheme based on the single-epoch framework for PPP-RTK is also proposed in order to exclude the effects caused by using observations from multiple epochs. Different solutions and their related availability are evaluated based on the satellite geometry in the global area.