Rapid Ambiguity Resolution In GNSS Precise Point Positioning

As a new GPS positioning technology developed in the late1990s, precise point positioning (PPP) combines the advantages of GPS standard point positioning and GPS relative positioning. It is one of current research frontier and hotspots for satellite navigation and positioning. In the past decades, the basic theoretical issues of PPP have been widely investigated. Currently, PPP is moving toward the practical application stage. However, most of the mature and applicable PPP services or softwares are based on float solution. The undifferenced ambiguity resolution is still under investigation and development. Especially, rapid ambiguity resolution in real time PPP is still a challenge.This thesis study on the theory and mathematic model of PPP, analysis the essential reason that undifferenced ambiguity can not be fixed to integers, and propose a new method for undifferenced integer ambiguity resolution. Furthermore, this paper carefully investigates the factors that preventing the rapid ambiguity resolution in PPP, and develops some new algorithms for rapid convergence and reconvergence in real time PPP. Integrating the advantages of PPP and network-based RTK, we establish a uniformed precise positioning service system. It is expected to build a solid theoretical and practical foundation for the wide applications of real time PPP techniqhe. The main work and contributions of this thesis are as follows:(1) This paper introduces the mathematic model, error sources and parameter estimation methods of PPP in detail. In order to satisfy the requirement of real time PPP, we develop an algorithm for rapid estimation and update of high rate precise satellite clock. The efficiency and accuracy are discussed, the estimated real time clock has very good consistence with IGS final product, the clock error is within0.1ns, the SISRE is better that10cm. A real time precise point positioning service system based on Internet is developed and the experimental results show that:the real time positioning accuracy of5cm in horizontal components and10cm in vertical component is available. Meanwhile, about the problem of small cycle slip detection and repairing in undifferenced phase observables, we propose a new cycle slip fixing and repairing method for real time PPP. In this method, all the errors are carefully isolated and then LAMBDA method is used to search integer cycle slip values.(2) Starting from the GNSS basic observational model, we analyze the reasons that ambiguity can not be fixed to integers in traditional PPP model. Base on this, we propose new model and method for undifferenced integer ambiguity resolution. Numurous experimental results show that PPP ambiguity resolution can significantly improve the accuracy of precise positioning and orbit determination. Meanwhile, we propose a new method of using predicted atmospheric delay to aid the rapid PPP ambiguity resolution. The new method makes full use of the derived precise atmospheric information after first initialization, single-epoch ambiguity fixing is achievable after short signal interruption, and thus PPP re-initialization is avoided. Numuoros experimental results show that:in the case of all the visiable satellites are loss of lock, PPP single-epoch ambiguity fixing is still achievable by using the proposed method.(3) The regional augmented PPP method is proposed. We implement the rapid intinialization of real time PPP by making full of the precise atmospheric corrections derived from regional reference network. The two techniques of real time PPP and network-based RTK can be integrated into a uniformed positioning service using the proposed method. In the case that no regional augmentation information is available, real time PPP service with accuracy of several cm is achievable in global scale. In the regions with regional augmentation information, rapid positiong service with better accuracy can be obtained. Meanwhile, we develop a multi-layer GNSS data processing strategy to implement PPP regional augmentation for huge reference network.(4) About the problem of long initialization time of PPP ambiguity, we propose a PPP model with ionospheric character consideration and develop a new algorithm for generating phase fractional-cycle bias. The new model can not only improve the quality of phase fractional-cycle bias, but also significantly shorten the initialization time of PPP ambiguity. Experimental results show that new method can shorten the initialization time of30%from about30minutes to about20minuties, and the time to fixed solution is reduced25%from20minutes to about15minutes.(5) This paper proposes a uniformed undifferenced uncombined precise positioning model with consideration of atomospheric constraints. In this model, undifferenced original observations are employed, ionospheric and tropspheric delays are estimated as parameters, and properly constrained by the temporal and spatial character and real time atmospheric model or regional atmospheric corrections. It is especially important for regional augmented PPP with sparse reference network, reasonable atmospheric constrainsts can conpensate the residual atmospheric errors caused by large inter-station distance. This new algorithm can not only integrate PPP and network-based RTK into a uniformed positioning service, but also integrate them into a uniformed model and algorithm. With real time product streams and the proposed uniformed processing strategy, we can provide real time kinematic positioning service as follows:standard PPP with5-10cm accuracy, ambiguity-fixed PPP with2-5cm accuracy; regional augmented PPP with1-3cm accuracy.