A New Method for Carrier-Phase-Based Precise Point Positioning

Abstract

INTRODUCTIONPrecise point positioning (PPP) is a new positioning technology that has received increased interest from the GPS community. Different from the traditional differential positioning technique, which requires access to observations from one or more reference stations with known coordinates, PPP involves only a single receiver; therefore, it is easy to deploy and cost-effective. PPP is also different from the conventional point positioning technique since it aims for decimeter-to centimeter-level positioning accuracy using carrier-phase observations. To date, only limited investigations have been conducted. However, using precise satellite orbit and clock products from organizations contributing to the International GPS Service (IGS), including Natural Resources Canada (NRCan), PPP has demonstrated such a potential in stand-alone static and kinematic modes on a global scale, with centimeter-and decimeterlevel positioning accuracy, respectively [1 -3]. Similar results have also been presented recently in [4,5]. As precise GPS orbit and clock products continue to improve in precision and timeliness, and real-time phase-based wide-area /global ionospheric correction becomes available, PPP for real-time decimeter-to centimeter-level positioning and navigation accuracy will become possible in the near future.PPP processing relies on the use of carrier-phase observations, the most accurate observable available from GPS. However, accurate position estimates at the decimeter to centimeter level are obtainable only after the phase ambiguities have converged, if treated as float values, or resolved as integer values. Previous PPP processing methods are commonly based on traditional ionosphere-free combinations, whereby the ambiguities can be estimated only as float values. Typically, 30 min is required for the float ambiguity unknowns to converge in a static mode, while 1 -2 h is required in a kinematic mode. The time required for the ambiguity parameters to converge therefore becomes the limiting factor for the use of PPP techniques for real-time applications. Further improvements would require the development of integer ambiguity resolution algorithms for PPP processing, but the integer characteristics of the phase ambiguities cannot be exploited with existing PPP processing methods. This paper presents a PPP processing method based on a new observation model. The method has resulted in a further reduction in observation noise level; more important, the new model allows for exploitation of the integer characteristics of carrierphase ambiguities. The latter capability opens the door for the development of new algorithms for ambiguity resolution in PPP processing. A stochastic estimation procedure has also been proposed to facilitate more robust stochastic estimation and to shorten the ambiguity convergence time.The paper is organized as follows. A new observation model for PPP processing is first described. Error mitigation using precise GPS orbit and clock correction data is then outlined. For more precise stoch...

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