Real-time Precise Point Positioning And Ambiguity Resolution

The regional constellation of BeiDou Navigation Satellite System(BDS) has been officially operation in the Asia-Pacific Region. Meanwhile, GPS and GLONASS can provide global service. The fusion of multi-system Precise Point Positioning(PPP) has been widely studied by many researchers in recent years. Aiming at problems that PPP suffered, such as slow convergences, unresolved ambiguities and its real-time application, firstly, PPP ambiguity resolution(PPP-AR) methods are investigated and a partial ambiguity resolution strategy based on cascaded quality control is proposed. Secondly, the positioning accuracy and convergence speed of combined system PPP is researched and the contribution of combined observations to the time to first PPP ambiguity-fixed solution is also investigated. Finally, the algorithm of real-time GPS/GLONASS satellite clock corrections is investigated. The contents and conclusions are summarized as follows.(1)A partial PPP ambiguity resolution(PAR) strategy based on cascaded quality control is proposed. First of all, the fractional cycle biases(FCBs) of uncalibrated phase delays which destroy the integer properties of PPP ambiguity is analyzed and the separation of FCBs from float ambiguity is the key point of PPP-AR. At the same time, the single differenced satellite FCBs-based method and zero differenced FCBs-based method are studied. The corresponding user PPP-AR method is introduced. Finally, as the ambiguities need long time to initialize under the situation of raising satellites and cycle slips, fixing all ambiguities are difficult. A partial PPP ambiguity resolution strategy based on cascaded quality control is proposed.(2)The single differenced FCBs and zero differenced FCBs products are estimated and then applied to perform PPP-AR in user client. The impact of PPP ambiguity fixing to hourly PPP solution is analyzed. Meanwhile, data sets are used to validate and demonstrate partial PPP ambiguity resolution strategy. Results have indicated that PPP ambiguity fixing can improve positioning accuracy of hourly PPP solution. When the strategy of PAR is applied, the success rate of PPP ambiguity fixing is improved and the influence of un-convergenced ambiguities can be controlled efficiently.(3)The combined multi-system PPP is investigated and focused on the accuracy and convergence speed of combined GPS/GLONASS and GPS/BDS/GLONASS PPP. Results have showed that the positioning accuracy and convergence speed of combined PPP is better than single system PPP in static and simulated kinematic mode with short time observations. The positioning accuracy of combined GPS/GLONASS and GPS/BDS/GLONASS PPP, however, is comparable.(4)The combined multi-system PPP is proposed to shorten the time to first ambiguity fixed solution. Only the GPS ambiguities are fixed based on zero differenced FCBs products. Due to the fact that combined system PPP can accelerate the convergence of float ambiguity, the impact of combined system PPP to ambiguity resolution is studied. Results have indicated that combined multi-system PPP can accelerate the time to first fixed solution.(5)The algorithm of real-time GPS/GLONASS satellite clock corrections is investigated and the accuracy and convergence speed of combined GPS/GLONASS RT-PPP are analyzed. The results have indicated that the real-time GPS/GLONASS clock corrections are comparable with the ESA final products. The RMS of real-time GPS and GLONASS clock corrections are better than 0.2ns and 0.5ns. When the real-time satellite clock corrections are used to GPS/GLONASS RT-PPP, the static positioning accuracy is centimeter and the simulated kinematic positioning accuracy is centimeter in horizontal components and better than 20 cm in vertical component. Meanwhile, the convergence speed of combined system PPP is better than single system PPP.