| The principle of Precise Point Positioning (referred to as PPP) is using a GNSS receiver, using precise ephemeris and satellite clock error provided by the 1GS, and combined with carrier phase observations of precise positioning. With development of more than ten years, the basic theory to be more fully, the process of practice to be more perfect. Compared with relative positioning, PPP can be liberated from the constraints of the observation distance between stations and can obtain high-precision station coordinates directly, can make the processing of data more convenient. In scientific research, therefore, high precision navigation and positioning and near earth satellite orbit determination, high precision engineering measurement, land resources surveying, and other fields has been more and more important applications.GPS, however, is based on observation satellite navigation and positioning system, the number of satellite observations impact on its positioning directly. As a result, the number of the satellite observed influenced by environment easily, like in the mountains, buildings and open-air mining area between observation condition not ideally, observed on the number of satellite is not enough to achieve high precision positioning standards, so how to increase the number of satellite observed? A method applicable currently is combined with other satellite positioning systems, such as BDS, GLONASS system. This era is the era of multiple satellite navigation systems coexist, as a result-of-the-rapid development of the satellite navigation system bring opportunities, also bring new challenges. Considering the existing problems on PPP, how to improve the accuracy and shorten the convergence time, this is a challenging task. With the development of recent years, BDS system and GLONASS system have improved considerable in all aspects. It’s necessary basis for integrating systems for the precise point positioning (PPP). The research on this article by the following aspects:1) Respectively expounds the establishment, development and development trend of GPS, BDS and GLONASS system, the comparison of the time system and the coordinate system and other aspects of the differences are given. Then discussed the positioning error and solutions in the process in details, including the error related with the receivers, the error related to the satellites, and error related to the propagation path;2) In addition, discussed multi-GNSS precise point positioning deeply, conclude the basic theory of multi-GNSS, including combination of observation equations, and gives the basic theory of kalman filter for data decoding, the theoretical basis of the observation models and estimation of parameters and so on has carried on the detailed study;3) On the basic of discussing the basic theory of PPP, by using the data of 3 days 24 h of eight stations measured, studying a single day of effective number of satellites and DOP, the results shows multi-GNSS PPP mathematical model can rich the resources of data obviously, improve the satellite space geometry structure are of great help. Then take the 8 station’s data to every 0.5 h,1 h,2 h observation length for segmentation, analysis of the three groups of data obtained is concluded, multi-GNSS PPP in a short period of time can improve convergence speed obviously, For example, the average convergence rate under the observation time of 0.5 h, GPS is 61.01%, BDS is 5.50%, GLONASS is 72.32%, GPS\BDS is 61.76%, GPS\GLONASS is 91.37%, BDS\GLONASS is 73.36%, GPS\BDS\GLONASS is 90.77%; and even can be obtained even higher accuracy than single system, embodies the superiority of the fusion positioning system fully. |
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