Theory And Applications Of Gps Central Differential Positioning System

With the development of the network real-time kinematic (NTRK) technology, wide area centimeter-level real-time kinematic (RTK) positioning service becomes true. However, the standard RTK positioning technology can not well meet the needs of high-precision position monitoring applications, such as kinematic deformation monitoring, precision agriculture, automated machinery construction. Firstly, since the differential computation is carried out by the rover, the (monitoring) server can not obtain the full information of the rover’s position. Secondly, the capability of differential computation of the carrier phase measurement is required on the user-side device, and the additional requirements will cause an increase in cost. Lastly but not the least, the standard RTK positioning technology is not conducive to the data fusion and overall analysis of the observations from different rovers, and even be against the further research and potential information mining.Central differential positioning technology is studied in this dissertation. Observations from all sites are sent back to the central differential positioning server, in which the differential computation is then carried out. The central server can provide standard RTK service, obtain the whole positioning information, and even deploy different data processing strategies to satisfy special location-based services. To give full play to their own advantages and cooperate with each other, the central differential positioning technology, along with the standard RTK positioning technology, will further improve the level and extent of GPS theoretical study.This dissertation focuses on the theory and methods involved in the central differential positioning system. The framework structure of the system is studied, the algorithms of some key techniques are improved, and the system is initially implemented. The main research contents and innovations are summarized as follows:1、Current research status of GPS positioning technology, the advantages and disadvantages of the standard RTK and the central differential positioning technology are analyzed. The significance of the central differential positioning system is also summarized.2、The system frame structure and the characteristics of the NRTK positioning and the central differential positioning are presented. The main components and key technologies of central differential positioning system are elaborated.3、Research contents and methods of GPS real-time data quality control are presented. A modified ionospheric residual cycle slip detecting and repairing method is proposed, which can detect and repair the carrier phase cycle slip for a specific frequency, and can deal with the small cycle slip of one cycle. Time baseline is employed to detect the outlier of carrier phase measurements for the kinematic application. Outliers of0.15cycles can be detected under the experimental conditions, without the need of ambiguity fixing.4、Different ambiguity resolution methods have been summarized, including ambiguity resolution/searching in measurement domain, in coordinate domain, and in integer ambiguity domain. Dual-frequency integer relationship constrained GNSS ambiguity resolution (FirCAR) method is proposed. FirCAR increases the equivalent wave length of the integer ambiguity up to9times of wave length of L1. The feasibility and applicability is experimentally tested. On the fly (OTF) ambiguity resolution method based on FirCAR is also presented, and it is also experimentally compared with LAMBDA.5、Wide range kinematic deformation monitoring methods are presented, including the kinematic precise point positioning (PPP) and the long range RTK positioning technology. Kinematic deformation monitoring method using double-differenced residuals model for high-rate GPS is proposed. Experimental results from a static baseline of about1100km show that the standard deviation of the kinematic position are6mm,6mm and13mm for N, E and U, respectively, in the predicted5minutes. The feasibility and reliability of the proposed method are further verified by GPS data obtained during El Mayor-Cucapah M7.2earthquake.6、GPS central differential positioning software system has been preliminarily developed. The system mainly includes the real-time data stream decoding module, the baseline processing module, the data storage module, and the visual analysis module. A24-hour static data set, a20-minute kinematic data set, and the data sets of the94GPS stations during El Mayor-Cucapah M7.2earthquake have been used, to test the functions of deformation monitoring, the kinematic positioning monitoring, and the seismic ground surface kinematic displacement monitoring, respectively. Experimental results show that, the proposed location information monitoring service system is capable of continuous operation, multiple locations monitoring, high precision and high reliability.