| Precise Point Positioning (PPP) technology can achieve high-precision positioning, provide static centimeter-level and dynamic centimeter to decimeter level global positioning by just one single station. PPP gradually become a hot topic in the field of satellite navigation and positioning internationally with the advantages of its single station solution, high precision, and so on. Since 1997, PPP technology has been developing rapidly, it has broad application in many areas, such as deformation observations, LEO satellite orbit determination, high precision navigation and positioning, precise areas of agriculture and transportation and electric power industry. However, traditional PPP technology is still in the form of float ambiguity solution, positioning accuracy and convergence speed need to be improved. Many phase bias in carrier phase observations bring out that the ambiguity is not integer. Therefore, fixed ambiguity solution becomes an urgent problem in PPP technology.In this paper, PPP principles and mathematical models were researched deeply, and the most common non-difference ambiguity fixed algorithms currently were analyzed. On this basis, the factors caused ambiguity is non-integer were researched. In addition, reason of ambiguity can be restored to integer was illustrated. Finally, Chongqing CORS data was collected in the paper to carry on examples of verification, and accuracy of fixed solution was analyzed after the examination. The main works and conclusions in the thesis are as follows.(1)Firstly, PPP principles, sources of errors and method of parameter estimation were illustrated. Three common PPP models internationally were introduced respectively. Sources of errors affect positioning accuracy were studied classified, corresponding error correction models for each kind of error were presented at the same time. Furthermore, principle and construction of Kalman filter was described in detail. On the basis, data provided by IGS was carried on examination validation.(2)Secondly, algorithms of un-differenced ambiguity fixing were studied profoundly. Algorithms of un-differenced ambiguity fixing are classified into three categories from different perspectives of FCBs solution in reference stations. They are:algorithm of ambiguity fixing based on FCBs, algorithm based on integer-recovery clocks (IRCs), and algorithm based on float solution. Each algorithm was elaborated and researched from respects of principle and implementation. Algorithm of ambiguity fixing based on FCBs was determined to realize algorithm of un-differenced ambiguity fixing in this paper, by analyze the positioning precision and data storage characteristics of each algorithm.(3)Thirdly, reason of ambiguity is non-integer was analyzed. Moreover, extraction of FCBs was achieved. Factors caused ambiguity is non-integer were summarized as follows: initial phase delays and hardware delays in carrier phase observations, and bias affected by ionosphere-free combination model. The possibility of ambiguity can be restored to integer was discussed based on previous research. Wide-lane FCBs was separated by un-differenced least squares method. Then wide-lane ambiguity was fixed, combine with PPP ambiguity obtain narrow-lane ambiguity which is float. Narrow-lane FCBs was solved take the same method as wide-lane. Example of Chongqing CORS data shows that:on one hand, satellite terminal wide-lane FCBs is extremely stable, fluctuation is less than 0.2 cycle all day. On the other hand, because of the shorter wavelength, narrow-lane FCBs fluctuate slightly, but narrow-lane FCBs by every 10 minutes is relatively stable.(4)Finally, algorithm of un-differenced ambiguity fixing was realized. Wide-lane and narrow-lane ambiguity of rover station was fixed through FCBs, then combine two ambiguities to get new ionosphere-free ambiguity, thus achieve algorithm of ambiguity fixing. All the algorithms were carried out by Program Visual C++6.0 in this thesis, including solution of FCBs in reference station and ambiguity fixing in rover station. Instance of Chongqing CORS data indicates that:compared with float solution algorithm, the precision of east and up direction for fixed solution algorithm has improved significantly. The accuracy of east and up direction become from 12millimeter and 20 millimeter to 6.5 millimeter and 14 millimeter, the precision has improved 47.3% and 29.1% respectively. Besides, convergence time has become from 64minutes to 41 minutes, time is significantly shorter than before. |
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