| The continuous development and improvement of the Global Navigation Satellite System(GNSS)has greatly increased the number of visible satellites in the same epoch.Compared with single-system GNSS,multi-system GNSS has obvious advantages in terms of the number of visible satellites,positioning accuracy,coverage integrity,real-time performance,and reliability.In addition,according to the GNSS rear rendezvous positioning theory,the correct satellite selection results are useful for the follow-up the accuracy of carrier phase calculation is also beneficial.However,while multi-system GNSS brings advantages,it also causes the amount of calculation in the receiver to increase exponentially during processing.Therefore,not only meeting the requirements of positioning accuracy,but also improving the efficiency of satellite selection is one of the important problems that need to be solved urgently in the current navigation and positioning field.The main research contents of the thesis are as follows:(1)Studying domestic and foreign GNSS satellite selection algorithms,analyzing their advantages and disadvantages,it is concluded that the smallest GDOP(Geometric Dilution of Precision)value and the largest volume of the polyhedron formed by the station and the visible navigator are still the theoretical basis for satellite selection.Conformal Geometric Algebra(CGA)has the advantage of combining numbers and shapes in terms of geometric configuration and description.Applying it to the satellite selection of the largest polyhedron can improve the processing efficiency of the multi-system satellite selection algorithm.(2)Introduced the Beidou/GNSS system composition,time system,and space coordinate system,and analyzed the compatibility of multi-system space-time systems.The basic principles of satellite navigation and the calculation process of satellite position are described.The main steps of the navigation optimal solution calculation and accuracy evaluation based on the least square method are given,and the evaluation index of satellite selection,namely the geometric precision factor,is derived,and its definition.(3)On the basis of analyzing the factors affecting the GDOP value and studying the theory of traditional satellite selection algorithms,a new satellite selection algorithm based on the vector-end polyhedron volume method based on the irregular triangulation projection is proposed.The algorithm uses the inscribed polyhedron of the sphere to project the Delaunay irregular triangulation,and quickly calculates the volume of the inscribed polyhedron,and obtains the relationship between the volume of the polyhedron and the GDOP value on this basis.The experimental results show that in the multi-system positioning,11 satellites with good spatial geometric distribution are selected as the solution satellites,the navigation and positioning accuracy is high,and the timeliness of the solution is taken into account.(4)Combining the partition method of the satellite selection algorithm at the altitude angle,the umbrella-shaped satellite selection model based on the CGA theory is constructed as the matching reference;according to the satellite ephemeris,the space coordinates are calculated and converted to the station center coordinate system,which is constructed based on the CGA theory The multi-vector set of visible satellites provides the basis for discriminating the angle-selected satellite matching based on the CGA theory.According to the measured BDS/GPS/GLONASS three-system observation data verification,it is shown that in the combined satellite selection from 6 to 17 satellites,the fast satellite selection algorithm based on CGA has the same GDOP value compared with the minimum GDOP value selection method;When the number reaches 11,the GDOP value is basically less than 2,which can meet the needs of high-precision navigation and positioning.In terms of computational time,the CGA-based satellite selection algorithm is much better than the minimum GDOP method.Compared with the traditional altitude angle selection algorithm,because the CGA-based satellite selection algorithm reasonably designs the uniformity threshold of the satellite spatial geometric distribution,its GDOP value stability and navigation accuracy are superior to the traditional altitude angle selection algorithm. |
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