Algorithm Research On Stochastical Model For GPS/COMPASS Combined System’s Point Positioning

This paper firstly explains the background of the research and summarises thedevelopment and system compositions as well as characteristics of GPS and COMPASSrespectively, also points out the significance of probably determing the stochasticalmodel of GPS/COMPASS combined system.The error sources and their correction models are discussed. Some special errors suchas satellite clock error, receiver clock error and ionosphere delay are analysised. Theprinciple of single satellite system’s point positioning and GPS/COMPASS combinedsystem’s point positioning are also discussed in this paper, and the process of thecoordinats’ computing is derived systematically.The three-dimension positon accuracy and internal accordant accuracy as well asexternal accordant accuracy are taken as the index of point positioning quality.Examples are applied to carry out the research from the following respects:(1) Compare the point positioning quality of GPS as well as COMPASS in China area,and analysis the reasons for the corresponding results deeply.(2) Emphatically discuss how to determine the weight matrix of the GPS/COMPASScombined system.By comparing the equal weight model with the elevation angle modeland Helmert posterior estimation, pointing out that determing the the weight matrix ofthe GPS/COMPASS combined system based on Helmert posterior estimation is mostpropable.(3) Comparisons are made for point positioning quality of both single system andcombined system, and the reasons for quality differences of different systems aresummarized.(4) By setting different cut-off satellite angles, the complex observational conditions aresimulated. The accuracy of Helmert posterior estimation weight model under differentcut-off satellite angles is compared with each other.(5) The visible satellite numbers and the effective epochs of single system andcombined system are counted and compared with each other in the whole observationtime. Also the causes of differences about point positioning quality among satellitesystems are further analysised.By serieses of researches and analysises, wu conclude that:(1) In China area the visible satellites amount of COMPASS is larger than that of GPS,and the satellite distribution structure of COPASS is good. Compared to GPS, COMPASS has a better performance in point positioning.(2) Helmert posterior estimation is an effective way to determine the stochstical modelof GPS/COMPASS combined system, and it can make the results more reasonable.(3) Generally speaking, the point positioning quality of the combined system is superiorto that of a single system. The combined system’s internal and external accordantaccuracy is almost the same as the single system while the spatial position accuracy ofthe combined system is better than that of single system and nearing the better one ofthe twe single systems.(4) Even if in the complex observation condition full of sheldings, the GPS/COMPASS combined system can still satisfy the amount of point positioning andmaintain a certain accuracy. Significantly, the area of application is expanded...