| Precise Point Positioning(PPP)technology makes use of Precise orbit,Precise satellite clock information and a large number of mathematical error model constraints,and can obtain high-precision spatial geometric position and atmospheric state information only through a single receiver.It has played an important role in engineering technology,scientific research and other fields.Since this technology was proposed more than twenty years ago,the bottleneck of its development and application has been the convergence time and the fuzzy degree fixed efficiency.In recent years,the success of the Beidou-3 generation navigation satellite network in China have provided abundant available resources for the development of precise single-point positioning.In this paper,BDS/GPS/GLONASS/GALILEO constellation combination positioning and fuzzy degree fixed methods have been deeply studied.The specific work contents are as follows:(1)With no deviation between the constellation system,detailed introduces the ionosphere combination function model and stochastic model,and a variety of empirical observations weighting method,and observation precision difference according to different system,the introduction of Helmert variance component estimation,through the observation of posteriori accuracy information,set up the precision factor,choose right into kalman filter iteration,adjusting between different systems,with different rights between the observed value ratio and stochastic model,to achieve reasonable fixed weight as well as the effect of resistance is poor.Experimental results show that the variance component weight determination can effectively improve the unreasonable weight ratio between different systems,and improve the convergence speed.Compared with the empirical weight determination method,the convergence time is shortened by 44%.(2)Based on the improved modified Geometric Free(m GF)observation quantity,a m GF enhanced ambiguity fixing method is proposed,which applies the m GF equation to the whole cycle ambiguity solving.The influencing factors of the fixed accuracy of the fuzzy degree of the method are analyzed theoretically,and the validity of the method is proved by the measured data.Experimental results show that the average fixed rate of ambiguity based on the m GF method is about 95%,and the fixed rate is better than the Lambda method when the cut-off altitude angle is high.Due to the low complexity of the algorithm,the solution speed of the m GF method is about 5.1 times higher than that of the LAMBDA method.(3)Implements the above positioning and ambiguity fixing algorithms independently,and analyzes the positioning performance of BDS/GPS/GLONASS/GALILEO single/multisystem combination point solution,as well as the influencing factors of positioning performance through experimental calculation of a large number of IGS station data.The fourconstellation combination significantly increases the number of visible satellites,and the average number remains above 20,which effectively improves the spatial geometry of satellites.The average PDOP of the four-constellation combination is 0.6,and the average PDOP of the single GPS system is 1.2.By comparing the PPP calculation results of the single/multi-system combination,the average positioning accuracy of the multi-system combination in the horizontal direction is 0.37 cm,0.36 cm,and the average positioning accuracy in the vertical direction is 0.61 cm,which is 25% higher than that of the single system in the convergence speed. |
