Research On Combined RTK Positioning Algorithm For Multi Satellite Navigation System

With the construction and improvement of the four global satellite navigation systems,the number of visible satellites is doubled,and the geometry of the satellite-station is better,which can improve the performance of ambiguity resolution and positioning accuracy,and make up the limitations of single-system RTK positioning.So Multi-system combination RTK has become a hot research.In this paper,we focus on the theory and positioning performance of RTK in multi-system combination.The main work is summarized as follows:(1)Research on Mathematical Model of Multi system Combination RTK.This paper analyzes the unified scheme of time-space bench for multi-system combination RTK,and deduces the single-difference and double-difference model.Thus the form of the solution equation between the different systems is unified.This can facilitate data processing and programming.According to the degree of error weakening in the double difference observation under different baseline length,the data processing strategies and models of short baseline and medium long baseline are proposed respectively.(2)Research and Improvement of Ambiguity Resolution Method.Aiming at the problem of low efficiency and success ratio exits in the methods for ambiguity resolution commonly used in geometry-based and geometry-free model,this paper proposes a modified three carrier ambiguity resolution method-MTCAR.Analysis by experiments showed that:the success rate of MTCAR is better than LAMBDA of geometry-based model and TCAR of geometry-free model.In terms of algorithmic resolution speed,the MTCAR method is slightly lower than the TCAR method,but it is about 60%higher than the most widely used LAMBDA method.(3)Improvement of partial ambiguity resolution method.Partial ambiguity resolution is applied to multi-system combination dual-frequency RTK.In this method,the ambiguity subset is selected by considering the satellite height angle,floating point solution variance factor,ambiguity fixed success rate and Ratio value.The experimental results show that the partial ambiguity resolution can effectively improve the fixed rate and positioning accuracy in the multi-system combination dual-frequency RTK.(4)Evaluation of positioning performance of Multi-system Combination RTK.In this paper,the performance of single frequency and dual frequency RTK of seven modes in static and dynamic baseline condition are evaluated in terms of ambiguity resolution and positioning accuracy.The experimental results show that:for single frequency RTK,the fixed rate of single system ambiguity is very low and it is difficult to be used in practice.The combination of dual system and three systems can significantly improve the fixed rate and success rate.So that the positioning performance of multi-system combination of single-frequency RTK is comparable with single-system dual-frequency RTK.It will help reduce the cost of RTK equipment,and has great application prospects.For dual-frequency RTK,the ambiguity fixed rate and success rate is low when single system in the high cut-off angle.It is difficult to adapt to high-rise,canyon and other high cut-off angle of the environment.The combination of dual system and three systems can ensure the number of satellites needed under high satellite cut-off angle conditions,quickly and reliably complete the ambiguity fixed and RTK positioning.It is beneficial to extend the application field of RTK technology.Under the three systems of GPS,GLONASS and BDS,GPS + BDS is the best for dual system combination.The combination of three systems is better than that of dual system combination,and has the best RTK performance.