Study Of Key Techniques In Multiple Systems Combined GNSS Receivers

With the GPS, GALILEO, GLONASS, Compass rapidly developing and improving, the number of navigation satellites will increase greatly, and the application of combining multiple systems is an important trend in GNSS technology. It can effectively improve the accuracy, integrity and availability. Therefore, development of the multi-system combined receiver is valuable.A number of key technologies must be solved to develop the multi-system combined receiver. This paper focuses on problems of space and time reference systems unifying, multi-system satellites selection, multi-system integrity monitoring and so on.The research includes the following four areas:(1) Different time reference systems are outlined, focusing on analysis of the system time of GPS, GALILEO, GLONASS and Compass, and the conversion relationships between different systems'time are given. The result is a theoretical foundation for the design of a reference time unifying algorithm in the multi-system combined receiver.(2) The different forms and reference systems'transformation of the coordinate reference are analyzed, and the accuracy of transforming different coordinate reference systems is researched. Finally, based on an example, the process and accuracy distribution of transforming BJ-54 to WGS-84 are obtained. After deriving the accuracy formula of transforming coordinate reference, we get the relationship between three-dimensional coordinate conversion error and the reference points: the conversion accuracy is related to the factors such as measurement accuracy, distribution and location of the reference points.(3) The problem of selecting multi-system satellites rapidly is studied. After analyzing the traditional satellite selection method based on DOP values, a simple multi-system satellite selection algorithm using elevation and azimuth is identified.(4) Receiver autonomous integrity monitoring (RAIM) for multi-system combined receiver is researched, focusing on RAIM availability. After introducing the principle of the snapshot RAIM methods, the problem of RAIM availability is analyzed. Finally RAIM availability of the GPS + BD2 constellation is simulated. The results show that the constellation of multi-system can increase the availability of RAIM.This research can provide a theoretical reference for developing the multi-system combined receiver.