Multi-GNSS Real-Time Data Analysis And Software Implementation

With the application of BDS (BeiDou Navigation Satellite System), the promotion of Galileo and GPS/GLONASS, satellite navigation has entered a multiple systems co-existence era. Multi-system and multi-frequency observation provides new technological support for improving the accuracy, reliability, effectiveness and continuity of positioning. Real-time decoding and quality analysis of raw GNSS (Global Navigation Satellite System) data stream is the premise and foundation to realize real-time technology such as network RTK(Real-time Kinematic) and real-time PPP(Precision Point Position). There are many problems and limitations with GNSS data conversion and quality analysis software, mainly reflected in:unable to analyze real-time data stream, unable to support BDS, complex operation, and unfriendly interface. Based on raw data stream which is compatible with BDS/GPS/GLONASS, a study of multi-GNSS message parsing, data quality analysis and evaluation method is conducted, and a multi-GNSS real-time data quality analysis software was implemented. The main research contents of this paper are as follows:(1) Contents, structures and application of each main GNSS raw data format are elaborated in this paper. Observation, navigation data, and all kinds of auxiliary information in each data format are analyzed. In order to make it compatible with the main message format, that is to say, to analyze multi-GNSS raw data stream, methods of message format analysis are studied and specific logic chart is proposed. In this paper, structures and characteristics of the latest differential message RTCM version3.2 were analyzed, and decoding methods were put forward in corresponding to the design philosophy of satellite signal and the division principle of observation, messages were completely extracted, and accuracy of results was tested through real-time data.(2) Indicators and methods of multi-GNSS data quality analysis are researched in detail. Data quality indicators, such as multipath effect, ratio of signal to noise, data integrity were studied from the aspects of environmental impact, receiver performance and the loss rate of data. Computational methods of multipath effect were studied, and through data analysis to prove that the effect of multipath on positioning can be obviously weakened by multi-GNSS. The relation between signal to noise and observation quality were also revealed. Indicator elaboration and analysis about data integrity which reflected the loss of epoch and observation was presented.In addition to the pure analysis of observation data quality, research about the significance and algorithm of PDOP(Position dilution of Precision) was carried out, which explores the geometric structure between satellites and stations. Data analysis of number of visible satellites and PDOP between multi-GNSS and single system can draw the conclusion that multi-GNSS can significantly improve the reliability of high precision positioning in complex environment.(3) Real-time multi-GNSS data analysis software was developed. Main parts of the software were designed, and collaborative workflow and data communication between threads were elaborated. Local receivers and remote base stations can access raw GNSS data stream real-timely in the way of serial and network communication. Tee-Chart control was used to plot and reveal the consequence of data parsing and quality analysis. Finally, verifications of real-time data parsing and quality analysis with different raw GNSS messages were conducted. The software was proved with high compatibility and reliability.