Research On Monitoring Key Technologies Of Integrity In Ground-based Augmentation System Of GNSS

Positioning accuracy, continuity, integrity and availability of the Navigation System are the most core indicators in navigation service performance. These indicators are increasingly attracting user’s attention. Integrity of the performance requirements is the hardest to satisfy in navigation service performance indicators. In order to improve the performance of the Navigation System in the Global Navigation Satellite System, researchers introduce the BOC signal modulation, improve the prediction accuracy of the satellite ephemeris, and add the third frequence of carrier signals and so on. In this context, in order to ensure precise approaching and safe landing of aircraft, the Ground-Based Augmentation System needs to solve many integrity problems related with the spread signals, broadcast data and measurement data. This paper focuses on key technologies of the Ground-Based Augmentation System integrity monitoring. The main researches were as follows:1. Based on precise approaching and safe landing of aircraft, this paper analyzes the overall structure of the Ground-Based Augmentation System. And then, the algorithms of the reference receiver using carrier phase measurements to smooth Pseudo-Random Noise(PRN) code measurements and the method of calculating differential error correction in the data processing center are introduced. Besides, this paper mainly analyzes several different integrity monitoring algorithms and logic process of the Executive Monitor.2. According to the events that the positioning precision degraded for the 2nd-Order Step Threat Model which happened in SV19 satellite, the BPSK modulated signal distortion model is extended to BOC modulated signal distortion model. By the analysis of BOC modulation, the paper derives the BOC modulated signal digital distortion models in time domain and frequence domain and the BOC modulated signal analog distortion in time domain. According to sufficient symmetry of the correlation peak of the BOC modulated signal, this paper designs the method of monitoring the BOC modulation signal analog distortion. And it uses the method of linear fitting to monitor the BOC modulation signal digital distortion.3. Both of impulse changes in ionosphere delay and ionosphere spatial gradient model have large influences on aircraft landing approach. Since small changes can’t be monitored by the Shewhart monitoring algorithm and the CUSUM algorithm can’t monitor impulse changes, the Shewhart algorithm and the CUSUM algorithm are combined to monitor ionosphere delay for ionosphere storm. The performance of the combinational algorithm is verified by real ionosphere data.4. Because the larger satellite position error may exist for the satellite navigation message broadcast data, the methods of new-old ephemeris comparison detection and almanac-ephemeris comparison detection are introduced to monitor the effectiveness of the new satellite ephemeris. This paper uses multiple monthes satellite ephemeris and almanac data to compute the position of satellites, and uses SPSS statistical software to count new-old satellite position difference distribution for ephemeris in two hours and almanac-ephemeris satellite position difference distribution in 10 hours. Then the current new-old ephemeris comparison detection threshold and almanac- ephemeris comparison detection threshold are obtained.