Theory And Technique On GNSS Integrity Augment

The dissertation mainly focuses on the theory and algorithms about GNSS integrity of Satellite-Based Augment System and Ground-Based Augment System, the main works and contributions are summarized as follows:1. The theory and methods are introduced and discussed on GNSS integrity. The GNSS performance requirements are analyzed, the conception of integrity is defined and the monitoring methods are studied, finally some technical challenges are listed which are the mianly works to study.2. Simulation system of GALILEO is built, through which the performance of GALILEO is analyzed, and the methods of integrity ensurement are studied. According the analysis with the simulation system, the conclusion can be drawn that the constellation of GALILEO is better than that of GPS because the value of GDOP of GALILEO is similar to that of GPS at low elevation and much better than that of GPS at high elevation.3. The base frame and key techniques of Wide Area Precise Point Position at decimeter-level is studied, and a primary accuracy analysis is made. Precise orbit and clock is determined by using combined measurement consisted of pseudorange and carrier phase.Though analyzing, it is shown that the error of pridicted orbit within 3 hours is less than 15 centimeter using the data from the sations allover the world, and the error of pridicted orbit within 2 hours is less than 20 centimeter using the data from the domestic and aboard sations of the first kind.The error of the pridicted clock is less than 0.3ns.The error of the ionosphere delay coreection built by SHSS reference station conducted from system bias using optimized grid ionosphere model is less than 0.2m.4. The SBAS message system is studied, it is expatiated how to define and transport the differential and integrity information exactly and roundly. The SBAS message system not only considers the fast correction, long term correction and ionosphere delay correction and bouds the error of these corrections, but also considers the degenerated factors, using these corrections and dagenetated factors, more exact error bound can be estimated at position domian.5. A new method which optimizing accuracy and stability is studied. If the requirement of integrity is relaxed and the value of UDRE and GIVE is adjusted so as to fit the reality, the position accuracy can be improved using Least-Squares based on the new weight. The VPL will be smaller than before using the adjusted sigma. The accuracy at position domain can be improved by adjusting adaptive carrier smoothing using code-carrier divergence .6. a x~2 monitoring method is studied to detect the atomic clock anomaly of the navigation satellites by making atomic clock bias twice difference and biulding the balanced time serial.Through analyzing, the conclusion can be drawn that double difference method is effective for the phase anomaly but not effective for frequency anomaly,and x~2 method based balancedtime serial is effective for both phase anomaly and frequency anomaly.7. The key principle and algorithoms of Joint Precise Approach System are studied. Through analyzing the conclusion can be drawn that the DFS algorithm of LB-JPALS is similar to the WLFS algorithm of SB-JPALS, and the diffrence between them is that the Wide-Lane mixed measurement of L1 and L2 frequence is smoothed by carrier phase towards WLFS algorithm and the pseudorange of single frequence is smoothed by carrier phase towards DFS algorithm. So the reciever of SB-JPALS must be double frequece reciever so as to satisfy WLFS algorithm, and WLFS algorithm need not care about code carrier divergence as the ionosphere delay has been removed befor smoothing.8. The integrity algorithom of GBAS based on non-gausss distribution is studied. The primary method of calculating VPL is based on the gauss distribution of the sigma of the residual pseudorange error, but multi-path error is the main component of the residual pseudorange error and is not gauss. A new method how to inflate the sigma is studied so as to ensure rigorous theoretically.9. The system and flow how to monitor anomaly of GBAS is designed. The system is consist of some algorithoms used to monitoring anomaly and execute logic, the system is more entirely and difficult than SBAS, with the system and the execute logic, mesurement and message can be monitored and can be isolated if they seems to be anomaly.10. The monitoring algorithm on Sigma anomaly based on B-Value is studied. Through the analysis it is shown that the Sigma Monitoring Algorithm based on B-Value and SUM Algorithm are also effective to anomaly error of the pseudorange correction.11. The effect toward GBAS when ionosphere storm occures is modeled and the monitoring algorithms are studied, and the method of Local Area Difference is improved.GBAS is based on the case that the errers on the pseudoranges observed by user and reference station is similar, so the correction provided by reference station is used to correct the pseudorange measurements observed by users. But when ionosphere anomaly is met, the errers between the the station and user is quit different and the positioning solution is effected.The dissertation provides CCDMA and DSCMA algorithm to detect the ionosphere anomaly, and the differential positioning solution of GBAS is improved. It's shown that the provided algorithm mitigrates the threat for GBAS.