Research On Method Of Multi-Frequency Multi-System Integrity Monitoring And Evaluation For GBAS

With the rapid development of GNSS,integrity issues become more and more obviously in applications related to life safety.Due to the potential to meet the highest standards of integrity performance requirements,GBAS has attracted extensive attention.GBAS Integrity monitoring technology has been developed over two decades,a large number of research results have been obtained in terms of integrity monitor algorithm and performance evaluation.However,there are still a series of problems that need to be further studied.In particular,the global satellite navigation system,represented by GPS,GLONASS,Galileo and BDS is booming,which brings new opportunities for multi-frequency multi-system integrity monitoring.Meanwhile,more satellite types,carrier frequencies,signal types,duplicate methods also brings more chanllenges to GBAS integrity monitor.The thesis aims to study on theory and methodology of integrity monitor and evaluation for GBAS,use statistical theory and modern quality control chart theory,enrich the multi-frequency and multi-system integrity monitoring algorithm,improve the GBAS integrity monitoring and processing strategy,and strive to provide theory reference and practice foundation for applications of GBAS integrity monitor.The main work and contributions of this thesis are as follows:The principle of GBAS is introduced systematically.The basic structure of the GBAS and the functions of each module are expounded.The single-frequency phase smoothing pseudorange and dual-frequency phase smoothing pseudorange preprocessing algorithm are given.The MW combination is discussed.The three cycle slip detection techniques based on MW combination,GF combination and three-frequency cycle slip detection are discussed,and the GBAS positioning model is introduced.The algorithm framework of the integrity system is combed,and the existing single-frequency single-system integrity monitoring platform is extended to the multi-frequency multi-system integrity monitoring platform,and the processing logic under the multi-frequency multi-system is optimized.Statistical analysis methods commonly used in integrity monitoring are given.Aiming at the standard deviation-mean monitoring problem of GBAS broadcast correction error in real-time,the existing standard deviation-mean monitoring algorithms are systematically summarized.The basic theories are given and their actual performance are analyzed with validation tests.A new kind of standard deviation-mean monitoring algorithm based on EWMA control chart is proposed,and the influence of control limit parameters and smoothing cofficients on EWMA control chart are analyzed.The performance of different standard deviation-mean monitoring algorithms are compared,the results show that the standard deviation-mean monitoring algorithm based on EWMA control chart optimizes the average running length under the uncontrolled state,which significantly improves the performance of real-time standard deviation-mean monitoring.The time-frequency characteristics of periodic pseudorange multipath are systematically analyzed by using short-time Fourier transform system,reached the conclusion that pseudorange periodic multipath has significant time-varying characteristics in spectral domain.Aiming at this problem,a multipath anomaly monitoring algorithm based on adaptive threshold adjustment strategy is proposed.The adaptive parameter estimation strategy considering spectrum prior information is designed.The results show that the algorithm overcomes the time-varying characteristics of pseudorange periodic multipath anomalies under multi-frequency and multi-system,and improves the effectiveness and reliability of pseudorange multipath anomaly monitoring.A GNSS multipath mitigation algorithm based on frequency domain filtering is proposed,which precisely suppressed the influence of abnormal peaks in the frequency domain and maximizes the original characteristics of the data in other frequency domain intervals.The results show that the algorithm is able to retain the original data features to the greatest extent and avoid the effects of excessive smoothing.For BDS GEO satellites without periodic multipath effects,the algorithm can retain its data characteristics to the maximum extent;for satellites with periodic anomalies,the pseudorange RMS is usually decreased in the range of 0.10~0.45 m,with a percent of 14.34~61.84%,and the improvement is related to the amplitude of the pseudorange periodic fluctuations received by the satellite observation.Among them,the improvement of pseudorange RMS after GPS correction is usually 0.11~0.16 m,with a percent of 19.05~40.90%;the improvement of GLONASS pseudorange RMS after correction is usually 0.10~0.45 m,with a percent of 14.34~50.73%;The improvement of pseudorange RMS of BDS non-GEO satellite after correction is usually 0.16~0.42 m,with a percent of 20.64~61.84%.Based on the measured dynamic data,the four-system GBAS integrity performance under dynamic conditions is comprehensively evaluated.The multipath and thermal noise level of GBAS rover station is systematically evaluated.The influence of baseline distance on GBAS integrity monitoring performance is analyzed.The statistical dispersion and probability density distribution of vertical and horizontal protection levels are given.The experimental results show that using vehicle data under the dynamic environment,the GBAS vertical integrity of the GBAS meets 100% of the CAT-I,and the percent of numbers of the CAT-III standard reaches 99.949%.The horizontal integrity of the CAT-I and CAT-III data reached 100%.The VPL achieved 99%,99.9%,and 99.99% availability in the range of 3.8m,4.8m,and 8.4m,respectively,and HPL achieved 99%,99.9% and 99.99% availability in the range of 3m,3.km and 5.2m respectively.