Performance Assessment And Optimization Research Of GNSS Receiver Autonomous Integrity Monitoring Algorithm

Global Navigation Satellite System(GNSS),as an infrastructure for national economy and national defense construction,has been widely used in military,civil,industrial,commercial,and scientific research fields,and has also increasingly influenced all aspects of people’s daily life,making people’s demand for accurate and reliable space-time information more and more intense.However,due to the inherent vulnerability of GNSS,the prevalence of errors,uncertainty and signal susceptibility to obscuration,GNSS navigation and positioning terminals will inevitably have various signal abnormalities or failures during the working process,leading to the destruction of the integrity of the system,which seriously threatens the safety of human lives and important properties,especially in the field of civil aviation,the integrity of GNSS system has more important significance and research value than accuracy.Based on this,this paper focuses on the theory and method of GNSS terminal integrity monitoring,mainly including Receiver Autonomous Integrity Monitoring(RAIM)algorithm and Advanced RAIM(ARAIM)algorithm,evaluating the performance of RAIM and ARAIM algorithms,and optimizing their shortcomings.The main work and the results of this paper are as follows:1.To address the problems of conservative calculation of protection level and insensitive effect of small fault detection in the least squares RAIM algorithm,this paper proposes a RAIM optimization algorithm that takes into account the satellite characteristic slope,which extracts the satellite characteristic slope from the redundant GNSS observations according to the satellite geometry to optimize the fault test statistics,and analyzes the influence of satellite characteristic slope on the localization solution.Finally,the reliability of the optimization algorithm is verified based on the measured and simulated data.The results show that the RAIM optimization algorithm considering the slope of satellite features significantly improves the accurate detection of small faults,i.e.,the improved algorithm can better avoid the insensitivity problem of high Missed Detection Risk(MDR)satellites in fault detection.Meanwhile,the protection level calculated by the improved algorithm can tighten the envelope position error,and its globally horizontal protection level(HPL)is less than 50 m and vertical protection level(VPL)is less than 60 m,which can better meet the end-user requirements for highly reliable.2.To solve the problem that the Multiple Hypothesis Solution Separation(MHSS)ARAIM algorithm is not ideal for coarse difference detection leading to low satellite utilization,this paper proposes a joint observation domain MHSS ARAIM algorithm,which reconstructs the fault test statistics based on the chi-square test.and combines the MHSS ARAIM algorithm to detect the faulty satellites.In addition,this paper designs three typical faults,namely,abrupt change,step,and ramp,to verify the detection effect of the improved MHSS ARAIM algorithm on faults.The results show that the improved MHSS ARAIM algorithm can accurately identify single/multiple faults,and the VPL can better envelop the Vertical Position Error(VPE),which can avoid the problem of wasted availability.The improved MHSS ARAIM algorithm is effective in detecting three typical faults and provides guarantee for navigation and positioning services for end navigation users.3.Considering the booming development of Low Earth Orbit(LEO)satellites brings new opportunities for GNSS ARAIM research,however,the performance of ARAIM under different LEO constellation enhancements may vary significantly.Based on this,this paper simulates three typical LEO constellations: high orbital inclination(80-satellite),medium orbital inclination(120-satellite)and mixed orbital inclination(168-satellite),and evaluates the availability of different LEO constellation enhanced BDS-3 ARAIM in LPV-200(Localizer Precision Vertical approach down to 200 feet)phase with the help of MGEX(Multi-GNSS Experiment)data and simulation.The results show that the availability effect of BDS-3 ARAIM enhanced by high orbital inclination constellation is most significant in the high latitude region.In the mid-latitude and low-latitude regions,the most significant improvement in the availability effect of BDS-3 ARAIM is mid-orbit inclination.Globally,the availability of BDS-3 ARAIM with mixed orbital inclination,high orbital inclination,and medium orbital inclination constellation enhancements has improved more than 90% coverage compared to BDS-3 by 48.2%,25.7%,and 32.0%,respectively.In summary,there are obvious differences in the improvement of BDS-3 ARAIM availability under different types of LEO constellation enhancements,among which,the LEO constellation with mixed orbital inclination corresponds to the best improvement of global BDS-3 ARAIM availability.