Research On GNSS Constellation Autonomous Integrity Monitoring And Maintenance Technology

In an ever more connected world, society’s reliance on high precision positional,navigational and timing (PNT) data provided by Global Positioning System (GPS)and other Global Navigation Satellite Systems (GNSS) is growing. The easy andcheap availability of Radio Navigation Satellite System (RNSS) has meant that theiruse can be found in an increasing number of products and services.The range ofapplications stretch from highly accurate surveying to in-car navigation, and fromnetwork synchronisation to climate research. The original implementation of GNSS,comprises ground based, space based and receiver segments, all of which aresusceptible to failures of various types. A failure, or loss of signal due to some outsideinfluence, can result in a range of consequences depending on the application. Thespace segment，which is at the top level of GNSS, addresses the primary source ofuser range error. In other words, the failures from the space segment would influencethe quality of receiving signals, no matter what the ground segment and receiversegment try to improve.A method of satellite autonomous integrity monitoring using inter-satellitemeasurements is proposed with the purpose of degrading GNSS space segmentvulnerability and implementing autonav function in modernized navigation system.This technique, used as a mechanism for autonomous integrity monitoring andwarning in GNSS, can undoubtedly benefit the real-time monitoring of satelliteparameters. Ranging measurements of inter-satellite links (ISL), validity of almanac,working status of satellite, are all brought into the vulnerability monitoringarchitecture. It protects the system running performance before the ground segmentand user segment play a role. Supported and promoted by―863‖program, named―GNSS vulnerability analysis and studies on signal transmission environment‖, thiswork has placed emphasis on the following aspects:（1） A general research about the conditions of ISL’s utility, structure,functions, payload, antenna beam, constraint, band selection, communicationmechanism, as well as the development of laser crosslinks. Somesuggestions are given considering that the BeiDou system hasn’t determine specific parameters for its ISLs.（2） With the purpose of exploring ISL’s topology network and minimumpower budget, GNSS constellations are simulated by Satellite Tool Kit(STK).（3） By simple rearangements of bidirectional inter-satellite measurements,the orbit errors and clock components can be decoupled. The comparison ofestimated orbit errors and monitoring thresholds calculated by the requiredintegrity standards can be used as judgement of SAIM states.（4） Finally, there are descriptions about constellation autonav based on ISL.With the help of orbit prediction algorithm，the performance of ephemeriscorrection is validated by tests containing broadcast ephemeris, preciseephemeris combinded with simulated data.And the results optimisticallyindicate that the application of the new method is beneficial to achievingadvanced GNSS autonav level.