An assessment of the autonomous integrity monitoring performance of a combined GPS/Galileo Satellite Navigation System, and its impact on the case for the development of Galileo

摘要

In 1999 Europe, through the European Commission and the EuropeanSpace Agency, began detailed definition of a second generation GlobalNavigation Satellite System (GNSS). This GNSS developmentprogramme, known as “Galileo”, was intended to both complement andcompete against the existing US Global Positioning System (GPS).Unlike GPS, Galileo is intended to be privately financed, following theinitial development investment from the EC and ESA, which implies thatGalileo should provide some revenue-earning services. From its earliestinception, the basis of these services has been assumed to be throughthe provision of Signal Integrity through an Integrity Flag broadcastthrough the Galileo system– a service which GPS cannot provide withoutsome external system augmentation. This thesis undertakes a criticalevaluation of the value of this integrity system in Galileo.This thesis has two parts. The first demonstrates that the conditionsrequired to attract adequate private finance to the Galileo programmeare incompatible with the system architecture derived from the earlyGalileo system studies and taken forward into the system earlydeployment phase, which includes an Integrity system within Galileo.The second part of this thesis aims to demonstrate that receivers whichcan combine the signals from GPS and Galileo may offer a free Integrityservice which meet the needs of the majority of users, possibly up to thestandards required for aviation precision approach. A novel ReceiverAutonomous Integrity Monitoring (RAIM) technique is described, usingan Errors in Variables/Total Least Squares approach to the detection ofinconsistencies in an over-determined set of GNSS signalmeasurements. The mathematical basis for this technique is presented,along with results which compare the simulated performance of receiversusing this algorithm against the expected performance of Galileo’sinternal integrity determination system.