Abstract:
In 1999 Europe, through the European Commission and the European
Space Agency, began detailed definition of a second generation Global
Navigation Satellite System (GNSS). This GNSS development
programme, known as “Galileo”, was intended to both complement and
compete against the existing US Global Positioning System (GPS).
Unlike GPS, Galileo is intended to be privately financed, following the
initial development investment from the EC and ESA, which implies that
Galileo should provide some revenue-earning services. From its earliest
inception, the basis of these services has been assumed to be through
the provision of Signal Integrity through an Integrity Flag broadcast
through the Galileo system– a service which GPS cannot provide without
some external system augmentation. This thesis undertakes a critical
evaluation of the value of this integrity system in Galileo.
This thesis has two parts. The first demonstrates that the conditions
required to attract adequate private finance to the Galileo programme
are incompatible with the system architecture derived from the early
Galileo system studies and taken forward into the system early
deployment phase, which includes an Integrity system within Galileo.
The second part of this thesis aims to demonstrate that receivers which
can combine the signals from GPS and Galileo may offer a free Integrity
service which meet the needs of the majority of users, possibly up to the
standards required for aviation precision approach. A novel Receiver
Autonomous Integrity Monitoring (RAIM) technique is described, using
an Errors in Variables/Total Least Squares approach to the detection of
inconsistencies in an over-determined set of GNSS signal
measurements. The mathematical basis for this technique is presented,
along with results which compare the simulated performance of receivers
using this algorithm against the expected performance of Galileo’s
internal integrity determination system.
