The integrity of positioning systems has become an increasingly important requirement for location-based ITS applications, such as electronic toll collection, pay-as-you-drive
and traffic control systems. GPS receivers are used to provide
vehicle position and velocity data. However, GPS cannot provide
the high quality positioning information required by ITS
applications due to atmospheric effects , receiver measurement
errors, and multipath errors. In addition, some ITS applications,
such as traffic law enforcement systems (e.g., speed fining), have
legal or economic consequences and require integrity in both
position and speed information. Therefore, the integrity of GPS
data is required to guarantee that navigation systems will not
produce misleading or faulty information. Instead, to achieve the
integrity goal, systems should warn the user if there is a potential
error in the GPS data. In this paper, a new technique for
providing high integrity GPS information for land vehicle
monitoring systems is proposed. The proposed method provides a
three level integrity check. Each level uses a different technique
to check the consistency of the GPS information. A receiver
autonomous integrity monitoring (RAIM) algorithm is used to
measure the quality of GPS positioning output. GPS Doppler
information is used to check the integrity of vehicle velocity,
which adds a new layer of integrity and could improve the
performance of the map matching process. The final level in the
integrity check requires confirming the integrity of the map
matching algorithm.