GPS integrity monitoring for an intelligent transport system

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.