Precise positioning with GPS near obstructions by augmentation with pseudolites

Position information is needed in situations that have reduced availability of the GPS satellites due to obstructions which cause high elevation mask angles. Previous research has shown the advantages of pseudolites in determining the carrier cycle ambiguities and in improving the Dilution of Precision (DOP) of positioning. This paper is about the use of GPS carrier phase differential tracking for precise positioning in situations where less than 4 satellites are in view. For example, some open pit mines may have an elevation mask angle of up to 45°, thereby reducing the probability to 20% that 4 satellites are in view for a full position solution. A building near a construction site may obstruct the GPS satellites increasing the DOP beyond the tolerable limit. Pseudolites (GPS ground transmitters) may be placed to provide additional availability as well as increased accuracy. A system providing precise position information was demonstrated using differential GPS carrier phase measurements of satellite and pseudolite signals