Real time differential GPS and GLONASS vehicle positioning in urban areas

This paper describes a research programme carried out by the Institute of Satellite Positioning (ISN) and Racal Survey Ltd. to examine the performance of differential positioning using both the GPS and satellite systems for vehicles. The work involved developing a differential GNSS positioning system for a vehicle using GNSS receivers developed by the ISN and Ashtech and using Racal´s Landstar differential system. The programme has involved extensive real-time vehicle positioning trials in urban areas. Two aspects of vehicle positioning performance have been concentrated on, (i) fix density, and (ii) positioning accuracy. The results show that combining GPS and GLONASS significantly improves both stand-alone and differential positioning accuracy compared to using just GPS alone. The results also show that combined GNSS supports a greater differential correction age without the same accuracy degradation that GPS exhibits. This, in turn, increases the GNSS fix density. Even with the same correction age, GNSS has 10% fix density improvement. This increase in fix density will allow improved vehicle positioning in an in-car navigation system with a lower level of augmentation with other sensors