Prediction of GNSS availability and accuracy in urban environments – case study schiphol airport

Abstract

Because of the increased call for positioning in urban areas, the performance of GNSS is analyzed under conditions with a decreased satellite visibility caused by buildings blocking the lines of sight. With GPS and Galileo almanacs and two city models visibility fingerprints of time-location combinations are computed. Outdoor availability and accuracy are predicted for both city models: Real-life data of Schiphol Airport, and an imaginary urban canyon model (located in the same area as Schiphol) with variable parameters for street width, street length and building block height. The accuracy is predicted based on dilution-of-precision values. GPS, Galileo, and a combined constellation are considered for single-frequency singleepoch positioning. Even for mildly difficult urban environments 95% availability is not reached for GPS (or Galileo) close to buildings or in streets in north-south directions. In the combined GPS-Galileo constellation a substantial improvement of 30%–50% availability can be reached as compared to GPS only for those locations where GPS availability is already more than ~10% (under severe conditions such a high increase cannot be achieved). At Schiphol Airport, however, conditions are very mild since there are only a few enclosed areas, surrounded by more than one building block and in most vital areas 95% availability can be reached even with GPS only. The accuracy close to the buildings and piers is, on average, decreased however, up to a factor of about three very close to buildings. This effect is even larger on the south-west and south-east side of buildings because there the high satellite density in north-east and north-west directions cannot be exploited.