GPS multipath detection and exclusion with elevation-enhanced maps

The reflections of satellite signals in the environment of Global Positioning Systems (GPS) receivers cause significant errors in their position estimates. Particularly critical are the errors due to the so called non-line-of-sight (NLOS) satellites. In a NLOS situation, the only way the satellite signal reaches the receiver is by means of reflections on plane surfaces, typically buildings, causing overestimates of the pseudoranges between the satellites and the antenna. Receivers not always distinguish between the direct signals and the multipath effects, leading to un-modelled GPS errors. This paper presents a solution to the problem of multipath effects in urban areas, by means of simple elevation models of the environment. The description of the buildings is stored in a elevation-enhanced digital map (EEMap) that can be consulted to decide whether a certain satellite may be in direct view or not. The validity of the concept is proven by means of real experiments in built-up areas of Spain.