Mobile location method for non-line-of-sight situation

Mobile station (MS) location is typically done using trilateration and triangulation techniques. Network aided GPS positioning exhibits good accuracy in a line-of-sight (LOS) propagation environment. In the high-rise urban environment however, where the majority of the rays propagating from the transmission sites to the receiving mobile are non-LOS, the location accuracy is degraded. This paper describes a mapping method used to improve GPS positioning for the non-LOS situation. We use a ray launch simulation tool that combines building height and location with GPS ephemeris information to map the GPS measured position to the actual (true) mobile position. These mappings are dynamically stored in a location database. The implications for emergency call location are tremendous since an erroneous GPS predicted location could still be retrospectively matched with a single record from the database to find the true caller's location. We present an example that shows how the mapping method can be used to predict the NLOS-induced GPS positioning errors.