Combination of GSM and GPS signals for Mobile Positioning and Location Service Using Kalman Filter

Location based services are becoming an emerging market due to technological advances achieved both at GSM phone operators and the multimedia nature of the mobile handsets. In this paper, a new methodology of mobile positioning integrating both GSM network using signal strengths and GPS readings in the light of an assisted GPS based approach. The methodology employs an extended Kalman filter approach in which the stochastic errors related to various measurements are appropriately characterized and modeled. The methodology uses Netmonitor software to retrieve network information including signal strength and cell-identities of various base transmitter stations (BTS). The distance from the mobile station (MS) to each BTS is therefore determined using Hata-Okumura radio propagation model. The different distances and the GPS readings are therefore combined in the framework of extended static Kalman filter. Once positioning is achieved, a .NET like application is implemented to access the Microsoft MapPoint Web Service, via the Internet (http protocol), which visualises the mobile's location on a map, finds nearby points of interest (POI) and computes routes between them. In order to demonstrate the feasibility of the proposal, experiment is carried out in Birmingham area and compared to the result yielded by the commercial software of MobileLocate Ltd. An accuracy of less than 70 meters has been achieved, which shows substantial improvement over standard Timing Advance related techniques and the commercial software.