Wi-Fi assisted GPS positioning with fixed geodetic height

Since signals are blocked by tall buildings, there are always less than four GPS satellites in view in urban canyons, thus position information using standard point positioning may not always be available. Since the development of Internet, more and more Wi-Fi hotspots are being installed in cities. In this context, this paper proposes a method called Wi-Fi assisted GPS positioning using only three satellites and fixed geodetic height. The proposed method includes two steps: firstly, the initial latitude and longitude are obtained by Wi-Fi positioning using a weighted-centroid algorithm; then final coordinates are worked out by combing three GPS observations and the fixed geodetic height. An experiment was carried out in an opening area and results showed that, positioning precision, as compared with that of Wi-Fi positioning, is improved significantly with GPS positioning using the proposed method.