Research on the Incomplete Constellation GPS Positioning Algorithm Aided by Altitude

GPS positioning is normally required that four GPS satellites are in view at least. However, due to the frequent blockage of GPS signals in worse environmental condition, such as canyons, forests and high buildings and so on, it is difficult to receive the signals of four satellites, that is GPS incomplete constellation. Therefore, the operation of the GPS receiver may be interrupted. Aiming at the poor positioning feature under GPS incomplete constellation environment, the altitude estimating algorithm is investigated, and its improved algorithm which aids the receiver to positioning is put forward. With the weighted altitude added into the navigation equations, which ensured the service of GPS receiver could be continuous even in incomplete constellation. The validation and analysis based on the real GPS data show that this proposed method not only increases availability of GPS positioning, but decreases GPS positioning error. Meanwhile, the method is much more convenient, effective and feasible when it is used in GPS receiver.