Research On Positioning Techniques For Fewer Than Four GPS Satellites In Urban

With the development of urbanization, GPS has been applied to all aspects of urban life.More and more users need to use GPS positioning and navigation. In order to functionproperly, GPS receiver generally requires that a minimum of four satellite signals bepresented at the same time, in order to solve for three-dimensional coordinates. This minimumrequirement of four satellite signals is particularly difficult to achieve in highly developedurban canyons due to the signals being blocked and interfered in these areas. At this time, theconventional GPS algorithms have been unable to meet their demands. Many approacheshave been proposed for use in conditions of fewer than four satellites. A lot of researches hadfocused on the integration of another sensor such as inertial navigation system orpseudo-satellite. But general consumers can not afford the expensive cost of equipment. Incomparison, it has an important significance to seek new valid algorithm from software forpositioning in conditions of fewer than four satellites.Based on research actuality of GPS in domestic and foreign, this paper investigated GPSpositioning in conditions of fewer than four satellites. It particularly focuses on some aspectsas follows.Firstly, we overviewed the principle of GPS. Based on investigation of polynomial fittingalgorithm and gray system theory in domestic and foreign, we analyzed prediction model ofreceiver clock error based on polynomial fitting and gray theory, and deduced the accuracyassessment formula of the model. Finally these algorithms were tested by collected data.Secondly, a single-point positioning program based on receiver clock-assisted model isdesigned and implemented. Experiments were carried out for testing the accuracy andeffective duration of models. Results presented that the proposed algorithms and modelsproposed in this paper were feasible and valid.