Fusion of WLAN and GNSS observables for positioning in urban areas: The position ambiguity

This paper proposes a positioning method that combines GPS pseudoranges and WLAN ranges when less than four GPS satellites are within sight. To enhance the positioning availability, a tight hybridization approach with both technologies is considered. Although the work has been performed considering WLAN and GPS, most of the presented ideas, procedures and results are also valid for generic tight non-synchronized fusion of GNSS with terrestrial signals. Special emphasis is placed on the phenomenon of positioning ambiguity that appears due to the combination of measurements with different characteristics. To solve this ambiguity, a method is proposed and studied. The availability and accuracy of the system are tested considering different satellite and terrestrial geometries. The results show that the proposed system is able to improve the availability while maintaining the accuracy of GPS as a standalone.