Low Satellite Visibility Areas: Extension of the GPS Capabilities to Deploy Location-Based Services

In this article, the use of IEEE 802.11 technology is used for the problem of augmenting the coverage of satellite positioning systems when less than four satellites are visible, by using a low complexity and effective technique involving a terrestrial radio technology. The solution consists of processing the information received by the terrestrial infrastructure for introducing virtual satellites to obtain the minimum number of satellites needed for fixing the receiver position. The feasibility and the achievable performance is demonstrated experimentally by implementing real prototypes using either sophisticated or low-cost receivers in different experiments. The results obtained are comparable, in terms of error magnitude, with those of a plain GPS receiver when four satellites are visible.