How to Use a Global Positioning System Without the Satellites

GPS receivers have become widely used in recent years, with satellite signals being used in navigating airplanes, ships and automobiles, and in cell phones, mining, surveying and even transferring money, but even the most expensive piece of technology can't function without a satellite uplink.

Is it? Well, almost. The northern regions, like the Scandinavian countries, can't use the GPS like the other countries, because of their low angle of view to the geosynchronous satellites that make up the system, meaning that the GPS coverage is much reduced.

To compensate for the geographical and technical difficulties, authorities in Helsinki harbor in Finland, deployed a network of pseudo-satellites, that can form a small scale GPS system, without the S. Two or three of these false satellites are usually installed in elevated locations and they transmit data sent by the European Geostationary Navigation Overlay Service (EGNOS) network and its data access system to the ships traveling through the harbor.

The system uses a sort of triangulation, the process of finding coordinates and distance to a point by calculating the length of one side of a triangle, given measurements of angles and sides of the triangle formed by that point and two other known reference points, using the law of sines.

Maximum range can vary between 1 and 10 kilometers, because the user terminals are actually pocket-PCs that can be carried by officials in various points of the port and can use a navigation software, coupled with a receiver unit that can track multiple pseudolites.

Signals are greatly amplified by the fact that these pseudosatellites can be placed in various points around the harbor, wherever GPS/EGNOS navigation is unavailable or poor, thus providing improved accuracy.

The psychological effects are also positive, since ship captains will know they can trust these applications even in bad weather or when satellite signal is unavailable.