Many geolocation systems use radio frequencies to provide two essential items of information: the receiver’s position and the exact time. A large number of applications using this data have been developed, ranging from creating itineraries on smart phones to precision agriculture, where detailed maps of fields are produced to improve crop management. Vehicle pools can be run more efficiently, using less fuel or reducing response times with the help of such data. Other means of transport also use geolocation: trains, ships and aircraft all need to know their positions to ensure the safety of passengers and freight, facilitate operations and optimise routes.
Time-stamping is an application often related to geolocation. Although the main objective of geolocation systems is to supply information on the receiver’s position, transmission of a synchronised time scale, in particular through satellite systems, has led to the development of applications using this function alone. They serve for example for the time synchronisation of electrical distribution networks, for communications (mobile telephones, the Internet) and television broadcasting (digital terrestrial television). They can also provide the precisely time-labelled messages which are of such crucial importance for the reliability of financial transactions and therefore of the banking system as a whole.
Of the various technical solutions for geolocation, one that has progressed in a particularly spectacular fashion in recent years is GPS, an American constellation of satellites sending signals that provide positioning and navigational data. There are other equivalent systems, less familiar to the general public: the Russian GLONASS and the Chinese BeiDou. A European system, Galileo, is now being deployed. All these systems share three frequency bands: 1559-1610 MHz (historic core band), 1215-1300 MHz (extension band) and 1164-1215 MHz (additional extension band).
The Galileo system is being deployed under the aegis of the European Commission by the European Space Agency and the European Global Navigation Satellite Systems Agency. Unlike other systems, it was designed to be a global system operated by civilian authorities and intended for primarily civilian use (although it does include a dedicated governmental signal). This approach is a guarantee of European independence which is a crucial economic necessity in today’s world: the European Commission estimated that some 6 or 7% of Europe’s GDP — close to €600 billion — depends on the accuracy of data supplied by satellite navigation systems.
The Galileo system is in the final roll-out phase and initial services were declared operational on 15 December 2016. Full operational capacity will become available in 2020. The spectrum the system uses has had guaranteed international status since 2003 and is registered with ITU.
At some future time, satellite systems could replace the older terrestrial positioning systems such as DECCA, LORAN and Omega, widely used for ships and aircraft. In contrast, the systems used specifically for aircraft (e.g. DME/TACAN) are likely to survive, mainly due to their resilience.
Some terrestrial positioning systems act as a complement to global satellite systems coverage, in particular to provide precise geolocation inside buildings (e.g. shopping centres or offices). Several technical possibilities are on offer, for instance transmission within such buildings of signals similar to those carried by GPS/Galileo or Wi-Fi networks.
Other ground-based positioning systems aim to reinforce the accuracy of GPS and Galileo signals by supplying corrective “Differential GPS” data, or to improve their reliability with higher reception levels making them less vulnerable to possible interference (pseudo-satellites or “pseudolites”).