pushes the accuracy of positions to centimetric precision (and to millimetric precision for altimetric application and also allows monitoring very tiny seasonal changes of Earth rotation and deformations), in order to build a much more precise geodesic reference system. LEO satellites The two current operational low Earth orbit (LEO) satellite phone networks are able to track transceiver units with accuracy of a few kilometres using doppler shift calculations from the satellite. The coordinates are sent back to the transceiver unit where they can be read using AT commands or a graphical user interface. This can also be used by the gateway to enforce restrictions on geographically bound calling plans. International regulation The International Telecommunication Union (ITU) defines a radionavigation-satellite service (RNSS) as "a radiodetermination-satellite service used for the purpose of radionavigation. This service may also include feeder links necessary for its operation". RNSS is regarded as a safety-of-life service and an essential part of navigation which must be protected from interferences. Classification ITU Radio Regulations (article 1) classifies radiocommunication services as: Radiodetermination service (article 1.40) Radiodetermination-satellite service (article 1.41) Radionavigation service (article 1.42) Radionavigation-satellite service (article 1.43) Maritime radionavigation service (article 1.44) Maritime radionavigation-satellite service (article 1.45) Aeronautical radionavigation service (article 1.46) Aeronautical radionavigation-satellite service (article 1.47) Examples of RNSS use Augmentation system GNSS augmentation Automatic Dependent Surveillance–Broadcast BeiDou Navigation Satellite System (BDS) GALILEO, European GNSS Global Positioning System (GPS), with Differential GPS (DGPS) GLONASS NAVIC Quasi-Zenith Satellite System (QZSS) Frequency allocation The allocation of radio frequencies is provided according to Article 5 of the ITU Radio Regulations (edition 2012). To improve harmonisation in spectrum utilisation, most service allocations are incorporated in national Tables of Frequency Allocations and Utilisations within the responsibility of the appropriate national administration. Allocations are: primary: indicated by writing in capital letters secondary: indicated by small letters exclusive or shared utilization: within the responsibility of administrations. See also Acronyms and abbreviations in avionics Geoinformatics GNSS positioning calculation GNSS reflectometry GPS spoofing GPS-aided geo-augmented navigation List of emerging technologies Pseudolite Receiver Autonomous Integrity Monitoring Software GNSS Receiver Space Integrated GPS/INS (SIGI) United Kingdom Global Navigation Satellite System UNSW School of Surveying and Geospatial Engineering Notes References Further reading Office for Outer Space Affairs of the United Nations (2010), Report on Current and Planned Global and Regional Navigation Satellite Systems and Satellite-based Augmentation Systems. External links Information on specific GNSS systems ESA information on EGNOS Information on the