ITU-R - International Telecommunication Union/ITU Radiocommunication Sector
Scope
Introduction The Global Positioning System (GPS) is a satellite navigation system being established by the United States. The navigational accuracy expected to be available to many users will be about 100 metres (with a 95% probability). This accuracy will be adequate for most general navigation requirements but not for some specific applications@ such as harbour approach@ Vessel Traffic Services (VTS) @ navigational surveying@ dredging@ cable and pipe-laying@ the positioning of buoys and other off-shore structures and position sensors for electronic chart systems. The navigational accuracy of GPS can be improved considerably by the transmission of differential corrections obtained from suitably located reference stations. Consideration of the technical@ administrative and economic factors which influence the choice of the means of transmitting differential corrections has indicated that the use of maritime radiobeacons operating in the band 285 - 315 kHz would be one feasible solution because: - propagation of transmissions in this frequency band is predominantly ground wave with a usable range of the same order of magnitude as the range of applicability of the reference station; - footnote 466 of the Radio Regulations permits radiobeacon stations in the maritime radionavigation service to transmit supplementary navigational information; - maritime radiobeacons currently provide coverage of coastal waters in many parts of the world. This would enable a world-wide standard of differential GPS transmissions to be introduced efficiently and economically. Although the present studies addressed specifically the GPS system@ the same principles apply to other radionavigational@ or satellite navigational systems@ such as Glonass or Loran-C.