Eleven gateways are scheduled to be in operation at the commencement of commercial service. Gateways are owned, operated and financed by one or more Iridium investors or their affiliates. These stations consist of equipment to communicate with the satellite constellation and with the international switching centers of the domestic fixed network. Their functions include registering of Iridium subscribers and providing access to existing ground-based telephone networks, so achieving the connectivity of the telecommunications networks worldwide. Interconnection to the existing wired and wireless networks, domestic and international, public and private, is performed through ground-based Iridium gateways which are located in key regions of the world. Gateways in the Iridium Communications Network make communications possible between Iridium telephones and any other telephone in the world.
The Ka-Band (19.4-19.6 GHz for downlinks 29.1-29.3 GHz for uplinks) serves as the link between the satellite and the gateways and Earth terminals. The Iridium subscriber equipments have been authorized by the European Administrations to operate in the band 1621.35 – 1626.5 MHz for both uplink and downlink. The L-Band serves as the link between the satellite and IRIDIUM subscriber equipment. The Iridium Communications Network utilizes a combination of Frequency Division Multiple Access and Time Division Multiple Access (FDMA/TDMA) signal multiplexing to make the most efficient use of limited spectrum. The transmissions take place in the Ka frequency band between 23.18 and 23.38 GHz. Intersatellite crosslinks reduce the number of Earth stations required and allow for lower operating costs compared to other systems in the Iridium Communications Network. By routing a call through the satellite network, the Iridium system is not dependent on availability of extensive terrestrial telecommunications facilities to deliver global telecommunications. These intersatellite links are essential for providing truly global communication coverage.Īs the only proposed mobile satellite service using intersatellite links, the IRIDIUM system allows users to make and receive calls from anywhere on Earth, including polar and ocean regions. True global connectivity is provided because each satellite is connected by radio transmission to four others through the use of crosslink antennas. The satellite constellation is controlled by a sophisticated ground control network, located in the U.S.A. Each satellite covers an area 4,000 kilometres wide, providing links to all Iridium subscribers roaming in such an area.ĭeveloped by Motorola’s Satellite Communications Division (SATCOM) in Chandler, Arizona, U.S.A., Iridium satellites within the Iridium Communications Network required impressive standards of manufacturing. In contrast with traditional wireless systems, coverage is achieved by satellites that project a grid of cells over the surface of the Earth. The satellite within the Iridium Communications Network is linked to callers by a main mission antenna that offers 16 decibels of link margin, a signal that is strong enough to deliver high quality communications to a hand-held telephone. Unlike geostationary communications satellites which are located 36,000 kilometres above the Earth, the Iridium satellites’ low Earth orbit makes it possible for the Iridium Communications Network directly with a hand-held telephone, in the meantime avoiding the typical delay of geostationary satellite transmissions. The satellite constellation is distributed on 6 near polar planes and each plane carries 11 operational satellites, as well as one spare satellite.Įach satellite weighs approximately 689 kilograms (1,500 pounds) and orbits at an altitude of 780 kilometers (420 nautical miles) above the surface of the Earth traveling around the planet once every 100 minutes. The Iridium Communications Network system is based on a network of 66 satellites.