Complementary Ground Component
A Complementary Ground Component (CGC) is ground-based infrastructure in a satellite network. The Complementary Ground Component is used to enhance the satellite coverage in highly shadowed areas, such as urban areas, and to enhance in-house coverage. The CGC is used in broadcasting and communication satellite systems that offer services to mobile users. The terrestrial repeaters are also known as gap fillers, because they fill the “holes” in the coverage of the satellite.
The CGC uses the same frequency range as the satellite itself. There excist different forms of complementary ground components. Broadcasting satellite systems can use a ground component that simply repeats the signal from the satellite. This kind of terrestrial repeaters is used in the USA by the XM-Radio and Sirius Radio systems in the 2320-2345 MHz band. A variation of this kind of repeaters is used by the Japanese MBSAT that operates in the 2.5 GHz band. In this system the information is transmitted to the terrestrial repeaters in the Ku band and not directly in the 2.5 GHz band.
In a satellite system for mobile communications a more advanced form of ground component is necessary, because the ground component must also have a return channel. To the mobile station the ground component acts the same as a satellite. The ground component has to be under control of the satellite operator to avoid interference in the satellite system. This kind of ground component is in the United States known under the name of Ancillary Terrestrial Component (ATC).