A complementary ground component is a terrestrial infill system for a mobile-satellite service that uses terrestrial base stations to provide connectivity in weak signal areas, such as urban areas. According to EU Decision 626/2008/EC:
"complementary ground components" of mobile satellite systems shall mean ground-based stations used at fixed locations, in order to improve the availability of the mobile-satellite service in geographical areas within the footprint of the system's satellite(s), where communications with one or more space stations cannot be ensured with the required quality”, page L 172/17, para 18
Such systems use the same frequencies assigned for space usage.
See also Repeater
References