10.2.1.1 Transmission medium

By providing point-to-multipoint communications from a point in space, satellites typically have the ability to create simultaneous links to users on Earth. Moreover, with satellites, capacity can be dynamically allocated in correspondence to the users needs.

Satellites that are used for broadcasting purposes are located in a geostationary orbit near the equator at an altitude of about 36,000 km. Because these satellites move as fast and in the same direction as the Earth rotates, perceived from the Earth s surface, they seem to hang still at a fixed point.

The energy needed for transmission is supplied by the satellite s solar system. As a result of the solar system s low efficiency, the power of the output signal is limited. However, the rich availability of bandwidth counters this limitation. Today s satellite systems use channel bandwidths from 26 MHz to 54 MHz.

The ITU, which acts under the authority of the United Nations (UN), has developed rules and guidelines called Radio Regulations ^[2]. Since 1903 a series of international radio conferences have been held. The...