Nowadays, satellites are used for a variety of purposes, including sensors and data collection, weather, maritime navigation and timing, Earth observation, and communications. In particular, satellite transmissions have an important role in telephone communications, television broadcasting, computer com- nications as well as navigation. The use of satellites for communications was a brilliant idea of Arthur C. ClarkewhowroteafamousarticleinOctober1945intheWirelessWorldjo- nal, entitled “Extra Terrestrial Relays - Can Rocket Stations Give Worldwide Coverage?” that described the use of manned satellites in orbits at 35,800 km altitude, thus having synchronous motion with respect to a point on the Earth. This article was the basis for the use of GEOstationary (GEO) sat- lites for telecommunications. Subsequently, he also proved the usefulness of satellites as compared to transatlantic telephone cables. Satellite communications deserve the special merit to allow connecting people at great distances by using the same (homogeneous) communication system and technology. Other very signi?cant advantages of the satellite - proach are: (i) easy fruition of both broadcast and multicast high bit-rate multimedia services;(ii)provision ofbackupcommunication servicesforusers on a global scale (this feature is very important for emergency scenarios and disaster relief activities); (iii) provision of services in areas that could not be reached by terrestrial infrastructures; (iv) support of high-mobility users.
