digital radio signal

A satellite radio or subscription radio (SR) is a digital radio signal that is broadcast by a communications satellite, which covers a much wider geographical range than terrestrial radio signals.
Satellite radio is currently at the forefront of the evolution of radio services. Mobile services, such as Sirius Satellite Radio and XM Satellite Radio in the United States, and Worldspace (outside of the USA, Japan, and South Korea) allow a listener to roam across an entire continent, listening to the same audio programming anywhere they go. Other services, such as Muzak's satellite-delivered content require a fixed-location receiver and a dish antenna. In all cases, the antenna must have a clear view to the satellites. In areas where tall buildings, bridges, or even parking garages obscure the signal, repeaters can be placed to make the signal available to listeners.
Radio services are usually provided by commercial ventures, and are subscription-based. The various services are proprietary signals, requiring specialized hardware for decoding and playback. Providers usually carry a variety of news, weather, sports, and music channels, with the music channels generally being commercial-free. source :binarywolf.com