Terrestrial radio and satellite radio service providers transmit radio programming via the open airwaves, cable networks, and communications satellites. They differ in terms of cost, coverage and capabilities. Some terrestrial radio and satellite radio service providers offer nationwide or regional coverage. Others serve a more limited geographic area such as a state, province, city, or county. Terrestrial radio service provides use land-based antennas and antenna systems for two-way radios, cellular telephones, personal communication systems (PCS), and microwave applications. A terrestrial radio infrastructure uses telecommunications hardware such as filters, amplifiers, duplexers, combiners, multi-couplers, power supplies, surge suppressors, and waveguides. Satellite radio service providers use one or more communications satellites and repeaters. Typically, these repeaters are located in urban areas where tall buildings or tunnels may interfere with line of sight (LOS) transmissions.
Terrestrial radio and satellite radio service providers differ in terms of capabilities. There are three basic types of terrestrial radio service providers: conventional, digital, and trunking. Conventional terrestrial radio uses analog, voice-only communications over a limited geographic area. Digital terrestrial radio is designed for voice and data networks with digital signaling, simulcasting, and multicasting. Trunking systems offer a wider calling range, faster channel access, improved security, and higher talk capacities. In the United States, military and emergency service personnel use a digital cell phone system called terrestrial trunked radio (TETRA). There are two major bands for commercial transmission: AM radio and FM radio. Specifications for terrestrial and satellite radio service providers include communication type and call type. Communication types are specified as analog or digital, voice or data. Call types include: conference, broadcast, group, and emergency calling.
Terrestrial radio and satellite radio service providers include satellite radio services that use communications satellites to broadcast encoded, digital signals to cars, homes and public spaces. Satellite radio service providers can cover a wider geographic area than terrestrial radio service providers and offer multiple channels. Listeners who purchase satellite radios pay a monthly or annual fee for service. Programming via the Internet is also available. When a listener activates a satellite radio subscription, an authorization code is passed to the digital stream, allowing the satellite radio receiver to access the encoded channels. In North America, there are two major satellite radio service providers: XM Satellite Radio and Sirius Satellite Radio. Both XM Radio and Sirius offer more than 120 digital channels of programming. Clear Channel and Viacom are also major terrestrial and satellite radio service providers.