8.4 Satellite services

One of the effective applications of SSS is the organization of television and radio broadcasting using communication satellites. In this case, the programs of the central studios of television and radio broadcasting are transmitted to the network of earth stations receiving satellite signals via repeaters of communication satellites. The further distribution of these signals over the terrestrial network is carried out in the traditional ways: via over-the-air or cable (wired) broadcasting.

Depending on the purpose of satellite communication systems and the type of earth stations, the following radiocommunication services are distinguished:

• fixed satellite service - for communication between stations located at specific, fixed points, as well as distribution of television programs;
• mobile satellite service - for communication between mobile stations located on vehicles (airplanes, ships, cars, etc.);
• the broadcasting satellite service for the direct reception of radio and television programs at terminals located at subscribers.

The fixed satellite service traditionally develops in the direction of creating backbone communication systems based on powerful earth stations with antenna systems of several tens of meters in size. Of the international communication systems, the most well-known is InTelSat, with the satellites transmitting about 2/3 of international telephone calls and the overwhelming majority of television programs. The Russian system Orbit uses satellites in the high elliptical orbit Molniya and the geostationary satellites Raduga and Horizont.

The mobile satellite service supports communication systems in which at least one station has been installed on mobile objects. For example, the InMarSat maritime satellite communications system, using geostationary satellites, provides communications between ships and coast stations in the Atlantic, Indian and Pacific oceans.

The combination of advances in microelectronics and space technology made it possible to create communication systems with acceptable characteristics based on low-orbit satellites. Low orbital height does not allow to establish long communication sessions with one satellite. The continuity of communication in such systems can be ensured by increasing the number of satellites that are simultaneously in orbit and alternately fly around the territory they serve. The low cost of launching light satellites makes it economically viable to place several dozen satellites in orbit simultaneously.

In satellite communication systems using low-orbit satellites, different communication arrangements between subscribers are possible. If both subscribers are in sight of one satellite, a direct radiotelephone connection is established between them through the satellite repeater. If subscribers are in sight of different satellites, then a special communication channel between these satellites is established. If the satellites are within mutual visibility, a special inter-satellite radio link may be established between them. In addition, communication between satellites can be established through terrestrial communication networks to which earth stations are located, which are in view of each of the satellites.

The broadcasting satellite service for the direct reception of television broadcasting (NTV) provides subscribers with television programs in the frequency range of 12 gigahertz. This frequency range is chosen from the condition of minimizing the cost of onboard and ground equipment of satellite communication systems. For direct reception of satellite television programs, subscribers (collective or individual) must have additional equipment. The equipment for receiving and converting signals from a satellite uses a converter (frequency converter of a signal from a satellite) and an antenna system with an antenna remote control device, which is used to set the direction of the antenna to the selected geostationary satellite.