Abstract chapter19

The telecommunications industry experienced some spectacular failures around the end of the twentieth century and the start of the twenty-first, but few could compare to satellite companies Iridium and Teledesic.
Its original plans called for a network of 840 satellites. This dropped to 288 satellites, then in February 2002 Teledesic announced that it was planning 20 medium Earth orbit (MEO) satellites.

Satellite communications had its beginning in 1962 with AT&T’s launch of its Telstar 1. Orbiting the Earth in about 2 h, Telstar was visible from the Earth station for less than half an hour, as the antennas followed its track across the sky.
From 1970, it is started satellite station in Mongolia.

Another application, direct broadcast television, was a long time in coming, but now high-quality TV can be received, even in remote locations. Very small aperture terminal (VSAT) enables users to mount small antennas on rooftops to run a multitude of applications such as point-of-sale, which need low bandwidth facilities distributed over a wide range.

A transponder is a radio relay station on board the satellite. Transponders are technically
complex, but their functions are identical with those of terrestrial microwave radio relay stations. Satellites are powered by solar batteries. Power is conserved by turning off
unused equipment with signals from the Earth.

Satellites are connected via intersatellite links to the four nearest neighbors
and to an Earth station.
The hubs control demand assignment to the satellite and monitor and diagnose
network performance.
The remote station has an antenna and a receiving unit, which is about the
size of a personal computer base unit. The primary advantage of VSAT is its ability to support multiple locations.