Satellite Communication Systems

The era of satellite systems began in 1957 with the launch of Sputnik by the Soviet Union.
However, the communication capabilities of Sputnik were very limited. The first real communication
satellite was the AT&T Telstar 1, which was launched by NASA in 1962. Telstar 1
was enhanced in 1963 by its successor, Telstar 2. From the Telstar era to today, satellite
communications [16] have enjoyed an enormous growth offering services such as data,
paging, voice, TV broadcasting, Internet access and a number of mobile services.
Satellite orbits belong to three different categories. In ascending order of height, these are
the circular Low Earth Orbit (LEO), Medium Earth Orbit (MEO) and Geosynchronous Earth
Orbit (GEO) categories at distances in the ranges of 100–1000 km, 5000–15 000 km andapproximately 36 000 km, respectively. There also exist satellites that utilize elliptical orbits.
These try to combine the low propagation delay property of LEO systems and the stability of
GEO systems.
The trend nowadays is towards use of LEO orbits, which enable small propagation delays
and construction of simple and light ground mobile units. A number of LEO systems have
appeared, such as Globalstar and Iridium. They offer voice and data services at rates up to 10
kbps through a dense constellation of LEO satellites.