Types of Satellite Networks
A Satellite Network is a combination of a satellite, earth station, end-user terminal or even a telephone. The basic objective of this is to transmit data from one point of the earth to another. In this type of network artificial satellites are used for communication to take place. Depending on the height of the orbit from the earth’s surface, there are mainly four types of satellites:
1. Geostationary Earth Orbit (GEO) satellites
2. Medium Earth Orbit (MEO) satellites
3. Global Positioning System (GPS) satellites
4. Low Earth Orbit (LEO) satellites
Geostationary Earth Orbit (GEO): Line of sight communication requires the sending and receiving stations to be locked to each other and for this to achieve the satellites must rotate at the same speed as the earth. These types of satellites are known as Geostationary Earth Orbit Satellites. They are always seen from some region on the earth’s surface.
The Geostationary Satellites can only be placed in the Geostationary orbit which is at a height of 35786 km above the earth’s surface and it lying in the equatorial plane. At least three Geostationary satellites are required to cover the whole earth’s surface. They are placed equidistant from each other making an angle of 120° at the centre of the earth.
Medium Earth Orbit (MEO): These satellites are placed between the two Van Allen belts. These satellites take about 6 hours to resolve the earth.
Global Positioning System (GPS): 24 GPS satellites are placed in 6 orbits at a height of about 18000 km from the earth’s surface. The orbits and the location of the satellites are such that at any point in time and from any point on the Earth’s surface four satellites are visible. A GPS receiver knows the current position of the satellites. It then sends signals to each of the satellites which are visible to it and calculates the return time. It measures the position of the earth’s surface.
Low Earth Orbit (LEO): These satellites lie at an altitude of 500 to 2000 km and take 90 to 120 min to revolve around the earth. It rotates at a very high speed of 2000 to 25000 mph. The footprint has a diameter of 800 km. As these satellites are very close to Earth the round-trip propagation delay is normally less than 20 msec which is quite acceptable for audio communication.