Satellite Communications

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Basics: Advantages of Satellites

The advantages of satellite communication over terrestrial communication are:
The coverage area of a satellite greatly exceeds that of a terrestrial system.
Transmission cost of a satellite is independent of the distance from the center of the coverage area.
Satellite to Satellite communication is very precise.
Higher Bandwidths are available for use.


Basics: Factors in satellite communication

Elevation Angle: The angle of the horizontal of the earth surface to the center line of the satellite transmission beam.
This effects the satellites coverage area. Ideally, you want a elevation angle of 0 degrees, so the transmission beam reaches the horizon visible to the satellite in all directions.
However, because of environmental factors like objects blocking the transmission, atmospheric attenuation, and the earth electrical background noise, there is a minimum elevation angle of earth stations.


Basics: How Satellites are used

Service Types
Fixed Service Satellites (FSS)
Example: Point to Point Communication
Broadcast Service Satellites (BSS)
Example: Satellite Television/Radio
Also called Direct Broadcast Service (DBS).
Mobile Service Satellites (MSS)
Example: Satellite Phones

Geostationary Earth Orbit (GEO)

These satellites are in orbit 35,863 km above the earth’s surface along the equator.
Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth.

LEO
Disadvantages
A network of LEO satellites is needed, which can be costly
LEO satellites have to compensate for Doppler shifts cause by their relative movement.
Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.

MEO
Advantage
A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network.
Disadvantage
A MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite.