Frequency Division Multiple Access (FDMA)

Wednesday, December 23rd, 2009

FDMA has been the most frequently used technique primarily because it is the simplest to implement. With FDMA, each earth terminal accessing a satellite merely transmits on a different frequency. The available bandwidth is subdivided into smaller frequency bands, or subchannels, in which each subchannel is assigned to a specific user.

Geostationary Orbit

Saturday, September 5th, 2009

This type of orbit is named the “Clarke Orbit” after the visionary science fiction writer Arthur C. Clarke who, in 1945, first described its use for orbiting communication stations. The geostationary orbit is a special type of geosynchronous orbit. This orbit is at 22,300 miles from the surface of the earth. The satellites in this orbit are positioned very close together and the orbit inclination is near zero. The orbit is as circular as possible, therefore eccentricity is near zero.


The geostationary orbit has become the world’s standard for most communications satellites with hundreds of satellites following each other. This orbit is highly controlled to prevent overcrowding of the orbit, space debris, and unauthorized use of resources.

Geosynchronous Orbit

Saturday, August 29th, 2009

In a geosynchronous orbit, a satellite’s motion is synchronized with an area of the earth below it and centered on the equator. The satellite completes an orbit in the same 24-hour period as the earth’s rotation. From the earth, such a satellite appears to be stationary in the sky.


A satellite with this orbit is considered to be in a high altitude orbit at approximately 13,000 to 23,000 miles above the surface of the earth. A geosynchronous orbit is said to be inclined when the plane of the satellite’s orbit is at an angle to the plane of the earth’s equator. For inclinations other than zero degrees, a geosynchronous satellites ground trace will be a figure eight straddling the equator.

Molniya Orbit

Saturday, August 15th, 2009

The Molniya orbit is a high elliptical type of orbit first used by Russia. A satellite in such an orbit is semi- synchronous, spending about six to eight hours of every 24 hours over a particular region of the earth. This is ideal for communications satellites used to provide coverage in the extreme northern latitudes where access to geostationary satellites can be difficult. There are systems of other satellites in Molniya orbits in which ground systems switch among three or four such satellites in order to receive continuous coverage.