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There are three types of satellite communication systems which differ in terms of orbit and signal strength.
1. Low earth orbit (LEO) satellites have small area coverage and they orbit below about 1,800 miles from the earth’s surface.
2. Medium earth orbit (MEO) satellites peak at 9,000 miles and are commonly used in navigation systems such as GPS
3. Geosynchronous earth orbit (GEO) satellites at 22,300 miles and they are positioned over the equator.
The distance of orbit from the earth has an inverse relationship with signal strength and positive one with a satellites lifespan.
Because of their proximity to the Earth, LEO satellites provide strong signals; LEO and MEO satellites are used most frequently by satellite phone services.
A satellite phone is in actuality nothing but a radio transceiver. It sends signals directly to a satellite (part of a network of satellites). When the satellite phone is turned on, the signal goes up to any number of satellites in a compatible constellation where it is then registered with the constellation.
Those signals are then sent back to earth to a station. The Gateway (earth station) processes and takes care of the switching of the calls rather than the satellite network. This station then directs the call to the Public Switched Telephone Network (PSTN) or to a cellular network.
If calling from a cell or wired phone to a satellite phone, the system works in reverse. Or suppose a satellite phone calling another satellite phone. The signal goes up to the satellite, down to earth, back up to a satellite and then back down to earth again.
The frequency specification of a satellite phone is 626.5 to 1660.5 MHz for transmitter and 1525.0 to 1559.0 MHz for receiver.
Shown below is how satellite phones work
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