Satellite Phones
Satellite Phone Overview
A satellite telephone or satphone is like a cellular phone which works by communicating through satellite. The satphone receives and sends the signals though satellite moving in the sky. The signals from satphone are picked by the satellite and retransmitted to satellite earth station from where the calls are sent to nearest exchange or onward transmission to the called party. The satellite phones work outdoors only as they need to look towards sky where satellite is located.
The satellite phones work through a satellite system. The satellite phones are designed to work with a particular system as most of the systems are of different type. Thus a satellite phone purchased for one satellite system may not work with other satellite system.
The satellites can be geosynchronous, which rotate above the earth equator in synchronism with earth’s surface, so that they appear stationary looking from the earth. Inmarsat is the oldest commercial geosynchronous satellites providing satellite phone service. Inmarsat was primarily created for making calls from ships. The geosynchronous satellites are located 36000 Kms above the earth and it takes signal around 250 ms sec to make a round trip from phone to satellite and back. This while communicating through geosynchronous satellites there is a delay in voice reception and the conversation style needs a little modification.
The other types of satellite are those which rotate near to earth. These satellites are always moving when seen from the earth. Thus each satellite can only be visible to the satellite phone for short duration & for proper communication a constellation (number) of satellite is used. The advantage of these is that there is no perceptible delay in receiving the voice while communicating. The three main commercial phone service providers using low earth satellites are Iridum, Thuraya, Globalstar etc.
Iridium system is one such constellation of 66 satellites in polar orbit and requires Iridium phones to work with the system. The Iridum network provides complete global coverage.
The Thuraya satellite phone network provides dual-mode GSM and satellite mobile telephone services. It provides coverage over Europe, the Middle East, Central and Northern Africa, Central Asia and the Indian subcontinent.
The Globalstar satellite phone network consists of constellation of 40 satellites. It provides coverage for most of North and South America, Europe, the Middle East, Northern Asia, and Australia.
The satellite phones are portable but bulky due the extra power they need to transmit along with larger battery size required. The smallest satellite phones of Inmarsat system are housed in briefcase size box with one cover of briefcase acting as antenna for the system. The phones using geosynchronous satellites need to look towards satellite to communicate. Each such satellite comes with easy guide to pint the phone antenna towards satellite.
The satellite phone is useful in areas where there are no other phones available such as remote areas, sea, etc. The cost of satellite phone starts from $1000 onwards. The calls made from these phones are expensive. Satellite phone may require special permission from regulatory authorities in some countries.
