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Satellite Phones

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Information about Satellite Phones
Technology

Published on February 25, 2014

Author: RamohanCHINTA

Source: slideshare.net

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Introduction: Communication is defined as exchange of thoughts, messages, or information, as by speech, signals, writing, or behavior. Types of communication system:  Communication systems are broadly classified as   Wired Wireless  An advanced wireless communication system includes the following types;  Satellite communication  Mobile communication  And now narrowing down to satellite communication:   Satellite phone Global positioning system

SATELLITE PHONE:  A telephone that transmits and receives from satellites that provides coverage around the world. Over eighty percent of the land on earth plus any body of water (we're talking oceans here) is without sufficient landline connection, depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions.

Need for Satellite Phone Systems:  There are only two ways to hook up two telephones in different parts of the world: they can be connected by a cable which runs on the surface of the earth and under the sea, or they can be connected by radio.  Not every place on the earth is served by a cable connection to the Public Switched Telephone Network (PSTN), and thus some locations must either have no telephone service or be connected to the PSTN by a radio link.

TYPES OF SATELLITE PHONE SYSTEMS:     There are four different satellite phone systems that have reached general popularity. They are GLOBALSTAR INMARSET IRIDIUM: THURAYA

WORKING:  Even though it is called a "phone", the satellite phone is in actuality a radio transmitter. It sends signals directly to a satellite (part of a network of satellites.).  When you turn on your satellite phone 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 you are calling from a cell or wired phone to a satellite phone, the system works in reverse.  think of 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.

LINE OF SIGHT:  With most satellite communication devices we need Line-of-Sight to the satellite we are communicating with which include GPS devices, satellite TV, satellite Internet, satellite modems, hand held satellite phones and fixed site satellite phones.  When using a hand held satellite phone we need at least 80% view of the sky to receive good service or we must use an external antenna with an 80% view of the sky.  The success in making calls would depend on where the satellites are positioned at the moment the phone is used. Globalstar and Iridium both have LEO Low Earth Orbiting satellites.

LOW EARTH ORBIT:  A LEO telephones utilizes LEO (low Earth orbit) satellite technology. This includes provision of worldwide wireless coverage with no gaps. Newer satellite phones tend to be LEOs.  LEO satellites orbit the earth at high speed, low altitude orbits with an orbital time of 70–90 minutes, an altitude of 640 to 1120 kilometers (400 to 700 miles), and provide coverage cells.  Since the satellites are not geosynchronous, they must fly complete orbits and thus further guarantee complete coverage over every area by at least one satellite at all times. Blimps are being considered as an alternative to satellites.

APPLICATIONS:  It is highly useful in rescue operations at the times of disasters.  It is also used by the deep sea vessels for communication.  The phones are mostly used by the confidential system of any nation.

ADVANTAGES:  Tracking the data transmitted is impossible.  This system covers the entire globe.1  This communication does not rely on land line systems.  Towers on the Earth are not required. DISADVANTAGES:  DELAY  BANDWIDTH  AFFORDABILITY

CONCLUSION:  However, these drawbacks are irrelevant when considering the function that a satellite phone serves. It can create a link to civilization from places where no other link is available.  It also allows loved ones to stay in touch, as in the case of researchers, adventurers and those in the military, and it can provide backup communication in disasters when cellular towers or landlines might not be functional.

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