Satellite Phones

Satellite Phones

Abstract-- This document gives overview of Satellite Phones

technology in terms of its evolution, parameters, advantage over other technology. This paper also briefs different service providers of satellite phones and their features also its scope in india.

I. INTRODUCTION

A satellite phone or sat phone is a mobile phone that sends and receives calls using satellites rather than landlines or cellular broadcasting towers

Sat phones are divided into 3 types: Installed, Laptop and Hand Held

All sat phones allow communication to the standard telephone network i.e. direct dial voice, fax and data communications

Satellites used for sat phones are basically

II.Geosynchronous satellites

Geostationary satellites, orbit around the equator in the same direction as the Earth rotates. They are positioned at a height above the Earth such that the same time for the satellite to complete its orbit is the same as the time it takes for the Earth to rotate once about its axis i.e. 24 hours

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Polar satellites

Polar satellites travel around the Earth in an orbit that travels around the Earth over the poles. The Earth rotates on its axis as the satellite goes around the Earth. Thus over a period of many orbits it looks down on every part of the Earth

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III.Data Transmission

Most satellite services permit data as well as voice to be sent and received.However, all such services have very slow data bandwidths, typically in the realm of about 2400 baud (ten to twenty times slower than a regular dialup modem, and 50+ times slower than broadband).

Add the slow data transfer rate to the reasonably high cost per minute of airtime, and you won't want to use your satellite phone to access the internet for casual web surfing.

Most of the satellite services allow for fax transmission.

IV.Signal Coverage

Satellite phone signals are very weak, and there needs to be an unobstructed line of sight between your phone's antenna and the satellite it is communicating with.

This means satellite phones will generally not work indoors, unless you are by a window and the window - by good chance - happens to be looking out to that part of the sky where an Iridium satellite currently is the Iridium satellites are moving all the time, there is no rule of thumb (such as 'you need to have a view of the southeast sky') as might have been the case with fixed satellites in terms of where to look for satellites. Satellites may be anywhere - north, south, east or west, and because they move across the sky quite quickly, if you start off a call with a clear view to a satellite, if the satellite then moves behind something that blocks your view to the satellite, and if there are no other satellites in clear view, your call may be dropped.

V.SATELLITE PHONE SERVICES

The four main satellite networks at present are Iridium, Globalstar, Thuraya and Inmarsat

1.Inmarsat

It started operations in 1979 as a non profit organization. It was launched to provide safety at sea.

Later the Inmarsat began to be used for commercial purposes.

Coverage is very good, being provided from a network of geosynchronous satellites, but doesn't extend all the way to the north or south poles

It is probably too bulky for people seeking a convenient portable solution

2.Thuraya

Started operating in 2001

Thuraya covers parts of India, Asia, Africa, the entire Middle East and Europe

It uses geosynchronous satellites

They cost about half the price of an Iridium phone

FEATURES:

SMS capability

9.6 kbits/s of data & fax service

60 kbit/s downlink and 15 kbit/s uplink

144 kbit/s high-speed data transfer

GPS is supported by all handsets

A number of value-added services, such as news, call back, call waiting, missed calls, voicemail, WAP, etc.

3.Globalstar

This service rolled out in late 1999

Globalstar covers about 80% of the earth's landmasses, excluding northern and southern polar regions

With over 315,000 subscribers (as of June 2008), Globalstar is the world's largest provider of mobile satellite voice and data services. Globalstar offers these services to commercial and recreational users in more than 120 countries around the world.

It uses LEO satellites

Offers data as well as voice service

Most Globalstar providers have roaming agreements with local cellular operators, enabling the use of a cellular SIM card with a Globalstar handset and vice versa.

4.Iridium

The concept that was to become Iridium was first mooted in the mid 1980s and the concept formalized in 1987, then developed during the 1990s

Bankruptcy in 1999

It is the only current satellite network that provides coverage over the entire earth, including the oceans

The current satellites are projected to remain operational at least through 2014

FEATURES:

The