1. Introduction to satellite phones

A satellite phone is a phone that uses satellites for communication (receiving and sending signals) instead of terrestrial lines. Ideally, these phones enable communication anywhere around the world irrespective of location whereas normal cell phones require proper terrestrial network coverage to enable communication.

Due to cost and other reasons such as government regulations on use, satellite phones are utilized primarily where there is no access to a telephone or cellular network.

Satellite phone

The major applications of satellite phones can be found in the following areas

• Marine Engineering (Ships)
• Aviation (Aero-planes)
• Military
• Emergency Conditions

2. How are satellite phones different from terrestrial network based cell phone?

A cellular phone functions on the basis of cells ( a cellular radio network distributed over land areas called cells, each served by at least one fixed-location transceiver), and hence are called cell phones. The whole network area is divided into small areas and an antenna is installed in each area. These are also called cell towers. Modern cellular phones in the industrial countries mostly work in the cities and on the major highways. This is because each cell is a radio link from the cell phone to the PSTN; and if a cell phone user is located where there are no cells, there is no service as it is not possible for cellular providers to put up cell towers in rural areas or in countries where there is low usage.

Satellite phones use Low Earth Orbiting (LEO)/MEO (Medium Earth Orbit/Geo-tationary satellites. They do not have any intermediate towers and they do not use cell towers, so communication link rarely gets broken.

3. Features of satellite phones

The features of satellite communication over terrestrial communication are:

1. Satellite phones provide a solution for communication when all other forms of communication are disrupted or limited in cases like earthquakes, floods etc.

2. The coverage area of a satellite greatly exceeds that of a terrestrial system.

3. Transmission cost of a satellite is independent of the distance from the center of the coverage area.

4. Satellite to Satellite communication is very precise.

5. Higher Bandwidths are available for use.

4. Components of a satellite phone network

A typical satellite phone network consists of components. These are

1. Satellite network,

2. The ground stations and

3. Subscriber products (The satellite phones and data units)

Satellite network consists of or more satellites for transmitting the signals for source to destination. For example, Iridium satellite network consists of 66 satellites circles around the earth along LEO. Each satellite traveling at 16,832 miles per hour, each satellite is able to circle the globe every 100 minutes. These satellites act as cellular towers in the sky. Voice and data messages can be routed anywhere in the world by the Iridium network.

The ground network consists of earth stations that are used for command and control, in addition to transmission/reception of user signals. The earth stations also work as Hubs for interconnecting with other communication systems. For example, Iridium gateways interconnect the iridium constellation with public switched telephone network, making communication possible between iridium phones and any other telephone in the world.