16-09-2009, 11:59 PM
Satellite telephones
there are confirmed reports that terrorists involved in Mumbai blast used sat phones for communication. Most of us are not familiar with satellite telephones. It comes to daily use for those who work in ship, military, disaster management, etc. Most mobile telephone networks operate close to capacity during normal times, and during emergency situations due to large call volumes, the telephone systems get overloaded. Satellite telephones are of use when we need congestion free, portable means of communication. A satellite phone, or sat phone, uses a network different from that of normal mobile phones. These do not use transmitting towers, but makes use of satellites directly. A number of technical challenges are involved in devising a satellite phone system. Path length between earth and satellite introduces significant losses due to divergence. To minimize this, most of the systems use low earth orbiting satellites. But then, a number of satellites are to be used; each satellite will be in view only for a certain amount of time. It is therefore necessary even for a stationary phone to be able to change over from one satellite to another. There are service providers who make use of geostationary satellites as well like Aces, Inmarsat , Thuraya and MSAT. Phones used for satellite communication are often larger in size. The antenna is often larger to ensure the required level of power. Any mobile phone requires speedy communication with the network to enable calls to be set up, controlled and finished. The round trip delay from the mobile to satellite and back to the earth is significantly long, and affects speed of communication and protocol exchanges. As a result, much of intelligence of the system has to be placed within the satellite so that the required protocol exchanges can take place fast. A satellite phone doesnâ„¢t rely on local telephone infrastructure to function. Because of this, they are used widely in regions which are disaster prone. Satellite phones are used widely in ships for communication. They are also used widely for communication in remote area where there are no mobile networks available. There are many disadvantages; high cost of both the handset and call, and bulky handset are some. Satellite phone networks themselves are prone to congestion as satellites cover a very large area with relatively less number of voice channels. Sat phones are built for one particular network and cannot be switched to other networks for dedicated and critical channels, satellite phones are very effective. While popularizing more efficient and strategic technologies, government and people must make sure that they donâ„¢t reach wrong hands. There are confirmed reports that terrorists involved in Mumbai blast used sat phones for communication
