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IRIDIUM TECHNOLOGY

The IRIDIUM phones and pagers work anywhere in the world by communicating with both terrestrial wireless networks and the Iridium network. Putting this technology in place represents a significant engineering achievement in satellite manufacture and deployment

With 66 satellites forming a cross linked grid above the earth ,Iridium system is the first low earth orbiting system for wireless telephone service. Only 780 km. high ,these satellites work differently from those at a much higher orbit(36,000 km.) in two major ways. First they are close enough to receive the signals of a handheld device and second ,they act like cellular towers in the sky where wireless signals can move overhead instead of through ground-based signals. The Iridium network integrates land-based phone lines, local cellular coverage and satellites.

IRIDIUM TELEPHONES

The Iridium phone is the primary means by which callers can communicate directly through the Iridium network. It’s multi-mode capability allows the telephone to work as a typical cellular phone(in areas where compatible cellular services exists)and as a satellite telephone. For Iridium subscribers this means one handheld phone providing both cellular and satellite access.

Located in key regions around the world, Iridium gateways interconnect the Iridium constellation with public switched telephone networks, making communication possible between Iridium phones and any other telephone in the world.

The Iridium system will employ a combination of frequency division multiple access and time division multiple access (FDMA/TDMA) signal multiplexing to make the most efficient use of the limited spectrum.

COMPARING IRIDIUM AND OTHER GLOBAL SATELLITE SYSTEMS

Comparing Iridium and other global satellite communication systems is like comparing apples and oranges. This is because the satellites used in the iridium system are quite different from your standard run of the mill satellite. The typical communications satellite is a signal repeater. It receives a signal on the uplink frequency and retransmits the signal on its downlink frequency. An Iridium satellite receives its data on the uplink frequency, but instead of just bouncing it back down to earth, it will decode the signal and route the corresponding calls to its four neighbor satellites. The satellite can be thought of as a node in a packet switching network. It will route data received from other iridium satellites as well as transmit or receive data from earth. The only time that the ground station is accessed is when a call is placed. The satellite that receives the call contacts the main ground station to determine where about in the world the destination phone is, and to set up billing information. 

Raina Bijlani ( B.E. Tele.) & Nishant Jadhav (B.E.Tele.)

©1999 IEEE VESIT Student Branch  Hits :

Webauthor : Saumitra M Das