Describe The Design Of Iridium System And Also Its Purpose?

The concept of iridium system, a 77-satellite network was started by Motorola in 1990. The project took 8 years to materialize. Iridium has gone through rough times. The system was halted in 1999 due to financial problems. it was sold and restarted in 2001 under new ownership.

The system has 66 satellites divided into six orbits, with 11 satellites in each orbit. The orbits are at an attitude of 750 km. The satellites in each orbit are separated from one another by approximately 32 of latitude. Since each satellite has 48 spot beams, the system can have up to 3168 beams. However, some of the beams are turned off as the satellite approaches the pole. The number of active spot beams at any moment is approximately 2000.

Each spot beam covers a cell on the earth, which means that the earth is divided into approximately 2000 overlapping cells. In the iridium system, communication between two users takes place through satellites. When a user calls another user, the call can go through several satellites before reaching the destination. This means relaying is done in space and each satellite needs to be sophisticated enough to do relaying.

The whole purpose of iridium is to provide direct world wide communication using hand held terminals. The system can be used for voice, data, paging, fax, and even navigation. The system can provide connectivity between users at locations where other types of communication are not possible. The system provides 2.4- to 4.8- Kbps voice and data transmission between portable telephones. Transmission occurs in the the 1.616- to 1.6126- GHz Frequency band. Inter satellite communication occurs in the 23.18- to 23.38- GHz frequency band.