What is the principle of iridium system?

To realize global personal communication, we need a modern communication network that can cover the whole world without any "dead angle". This network should be able to find and track every elusive user automatically and very quickly. In addition, it is also required to have very portable, compact and movable communication terminal equipment, such as telephones, fax machines and data terminals.

At present, many international consortia are participating in the competition to develop global personal communication systems. Among the systems being developed, Motorola's "Iridium System" is particularly eye-catching.

"Iridium system" is actually a low-orbit global satellite mobile communication network. The satellite "constellation" consists of 66 low-orbit satellites with an operating height of more than 780 kilometers. These 66 small satellites with a diameter of about 1 m are distributed in six elliptical orbits, and each orbit is 1 1. The radio waves emitted by these satellites cover the whole earth. When any phone in the system is started, the nearest satellite and Iridium Network will automatically verify the account number and its location. Then, the user can choose to use cellular communication system or satellite relay system to transmit the information to the destination. Using microwaves, information is relayed between 66 satellites, which shuttle back and forth, much like the relay race of athletes. On the ground, an earth station named "Gateway Station" connects the iridium satellite system with the ground public telephone network, so that any telephone, fax machine, pager and data terminal on the ground can establish communication links with other communication terminals through the iridium satellite system.

For global personal communication, each user has a unique "personal number" that belongs to him. It is estimated that by 200 1, there will be as many users with personal numbers as 1.8 million, joining the ranks of iridium satellite systems. If users of other similar systems are added, the global personal communication will have a considerable scale.