Iridium Mobile Communication in LEO Satellite System

Iridium system is a global satellite mobile communication scheme proposed by Motorola. This is the earliest known LEO satellite system. Fund raising and technology development are progressing smoothly. Technically, Motorola's technicians verified all the arguments in the laboratory. The simulation test has achieved satisfactory results.

The initial design of iridium satellite system is that 77 small intelligent satellites are evenly and orderly distributed on seven orbital planes 785 kilometers from the ground, forming a global connection network through microwave links. Because it is similar to the outer electron distribution of iridium atom, it is named iridium system. Later, in order to reduce the investment intensity, simplify the structure and enhance the competitiveness with other LEO systems, Motorola reduced the number of its satellites to 66 and the orbital plane to six circular polar orbits. The number of satellites in each polar orbit was still 1 1, the orbital height was changed to 765KM, the satellite diameter was 1.2M, the height was 2.3M, and the weight was 3,800.

Iridium satellite system mainly consists of the following parts: satellite constellation, ground control facilities, gateway stations and user terminals (voice, data and fax). Each star can provide 48 (originally designed as 37) spot beams, each beam contains 80 channels on average, and each star can provide 3840 full-duplex circuit channels. Each star uses interplanetary cross links as networking means, including forward-looking and backward-looking links connecting two adjacent stars in the same orbital plane, and two links with satellites in different orbits. The system has the functions of space exchange and routing. The system adopts "inverted" honeycomb structure. The multi-beam projected by each star forms 48 honeycomb areas on the earth's surface, each with a diameter of about 667KM. They are combined with each other, with a total coverage diameter of about 4000KM, and there are 2 150 communities in the world. The system adopts seven-cell frequency reuse method, and any two cells using the same frequency are separated by two buffer cells, which can

The basic structure and processing of iridium satellite system are all on the satellite, and the honeycomb area quickly sweeps across the earth's surface with the earth's rotation. The handover of iridium satellite system is that the cells move across users, not users move across cells, which is different from the future public land mobile telecommunication system. Iridium system costs about $3.4 billion. It was first published in June 1990. 1990 applied for a license from the FCC of the United States in February, and obtained the license from the FCC in September 1992. At that time, iridium satellite system was the most complete and concrete design scheme, which made rapid progress and was a very promising scheme. Unfortunately, due to various reasons, the iridium system fell short and declared bankruptcy!