Introduction to Data Communications
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The uplink is the transmitter of data to the satellite. The downlink is the receiver of data. Uplinks and downlinks are also called Earth stations due to be located on the Earth. The footprint is the "shadow" that the satellite can transmit to. The shadow being the area that can receive the satellite's transmitted signal.

16e. Iridium Telecom System

The Iridium telecom system is a new satellite sytem that will be the largest private aerospace project. It is a mobile telecom system to compete with cellular phones. It relies on satellites in Lower Earth Orbit (LEO). The satellites will orbit at an altitude of 900 - 10,000 km and are a polar non-stationary orbit. They are planning on using 66 satellites. The user's handset will require less power and will be cheaper than cellular phones. There will be 100% coverage of the Earth.

They were planning to launch starting 1996-1998 and having 1.5 million subscribers by end of the decade. Unfortunately at the time of this writing, the Iridium project looked very financially unstable.

Introduction to Data Communications
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