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Unit 12: Space-based Wireless WANs

(unlike a GEO which is only overhead to ground stations on the equator). This can enable Notes
communication in urban areas where obstacles such as tall buildings can block the path to a
satellite. Lastly, the transmission delay is very small.
Any LEO or MEO system however, for continuous operation, requires a constellation of satellites.
The satellites also move relative to the Earth so widebeam or tracking narrowbeam antennas are
needed.

Elliptical Orbits

Figure 12.4: Diagram of Elliptical Orbits

Source: http://www.satcom.co.uk/article.asp?article=11
A satellite in elliptical orbit (figure 12.4) follows an oval-shaped path. One part of the orbit is
closest to the centre of Earth (perigee) and another part is farthest away (apogee). A satellite in
this type of orbit generally has an inclination angle of 64 degrees and takes about 12 hours to
circle the planet. This type of orbit covers regions of high latitude for a large fraction of its orbital
period.

Task Critically examine the different applications of satellite TV viewing depending on
the needs and objectives of the broadcaster or the viewers.

Self-Assessment

State whether the following statements are true or false:
1. Satellites have to be light, as the cost of launching a satellite is quite cheap and based on
weight.
2. Satellite communications play a vital role in the global telecommunications system.

3. By 1924, two TELSTARs, two RELAYs, and two SYNCOMs had operated successfully in
space.

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