Page 196 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes Satellite communications technology is often used during natural disasters and emergencies
when land-based communication services are down. Mobile satellite equipment can be deployed
to disaster areas to provide emergency communication services.
One major technical disadvantage of satellites, particularly those in geostationary orbit, is an
inherent delay in transmission. While there are ways to compensate for this delay, it makes some
applications that require real-time transmission and feedback, such as voice communications,
not ideal for satellites.
Satellites face competition from other media such as fibre optics, cable, and other land-based
delivery systems such as microwaves and even power lines. The main advantage of satellites is
that they can distribute signals from one point to many locations. As such, satellite technology is
ideal for “point-to-multipoint” communications such as broadcasting. Satellite communication
does not require massive investments on the ground—making it ideal for underserved and
isolated areas with dispersed populations.
Satellites and other delivery mechanisms such as fibre optics, cable, and other terrestrial
networks are not mutually exclusive. A combination of various delivery mechanisms may be
needed, which has given rise to various hybrid solutions where satellites can be one of the links
in the chain in combination with other media. Ground service providers called “teleports” have
the capability to receive and transmit signals from satellites and also provide connectivity with
other terrestrial networks.

Example: Satellite transmission technologies can be used to bring the signal that needs to
be broadcast to the place where it can be processed and prepared for re-distribution, for example:
to a broadcaster’s main studio; to a number of cable-head end stations; to an Internet Service
Provider where it can be injected into the Internet; or to a network of local Points-of-Presence for
distribution in local networks. These links respond to the need for point-to-point and point-to-
multipoint transmission and are often called a ‘hop’. The signal can be digital or analogue and
can include video, audio, data or multimedia.

12.1.4 The Future of Satellite Communication

In a relatively short span of time, satellite technology has developed from the experimental
(Sputnik in 1957) to the sophisticated and powerful. Future communication satellites will have
more onboard processing capabilities, more power, and larger-aperture antennas that will enable
satellites to handle more bandwidth. Further improvements in satellites’ propulsion and power
systems will increase their service life to 20–30 years from the current 10–15 years. In addition,
other technical innovations such as low-cost reusable launch vehicles are in development. With
increasing video, voice, and data traffic requiring larger amounts ofbandwidth, there is no dearth
of emerging applications that will drive demand for the satellite services in the years to come.
The demand for more bandwidth, coupled with the continuing innovation and development of
satellite technology, will ensure the long-term viability of the commercial satellite industry well
into the 21st century.

12.1.5 Orbits for Communication Satellite

There is only one main force acting on a satellite when it is in orbit, and that is the gravitational
force exerted on the satellite by the Earth. This force is constantly pulling the satellite towards
the centre of the Earth. A satellite doesn’t fall straight down to the Earth because of its velocity.
Throughout a satellites orbit there is a perfect balance between the gravitational force due to the
Earth, and the centripetal force necessary to maintain the orbit of the satellite.
The formula for centripetal force is: F = (mv2)/r
The formula for the gravitational force between two bodies of mass M and m is (GMm)/r2

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