The use of satellite in communication systems has become
very common now - a- days. This is because the satellite
can “see” a very large area of the earth.
Hence satellites can form a star point of a communication
net, to link many users together, simultaneously. This will
include users widely separated geographically.
A communication satellite is a station in space that is used
for telecommunication, radio and television signals.
The construction and launch cost of a satellite are
These costs are “distance insensitive”, that means the cost
of a short distance satellite link is approximately same as
that of a long distance link.
Therefore a satellite communication system is economical
only where the system is used continuously and a large
number of users use it.
• 4th October 1957 first Satellite SPUTNIK-1 (Russia) was
• 3rd November 1957 launched Second satellite SPUTNIK-2
(Russia) carried with female DOG (Laika).
• 1958 first active communication satellite TELSTAR-1.
• 1960 ECHO 1(U.S).
• 1963 first geostationary satellite SYNCOM 2(NASA).
• 1965 The world's first commercial communications
satellite was “Early Bird”, built for the Communications
Satellite Corporation (COMSAT) 240 duplex telephone
channels or 1 TV channel by huges.
• 19th April 1975 India’s first satellite launched by
• 1979 first mobile satellite telephone system INMARSAT.
• 1987 TVSAT first DBS- satellite (Direct Broadcast
satellite, Television broadcasts directly to home).
• 1993 ACTS (NASA).
How does a satellite
1. Two Stations on Earth want to communicate through
radio broadcast but are too far away to use conventional
2. An Earth Station sends message in GHz range. (Uplink)
3. Satellite Receive and retransmit signals back (Downlink)
4. Other Earth Stations receive message in useful strength
5. Main Earth Station is in Delhi, Kolkata, Chennai,
Mumbai and Shilling
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Satellites are divided in four major categories
Geostationary satellites when used for the communication
application are called communication satellite.
They are used in applications such as point to point
communication radio broadcasting, TV transmission,
military application, Commercial application.
Communications satellites are classified based on the
coverage are as global, regional or domestic satellites.
A term “INTELSAT” is often used in satellite
communication. INTELSAT means International
These are communication satellites which are used for
communication of telephony, computer data, TV signals
etc… More than 140 nations are interconnected via the
These satellites are used for weather prediction, for
taking the photographs of clouds. TIROS-1 was the
first weather satellite. Other weather satellites are
Nimbus and Meteosat.
India’s “INSAT” satellite is being used for three
application i.e. communications. TV transmission
and meteorology or weather prediction. Thus it is s
This type of satellites can be used to find out the
condition of crops , forests or minerals underground ,
condition of soil etc. Indian satellite IRS is a remote
From the information obtained from the remote
sensing satellite detailed maps can be prepared.
These satellites are relatively simpler and of short life
They are used to carry out various scientific studies.
India’s “Aryabhatta” was a scientific satellite.
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A geostationary communication satellite is basically a
relay station in space.
It receives signal from one earth station, amplifies it,
improves the signal quality and radiate the signal back to
other earth stations.
Such a relay system allows us to communicate with any
corner of the world.
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The main application of satellite communication is in the
field of communication. The communication of video
signals (TV), audio signals (telephones, satellites phones)
and computer data (internet).
To gain meteorological or weather information. The
photographs taken by the satellites are analyzed for
To monitor the status of earth’s resources such as land,
forests and oceans. We can get very important information
about crops, lakes, rivers, forests, fire etc…
To spot our mineral resources, polluted areas, sources of
In space, satellites move in certain specific paths.
These paths are called as orbits.
A result stays in an orbit because the two forces
acting on it namely the centripetal force and the
gravitational force are equal.
The selection of a particular orbit depends on the
Transmission path loss.
Earth coverage area.
Time period for which the satellite should
Types of Satellite Orbits:-
1. Low Earth Orbit (LEO) satellites.
2. Medium Earth Orbit (MEO) satellites.
3. Geosynchronous Earth Orbit (GEO)
Low Earth Orbit (LEO)
LEO is the short form of low earth orbit satellites.
They revolve around the earth in the orbits which are
500 to2000km above the earth.
LEO satellites don’t stay in fixed position relative to
the surface, and are only visible for 15 to 20 minutes
The time taken for one revolution around the earth is
about one to one and half hours.
Medium Earth Orbit (MEO)
The medium earth orbit satellites (MEO) are at
much lower altitudes as compared to GEO satellite.
MEO satellites are similar to LEO satellites in
Typically the MEO satellites operate in the range of
5000km to 15000km above the earth.
As observed from the earth, they drift slowly in
longitude, taking about 6hours to circle the earth.
MEO satellites have a larger coverage area than
Geosynchronous Earth Orbit
The satellites orbiting in the geostationary orbit are
called geostationary satellites. They travel at the velocity
of revolution of earth, hence complete one revolution
around the earth in one day i.e. 24hours.
This is the reason why geostationary satellites appear to
These satellites are at about 36000km above the earth’s
1.Systems using geostationary satellites:
Inmarsat (International Maritime Satellite
Organization) used for voice, data, especially
for ships worldwide except Polar Regions.
MSAT (Mobile Satellite) used for voice data,
mainly for land mobile western hemisphere.
2.Systems using low-earth-orbit (LEO)
Iridium: major uses are voice, paging, low
Globalstar: major uses are voice paging, low
Teledesic: major uses high speed data, voice.
3.Systems using little LEO satellite:
ORBCOMM: major uses are paging, short
messaging, e-mail, vehicle location.
LEO: one major uses are paging, short
messaging, e-mail vehicle location.
E-sat: major uses are remote meter reading.
4.Systems using Medium earth orbit (MEO):
Ellipso: major uses are voice
communication using portable and mobile
ICO (Intermediate Circular Orbit): major
uses are satellite to mobile links.
Advantages of Satellites:-
• The advantages of satellite communication over terrestrial
The coverage area of a satellite greatly exceeds that of
a terrestrial system.
Transmission cost of a satellite is independent of the
distance from the center of the coverage area.
Satellite to Satellite communication is very precise.
Higher Bandwidths are available for use.
Disadvantages of Satellites
The disadvantages of satellite communication:
Launching satellites into orbit is costly.
Satellite bandwidth is gradually becoming used
There is a larger propagation delay in satellite
communication than in terrestrial communication.
How Satellites are used?
• Service Types:-
Fixed Service Satellites (FSS)
• Example: Point to Point Communication
Broadcast Service Satellites (BSS)
• Example: Satellite Television/Radio
• Also called Direct Broadcast Service (DBS).
Mobile Service Satellites (MSS)
• Example: Satellite Phones