2. • Satellite technology has progressed tremendously over the last 50
years since Arthur C. Clarke first proposed its idea in 1945 in his
article in Wireless World.
• Today, satellite systems can provide a variety of services including
broadband communications, audio/video distribution networks,
maritime navigation, worldwide customer service and support as
well as military command and control.
• Satellite systems are also expected to play an important role in the
emerging 4G global infrastructure providing the wide area coverage
necessary for the realization of the “Optimally Connected Anywhere,
Anytime” vision that drives the growth of modern telecom industry.
3. • The use of satellite in
communication system is
very much a fact of everyday
in life.
• This is evidence by the many
homes, which are equipped
with antennas and dishes.
• These antennas were used
for reception of satellite
signal for television.
• What may not be well
known that satellites also
form an essential part of
communication system
worldwide carrying large
amount of data, telephone
traffic in addition to
television signals.
4. REQUIREMENT FOR SATELLITE
COMMUNICATION
• The communication
between one point to
other depends upon
frequency of the
transmitted signal as well
as mode of
communication.
• The frequency up to
appropriately 10 MHz was
used for small distance
• Satellite & Cable TV
communication through
Ground Wave Propagation
5. • As frequency increases, the attenuation of ground wave
increases (Earth starts behaving like absorber for high frequency
signals) because of which, it is not possible
to establish a reliable communication link through ground waves for
frequencies more than 10 Mhz.
Since Earth is elliptical in shape, thus direct wave which are reaching
at receiving antenna are restricted by
curvature of Earth (The direct wave communication is not possible
beyond Line of Sight).
6. • The above limitation for long distance communication requires a
reflector above the earth surface, which reflects the signal towards
receiving antenna.
• The Sky Wave Propagation is possible due to Ionosphere present in
the atmosphere.
• The ionosphere has property that it reflect transmitted signals up to
a certain frequency and after that the layer is behaving as
transparent medium and signal passes the layer.
• This natural reflector present in the atmosphere provides radio
broadcasting link to larger area of Earth beyond Line of Sight
7. • The signals having frequency more than 30 MHz are pass
through ionosphere and these are required to reflected back
to earth by some artificial medium for establishing reliable
communication between transmitter and receiver.
• For fulfilling the requirement of high frequency and long
distance communication across the globe, the artificial
reflector (Satellite) above the ionosphere are required for
transmitted signal.
8. • The satellites were used for reflecting the signals having frequencies
more than 30MHz.
• The transponders in the satellite receive the signal and after signal
conditioning (suppressing noise, amplification) re-transmit back to
ground for reception.
• The frequency at which signal is transmitted from ground to satellite
is known as uplink frequency and signal frequency transmitted from
satellite to ground is known as downlink frequency.
• It has been decided by international community that uplink
frequency is always higher than downlink frequency.
• It is to be noted that as frequency of communication increases, the
size of transmitting and receiving antenna as well as the size of the
electronics components required are decreases drastically (Inversely
proportional).
9. • A communications satellite is an orbiting artificial earth satellite that
receives a communications signal from a transmitting ground station,
amplifies and possibly processes it, then transmits it back to the earth
for reception by one or more receiving ground stations.
• Today’ s communications satellites offer extensive capabilities in
applications involving data, voice, and video, with services provided
to fixed, broadcast, mobile, personal communications, and private
networks users.
10.
11. ADVANTAGES OF SATELLITE COMMUNICATION
• Distance Independent Costs: The cost of satellite transmission is
basically the same, regardless of the distance between the
transmitting and receiving earth stations. Satellite based
transmission costs tend to be more stable, particularly for
international or intercontinental communications over vast
distances.
• Fixed Broadcast Costs: The cost of satellite broadcast transmission,
that is, transmission from one transmit ground terminal to a number
of receiving ground terminals, is independent of the number of
ground terminals receiving the transmission.
12. • High Capacity: Satellite communications links involve
high carrier frequencies, with large information
bandwidths.
• Capacities of typical communications satellites range
from 10s to 100s of Mbps (Mega-bits per second),
and can provide services for several hundred video
channels or several tens of thousands of voice or
data links.
13. • Low Error Rates. Bit errors on a digital satellite link tend to be
random, allowing statistical detection and error correction
techniques to be used. Error rates of one bit error in 106 bits or
better can be routinely achieved efficiently and reliably with
standard equipment.
• Diverse User Networks. Large areas of the earth are visible from the
typical communications satellite, allowing the satellite to link
together many users simultaneously. Satellites are particularly useful
for accessing remote areas or communities not otherwise accessible
by terrestrial means. Satellite terminals can be on the surface, at sea,
or in the air, and can be fixed or mobile.
14. History of satellite communication
• How I lost a billon dollar in my spare time was is a partial title
of Arthur C. Clark ‘s 1965 essay on why and how he didn’t
patent the idea of geostationary satellite which he detailed
and publicized in 1945.
• Arthur C. Clark wrote the first well-known article on
communication satellites. "Extra-Terrestrial Relays" was
published in Wireless World in 1945. In the article, Clark
discussed geosynchronous earth orbit and the possibility of
covering the earth with three satellites.
• Marvel is that sir arthur survived to see his concept fulfilled
by approximately 250 geo stationary satellites ringing the
globe.
15. • People considered consider Clark to be the father of sat..
Comm. Bt he consider himself the God father of satellite
communication and other two scientists as father who gave
technical concepts….
Dr. John R Pierce and Dr. Harold Rosen.
• As a honour the orbit where satellite seem to be stationary
from the surface is called as clark’s orbit.
16. • The actual journey into space began October 4, 1957, when the
Soviet Union launched Sputnik 1, the world's first orbital spacecraft,
which orbited the world for three months.
• The first communication satellite was launched on December 18,
1958.
• Signal Communication by Orbital Relay (SCORE), which broadcasted
a Christmas message from President Eisenhower - "Peace on Earth,
Good will toward men" - orbited the earth for 12 days until the
batteries failed.
• The main purpose of the SCORE project was to prove that an atlas
missile could be put into orbit.
17. Combined, the U.S. and U.S.S.R. launched six satellites in 1958, 14
satellites in 1959, 19 in 1960 and 35 in 1961. In 1962, the United
Kingdom and Canada launched satellites of their own, along with
the 70 satellites launched by the U.S. and U.S.S.R.
• On August 12, 1960, the United States launched Echo 1, a passive
reflector satellite with no amplification possibilities.
• Echo 1 could only reflect the radiation back to earth. At the time of
its launch, it was thought that passive reflector satellites could serve
a purpose in communications, but the technology was soon
abandoned.
18. In 19th century a foresighted writer described a satellite that
communicated to earth by having people on the satellite jump up
and down.
The brillient and pioneering German Hermann Oberth wrote of
communicating with manned satellite by mirrors and lights in
1923 when radio was still in its infancy.
Other writers including a little known Austrian army officer
named Hermann Potonik has proposed a manned name station
in his 1928 book The Problem Of Spaceflight placing it in a
geostationary orbit to facilitate radio communication with earth .
In 1942 an Engineer writer George .O, Smith proposed a radio
relay satellite in Venus orbit to permit communication between
that planet and earth when they were on opposite sides of the
sun.
19. History of satellite communication
• 1945 Arthur C. Clarke publishes an essay about “Extra
Terrestrial Relays“ Satellite communication began after
Second World War. Scientists knew that is was possible to
build rockets that could carry radio transmitters into space.
• 1957 first satellite SPUTNIK :The satellite was launched by the
Soviet Union and the event chocked the Western world.
• 1965 first commercial geostationary satellite Satellite “Early
Bird“ (INTELSAT I): It weighed 68 kg and offered 240 duplex
telephone channels or 1 TV channel, 1.5 years lifetime.
• 1982 first mobile satellite telephone system INMARSAT-A
• 1998 global satellite systems for small mobile phones
• Today more than 250 geostationary satellites orbit the
earth!!
