08-11-2012, 11:23 AM
ADVANCEMENTS IN SATELLITE COMMUNICATION
[attachment=38531]
ABSTRACT:
Satellites have evolutionized communication. Satellite communication
has served mankind in many ways for instance its is used to predict weather and
broadcast storm warnings and also provides a wide range of communication services
in the fields of relaying television programs, digital data for a multitude of business
services. It might not surprise us if, in near future satellite links are used for voice and
fax transmission to aircraft on international routes. Communications satellite systems
have entered a period of transition from point-to-point high-capacity trunk
communications between large, costly ground terminals to multipoint-to-multipoint
communications between small, low-cost stations. As any invention develops with the
passage of time, satellite communication has also moved a step ahead from what it
was in the past with the use of several techniques such as frequency reuse,
interconnecting many ground stations spread over the world, concept of multiple spot
beam communications, these days lasers are effectively used for transmission through
satellites. The latest development in satellites is the use of networks of small satellites
in low earth orbits.
INTRODUCTION
In this present era, communication plays a vital role. We use a wide
range of devices to communicate between two persons placed at different places
(irrespective of the distance between them). Any earth-orbiting spacecraft that
provides communication over long distances by reflecting or relaying radio-frequency
signals. Satellites have evolutionized communication by making worldwide telephone
links and live broadcasts common occurrences. A satellite receives a microwave
signal from a ground station on the earth (the uplink), then amplifies and retransmits
the signal back to a receiving station or stations on earth at a different frequency (the
downlink). A communication satellite is in geosynchronous orbit, which means that it
is orbiting at the same speed as the earth is revolving. The satellite stays in the same
position relative to the surface of the earth, so that the broadcasting station will never
lose contact with the receiver.
DEVELOPMENT IN SATELLITE COMMUNICATION:
Some of the first communications satellites were designed to operate in a
passive mode. Instead of actively transmitting radio signals, they served merely to
reflect signals that were beamed up to them by transmitting stations on the ground.
Signals were reflected in all directions, so receiving stations around the world could
pick them up. Echo 1, launched by the United States in 1960, consisted of an
aluminized plastic balloon 30 m (100 ft) in diameter. Launched in 1964, Echo 2 was
41 m (135 ft) in diameter. The capacity of such systems was severely limited by the
need for powerful transmitters and large ground antennas.
Score, launched by the United States in 1958, was the first active
communications satellite. It was equipped with a tape recorder that stored messages
received while passing over a transmitting ground station. These messages were
retransmitted when the satellite passed over a receiving station. Telstar 1, launched by
American Telephone and Telegraph Company in 1962, provided direct television
transmission between the United States, Europe, and Japan and could also relay
several hundred-voice channels. Launched into an elliptical orbit inclined 45° to the
equatorial plane, Telstar could only relay signals between two ground stations for a
short period during each revolution, when both stations were in its line of sight.
GEOSYNCHRONOUS ORBIT:
A satellite in a geosynchronous orbit follows a circular orbit over the equator
at an altitude of 35,800 km (22,300 mi), completing one orbit every 24 hours, in the
time that it takes the earth to rotate once. Moving in the same direction as the earth's
rotation, the satellite remains in a fixed position over a point on the equator, thereby
providing uninterrupted contact between ground stations in its line of sight. The first
communications satellite to be placed in this type of orbit was Syncom 2, launched by
the National Aeronautics and Space Administration (NASA) in 1963. Most
communications satellites that followed were also placed in geosynchronous orbit.
COMMERCIAL COMMUNICATIONS SATELLITES:
Deployment and operation of communications satellites on a commercial basis
began with the founding of the Communications Satellite Corporation (COMSAT) in
1963. When the International Telecommunications Satellite Organization
(INTELSAT) was formed in 1964, COMSAT became the U.S. member. Based in
Washington, D.C., INTELSAT is owned by more than 120 nations. Intelsat 1, known
as Early Bird, launched in 1965, provided either 240 voice circuits or one two-way
television channel between the United States and Europe. During the 1960s and
1970s, message capacity and transmission power of the Intelsat 2, 3, and 4
generations were progressively increased.
The first of the Intelsat 4s, launched in 1971, provided 4,000 voice circuits.
With the Intelsat 5 series (1980), innovations in signal focusing resulted in additional
increases in capacity. A satellite's power could now be concentrated on small regions
of the earth, making possible smaller-aperture, lower-cost ground stations. An Intelsat
5 satellite can typically carry 12,000 voice circits. The Intelsat 6 satellites, which
entered service in 1989, can carry 24,000 circuits and feature dynamic on-board
switching of telephone capacity among six beams, using a technique called SSTDMA
(satellite-switched time division multiple access). In the early 2000s,
INTELSAT had 21 satellites in orbit, providing the world's most extensive
telecommunications system. Other systems also provide international service in
competition with INTELSAT. The growth of international systems has been
paralleled by domestic and regional systems, such as the U.S. Telstar, Galaxy, and
Spacenet programs and Europe's Eutelsat and Telecom.
SERVICES:
Broadcasters use data from meteorological satellites to predict weather and to
broadcast storm warnings when necessary. Satellites such as the Geostationary
Operational Environmental Satellite (GOES) collect meteorological and infrared
information about the atmosphere and the ocean. A camera on the GOES is
continuously pointed at Earth, broadcasting satellite images of cloud patterns both day
and night. Here, the GOES-C satellite is being encapsulated inside its payload fairing
aboard a Delta rocket.
Commercial satellites provide a wide range of communications services.
Television programs are relayed internationally, giving rise to the phenomenon
known as the “global village.” Satellites also relay programs to cable television
systems as well as to homes equipped with dish antennas. In addition, very small
aperture terminals (VSATs) relay digital data for a multitude of business services.
Intelsat satellites now carry over 100,000 telephone circuits, with growing use of
digital transmission. Digital source coding methods have resulted in a ten-fold
reduction in the transmission rate needed to carry a voice channel, thus enhancing the
capacity of existing facilities and reducing the size of ground stations that provide
telephone service.
CONCLUSION:
Looking at the rate of advancement in satellite communication one would foresee the
use of satellites in every field where communication is required such as relaying
television and radio signals. Special telephones that communicate with these satellites
allow users to access the regular telephone network and place calls from anywhere on
the globe.
[attachment=38531]
ABSTRACT:
Satellites have evolutionized communication. Satellite communication
has served mankind in many ways for instance its is used to predict weather and
broadcast storm warnings and also provides a wide range of communication services
in the fields of relaying television programs, digital data for a multitude of business
services. It might not surprise us if, in near future satellite links are used for voice and
fax transmission to aircraft on international routes. Communications satellite systems
have entered a period of transition from point-to-point high-capacity trunk
communications between large, costly ground terminals to multipoint-to-multipoint
communications between small, low-cost stations. As any invention develops with the
passage of time, satellite communication has also moved a step ahead from what it
was in the past with the use of several techniques such as frequency reuse,
interconnecting many ground stations spread over the world, concept of multiple spot
beam communications, these days lasers are effectively used for transmission through
satellites. The latest development in satellites is the use of networks of small satellites
in low earth orbits.
INTRODUCTION
In this present era, communication plays a vital role. We use a wide
range of devices to communicate between two persons placed at different places
(irrespective of the distance between them). Any earth-orbiting spacecraft that
provides communication over long distances by reflecting or relaying radio-frequency
signals. Satellites have evolutionized communication by making worldwide telephone
links and live broadcasts common occurrences. A satellite receives a microwave
signal from a ground station on the earth (the uplink), then amplifies and retransmits
the signal back to a receiving station or stations on earth at a different frequency (the
downlink). A communication satellite is in geosynchronous orbit, which means that it
is orbiting at the same speed as the earth is revolving. The satellite stays in the same
position relative to the surface of the earth, so that the broadcasting station will never
lose contact with the receiver.
DEVELOPMENT IN SATELLITE COMMUNICATION:
Some of the first communications satellites were designed to operate in a
passive mode. Instead of actively transmitting radio signals, they served merely to
reflect signals that were beamed up to them by transmitting stations on the ground.
Signals were reflected in all directions, so receiving stations around the world could
pick them up. Echo 1, launched by the United States in 1960, consisted of an
aluminized plastic balloon 30 m (100 ft) in diameter. Launched in 1964, Echo 2 was
41 m (135 ft) in diameter. The capacity of such systems was severely limited by the
need for powerful transmitters and large ground antennas.
Score, launched by the United States in 1958, was the first active
communications satellite. It was equipped with a tape recorder that stored messages
received while passing over a transmitting ground station. These messages were
retransmitted when the satellite passed over a receiving station. Telstar 1, launched by
American Telephone and Telegraph Company in 1962, provided direct television
transmission between the United States, Europe, and Japan and could also relay
several hundred-voice channels. Launched into an elliptical orbit inclined 45° to the
equatorial plane, Telstar could only relay signals between two ground stations for a
short period during each revolution, when both stations were in its line of sight.
GEOSYNCHRONOUS ORBIT:
A satellite in a geosynchronous orbit follows a circular orbit over the equator
at an altitude of 35,800 km (22,300 mi), completing one orbit every 24 hours, in the
time that it takes the earth to rotate once. Moving in the same direction as the earth's
rotation, the satellite remains in a fixed position over a point on the equator, thereby
providing uninterrupted contact between ground stations in its line of sight. The first
communications satellite to be placed in this type of orbit was Syncom 2, launched by
the National Aeronautics and Space Administration (NASA) in 1963. Most
communications satellites that followed were also placed in geosynchronous orbit.
COMMERCIAL COMMUNICATIONS SATELLITES:
Deployment and operation of communications satellites on a commercial basis
began with the founding of the Communications Satellite Corporation (COMSAT) in
1963. When the International Telecommunications Satellite Organization
(INTELSAT) was formed in 1964, COMSAT became the U.S. member. Based in
Washington, D.C., INTELSAT is owned by more than 120 nations. Intelsat 1, known
as Early Bird, launched in 1965, provided either 240 voice circuits or one two-way
television channel between the United States and Europe. During the 1960s and
1970s, message capacity and transmission power of the Intelsat 2, 3, and 4
generations were progressively increased.
The first of the Intelsat 4s, launched in 1971, provided 4,000 voice circuits.
With the Intelsat 5 series (1980), innovations in signal focusing resulted in additional
increases in capacity. A satellite's power could now be concentrated on small regions
of the earth, making possible smaller-aperture, lower-cost ground stations. An Intelsat
5 satellite can typically carry 12,000 voice circits. The Intelsat 6 satellites, which
entered service in 1989, can carry 24,000 circuits and feature dynamic on-board
switching of telephone capacity among six beams, using a technique called SSTDMA
(satellite-switched time division multiple access). In the early 2000s,
INTELSAT had 21 satellites in orbit, providing the world's most extensive
telecommunications system. Other systems also provide international service in
competition with INTELSAT. The growth of international systems has been
paralleled by domestic and regional systems, such as the U.S. Telstar, Galaxy, and
Spacenet programs and Europe's Eutelsat and Telecom.
SERVICES:
Broadcasters use data from meteorological satellites to predict weather and to
broadcast storm warnings when necessary. Satellites such as the Geostationary
Operational Environmental Satellite (GOES) collect meteorological and infrared
information about the atmosphere and the ocean. A camera on the GOES is
continuously pointed at Earth, broadcasting satellite images of cloud patterns both day
and night. Here, the GOES-C satellite is being encapsulated inside its payload fairing
aboard a Delta rocket.
Commercial satellites provide a wide range of communications services.
Television programs are relayed internationally, giving rise to the phenomenon
known as the “global village.” Satellites also relay programs to cable television
systems as well as to homes equipped with dish antennas. In addition, very small
aperture terminals (VSATs) relay digital data for a multitude of business services.
Intelsat satellites now carry over 100,000 telephone circuits, with growing use of
digital transmission. Digital source coding methods have resulted in a ten-fold
reduction in the transmission rate needed to carry a voice channel, thus enhancing the
capacity of existing facilities and reducing the size of ground stations that provide
telephone service.
CONCLUSION:
Looking at the rate of advancement in satellite communication one would foresee the
use of satellites in every field where communication is required such as relaying
television and radio signals. Special telephones that communicate with these satellites
allow users to access the regular telephone network and place calls from anywhere on
the globe.