communications satellite

communications is an artificial satellite stationed in space for the purpose of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, otherelliptical orbits and low (polar and non-polar) Earth orbits.For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of submarine communication cables. They are also used for mobile applications such as communications to ships, vehicles, planes and hand-held terminals, and for TV and radio broadcasting,


Basic Elements
Satellite communications are comprised of 2 main components:
1. The Satellite
2. The Ground Station
The Satellite

The satellite itself is also known as the space segment, and is composed of three separate units, namely the fuel system, the satellite and telemetry controls, and the transponder. The transponder includes the receiving antenna to pick-up signals from the ground station, a broad band receiver, an input multiplexer, and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink. The primary role of a satellite is to reflect electronic signals. In the case of a telecom satellite, the primary task is to receive signals from a ground station and send them down to another ground station located a considerable distance away from the first. This relay action can be two-way, as in the case of a long distance phone call. Another use of the satellite is when, as is the case with television broadcasts, the ground station's uplink is then downlinked over a wide region, so that it may be received by many different customers possessing compatible equipment. Still another use for satellites is observation, wherein the satellite is equipped with cameras or various sensors, and it merely downlinks any information it picks up from its vantagepoint.

The Ground Station.
This is the earth segment. The ground station's job is two-fold. In the case of an uplink, or transmitting station, terrestrial data in the form of baseband signals, is passed through a baseband processor, an up converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. In the case of a downlink, or receiving station, works in the reverse fashion as the uplink, ultimately converting signals received through the parabolic antenna to base band signal.

And The Various use of Satellite Communication are

1. Cellular
2. Television Signals
a. C-Band
b. Digital
3. Marine Communications
4. Spacebourne Land Mobile
5. Satellite Messaging for Commercial Jets
6. Global Positioning Services


to get full report and presentation of satellite communication
please visit this link
http://studentbank.in/report-satellite-c...ull-report
http://studentbank.in/report-optical-sat...ars-report

for more info read
en.wikipediawiki/Communications_satellite
http://cse.wustl.edu/~jain/cis788-97/ftp...e_nets.pdf

hey
how is this satellite communication pdf report
i hope you enjoy it..and come to participate in discussions for help others

[attachment=9897]
Satellite Communication
Introduction
A Satellite is a solid object which revolves around some heavenly body due to the effect of gravitational forces which are mutual in nature. We can categorize satellites in two types, namely Passive Satellites and Active satellites. Passive satellites are not like active satellites. Even a moon can be a passive satellite. Thus passive satellites are relay stations in space. A passive satellite can be further subdivided into two types, namely Natural satellites and artificial satellites. A moon is a natural satellite of earth. But spherical balloon with metal coated plastic serve as artificial satellites.
Active satellites are complicated structures having a processing equipment called Transponder which is very vital for functioning of the satellite. These transponders serve dual purpose i.e. provides amplification of the incoming signal and performs the frequency translation of the incoming signal to avoid interference between the two signals.
History of Satellite Communication
 USSR launched the first artificial earth satellite, Sputnik in 1957.
 US launched the first GEO satellite, Relay-1 in 1962.
 First trans pacific TV traffic distribution in 1963.
Satellite Communication in the Early Internet
 First satellite packet radio network in 1970.(ALOHAnet).
 Satellites connected the American continent and UK in 1975.(SATNET).
 First demonstration of interconnection between ARPANET, SATNET and PRNET in 1977.
 First TCP specification was released in 1982.
Satellite Communication in India
The first satellite that was used for communication purpose in INDIA was ARYABHATTA and it was launched in 19th April.1975. It was made and assembled by an organization called Indian Space Research Organization (ISRO). In the year 1981, a satellite named APPLE was launched in space which was the first Indian Experimental communication satellite. The unique feature of it was that it was a three axis stabilization geosynchronous satellite and weighed around 645 kg. The term APPLE is an abbreviation for Ariane Passenger Payload Experiment. It consisted of a (6/4 Ghz) processing equipment called Transponder. Various experiments were carried out with APPLE, [SITE, STEP (Other satellite telecommunication experiment projects)] and the results obtained from these experiments provided an impetus for Govt. of India to have its own multipurpose Geosynchronous Earth Orbit satellite under INSAT (Indian National Satellite) program. The first satellite INSAT-1A was launched in the year 1982 which was under this INSAT program, but this effort went in vain as the power house of this satellite consisting of solar cells did not operate properly( failed to open) and this satellite was unused latter on. The average electrical power required by INSAT-1 was approximately 1000W and was provided by the power house subsystem of the satellite. The payload was one C-band transponder and two S-band transponders. Later succession of INSAT-1 series was launched like INSAT-1B, INSAT-C and INSAT-D. After this due to the success of the first generation satellites, INSAT-2 series was launched viz. INSAT-2A, INSAT-2B, INSAT-2C, INSAT-3D and INSAT-2E which provided variety of services.
Components & Working of Satellite Communication
The term Satellite communication is very frequently used, but what is satellite communication? It is simply the communication of the satellite in space with large number of earth stations on the ground. Users are the ones who generate baseband signals, which is processed at the earth station and then transmitted to the satellite through dish antennas. Now the user is connected to the earth station via some telephone switch or some dedicated link. The satellite receives the uplink frequency and the transponder present inside the satellite does the processing function and frequency down conversion in order to transmit the downlink signal at different frequency. The earth station then receives the signal from the satellite through parabolic dish antenna and processes it to get back the baseband signal. This baseband signal is then transmitted to the respective user via dedicated page link or other terrestrial system. Previously satellite communication system used large sized parabolic antennas with diameters around 30 meters because of the very faint and weak signals received. But nowadays satellites have become much stronger, bigger and powerful due to which antennas used have become automatically smaller in size. Thus the earth station antennas are now not large in size as the antennas used in olden days. A satellite communication system operates and works in the millimeter and microwave wave frequency bands from 1 Ghz to 50 Ghz. There are various frequency bands utilized by satellites but the most recognized of them is the uplink frequency of 6 Ghz and the downlink frequency of 4 Ghz. Actually the uplink frequency band is 5.725 to 7.075 Ghz and the actual downlink frequency band is from 3.4 to 4.8 Ghz. The major components of a Satellite Communication system is spacecraft and one or more earth earths.
THE EXCITING COMPONENTS OF SATELLITE i.e ITS SUBSYSTEMS
• Attitude & orbit control system:
This subsystem comprises of rocket motors that keeps the correct orientation of the satellite in space by moving it back to the correct orbit. Various external forces cause to change the parking position of the satellite. The primary factors are gravitational forces of sun, moon earth and also other planets of solar system. Other factors include solar pressure on the antennas and solar sails, which is present on the body of the satellite. All these factors are hugely responsible for misbalancing of the satellite and also responsible for changing the parking position of the satellite. Apart from this the earth’s magnetic field is also playing a major role in changing the parking position of satellite. The earth’s magnetic field generates eddy currents in the metallic structure of the satellite as the satellite moves through the magnetic field. Thus the body of the satellite gets rotated called as wobble of the satellite.
Remedy for Misbalancing of the satellite: station keeping:
It is a method of periodically accelerating the satellite in the opposite direction against the forces acting on the body of the satellite like gravitational forces, eddy currents etc. in order to maintain the correct orientation of satellite in space and maintaining its orbit. The two most common methods employed to keep the satellite stable in orbit are: spin stabilization and three axes body stabilization.
• TTC and M SUBSYSTEMS:
These subsystems are found partly on the satellite and partly on the earth stations. Data obtained from the sensors present on the spacecraft are sent by the Telemetry systems through telemetry page link to the controlling earth stations. The telemetry system monitors the condition of the spacecraft. Furthermore the Tracking system is present on the earth station which is all concerned about range, azimuth angles and elevation angles of the spacecraft by providing necessary information on it. There are various techniques used for tracking of satellite:
1. Velocity and acceleration sensors on the satellite can be used to establish the change in orbit.
2. Doppler shift of the telemetry carrier from the earth station or beacon transmitter may be measured to determine the rate at which the range is changing.
3. Ranging tones may be used for range measurement.