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Satellite Communication

Satellite Communication. Introduction : . A satellite is something that goes around and around a larger something, like the earth or another planet. Some satellites are natural, like the moon, which is a natural satellite

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Satellite Communication

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  1. Satellite Communication

  2. Introduction : • A satellite is something that goes around and around a larger something, like the earth or another planet. • Some satellites are natural, like the moon, which is a natural satellite of the earth.Other satellites are made by scientists and technologists to go around the earth and do certain jobs. • Some satellites send and receive television signals. The signal is sent from a station onthe earth’s surface. • The satellite receives the signal and rebroadcasts it to other places on the earth.

  3. Why Satellite??? • To Avoid number of Repeaters on the earth surface. • Avoiding Line of Sight Propagation. • High coverage area i.e. a single satellite covers 48% earth surface. For this we require 3 satellites to cover the total surface. • To avoid obstacles like building, tree, mountain etc.

  4. Structure of a Satellite Link • A satellite link is similar to a terrestrial microwave link with two hops, the satellite playing the role of a repeater. • Two distinctly separated frequency bands for • the uplink path from the earth station to the satellite and • the downlink path from the satellite to the earth station

  5. The satellite, as a repeater. • receives the uplink signals from the earth stations, • translates them to the down link frequency band • amplifies them, and • transmits back to the earth station. • The up-link and down-link signals are modulated carriers as in terrestrial microwave links. • The satellite as repeater, does not distinguish between the type of modulated used in the carrier. • It can be a frequency modulated carrier.

  6. Choice of Frequency of Operation : • The majority of present day communication satellites use the following frequencies in the C-band and other bands assigned by CCIR.

  7. Orbit of Satellite : • Orbit is a path traversed by a satellite, orbit may be Equilateral, inclined and Polar. • The parameters of the orbit are defined by three laws of Kepler. • Following figure shows the period of revolution of a satellite as a function of its altitude.

  8. Geostationary Satellite: • If the revolution of satellite around the earth is equal to rotation of the earth along its axis, then the satellite is called Geostationary satellite. • The satellite orbit is placed at a distance of 36000 km from the centre of the earth. • On the other hand, a satellite which appears to be immobile when seen from the earth, is called geostationary. • Majority of the communication satellites are geostationary for the very practical reason that an earth station antenna can be easily pointed towards its.

  9. Satellite Delay: • Transmission path of a communication link through a satellite is about 72000 km long (36000 km uplink path and 36000 km downlink path). • Electromagnetic waves traveling at 3 x 105 km/sec take about 240 ms. from one end to the other. • Such large propagation delay is at the limit of psychologically tolerable values in telephony. • The propagation delay results in “echo” in a telephony channel. • A special equipment called echo suppressors is incorporated in the earth station to counteract the echo.

  10. Equipment in a communication Satellite • The equipment carried about a satellite essentially consists of • Payload • Support subsystems • Payload refers to the equipment used to provide the service for which the satellite has been launched. • In communication satellites, payload consists of transponders which carry out the repeater function and the transmit and receive antennas. • Support subsystems include altitude and orbit control equipment, power subsystem, telemetry and tele-command subsystem, etc.

  11. Transponders : • A transponder is a series of interconnected units which form a single chain for processing an RF channel between the receive and transmit antennas. Choice of Transponder : • One-Way Communication: Data Relay Transponder • Two-Way Communication: MSS Transponder

  12. Types of Satellite : • Anti-Satellite weapons, sometimes called "Killer satellites" are satellites designed to destroy "enemy" satellites, other orbital weapons and targets. • Astronomical satellitesare satellites used for observation of distant planets, galaxies, and other outer space objects. • Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation. • Communications satellites • are an artificial satellite stationed in space for the purposes of telecommunications. • Modern communications satellites typically use geosynchronous orbits, Molniya orbits or low Earth orbits. • Navigation satellites are satellites which use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location.

  13. Altitude Classifications • LOW EARTH ORBIT(LEO): • Low Earth Orbit (LEO)) refers to a satellite which orbits the earth at altitudes between (very roughly) 200 miles and 930 miles. • Medium Earth Orbit (MEO): • Medium Earth Orbit (MEO) refers to a satellite which orbits the earth at an altitude below 22,300 miles (geostationary orbit) and above the altitude of Low Earth Orbit (LEO) satellites. • High Earth Orbit (HEO): • Geocentric orbits above the altitude of geosynchronous orbit 35,786 km (22,240 miles). • Geosynchronous Orbit (GEO): • In other words, if a satellite in a geostationary orbit is in a certain place above the earth, it will stay in that same spot above the earth. • Geostationary satellites are commonly used for communications and weather-observation

  14. Advantages of Satellite Communications: • Wide coverage • Suitable for both Digital and Analog Transmission • High Quality • Flexibility • Quick Provision of Services • Mobile and Emergency Communication

  15. Satellite Communication in India : • In India, satellite communication has been in use for overseas communication by Videsh Sanchar Nigam Ltd. for many years. • This service is provided through INTELSAT satellite. • Two locations in the geostationary orbit were reserved for Indian satellites i.e.74o east and 93.5o west. • Series of four satellites (INSAT–I series) was planned . INSAT : • Indian National Satellite System • INSAT—1 in April 1982 • 5 Satellites in INSAT-2 and INSAT-3 • 5 Communication Satellite planned in INSAT-4 Series.

  16. Conclusion: By going through the above slides we came to know that satellite is mostly responsible for telecommunication transmission and reception of television signals and wheatherforcasting which is very important in our daily life. Satellites are having some disadvantages till now.if they are improved to an extent that the delay will be minimized then I will be a golden achievement of science in our life.

  17. THANK YOU

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