BYG.VARUN KUMAR(B14EC004)

SATELLITE COMMUNICATION

UNDER SUPERVISIONProf.K.Ashoka ReddyDepartment of ECE

CONTENTS• INTRODUCTION•WORKING•ORBITS• FREQUENCY ALLOCATION FOR SATELLITE SYSTEMS•SATELLITE LAUNCH VEHICLES•ADVANTAGES OF SATELLITE COMMUNICATION•DISADVANTAGES OF SATELLITE COMMUNICATION•APPLICATIONS•CONCLUSION

INTRODUCTIONThe word satellite originated from the Latin word “Satellit”- meaning an attendant, one who is constantly hovering around & attending to a “master”A satellite is simply any body that moves around another (usually much larger) one in a mathematically predictable path called an orbit

WORKING

• The basic elements of a satellite communications system are shown in next slide. The process begins at an earth station an installation designed to transmit and receive signals from a satellite in orbit around the• earth. • Earth stations send information in the form of high powered, high frequency (GHz range) signals to satellites which receive and retransmit the signals back to earth where they are received by other earth stations in the coverage area of the satellite.•

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•The area which receives a signal of useful strength from the satellite is known as the satellite's footprint. •The transmission system from the earth station to the satellite is called the uplink, and the system from the satellite to the earth station is called the downlink.

ORBITSGEO: ~ 36000 km from the earthMEO: 6000 - 20000 kmLEO: 500 - 1500 kmHEO: Highly Elliptical Orbit Elliptical orbits aredifficulties from radiation belts.

GEOSTATIONARY EARTH ORBIT (GEO)

• Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates • This means GEO satellites remain in the same position relative to the surface of earth• Because of the long distance from earth it gives a large coverage area, almost a fourth of the earth’s surface but, this distance also cause it to have both a comparatively weak signal and a time delay in the signal, which is bad for point to point communication.

High transmit power needed and launching of satellites to orbit are complex and expensive.Not useful for global coverage for small mobile phones and data transmission, typically used for radio and TV transmission

MEDIUM EARTH ORBIT (MEO)• MEO satellites have a larger coverage area than LEO satellites• A MEO satellite’s longer duration of visibility and wider footprint

means fewer satellites are needed in a MEO network than a LEO network• A MEO sMEO satellites have a larger coverage area than LEO

satellites• A MEO satellite’s longer duration of visibility and wider footprint

means fewer satellites are needed in a MEO network than a LEO network• A MEO satellite’s distance gives it a longer time delay and weaker

signal than a LEO satellite, though not as bad as a GEO satellite• atellite’s distance gives it a longer time delay and weaker signal

than a LEO satellite, though not as bad as a GEO satellite

LOW EARTH ORBIT (LEO)•LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface•LEO satellites don’t stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass•A network of LEO satellites is necessary for LEO satellites to be useful to handover necessary from one satellite to another need for routing.

FREQUENCY ALLOCATIONS•Frequency bands for satellite services are shared •with terrestrial services•Satellite signal strength is constrained to avoid interface by it to others•Thus a large antenna and sensitive receiver are •needed at the earth station

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•Many satellites have to share a limited frequency•band,thus co-ordination in frequency and orbital•Location is important•Frequency allocation all done by international•agreements

FREQUENCY BANDS•Different kinds of satellites use different frequency• bands• L-Band:1 to 2 GHz• S-Band:2 to 4 GHz• C-Band:4 to 8 GHz• X-Band:8 to 12.5 GHz• Ku-Band:12.5 to 26.5 GHz• K-Band:18 to 26.5 GHz• Ka-Band:26.5 to 40 GHz

SATELLITE LAUNCH VEHICLES• In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from Earth's surface into outer space. • A launch system includes the launch vehicle, the launch pad, and other infrastructure.• Although a carrier rocket's payload is often an artificial satellite placed into orbit, some spaceflights, such as sounding rockets, are suborbital, while others enable spacecraft to escape Earth orbit entirely.•One of the example for satellite launch vehicle is PSLV(Polar Satellite• Launch Vehicle)

PSLV• The PSLV is one of world's most reliable launch vehicles. • It has been in service for over twenty years and has launched various satellites• Historic missions like Chandrayaan-1, Mars Orbiter Mission, Space Capsule Recovery Experiment, Indian Regional Navigation Satellite System (IRNSS) etc. • PSLV remains a favourite among various organisations as a launch service provider and has launched over 40 satellites for 19 countries. • In 2008 it created a record for most number of satellites placed in orbit in one launch by launching 10 satellites into various Low Earth Orbits.

VEHICLE SPECIFICATIONS Height : 44 m•Diameter : 2.8 m•Number of Stages : 4•Lift Off Mass : 320 tonnes (XL)•Variants : 3 (PSLV-G, PSLV - CA, PSLV - XL)•First Flight : September 20, 1993

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• Payload to SSPO: 1,750 kg• PSLV earned its title 'the Workhorse of ISRO' through consistently delivering various

satellites to Low Earth Orbits, particularly the IRS series of satellites. • It can take up to 1,750 kg of payload to Sun-Synchronous Polar Orbits of 600 km altitude.• Payload to Sub GTO: 1,425 kg• Due to its unmatched reliability, PSLV has also been used to launch various satellites into

Geosynchronous and Geostationary orbits, like satellites from the IRNSS constellation.• Fourth Stage: PS4• The PS4 is the uppermost stage of PSLV, comprising of two Earth storable liquid engines.• Engine : 2 x PS-4• Fuel : MMH + MON• Max. Thrust : 7.6 x 2 kN

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• Third Stage: PS3• The third stage of PSLV is a solid rocket motor that provides the upper stages high thrust

after the atmospheric phase of the launch.• Fuel : HTPB• Max. Thrust : 240 kN• Second Stage: PS2• PSLV uses an Earth storable liquid rocket engine for its second stage, know as the Vikas

engine, developed by Liquid Propulsion Systems Centre.• Engine : Vikas• Fuel : UDMH + N O• Max. Thrust : 799 kN• First Stage: PS1• PSLV uses the S139 solid rocket motor that is augmented by 6 solid strap-on boosters.• Engine : S139• Fuel : HTPB• Max. Thrust : 4800 kN

ADVANTAGES•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 centre of the coverage area•Satellite to satellite communication is very precise•Higher bandwidths are available for use

DISADVANTAGES•Launching satellites into orbits is costly•Satellite bandwidth is gradually becoming used up

There is larger propagation delay in satellite comm- unication than in terrestrial communication

APPLICATIONS• Telephony

- Fixed points, earth station, Satellite, earth station, fixed points. • Television & Radio

- e.g. Direct broadcast satellite (DBS) & Fixed service satellite (FFS) • Mobile satellite technology

- Special antenna called mobile satellite antenna.• Amateur radio

- Access to OSCAR satellite. - Low earth orbits. • Internet

- High Speed. - Useful for far away places. • Military

- Uses geostationary satellites.

First Launching Of Satellites By Country 

Communication satellites bring the world to you anywhere and any time….

CONCLUSIONS........•Satellite systems are not aimed to replace terrestrial system but at complementing them •GEO’s are ideal for TV and Radio broadcasting and they do not need handover because of its larger footprint.•Lifetime of GEO’s are rather high, about 15 years•LEO’s need a network of satellites and are appropriate for voice communications• In LEO’s handover is frequent and routing is must•MEO’s are in between LEO’s and GEO’s in every aspect

REFERENCES•Books:• Introduction to satellite communication by Bruce R.Elbert•LINKS:•www.wikipedia.com•www.isro.gov.in•www.nasa.gov.in

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