Satellite communication


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Satellite communication

  1. 1. SATELLITE COMMUNICATION Presented by:- Satyajit Das ECE,7 th Sem GITA,BBSR.
  2. 2. CONTENTS • What is satellite?. • Types of Satellite & its advantages over terrestial communication. • Why do satellites stay moving and in orbit?. • Components of Satellite. • TTC & M. • Look Angle Determination. • Types of Antenna. • Link Design for Satellite Communication. • Satellite Orbit. • Applications of Satellite Communication. • Effects of Earth and Third body effects on Satellite. • Satellite Communication – “Future”.
  3. 3. What is a Satellite? • The word satellite originated from the Latin word “Satellit”- meaning an attendant, one who is constantly hovering around & attending to a “master” or big man. • For our own purposes however a satellite is simply any body that moves around another (usually much larger) one in a mathematically predictable path called an orbit. • From a Communication stand point, a satellite may be considered as a distant microwave repeater that receives uplink transmission and provides filtering , amplification, processing and frequency translation to the downlink band for transmission.
  4. 4. Demo of satellite coverage
  5. 5. Types of Satellite • Anti-Satellite weapons (Killer satellites) • Astronomical satellites • Biosatellites • Communications satellites • Miniaturized satellites • Navigational satellites(mobile communication for location) • Reconnaissance satellites( for military or intelligence) • Earth observation satellites (environmental monitoring) • Solar power satellites • Weather satellites
  6. 6. Satellite vs Terrestial Communication Advantages of satellites:  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 center of the coverage area.  Satellite to Satellite communication is very precise.  Higher Bandwidths are available for use. Disadvantages of satellites:  Launching satellites into orbit is costly.  Satellite bandwidth is gradually becoming used up.  There is a larger propagation delay in satellite communication than in terrestrial communication.
  7. 7. How does a satellite stay in it’s orbit?
  8. 8. How do we escape gravity & place an object in orbit? • If an object is fired fast enough it should escape the earths pull. • This is done through the use of Rocket Launchers
  9. 9. Multi-stage Rockets • Stage 1: Raises the payload e.g. a satellite to an elevation of about 50 miles. • Stage 2: Satellite 100 miles and the third stage places it into the transfer orbit. • Stage 3: The satellite is placed in its final geo- synchronous orbital slot by the AKM, a type of rocket used to move the satellite.
  11. 11. Satellite TTC &M antenna Receiver Transmit antenna antenna Tele- Telemetry commnd receiver Tracking transmitter System Data Processor Computer For altitude and Controller orbital control
  12. 12. Look Angle Determination The elevation of a satellite,η is the angle which a satellite makes with the tangent at the specified point on the earth. η = arc tan [(cosψ-σ)/ sin ψ] Where, coverage angle ψ = arc cos (cosθc cosφcs ) φcs = φc - φs and σ =R /(R+h) = 0.151 In terms of elevation angle: ψ = 900 – η-sin-1(cos η / 6.63235) In terms of tilt angle : ψ = sin -1(6.6235 sinγ- γ) where θc = latitude of earth station, φc = the longitude, φs = longitude of sub satellite point, R=radius of earth, h=satellite height above equator Tilt angle γ = arc tan [sin ψ / (6.6235-cos ψ)
  13. 13. Azimuth: The azimuth ξ is the angle which the satellite direction makes with the direction of true north measured in the clockwise direction. The azimuth ξ = arc tan [tan φcs /sinθc] in northern hemisphere: ξ =1800 + A0;when the satellite is to the west of earth station. ξ =1800 - A0;when the satellite is to the east of earth station in southern hemisphere. ξ =3600 - A0;when the satellite is to the west of earth station. ξ =A0;when the satellite is to the east of earth station.
  14. 14. Consider the light bulb example:-
  15. 15. LINK DESIGN Satellite Uplink Downlink Earth Station Earth Station Tx Source Output Rx Information Information
  16. 16. Satellite Communications • Based on RF transmissions. • Satellite communication systems consist of ground-based or earth stations (i.e.parabolic antennas) and orbiting transponders. SHF • The transponder receives HF microwaveSsignal from AM a VHF UHF L C X KuKa V Q the ground unit (the uplink) amplifies it and then100 0.1 1 10 100 1 10 transmits it back to earth (the downlink). MHz GHz • For a communication satellite to function properly, it must remain stationary with respect to its position over the earth i.e it mustBands within line of Terrestrial be sight of its earth stations at all times.To remain stationary, the satellite mustSpace Bands traverse its orbit at the same rate as the earth rotates.and Space) Shared (Terrestrial
  17. 17. Simple Transponder IN P U T R F BPF LNA 500 MH z M IX E R LO BPF HP A DA 500 MH z O U TP U T RF
  18. 18. Earth Station Architecture Antenna Axis Elevation Angle Local Horizon Power Supply Monitoring Diplexer Tracking & Control RF IF Baseband HPA Modulator Signals I/P RF IF Baseband LNA Demodulator Signals O/P
  19. 19. Television Uplink Service Customer Interface FM Up Baseband HPA Mod Converter processor
  20. 20. Television Downlink Service Customer Interface Baseband FM Down LNA processor Demod Converter
  21. 21. Satellite orbits Classification of orbits:
  22. 22. * Circular orbits are simplest * Inclined orbits are useful for coverage of equatorial regions. * Elliptical orbits can be used to give quasi stationary behavior viewed from earth using 3 or 4 satellites. * Orbit changes can be used to extend the life of satellites.
  23. 23. Satellite orbits are also classified based on their heights above the earth: GEO(Geostationary Earth Orbit ) LEO(Low Earth Orbit ) MEO (Medium Earth Orbit ) Molniya Orbit HAPs (High Altitude Platform )
  24. 24. Satellite Orbits LEO GEO MEO LEO: Low Earth Obit MEO: Medium Earth Orbit LEO: 500 - 900 km GEO: Geostationary Earth Orbit MEO: 5,000 - 12,000 km GEO: 36,000 km
  25. 25. GEO:-These satellites are in orbit 35,786 km above the earth’s surface along the equator.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. 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. MEO:-A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earth’s surface. MEO satellites are similar to LEO satellites in functionality.MEO satellites are visible for much longer periods of time thanLEO satellites, usually between 2 to 8 hours.MEO satellites have a larger coverage area than LEO satellites.
  26. 26. MOLNIYA:-Used by Russia for decades. Molniya Orbit is an elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours.A series of three Molniya satellites can act like a GEO satellite.Useful near polar regions. HAP:-One of the newest ideas in satellite communication.A blimp or plane around 20 km above the earth’s surface is used as a satellite.HAPs would have very small coverage area, but would have a comparatively strong signal.Cheaper to put in position, but would require a lot of them in a
  27. 27. Applications
  28. 28. Satellite Communications - Future • Government and private satellite systems for telecom and broadcast services • Capacity enhancement in tune with demands • Diversity of services through new technologies : • Direct to Home (DTH) Broadcast System(with moe clarity) • Mobile communications service • Digital Audio Broadcast System • Wide Area, Wide band Multimedia Services • Satellite assisted navigation and positioning • Emergency Alert Services & Disaster Management • Health Communications Support Services • Backbone for National Information
  30. 30. SLV-3 ASLV PSLV GSLV WEIGHT(T) 17 40 294 400 PAYLOAD 40 kg IN LEO 150 kg IN LEO 1200 kg SSO 2000 kg GTO LAUNCHES 4 (79-83) 4 ( 87-94) 5 (93-to-date ) (Year 2000)