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Unit 6 Satellite Communication

Unit 6 Satellite Communication. - K.M.Thanvi. What is satellite??. A natural or manmade(artificial) body that is designed to place in orbit around a celestial body , generally to relay information , data etc to the earth. Satellite communication.

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Unit 6 Satellite Communication

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  1. Unit 6Satellite Communication - K.M.Thanvi

  2. What is satellite?? • A natural or manmade(artificial) body that is designed to place in orbit around a celestial body , generally to relay information , data etc to the earth

  3. Satellite communication • When communication take place with the help of satellite then it is called as satellite communication

  4. History • 1920--- long range communication via modulated electromagnetic waves were first introduced • 1947--- unnamed American rocket carried a camera into outer space • 1957--- 4 October 1957, first artificial satellite named “spuntik” was successfully launched • 1960--- first whether satellite called Television infrared observational satellite was launched • 1966--- US placed application technology satellite ,a whether satellite at higher distance

  5. …few images

  6. TIrOS

  7. ATS

  8. ORBITS OF SATELLITE • Orbit: PATH of one object around second object • Satellite may orbit circular or elliptical • A satellite may orbit around the earth in different planes. • Equatorial orbit • Polar orbit • Inclined orbit • Based on their altitude • LEO-LOW EARTH ORBIT (500-1500KM) • MEO-MEDIUM EARTH ORBIT(5,000-15,000KM) • GEO-GEOSTATIONARY EARTH ORBIT(35,786KM)

  9. Circular and elliptical

  10. Equatorial polar and inclined

  11. LEO MEO &GEO LEO--500-1500KM MEO-5,000-15,000KM GEO--35,786KM

  12. Escape and orbital velocity • Orbital velocity is the velocity needed to achieve balance between gravity pull on the satellite and the inertia of the satellite motion

  13. Communication with satellite

  14. Types of satellite • Passive satellite • Active satellite

  15. Different types of satellites Based on their mission 1.weather satellite 2.broadcast satellite 3.communication satellite 4.scientific satellite 5.navigational satellite 6.rescue satellite 7.earth observation satellite 8.photoraphy satellites

  16. Types of satellite communication system • Ground to ground • Ground crosslink ground • Ground user relay

  17. Components of satellite

  18. Frequency bands used

  19. Important definitions • footprint

  20. Look angles • Inclination angle

  21. - elevation angle

  22. Path diversity

  23. Different satellites on the basis of orbit • Orbits can be classified depending on their altitude • Depending on which orbit a satellite revolves, satellites can be classified as LEO , MEO and GEO satellites

  24. LEO satellite- • They are at altitude of 500-1500 Km • Visibility duration of such satellites are 15 to 20 min/pass • Round trip propagation delay is several milliseconds • Orbital period 1.5 to 2 hours • Instantaneous ground coverage 6000 km • Eg: Iridium ,Globstar ,Teledesic, orbcomm, skybridge

  25. Doppler shift is more • Atmospheric drag on such satellites is more • Multiple orbital planes with multiple satellites in the orbit are required • Number of handoff are required • Signal received by LEO system is much stronger , as compared to GEO and MEO , for the same transmission power. • Used for communication Services and surveillance

  26. IRIDIUM • GLOBSTAR

  27. MEO satellites • They are at altitude of 5000-15000 Km • Visibility duration of such satellites are 2 to 8 hr/pass • Round trip propagation delay is tens of milliseconds • Orbital period 5 to 10 hours • Instantaneous ground coverage 12000 to 15000km • Eg: odyssey, telestar landsat& GPS

  28. Number of handoff are required are less compared to LEO • While propagation delay to earth and power required by such satellites is greater than LEO, they are still substantially less. • Less satellites compared to MEO are required to provide entire coverage

  29. GEO satellites • They are at altitude of 35,863Km • Visibility duration of such satellites are permanent • Round trip propagation delay is 250milliseconds • Orbital period 24 hours • Instantaneous ground coverage 16000 km • Eg: intersputnik

  30. They are most common type of communication satellite • When satellite is in circular orbit 35863 km above the surface of the earth in the equatorial plane, it will rotate with the same angular speed as earth . • Hence they seem to be stationary with respect to a point on earth • Hence there is no problem of frequency shift • Tracking is easy • 3 satellites spaced 120 degrees apart can cover the entire earth • However signal get weak after traveling longer distance • Also propagation delay is more

  31. HEO SATELLITE • As the name implies, an elliptical orbit or as it is more commonly known the highly elliptical orbit, HEO, follows the curve of an ellipse. • However one of the key features of an elliptical orbit is that the satellite in an elliptical orbit about Earth moves much faster when it is close to Earth than when it is further away. • Another feature of an elliptical orbit is that there are two other major points. One is where the satellite is furthest from the Earth. This point is known as the apogee - this is where the satellite moves at its slowest as the gravitational pull from the earth is lower. The point where it is closest to the Earth is known as the perigee - this is where the satellite moves at its fastest.

  32. If the satellite orbit is very elliptical, the satellite will spend most of its time near apogee where it moves very slowly. • This means that the satellite can be in view over its operational area for most of the time, and falling out of view when the satellite comes closer to the Earth and passes over the blind side of the Earth. • By placing a number of satellites in the same orbit, but equally spaced apart, permanent coverage can be achieved. • Eg: Molnya Tundra

  33. Other options • VSAT • HALO network

  34. VSAT • VSAT is short for very small aperture terminal • In earlier days ES antennas used were in commercial satellite communication systems were very large(typical diameter of 30 m)and expensive and operated in C band. • However as satellite telecommunication expanded over, there was a need to decrease in the size and cost of the ES antenna.

  35. This need was meet by two developments in satellite technology: • Increase in the transmit power capabilities of satellites • Move to frequency bands above C band The above two developments lead to the development of VSAT satellite system Example: VSAT systems are used to link businesses and stores to a central computer system so that sales transactions can be completed more rapidly than by using a telephone line, and so that central office can rapidly distribute and collect information from number of locations in a region or country.

  36. Components of VSAT • VSAT earth station consist of two main components • Outdoor unit • It is located where it will have clear line of sight to the satellite and is free from casual blockage by people and/or equipment moving in front of it.

  37. Indoor unit • The indoor data unit is usually housed in a desktop computer at the users workstation and consist of the baseband processor units and interface equipment(e.g. computer screen ,keyboard). It also has modem , mux/demux. (Front) (Rear)

  38. VSAT implementation • one way implementation • This mode of a satellite is used in broadcast satellite service(BSS). • Split two way implementation • This system is used when there is no normal return channel. As this Return link from the user is not via satellite, return link may be formed via telephone line etc. • two way implementation • This system has a return link so two way communications can be set up over the same satellite,from hub to user and from user back to hub

  39. Network architecture of VSAT • STAR • MESH

  40. HALO network • The High Altitude Long Operation (HALO) Network is a broadband wireless metropolitan area network (MAN) consisting of HALO aircraft operating at high altitude and carrying an airborne communications network hub and network elements on the ground. • The HALO Network combines the advantages of two well-established wireless communication services: satellite networks and terrestrial wireless networks like cellular and personal communication systems • Satellite networks are deployed at LEO, MEO,HEO, and GEO , provide larger coverage with big look angles. Their disadvantages include expensive high-power user terminals, long propagation delays, and stagnant performance growth. Also, system capacity is practically fixed and can be increased incrementally only by adding satellites.

  41. In contrast, terrestrial wireless networks have advantages such as low-cost, low-power user terminals, short propagation delays, and good scalability of system capacity. However, their disadvantages include low look angles, complex infrastructures etc. They require many base stations that must be interlinked. They often require significant reengineering to increase capacity when using cell-splitting techniques • The HALO network will be located in the atmosphere, at an altitude miles above terrestrial wireless, but hundreds to thousands of miles below satellite networks. It will provide broadband services to businesses and small offices/home offices in an area containing a typical large city and its neighboring towns. To each end user it will offer an unobstructed line of sight and a free-space-like channel with short propagation delay, and it will allow the use of low-power low-cost user terminals

  42. GPS- global positioning system • History • Most critical issues for travelers has been has been how to get from location to location without getting lost • Use of landmarks ,compass, dead reckoning and celestial navigation were the common means of finding location • In the beginning observation of landmarks and celestial bodies were used • However they are usable only by local public and subject to destruction

  43. One of most famous landmark was light house of Alexandria(which was destroyed due to several earthquakes) • Then compass was developed which freed the navigators from landmarks • In 13 century the fact was discovered that a free floating magnet aligns itself to the Earths magnetic field

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