Satellite communication


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Satellite communication

  2. 2. A satellite is an object put into orbit around the earth orany other planet in order to relay communication signalsor transmit scientific data
  3. 3. Keppler’s Law -laws concerning the motions of planets formulated by German astronomer Johannes Kepler• First Law – the orbit of a planet around the sun is ellipse• Second Law ( Law of areas) -orbital velocity• Third Law (Law of Periods or Harminc Law) – revolution function of distance
  4. 4. Types of Satellite• Astronomical satellites• Communication satellites• Weather satellites• Navigation satellites
  5. 5. Types of Satellite• Astronomical satellites• Communication satellites• Weather satellites• Navigation satellites
  6. 6. Communications Satellite• A spacecraft placed in orbit around the earth which carries on board microwave transmitting and receiving equipment capable of relaying signals from one point to another.• It uses microwave frequency (1-100 Ghz)
  7. 7. Reasons for Using Microwave Frequency • To penetrate the atmosphere • To handle wideband signals encountered in present day communications • To make practical use of high gain antennas aboard the spacecraft
  8. 8. Satellite Communications
  9. 9. Satellite Communications
  10. 10. Satellite Communications
  11. 11. Anatomy of Satcom Terminal
  12. 12. Anatomy of SatcomTerminal
  13. 13. Satellite Service Categories1. Fixed Satellite Service (FSS) cover links between satellites and fixed (non moving earth stations)2. Mobile Service (MSS) cover links to stations that maybe in motion (mobile) including ships (maritime mobile-MMSS), aircraft (aeronautical mobile-AMSS),and land vehicles (land mobile LMSS)3. Broadcast Services include TV (DBS-TV) and audio (DBSA)4. Intersatellite Service –satellite-to-satellite cross links
  14. 14. DVB
  15. 15. Satellite System Elements
  16. 16. Space Segment• It contains the satellite and all terrestrial facilities for control and monitoring of the satellite• This includes the tracking,telemetry, and command stations(TT&C) with satellite control center–Payload – It consists of thereceiving and transmitting antennasand all the electronic equipment thatsupports the transmission of carriers–Platform – It consists of allsubsystems that permits the payloadto operate
  17. 17. Ground Segment• It consists of all the earth stations most often connected to the end user’s equipment by a terrestrial network, or in case of VSAT, directly connected to the end user’s equipment
  18. 18. Frequency Bands
  19. 19. Broad Categories of Satellites• Passive Satellite – Simply reflects a signal back to earth – No gain devices on board to amplify or repeat the signal – Otherwise called bent pipe satellite (frequency translating RF repeater)• Active Satellite – Receives,amplifies,retransmits the signal – Also called processing satellite (used in digital circuits where the signal is demodulated to baseband and regenerates the signal)
  20. 20. Satellite Evolution1. Moon – in the late 1940’s became the first satellite transponder2. Sputnik 1 – the first active earth satellite launched in 1957 by Russia.It transmitted telemetry information for 21 days3. Explorer 1 – lunched by USA late that year. It transmitted telemetry information for nearly five months.4. Score – a 150-lb conical shaped satellite.It is the first artificial satellite used for terrestrial communications5. Echo- a 100-ft diameter plastic balloon with aluminum coating.It achieved the first transatlantic transmission using a satellite.
  21. 21. Satellite Evolution6. Telstar 1- the first satellite to receive and transmit simultaneously. It was damaged by the radiation of the newly discovered Van Allen belts.7. Telstar II – accomplished the first successful transatlantic transmission of video8. Syncom 1- was the first attempt to place a geosynchronous satellite into orbit but was lost during orbit injection9. Intelsat – International Telecommunications Satellite Organization10. Early Bird – the first Intelsat Satellite.It provided over 480 voice channels
  22. 22. Satellite Orbits• The trajectory followed by the satellite in equilibrium between two opposing forces (gravitational force and inertial centrifugal force)• Maximum extension at apogee and minimum at perigee
  23. 23. Satellite Orbits (by inclination)
  24. 24. Satellite Orbits(By Inclination) Ascending Node Descending Node
  25. 25. Satellite Orbit (By Shape)• Elliptical Orbit (64 deg inclination)• Circular Inclined (Polar orbit)• Circular orbit with Zero Inclination (Equatorial)
  26. 26. Geosynchronous OrbitGeosynchronous or GeostationaryNon synchronous Satelllites –Prograde or Posigrade –Retrograde
  27. 27. Satellite Orbit (by Altitude)
  28. 28. Satellite Orbits(By Altitude and Shape)
  29. 29. Orbit Types by Altitude
  30. 30. LEO• Circular or inclined orbit < 1400 km altitude• Satellite travels across sky from horizon to horizon in 5 to 15 mins =>needs hand off• Earth station must track satellites• Large constellation of Satellites (66 needed to cover earth)• Requires complex architecture• LEO sats need lower RF freq (low distances bet sat and ground means lower antenna gains=>lower frequencies
  31. 31. LEO Applications• Communications (voice and high speed data) – Iridium (comprises 66 LEO satellites) – Globalstar (fourty-eight satellites) – Teledesic (288 satellites for high speed data service)• Military Surveillance• Weather• Atmosphere Studies• Earth Observation Remote Sensing – Polar ice cap monitoring – Tracking plantation changes – Rescue and Search
  32. 32. MEO HEO • Molniya• Ellipso • Tundra• ICO (Intermediate Circular Orbit) • Communication Services at High• Odyssey altitudes• Navistar• Archemedis GEO – Voice and Data •Direct Broadcast communications – Radiodetermination •Fixed Satelite Service and radionavigation •Inersatellite Links
  33. 33. HEO
  34. 34. MEO Applications• GPS is MEO satellite system – GPS satellites broadcast pulse trains with very accurate time signals – A receiver able to see four GPS satellites can calculate its position within 30 m anywhere in the world – 24 satellites in clusters of four, 12 hour orbital period
  35. 35. DisadvantagesAdvantages GEO GEO • They suffer great• Stationary deal FSL due to• No switching distance required • Time delay• They cover larger • Congestion area • Coverage problem• The effects of (about above 80 Doppler shift are deg) negligible • Lower angle of elevation
  36. 36. GEO Applications• Initial application-telephony• Broadcasting (Direct TV)• Point to multipoint – Video Distribution for Cable TV• Mobile Services – Inmarsat (International Maritime Satellite Org ) – MSAT (Mobile Satellite)• Weather Observation
  37. 37. Comparison of Orbit Types
  38. 38. Orbital Calculations• Any satellite orbiting the earth needs to satisfy this equation: 11 4 x10 v = (d + 6400)Where v = velocity in meters/second d = distance above the earth’s surface in km
  39. 39. Sample Problem 01• Find the velocity and orbital period of a satellite in a circular orbit a) 500 km above the earth’s surface b) 36,000 km above the earth’s surface
  40. 40. Classifications According to Stabilization Method• Spinner Satellite – Use the angular momentum of its spinning body to provide roll and yaw stabilization• Three-Axis Stabilizer – The body remains fixed relative to earths surface – Internal subsytem provides roll and yaw stabilization
  41. 41. Classifications According to Territorial Coverage• Domestic Satellite – Domsat – Single country• Regional Satellite – Specific regions• Global Satellite – Earth
  42. 42. Look Angles• Angle of Elevation – The angle formed between the direction of travel of a wave radiated from earth station antenna and the horizontal – 5 degrees is the minimum acceptable angle of elevation• Azimuth – The horizontal pointing angle of an antenna – Measured in clockwise direction in degrees from true north
  43. 43. Look Angles
  44. 44. Look Angles
  45. 45. • PAS 4 – 72• APSTAR 2R – 76.5 Satellite Location• THAICOM 3 – 78.5• ST 1 - 88• INSAT 1 – 93.7• ASIASAT 2 – 100.5• ASIASAT 3 – 105.5• BS 2 – 110• PALAPA C2 – 113• JCSAT 3 – 128• APSTAR 1A - 134• AGILA 2 – 146• MEASAT - 148• PAS 8 – 166• PAS 2 - 169
  46. 46. Footprint• Spot Beams – Small geographic area• Zonal Coverage – Less than one-third of the earth’s surface• Earth Coverage – One-third of the earths surface with approximate antenna beamwidth of 17 degrees.
  47. 47. Footprint
  48. 48. Spacing or Spatial IsolationFactors to be Considered:• Bamwidths and sidelobe radiation of both the earth sattion and satellite antennas• RF Carrier Frequency• Encoding or modulation techniques• Acceptable limits of interference• Transmit carrier powerNote: 3 to 5 deg is required
  49. 49. Frequency ReuseA way to increase the capacity of alimited bandwidth when an allocatedband is filled Methods Frequency Reuse – Reducing antenna beamwidth so that different beams of the same frequency can be directed to different geographical areas on earth – Dual Polarization (less effective because the atmosphere has a tendency to reorient or repolarize electromagnetic wave)
  50. 50. Satellite Communications
  51. 51. TVRO Diagram
  52. 52. Antenna Theory
  53. 53. Satellite System Parameters Path Loss CalculationsPR (dB) = + − +d +f ) GT (dBi) G R (dBi) (32.44 20log 20logPT
  54. 54. Sample Problem 2• Calculate the length of the path to a geostationary satellite from an earth station where the angle of elevation is 30 degrees
  55. 55. Sample Problem 3• A satellite operates at 4 GHz with a transmitter power of 7 W and an antenna gain of 40 dBi. The receiver has an antenna gain of 30 dBi, and the path is 40,000 km. Calculate the signal strength at the receiver
  56. 56. Satellite System Parameters Antenna Calculations• GAIN • BEAMWIDTH
  57. 57. Sample Problem 4• A TVRO installation for use with C-band satellites (downlink at approximately 4 GHz) has a diameter of about 3 m and an efficiency of about 55%. Calculate its gain and beamwidth.
  58. 58. Satellite System ParametersTransmit Power and Bit Energy
  59. 59. Sample Problem 5• For a total transmit power (Pt) of 1000 W, determine the energy per bit (Eb) for a transmission of 50 Mbps.
  60. 60. Satellite System ParametersEffective Isotropic Power (EIRP)-defined as an equivalent transmit power
  61. 61. Sample Problem 6• For an earth station transmitter wit an output power of 40 dBW (10,000), a back- off loss of 3 dB, a total branching loss and feeder loss of 3 dB, and a transmit antenna gain of 40 dB, determine EIRP
  62. 62. Satellite System Parameters Equivalent Noise Temperature
  63. 63. Sample Problem 7• A receiver has a noise figure of 1.5 dB. Find its equivalent noise temperature.
  64. 64. Satellite System Parameters Noise Density
  65. 65. Sample Problem 8• For an equivalent noise bandwidth of 10 MHz and a total noise power of 0.0276 pW, determine the noise density and equivalent noise temperature
  66. 66. Satellite System Parameters Carrier-to-Noise DensityRatio• The average wideband carrier power-to-noise density ratio• The wideband carrier power is the combined carrier power of the carrier and its associated sidebands
  67. 67. Satellite System ParametersEnergy of Bit-Noise Density Ratio• One of the most important and most often used parameters when evaluating a digital radio system
  68. 68. Satellite System ParametersGain-to-Equivalent Noise Temperature Ratio• Is a figure of merit used to represent the quality of a satellite or an earth station receiver
  69. 69. Satellite System ParametersAntenna Noise Temperature (cont’)
  70. 70. Sample Problem 9• A receiving antenna with a gain of 40 dBi looks at sky with a noise temperature of 15 K. The loss between the antenna and the LNA input due to feedhorn is 0.4 dB, and the LNA has a noise temperature of 40 K. calculate G/T (in dB).
  71. 71. Satellite System Link Equations
  72. 72. Downlink Equation
  73. 73. Sample Problem 10• A ground terminal receives a signal from satellite at a distance of 38,000 km. The satelitte has a transmitter power of 50 watts and an antenna gain of 30 dBi. Assume losses between the satellite transmitter and its antenna are negligible. The frequency is 12 Ghz. Calculate the carrier-to-noise ratio at the receiver for a bandwidth of 1 MHz. Te earth station is found to have G/T of 20.6 dB.
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