Satellite communications ppt

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Satellite communications ppt

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• Satellites communicate to each other and earth via electromagnetic radio waves that propagate through free space
  Friis Free Space Equation: power of received signal decays as the square of the distance between the transmiter and receiver
• Birefringence modulation: modulates the laser output by rotating the polarized incident light
  if no voltage is applied, linearly polarized light exits the modulator in same plane it entered
  when apply a voltage, the induced birefringence slows the rotation of one of the circularly polarized vectors, bbut not the other. This is the retardation of the light vector. Emerging light is rotated by some angle – the
  retardation angle

1. 1. UNDER THE ESTEEMED GUIDANCE Ms. S.Kaur Assistance professor Dept of Eloctronics & communication Engg IMS Engineering College, Ghaziabad Presented By, Niranjan kumar EC-2 (3rd Yr) 1114331107 Oct 29, 2014 satellite communication 1
2. 2.  Introduction  Working  Types of satellites  ISL (Inter Satellite Links)  Routing  Operation  Applications  Recent developments  Conclusion  Questions Oct 29, 2014 satellite communication 2
3. 3. What is satellite  A satellite is simply any body that moves around another (usually much larger) one in a mathematically predictable path called an orbit  A communication satellite is a microwave repeater station in space that is used for telecommunication , radio and television signals  The first man made satellite with radio transmitter was in 1957  There are about 750 satellites in the space, most of them are used for communication Oct 29, 2014 satellite communication 3
4. 4. Communication satellites bring the world to you anywhere and any time….. Oct 29, 2014 satellite communication 4
5. 5. Working… Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional repeater. The two stations can use a satellite as a relay station for their communication One Earth Station transmits the signals to the satellite. Up link frequency is the frequency at which Ground Station is communicating with Satellite The satellite Transponder converts the signal and sends it down to the second earth station. This frequency is called a Downlink frequency Oct 29, 2014 satellite communication 5
6. 6. Oct 29, 2014 satellite communication 6
7. 7. Oct 29, 2014 Wirseatdell itsea ctoemlmliutneic actioonmmunication 7
8. 8. Wireless Satellite communication sysytem Inter Satellite Link (ISL) Mobile User Link (MUL) Gateway Link (GWL) base station or gateway footprint small cells (spotbeams) ISDN PSTN GSM User data GWL MUL PSTN: Public Switched Telephone Network Oct 29, 2014 8
9. 9. Types of Orbits Geosynchronous Same rotational velocity as earth Maintains position relative to earth Altitude – 35 786 km Velocity – 11 300 km/hr Asynchronous Much lower altitude = much higher velocity Position over earth constantly changing Contd…. Oct 29, 2014 satellite communication 9
10. 10. Types of orbits… GEO: ~ 36000 km from the earth MEO: 6000 – 20000 km LEO: 500 – 1500 km HEO: Highly Elliptical Orbit, elliptical orbits Difficulties from radiation belts. Oct 29, 2014 satellite communication 10
11. 11. 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 Oct 29, 2014 satellite communication 11
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13. 13. How to connect internet ? Oct 29, 2014 satellite communication 13
14. 14. 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 satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite Oct 29, 2014 satellite communication 14
15. 15. 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 Handover necessary from one satellite to another Need for routing Oct 29, 2014 satellite communication 15
16. 16. Low Earth Orbit ISL Inter Satellite Link GWL – Gateway Link UML – User Mobile Link Oct 29, 2014 satellite communication 16
17. 17. ISL (Inter Satellite Links) Intra-orbital links: connect consecutive satellites on the same orbits Inter-orbital links: connect two satellites on different orbits
18. 18. Routing… If satellites offer ISL’s Traffic can be routed between satellites Only one uplink and one downlink per direction needed for the connection of two mobile phones Ability of routing within the satellite n/w reduces the number of gateways needed on earth Else if, satellites do not offer ISL’s Solution requires two uplinks and two downlinks
19. 19. Oct 29, 2014 satellite communication 19
20. 20. Minimum Hops Algorithm (MHA) Given a pair of source and destination satellites, the MHA finds a path with minimum number of hops The MHA can be implemented by the Dijkstra’s shortest algorithm with cost of each edge set to 1 Min-hop: 4 G-H-I-J-P, G-M-N-O-P,….
21. 21. Minimum Cost Algorithm (MCA)
22. 22. Transmission Receptiom Low Noise conveter Polarization Operation of satellite Tuner Oct 29, 2014 satellite communication 22
23. 23. Radio Signal Propagation Free Space Propagation Model Line-of-sight with no obstructions Friis free space equation Pr×(d) Pt×Gt×Gr l2 × ( 4×p) 2 ×d2×L G 4×p×Ae l2 Oct 29, 2014 satellite communication 23
24. 24. Path Loss (PL) Fading of electromagnetic signal Positive difference between received power and transmitted power (in dB) PL -10 log Gt×Gr l2 × ( 4p) 2 d2 éêêë ùúúû × Oct 29, 2014 satellite communication 24
25. 25. Modulation What actually drives the communication Birefringence modulator most useful Uses electric-field induced birefringence of the crystal to rotate polarized light Oct 29, 2014 satellite communication 25
26. 26. Birefringence modula t ion: modulates the laser output by rotating the polarized incident light. if no voltage is applied, linearly polarized light exits the modulator in same plane it entered when apply a voltage, the induced birefringence slows the rotation of one of the circularly polarized vectors, but not the other. This is the retardation of the light vector. Emerging light is rotated by some angle – the retardation angle. Oct 29, 2014 satellite communication 26
27. 27. Pulse Interval Modulation Most efficient type of modulation N separate time slots in pulse interval Transmit log2(N) bits per pulse Pulse sent during one of these time slots Time slot is value of the word Translated in binary data Oct 29, 2014 satellite communication 27
28. 28. Example of PIM Oct 29, 2014 satellite communication 28
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42. 42. Recent development Oct 29, 2014 satellite communication 42
43. 43. Recent development development Oct 29, 2014 satellite communication 43
44. 44. Recent development Oct 29, 2014 satellite communication 44
45. 45. Recent development Oct 29, 2014 satellite communication 45
46. 46. Oct 29, 2014 satellite communication 46
47. 47. Development Lab…. Oct 29, 2014 satellite communication 47
48. 48. 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
49. 49. References 1. Jochen H. Schiller “Mobile communications-second edition” 2. Ivan Stojmenovic “Handbook of Wireless Networks and Mobile Computing” 3. Peter T. S. Tam, John C. S. Lui, H. W. Chan, Cliff Cliff N. Sze, and C. N. Sze, “An optimized routing scheme and a channel reservation strategy for a low earth orbit satellite system” 4. www.google.com/images 5. http://www.authorstream.com/Presentation/Ravi4000-479427-6. http://www.authorstream.com/Presentation/girishkp-117951-
50. 50. Have u any query ?? Oct 29, 2014 satellite communication 50
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