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Satellite Communication Fundamentals. History of International Communication ► 1850 - Submarine Telephone cable (UK & France) ► 1901 – Transoceanic Long.

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Presentation on theme: "Satellite Communication Fundamentals. History of International Communication ► 1850 - Submarine Telephone cable (UK & France) ► 1901 – Transoceanic Long."— Presentation transcript:

1 Satellite Communication Fundamentals

2 History of International Communication ► 1850 - Submarine Telephone cable (UK & France) ► 1901 – Transoceanic Long Wave Communication (Europe & America) ► 1926 – Short wave communication (UK & Europe) ► 1945 – Microwave Transmission System (Europe & America) ► 1945 – Geo stationery Satellite concept by Arthur C Clarke ► 1956 – Co-axial multi channel submarine cable (UK & USA) ► 1957 – First man made satellite Sputnik by USSR ► 1964 – Formation of Intelsat Organization (UK, USA, Australia, Japan, Germany, Italy & France) Japan, Germany, Italy & France) ► 1965 – First Communication Satellite (Intelsat - 1)

3 Satellites ► Arthur C. Clarke’s vision:  3 Geostationary satellites illuminate the Earth Illumination Lines Satellite 1Satellite 2 Satellite 3 17.4° 120°

4 Polar Orbit Inclined Orbit Equatorial Orbit Equator Satellites ► Three Basic Orbits

5 Satellites ► What does Geostationary mean?  Geo = Earth, Stationary = Not Moving  Satellite is a Fixed Point in the Sky ► Rotation of the Satellite = Rotation of the Earth (~24 Hrs/Rot) ► Equatorial Plane (only possible orbit) ► 35,786 km above the Earth’s surface (only possible distance)

6 Satellites ► Geostationary Orbits  Satellite needs to stay within designated area: ► Station-keeping box

7 Transmit Antenna Transponder (incl. Switching Matrix) Receive Antenna “Spinner” “3-Axis Stabilized” Communications Satellites ► What is a Communications Satellite?  A “Radio Relay” in the Sky ► Receives, amplifies and re-directs analog and digital signals carried within a carrier frequency

8 Electrical Power Communication Antenna Payload Spacecraft Control/Propulsion Communications Satellites ► What are the Satellite Components?  Main subsystems:

9 Communication Satellite Earth (M) Satellite (m) Gravitational Force GmM/R 2 Centrifugal Force mV 2 /R At equilibration mV 2 /R=GmM/R 2 Since V=R ω R=(GM) 1/3 /ω 2/3 Resolving R=42,000 km From Surface of Earth R’=42,000km-6,378km=35,786km

10 ► Spin Stabilization ► Three Axis Stabilization Satellite Stabilization wheel motor satellite rotation Motor applies torque to wheel (red) Reaction torque on motor (green) causes satellite to rotate Spin Stabilization For (cylindrical shape)

11 Three Axis Stabilization (For cubical shape) N S Satellite Position (South - North Drift) Orbital Path Roll Yaw Pitch Local Vertical (East-West Drift) ► Geostationary Orbits (especially 3-Axis Stabilized S/C)  Station-keeping for East-West & North- South drift

12 S N Sub Satellite Point Longitude (Long=342° for IS-705) Latitude (Lat=0° for all Intelsat Satellites) Communications Satellites ► What identifies a S/C?  Each satellite is defined by its Sub Satellite Point (SSP)

13 Satellite Architecture ► Communications data passes through a satellite using a signal path known as a Transponder. ► Typically satellites have between 24 and 72 transponders. ► A single transponder is capable of handling up to 155 million bits of information per second. ► Simple voice or data to the most complex and bandwidth-intensive video, audio and Internet content.

14 Radio frequency bands BandFrequency/(GHz) UHF 0.3 – 1.0 L 1.0 – 1.5 S 1.5 – 3.9 C 3.9 – 8.0 X 8.0 – 12.5 Ku 12.5 – 18.0 K 18.0 – 26.5 Ka 26.5 – 40.0

15 Communications Satellites ► Why do we use satellites?  Global reach  Distance insensitive  Mobility and flexibility  Rapid deployment of ground equipment / ease of expansion  Bundling of applications

16 Indian/APR Ocean Region 33°E 64°E 85°E 60°E 66°E 110.5 °E 62°E 83°E 157 °E Atlantic Ocean Region Pacific Ocean Region 304.5°E 328.5°E 340°E 307°E 330.5°E 342°E 310°E 332.5°E 359°E 325.5°E 335.5°E 174°E 178°E 176°E 180°E Communications Satellites ► Where are the satellites located?  Three Orbital Regions ► AOR, IOR/APR, POR

17 Co-located S/C

18 Communications Satellites ► How is simultaneous operation of satellites possible?  Spacing (2-degree, 3-degree)  Coverage (different footprints)  Frequency (C-band, Ku-band, Ka-band …) ► How close can simultaneous satellites operate?  At different frequency bands: ► Co-location: typically at 0.2° (~ 120 km)

19 E/S Distance between 2-degree Satellites: ~ 1200 km Distance between 3-degree Satellites: ~ 1900 km S/C 1 S/C 2 2° 35,786 Km 3° S/C 3 Communications Satellites ► Spacing  Why is the satellite spacing important? ► Pointing error (E/S mispointing)  System margins (small error => BIG mistake)

20 ► Spacing  Why is the satellite spacing important? (Continued) ► Antenna size (radiation pattern)  Small E/S (wide beam, low gain)  Large E/S (narrow beam, high gain)  What to keep in mind? ► Interference margins (ASI) Communications Satellites Antenna Peak Gain Large E/S Small E/S

21 Communications Satellites ► Satellite Spacing:  Desired and un-desired RADIO LINK DESIRED SATELLITE SPACING UNWANTED SIGNALS WANTED SIGNALS SATELLITE ANTENNA UNDESIRED SATELLITE SPACING

22 ► What is a Footprint? Communications Satellites Composite Plot/IBN 1-dB Contour Plot Composite Plot / Satellite Guide

23 ► How to visualize a footprint? Communications Satellites Like Mountain’s Profile: Antenna Radiation Pattern: Cartesian Representation Full Gain Grid - 1 dB steps

24 Satellite Communication ► How can so many beams co-exist?  Frequency isolation ► Multiple 72 MHz and 36 MHz transponders Frequency Slots: 1-2 to 9 10 to 12 Zone Global Hemi

25 (Ka-Band) C-BandKu-Band Satellite Communication ► Why C- and Ku-band?  ITU-assigned frequency band: 1 - 30 GHz  Low rain degradation  Low sky noise

26 ► What is Polarization?  Linear (vertical / horizontal) ► All Intelsat Ku-band ► C-band on IS-805@304.5°E, APR-1@83°E and APR- 2@110.5°E => When used Simultaneously: Double the Bandwidth  Circular (left-hand / right-hand) ► C-band on most Intelsat satellites => When used Simultaneously: Double the Bandwidth Satellite Communication

27 Horizontal Polarization Vertical Polarization Linear Polarization

28 Circular Polarization

29 Communications Satellites ► Why do we need solar panels?  Convert sunlight into electric power ► Primary power supply ► Only 10% - 14% of sunlight can be converted  Charge satellite battery system ► Ceases during eclipse

30 Communications Satellites ► What is the impact of an eclipse?  No solar power  Error in earth sensor  Service outages Eclipse: 21 March Max. Outage = 70 min. + preceding & following days Eclipse: 23 September Max. Outage = 70 min. + preceding & following days

31 Satellite Communication ► What is the Communication Subsystem?  Transponder – satellite bandwidth  Receiver – satellite antenna (G/T)  Amplifier – TWTA/SSPA (wattage)  Switching matrix – connectivity  Transmitter – transmit power (D/L e.i.r.p.) Full Transponder Layout:

32 Satellite Communication ► Some typical carriers  Voice: ► 8 kb/s ► 16 kb/s ► 64 kb/s  Data: ► 64 kb/s ► up to 155 Mb/s  Video: ► 2 Mb/s ► 8 Mb/s

33 ► What to keep in mind?  Time delay ► One-way delay: location dependant  Sub-satellite point: 119.3 ms  Horizon: 138.9 ms ► Path length:  Location dependant (elevation angle) ► Sub-satellite point: 71,572 km ► Horizon: 83,360 km  Dependant on actual elevation angle ► C-band: ~200 dB ► Ku-band: ~206 dB Satellite Communication SSP Horizon

34 Earth Station Technology

35 Earth Station Equipment For Data U/C HPA IF COMB RF COMB MOD U/C HPA IF COMB RF COMB MOD D/C LNA IF DIV RF DIV DEMOD D/C LNA IF DIV RF DIV DEMOD RHCP LHCP RHCP LHCP TRANSMIT PATH RECEIVE PATH

36 Earth Station Equipment For TV U/C HPA IF COMB RF COMB ENCODER U/C HPA IF COMB RF COMB ENCODER D/C LNB IF DIV RF DIV DECODER D/C LNB IF DIV RF DIV DECODER RHCP LHCP RHCP LHCP TRANSMIT PATH RECEIVE PATH

37 Typical Parameters for Earth Station Antennas: C Band Intelsat Standard G/T (dB/°K) Antenna Diameter (typical) A 35 (35 + 20 Log f/4) 18 - 21 m B31.7 11 - 13 m F329 9 – 10 m F227 6.5 – 7.3 m F122.7 3.7 – 4 m H 22.1 for H4 18.3 for H3 15.1 for H2 3.7 m 2.4 m 1.8 m

38 Typical Parameters for Earth Station Antennas: Ku Band Intelsat Standar d G/T (dB/deg K) Antenna Diameter (typical) C37 11 m E334 7 - 8 m E229 3.7 – 4.5 m E125 2.4 - 3.7 m K323.3 1.8 m K219.8 1.2 – 1.5 m

39 CASSEGRAIN FEED SYSTEM PARAXIAL FOCUS Earth Station Antenna Configurations ► Common Antenna Feed Systems FOCAL FEED PARABOLOID HYPERBOLOID GREGORIAN FEED SYSTEM ELLIPSOID SPHERICAL REFLECTOR FEEDER PHOTO REQUIRED

40 Prime Focus & Cassegrain Antenna Optics

41 Antenna Radiation Pattern (1)

42 Satellite Communication ► Transmission via satellite  Modulation (change of properties of an electrical signal)  Coding (change an analog signal to a digital signal)  Multiplexing (combine several signals)  Up/Down converter (change of frequency)  Amplifier (enhance signal strength)  Multiple access techniques (procedure to access the satellite)

43 Types of Propulsion  Chemical Propulsion ► Performance is energy limited ► Propellant Selection  Electric Propulsion ► Electrostatic—Ion Engine ► Electro thermal—Arc Jet ► Electromagnetic—Rail gun  Solar Sails ► Would use large (1 sq. km.) reflective sail (made of thin plastic) ► Light pushes on the sail to provide necessary force to change orbit. ► Still on the drawing board, but technologically possible!  Nuclear Thermal

44 Vp Transfer orbit Launching Earth Geo stationary orbit Va Parking orbit

45 S S N N E E W W Transfer orbit Equator Orbital velocity Velocity accelerated by Apogee motor Velocity accelerated by Apogee motor Geo St. velocity Launching


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