1. Satellite Communication
Prepared By:
Ismail Mehrez Mohamed Khaled

2. Satellite Communications*
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Satellite Communications
General concepts
Satellite characteristics
System components
Orbits
Power sources
Communications
Frequencies
Path losses
GPS Satellite - NASA *

3. General Concepts Satellite is in the orbit of the earth*
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General Concepts
Satellite is in the orbit of the earth
Special orbits have particularly useful properties
Carries its own source of power
Communications possible with:
Ground station fixed on earth surface
Moving platform (Non-orbital)
Another orbiting satellite *

4. Satellite Characteristics
Orbital parameters
Height
Orientation
Location
Power sources
Principally solar power
Stored gas/ion sources for position adjustment
VHF, UHF, and microwave radiation used for communications with Ground Station(s)
Signal path losses - power limitations

5. Types of Orbits

6. Types of Orbit
Dr. Leila Z. Ribeiro, George Mason University

7. Orbital Altitudes and Problems*
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Orbital Altitudes and Problems
Low Earth Orbit (LEO)
km altitude
Atmospheric drag below 300 km
Medium Earth Orbit (MEO)
km altitude
Van Allen radiation
Geostationary Orbit (GEO)
35,786 km altitude
Difficult orbital insertion and maintenance
A layer of energetic charged particles that is held in place around a magnetized planet by its magnetic field *

8. Important Angles By the Law of Sines: and,
The elevation angle is approximately,
Elevation Angle
Inclination Angle

9. Coverage vs Satellite Altitude

10. System Components Satellite(s) Ground station(s) Computer systems*
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System Components
Satellite(s)
Ground station(s)
Computer systems
Information network *

11. Basic Satellite Network*
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Basic Satellite Network
Satellite network with earth stations. *

12. Satellite Components Receiving antenna Receiver*
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Satellite Components
Receiving antenna
Receiver
Processing (decode, security, encode, other)
Transmitter
Transmitting antenna
Power and environmental control systems
Possible position control (geosynchronous) *

13. Simple Satellite Schematic*
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Simple Satellite Schematic *

14. *
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System Block Diagram *

15. Satellite Power Sources*
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Satellite Power Sources
Solar panels (near-earth satellites)
Power degrades over time - relatively long
Radioactive isotopes (deep space probes)
Lower power over very long life
Fuel cells (space stations with resupply)
High power but need maintenance and chemical resupply
isotope with an unstable nucleus, characterized by excess energy *

16. Communications Link Via electromagnetic waves (“radio”)
Typically at microwave frequencies
High losses due to path length
Many interference sources
Attenuation due to atmosphere and weather
High-gain antennas needed

17. Channel Capacity
The capacity C [bits/s] of a channel with bandwidth W, and signal/noise power ratio S/N is
Wavelength = Velocity/Frequency
where,
velocity ≈ velocity of light in vacuum ( about 3 x 108 meters/sec)

18. Satellite Communications Frequencies
Generally between 300 MHz and 300 GHz.
i.e. The microwave spectrum
- Line of sight propagation (space and atmosphere).
- Blockage by dense media (hills, buildings)
Wide bandwidths compared to lower frequency bands.
Properties vary according to the frequency used:
Propagation effects (diffraction, noise, fading)
Antenna Sizes

19. Electromagnetic Spectrum
Wikipedia

20. Designated Microwave Bands
Standard designations
For microwave bands
Common bands for satellite communication are the L, C and Ku bands.
Wikipedia

21. Antenna Power Gain Dish-Antenna Power Gain: G =
A is the area of the antenna aperture
D is the diameter of the parabolic reflector
lambda is the wavelength of the radio waves.
eA: is a dimensionless parameter between 0 and 1 called the aperture efficiency.

22. Antenna Gain Example Example:
Calculate the Power gain of a Ku-Band antenna With average aperture efficiency of 0.6 at a wavelength of 0.02m. The diameter of the reflector is known to be 80cm.
Solution:
Power Gain = 0.6*(3.14*40)2 = 9465 GdB = 10 log10[Power Gain ] = 40 dB

23. Antenna Gain Efficiency
Example 2:
Repeat example 1 with D = 9m
Solution: GaindB = 10 log10EA (pd/l)2 = 60 dB
Conclusion?.....
Bigger antennas have higher gain.

24. Path Loss Losses increase with frequency
Long path lengths (dispersion with distance)
( Path lengths can be over 42,000 km )
Atmospheric absorption
Rain, snow, ice, & cloud attenuation

25. Antenna Gain and Link Losses
Pt = transmitted power
Pr - received power
At = transmit antenna aperture
Ar = receive antenna aperture
Lp = path loss
La = atmospheric attenuation loss
Ld = diffraction losses

26. Simple Path Loss Model where: d is the path distance in m
Free-space power loss = (4pd / l)2 In dB this becomes,
where:
d is the path distance in m
f is the frequency in Hz

27. Sample Path Loss Example
Calculate the power loss of a Ku band geosynchronous satellite with the given parameters: f = 15,000 MHz d = 42,000 km
Solution:
LossdB =
20 log10(40,000) + 20 log10(15,000) – = 208 dB

28. *
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Bit Error Rate Graph
is the signal-to-noise ratio (SNR) of a modulated signal *

29. Remedies for Path Loss High gain antennas High transmitter power
Low-noise receivers
Error correcting codes
Frequency selection

30. Application Examples Telecommunications Military communications*
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Application Examples
Telecommunications
Military communications
Navigation systems
Remote sensing and surveillance
Radio / Television Broadcasting
Astronomical research
Weather observation *

31. Advantages of Satellites
High channel capacity (>100 Mb/s)
Low error rates (Pe ~ 10-6)
Stable cost environment (no long-distance cables or national boundaries)
Wide area coverage (whole North America, for instance)
Coverage can be shaped by antenna patterns

32. Disadvantages of Satellites
Expensive to launch
Expensive ground stations required
Very hard to be maintained
Limited frequency spectrum
Limited orbital space (geosynchronous)
Constant ground monitoring required for positioning and operational control
Sensitive political environment, with competing interests and relatively limited preferred space

33. Satellite Communications Needs
Space vehicle used as communications platform
(Earth-Space-Earth, Space-Earth, Space-Space)
Ground station(s) (Tx/Rx)

34. *
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References
Text
Satellite Communications, Second Edition, T. Pratt, C. Bostian, and J. Allnut, John Wilen & Sons, 2003. *

35. References
Ippolito, Louis J., Jr., Satellite Communications Systems Engineering, John Wiley, 2008.
Kraus, J. D., Electromagnetics, McGraw-Hill, 1953. 
Kraus, J. D., and Marhefka, R. J., Antennas for All Applications, Third Edition, McGraw-Hill, 2002. 
Morgan, W. L. , and Gordon, G. D., Communications Satellite Handbook, John Wiley & Sons, 1989.
Proakis, J. G., and Salehi, M., Communication Systems Engineering, Second Edition, Prentice-Hall, 2002.
Roddy, D, Satellite Communications, Fourth Edition, Mc Graw-Hill, 1989.
Stark, H., Tuteur, F. B., and Anderson, J. B., Modern Electrical Communications, Second Edition, Prentice-Hall, 1988.
Tomasi, W., Advanced Electronic Communications Systems, Fifth Edition, Prentice-Hall, 2001.