1. Satellite Communications
© 2012 Raymond P. Jefferis III
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Satellite Communications
Introduction
General concepts
Needs, advantages, and disadvantages
Satellite characteristics
Orbits
Earth coverage
System components and design
Power sources
Communication characteristics
Spectrum and Bandwidth
Channel capacity
Frequency and Wavelength
Path losses
Antennas and beam shaping
GPS Satellite - NASA
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© 2012 Raymond P. Jefferis III
Satellite Communications

2. © 2012 Raymond P. Jefferis III
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Text
Text
Satellite Communications, Second Edition, T. Pratt, C. Bostian, and J. Allnut, John Wilen & Sons, 2003.
Lect 01
© 2012 Raymond P. Jefferis III
Satellite Communications

3. Other Useful 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.
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© 2012 Raymond P. Jefferis III

4. General Concepts of Satellites:
© 2012 Raymond P. Jefferis III
Lect01
General Concepts of Satellites:
They orbit around the earth
Have various orbital paths (to be discussed)
They carry their own source of power
They can communicate with:
Ground stations fixed on earth surface
Moving platforms (Non-orbital)
Other orbiting satellites
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© 2012 Raymond P. Jefferis III
Satellite Communications

5. Needs, Advantages & Disadvantages
© 2012 Raymond P. Jefferis III
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Needs, Advantages & Disadvantages
• Communications needs
Advantages of using satellites
Disadvantages of using satellites
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© 2012 Raymond P. Jefferis III
Satellite Communications

6. Satellite Communications Needs
Space vehicle to be used as communications platform
(Earth-Space-Earth, Space-Earth, Space-Space)
Space vehicle to be used as sensor platform with communications
Ground station(s) (Tx/Rx)
Ground receivers (Rx only)
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© 2012 Raymond P. Jefferis III

7. List Advantages & Disadvantages
List these on the sheet supplied.
Five minutes allowed.
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© 2012 Raymond P. Jefferis III

8. Advantages of Using 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
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© 2012 Raymond P. Jefferis III

9. Disadvantages of Using Satellites
Expensive to launch
Expensive ground stations required
Cannot be maintained
Limited frequency spectrum
Limited orbital space (geosynchronous)
Constant ground monitoring required for positioning and operational control
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© 2012 Raymond P. Jefferis III

10. Satellite Characteristics
© 2012 Raymond P. Jefferis III
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Satellite Characteristics
Orbiting platforms for data gathering and communications – position holding/tracking
VHF, UHF, and microwave radiation used for communications with Ground Station(s)
Signal path losses - power limitations
Systems difficult to repair and maintain
Sensitive political environment, with competing interests and relatively limited preferred space
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© 2012 Raymond P. Jefferis III
Satellite Communications

11. Mission Dependent Characteristics
Orbital parameters
Height (velocity & period related to this)
Orientation (determined by application)
Location (especially for geostationary orbits)
Power sources
Solar (principal), nuclear, chemical power
Stored gas/ion sources for position adjustment
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© 2012 Raymond P. Jefferis III

12. Satellite Application Examples
© 2012 Raymond P. Jefferis III
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Satellite Application Examples
Telecommunications
Military communications
Navigation systems
Remote sensing and surveillance
Radio / Television Broadcasting
Astronomical research
Weather observation
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© 2012 Raymond P. Jefferis III
Satellite Communications

13. © 2012 Raymond P. Jefferis III
Orbits
Have particular advantages and disadvantages (See text Chapter 1)
Are determined by satellite mission
Keppler’s Laws of planetary motion describe certain orbital properties (Covered in Lecture 2)
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© 2012 Raymond P. Jefferis III

14. © 2012 Raymond P. Jefferis III
Orbital Properties
Altitude (radius to center of the earth)
Inclination with respect to the earth axis
Period of rotation about the earth
Ground coverage by the satellite
Communications path length(s)
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© 2012 Raymond P. Jefferis III

15. © 2012 Raymond P. Jefferis III
Types of Orbit
Dr. Leila Z. Ribeiro, George Mason University
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© 2012 Raymond P. Jefferis III

16. Missions Associated with Orbit Types
GEO
Primarily commercial communications
MEO
Military and research uses
LEO
Remote sensing
Global Positioning Systems
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© 2012 Raymond P. Jefferis III

17. © 2012 Raymond P. Jefferis III
LEO and MEO Features
Earth coverage requires multiple passes
Typical pass requires about 90 minutes
Signal paths relatively short (lower losses)
Small area, high resolution ground image
Earth station tracking required
Multiple satellites for continuous coverage (Decreases with increasing altitude - “Telstar”)
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© 2012 Raymond P. Jefferis III

18. The Geostationary (Clarke) Orbit
Arthur C. Clarke, Wireless World, February, 1945, p58.
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© 2012 Raymond P. Jefferis III

19. Geo-Synchronous Satellite (GEO) Features
Appears fixed over point on earth equator
Each satellite can cover 120 degrees latitude
Orbital Radius = 42, km
Earth Radius = 6, km (avg)
Period (Sidereal Day) = hr
( seconds)
Long signal path - large path losses
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© 2012 Raymond P. Jefferis III

20. GEO Features (continued)
Ground image area (instantaneous)
Ground track coverage (multiple orbits)
Stationarity (geostationary orbit)
Space coverage (satellite-satellite)
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© 2012 Raymond P. Jefferis III

21. Orbital Altitudes and Problems
© 2012 Raymond P. Jefferis III
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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 between km
Geostationary Orbit (GEO)
35,786 km altitude (42, km radius)
Difficult orbital insertion and maintenance
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© 2012 Raymond P. Jefferis III
Satellite Communications

22. © 2012 Raymond P. Jefferis III
Orbital Inclinations
Equatorial
Prograde – inclined toward the east
Retrograde – inclined toward the west
Inclined
Various inclination angles with respect to the spin axis of the earth, including polar
Geostationary (on equator; no inclination)
Sun synchronous
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© 2012 Raymond P. Jefferis III

23. Earth Coverage Calculation
By the Law of Sines:
and,
The elevation angle is approximately,
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© 2012 Raymond P. Jefferis III

24. Earth Coverage Calculation (continued)
The total coverage area on the surface of the earth, using the previously calculated value of δ) is given by the equation,
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© 2012 Raymond P. Jefferis III

25. Try the Calculation Yourself
Show Lect01S24calc.nb Mathematica®®program
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© 2012 Raymond P. Jefferis III

26. Sample Calculation [Mathematica®]
re = ; (* km *) delta = ; (* degrees *) area = 2 p re^2 (1 - Cos[delta Degree]); Print["Area = ", area, “[km^2]"] Area = *10^7 [km^2]
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© 2012 Raymond P. Jefferis III

27. Alternate Earth Coverage Calculation
Coverage variation as a function of satellite altitude (rsat)
rsat is the radius to the satellite from the center of the earth
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© 2012 Raymond P. Jefferis III

28. Calculation: CoverageArea.nb
re = ; (* km *) rs = re + hs; alpha = ArcSin[re/rs] ad = alpha/Degree delta = ArcSin[(rs/re)*Sin[alpha]] - alpha dd = delta/Degree A = 2 p re^2 (1.0 - Cos[delta]) Plot[A, {hs, 1000, 2000}, AxesLabel -> "Coverage [km^2]", Frame -> True, FrameLabel -> {"Altitude [km]", "Coverage [km^2]"}]
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© 2012 Raymond P. Jefferis III

29. Earth Coverage vs Satellite Altitude
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© 2012 Raymond P. Jefferis III

30. Advanced Earth Coverage Calculations
© 2012 Raymond P. Jefferis III
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Advanced Earth Coverage Calculations
In:
Orbital Mechanics with MATLAB
Recommended download:
Coverage Characteristics of Earth Satellites
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© 2012 Raymond P. Jefferis III
Satellite Communications

31. “Satellite System” Components
© 2012 Raymond P. Jefferis III
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“Satellite System” Components
Satellite(s)
Earth station(s)
Computer systems
Information network (Example: Internet)
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© 2012 Raymond P. Jefferis III
Satellite Communications

32. Satellite System Design
© 2012 Raymond P. Jefferis III
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Satellite System Design
Satellite network with earth stations.
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© 2012 Raymond P. Jefferis III
Satellite Communications

33. © 2012 Raymond P. Jefferis III
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Satellite Components
Receiver (receives on an uplink)
Receiving antenna
Signal processing (decode, security, encode, other)
Transmitter (transmits on a downlink)
Transmitting antenna (beam shaping)
Power and environmental control systems
Attitude control
(De)multiplexing (used in rotating satellites)
Position holding (mission dependent option)
Lect 01
© 2012 Raymond P. Jefferis III
Satellite Communications

34. Simple Satellite Schematic
© 2012 Raymond P. Jefferis III
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Simple Satellite Schematic
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© 2012 Raymond P. Jefferis III
Satellite Communications

35. Satellite Power Sources
Solar power panels (near-earth satellites)
Power degrades over time - relatively long
Radioactive isotopes (deep space probes)
Lower power over very long life, rarely used.
Fuel cells (space stations with resupply)
High power but need maintenance and chemical resupply, rarely used.
Example: International Space Station
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© 2012 Raymond P. Jefferis III

36. © 2012 Raymond P. Jefferis III
Solar Power
Power available in orbit: ~1400 watts of sunlight per square meter
Conversion efficiency: ~25%
Useful power: ~350 Watts/square meter
Panel steering required for maximum power
Typical power levels: kW
Photocell output degrades over time
Lect 01
© 2012 Raymond P. Jefferis III

37. Typical Solar Power Panel Example
Type: GaAs/Ge
Voltage: 53.1 Volts
Power: 1940 Watts
( Effective Load + Source Resistance: Ω )
Geostationary Operational Environmental Satellites (GOES) - Ground testing of solar panels, NASA
Lect 01
© 2012 Raymond P. Jefferis III

38. Satellite Communication Characteristics
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 (“dish”) to make up for path loss and noise
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© 2012 Raymond P. Jefferis III

39. Communication Characteristics (continued)
Spectrum and Bandwidth
Channel capacity
Frequency and Wavelength
Path losses
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© 2012 Raymond P. Jefferis III

40. Spectrum and Bandwidth
• Electromagnetic spectrum allocations
(“DC to light” – see next slide)
Bandwidth: the size or “width” (in Hertz) of a spectrum frequency band
Frequency band: a range of frequencies in the available spectrum.
• Channel capacity increases with the bandwidth (see Slide 42)
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© 2012 Raymond P. Jefferis III

41. Electromagnetic Spectrum
Wikipedia
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© 2012 Raymond P. Jefferis III

42. © 2012 Raymond P. Jefferis III
Channel Capacity
The number of error free bits of information transmitted and received per second
Shannon (BSTJ, Vol. 27,1938)
The capacity C [bits/s] of a channel with bandwidth W, and signal/noise power ratio S/N is
Lect 01
© 2012 Raymond P. Jefferis III

43. Frequency and Wavelength Formula
Microwave energy, at a given frequency, f [Hz]
Moves at a velocity, v [m/s]
And has a wavelength (distance between peak intensities), λ [m]
Formula: λ = v / f (v = c for space) Note: The speed of light, c, in a vacuum (space) is fixed at, c = [m/s]
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© 2012 Raymond P. Jefferis III

44. Frequencies of Interest for Satellites
Generally between 300 MHz and 300 GHz.
The microwave spectrum
Allows efficient generation of signal power
Energy radiated into space
Energy may be focused (beam shaping)
Efficient reception over a specified area.
Properties vary according to the frequency used:
Propagation effects (diffraction, noise, fading)
Antenna Sizes
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© 2012 Raymond P. Jefferis III

45. © 2012 Raymond P. Jefferis III
Microwaves
Include frequencies from 0.3 GHz to 300 GHz.
- Line of sight propagation (space and atmosphere).
- Blockage by dense media (hills, buildings, rain)
- Wide bandwidths compared to lower frequency bands.
- Compact antennas, directionality possible.
Reduced efficiency of generation
1 GHz to 170 GHZ spectrum divided into bands with letter designations (see next slide)
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© 2012 Raymond P. Jefferis III

46. Designated Microwave Bands
Standard designations
For microwave bands
Common bands for satellite communication are the L, C and Ku bands.
Wikipedia
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© 2012 Raymond P. Jefferis III

47. Common Microwave Frequency Allocations
L band
GHz
Note: GPS at GHz
C band
GHz (Downlink)
GHz (Uplink)
Ku band
GHz (Downlink)
GHz (Uplink)
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© 2012 Raymond P. Jefferis III

48. Common Microwave Frequency Allocations
Ka band
, GHz (Downlink)
30 GHz (Uplink)
V band
GHz
60 GHz allocated for unlicensed (WiFi) use
70, 80, and 90 GHz for other wireless
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© 2012 Raymond P. Jefferis III

49. © 2012 Raymond P. Jefferis III
L-Band GPS Receiver
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50. © 2012 Raymond P. Jefferis III
L-Band
Frequencies: – GHz (λ ~30cm)
Uses:
Amateur radio communications
GPS devices
Features:
Patch antenna used for GPS receivers
Low rain fade - Low atmospheric atten. (long paths)
Low power
Small receiver configurations
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© 2012 Raymond P. Jefferis III

51. © 2012 Raymond P. Jefferis III
C-Band
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52. © 2012 Raymond P. Jefferis III
C-Band
Frequencies: GHz (λ ~5cm)
Uses:
TV reception (motels)
IEEE WiFi
VSAT
Features:
Large dish antenna needed (3m diameter)
Low rain fade - Low atmospheric atten. (long paths)
Low power - terrestrial microwave interferences
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© 2012 Raymond P. Jefferis III

53. © 2012 Raymond P. Jefferis III
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Ku-Band
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© 2012 Raymond P. Jefferis III
Satellite Communications

54. © 2012 Raymond P. Jefferis III
Ku-Band
Frequencies: GHz (λ ~ 2cm)
Uses:
Remote TV broadcasting
Satellite communications
VSAT
Features:
Rain, snow, ice (on dish) susceptibility
Small antenna size - high antenna gain
High power allowed
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© 2012 Raymond P. Jefferis III

55. © 2012 Raymond P. Jefferis III
Ka-Band
Frequencies: GHz (λ ~ 1cm)
Uses:
High-resolution radar
Communications systems
Deep space communications
Features:
Obstacles interfere (buildings, vegetation, etc.)
Atmospheric absorption
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© 2012 Raymond P. Jefferis III

56. © 2012 Raymond P. Jefferis III
V-Band
Frequencies: 40 to 75 GHz. (λ ~ 5 mm)
Uses:
Millimeter wave radar research (very expensive!)
High capacity millimeter wave communications
Point-to-point fixed wireless systems (WiFi)
Features:
Rain fade
Obstacles block path
Atmospheric absorption
Expensive equipment
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© 2012 Raymond P. Jefferis III

57. © 2012 Raymond P. Jefferis III
Millimeter Waves
Planck space exploration satellite
Planck is a flagship mission of the European Space Agency (Esa). It was launched in May 2009 and moved to an observing position more than a million km from Earth on its "night side".It carries two instruments that observe the sky across nine frequency bands. The High Frequency Instrument (HFI) operates between 100 and 857 GHz (wavelengths of 3mm to 0.35mm), and the Low Frequency Instrument (LFI) operates between 30 and 70 GHz (wavelengths of 10mm to 4mm).
Johnson noise problems addressed
Some of its detectors operate at minus C
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© 2012 Raymond P. Jefferis III

58. © 2012 Raymond P. Jefferis III
Path Losses
The loss of a radiated signal with distance
Losses increase with frequency
Satellites typically require long path lengths ( Path lengths can be over 42,000 km )
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59. © 2012 Raymond P. Jefferis III
Causes of Path Loss
Dispersion with distance
Atmospheric absorption (Calculated in Lecture 11)
Rain, snow, ice, & cloud attenuation (Calculated in Lecture 12)
Atmospheric noise effects resulting in increased Bit Error Rate (BER) (Calculated in Lecture 6)
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© 2012 Raymond P. Jefferis III

60. © 2012 Raymond P. Jefferis III
Simple Path Loss Model
Free-space power loss = (4πd / λ)2 In dB this becomes,
where:
d is the path distance in km
f is the frequency in MHz
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© 2012 Raymond P. Jefferis III

61. Calculation of Sample Path Loss Model
Ku band geosynchronous satellite: f = 15,000 MHz d = 42,000 km
LossdB = log10(40,000) log10(15,000) = 208 dB
Atmospheric losses must be added to this
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© 2012 Raymond P. Jefferis III

62. Atmospheric Attenuation (Loss)
GHz
H2O
22.2 GHz
Microwave Attenuation [dB/km] vs Frequency [GHz], Wikipedia
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© 2012 Raymond P. Jefferis III

63. H2O vs Dry Air Absorption (Loss)
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© 2012 Raymond P. Jefferis III

64. © 2012 Raymond P. Jefferis III
Remedies for Path Loss
High gain antennas
High transmitter power
Low-noise receivers
Tracking of steered antennas
Modulation techniques
Error correcting codes
Frequency selection
Beam shaping to focus energy
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© 2012 Raymond P. Jefferis III

65. Constraints Limiting Path Loss Remedies
Maximal antenna sizes push satellite radio wavelengths below 2m.
Requirements for antenna gain, due to communication path losses, reduce the practical wavelengths to below 20cm. (Diameter, d, of many wavelengths, λ)
Dish-Antenna Power Gain = η(πd/λ)2 (where η is antenna efficiency)
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© 2012 Raymond P. Jefferis III

66. Antenna Gain Calculation
Ku-Band antenna
Diameter 80 cm (d/λ = 40), η = 0.6 (about 40 wavelengths at 15GHz)
Power Gain = 0.6*(3.14*40)2 = GdB = 10 log10[Power Gain ] = 40 dB Note: Losses and sidelobe effects can reduce this gain to 60% or less of its possible value.
Lect 01
© 2012 Raymond P. Jefferis III

67. Antenna Gain Efficiency Loss
From text, p115 d / λ = 5.6 (4GHz), η = 0.35 GaindB = 10 log10η(πd/λ)2 = 20.9 dB
From text, p116 d = 9m, λ = 0.075m (4GHz), η = 0.6 GaindB = 10 log10η (πd/λ)2 = 49.3 dB Note: Smaller antenna has lower efficiency.
Lect 01
© 2012 Raymond P. Jefferis III

68. Beam Shaping through Antenna Design
Antenna radiation patterns (the beam) can be shaped to redistribute the radiated energy, by antenna design
Shaping radiation patterns can increase signal strength in selected areas
Allows for more signal energy where higher noise levels are expected
Allows energy to be conserved for areas of low noise or low economic concern
Lect 01
© 2012 Raymond P. Jefferis III

69. Intelsat Galaxy-11 Example
Location: 91W
Power: Solar, 10.4 KW
Antennas:
C-Band: 2.4m
Ku-Band: 1.8m
Transponders:
24 channels C-Band: 20W each
24 channels Ku-Band: 75W (data)
16 channels Ku-Band: 140W (TV video)
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© 2012 Raymond P. Jefferis III

70. Intelsat Galaxy-11 C-Band Coverage
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© 2012 Raymond P. Jefferis III

71. Intelsat Galaxy-11 Ku-Band Coverage
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72. © 2012 Raymond P. Jefferis III
Conclusions
Design constraints limit the power avaiable to satellite communications equipment
Path losses limit communication capacity
High gain antennas can overcome some limitations
Antenna patterns can be shaped to favor desired locations on the earth
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© 2012 Raymond P. Jefferis III

73. © 2012 Raymond P. Jefferis III
Questions?
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74. © 2012 Raymond P. Jefferis III
Reminders
Check access to a math package (Mathematica® or MATLAB®)
Do homework
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75. © 2012 Raymond P. Jefferis III
End
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© 2012 Raymond P. Jefferis III