Basic%20Satellite%20Communication%20(2)%20Frequency%20Allocation,%20Spectrum%20and%20Key%20Terms

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Basic Satellite Communication (2)Frequency
Allocation, Spectrum and Key Terms

• Dr. Joseph N. Pelton

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Satellite Frequencies Spectrum

• Radio Frequencies are simply a part of the
  electromagnetic spectrum. This extends from
  Extremely Low to Extremely High Frequencies to
  Infra-red to Visible Light (Photons) to
  Ultra-Violet to X-rays to Cosmic Radiation that
  represents the highest frequencies of all and at
  the highest energy. Spectrum is truly a vital
  resource for communications satellites. Formula C
  (or 3x108 m/sec) Wavelength x Frequency
• The radio wave band that is used by satellites is
  divided into the following categories that have
  been named over time.

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Satellite Frequencies Spectrum
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Satellite Frequencies Fixed Satellite Services
(FSS)
Status Available Usable Band Up Down Links Name of Band
Virtually saturated band 500MHz 500MHz 6GHz-Up 4GHz-Down C-Band
Very heavily used band 500MHz250MHz 500MHz250MHz 14 GHz-Up 11/12 GHz-Down Ku-Band
Just beginning to be used 3000 MHz 2500 MHz 27-30 GHz-Up 17-20 GHz-Down Ka-Band
Largely experimental 2000 MHz 2000 MHz 48-50 GHz-Up 38-40 GHz-Down Q/V Band
Note Other allocations in X band 8/7 GHz for
government services
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Satellite Frequencies Mobile Satellite Services
(MSS)

• Major MSS Assigned Bands
• 15251559 MHz (L-Band)
• 16101626.5 MHz (L-Band)
• 1626.51660.5 MHz (L-Band)
• 19802025 MHz (L-Band)
• 21602200 MHz (S-Band)
• 24832500 MHz (S-Band)
• 30/20 GHz (Ka/Ku Band)
• Available spectrum in L-Band is allocated in
  units of 5.25. MHz and thus very intensive reuse
  is needed to support global demands
• Feeder Links in the Fixed Satellite Services
  (FSS) Bands.

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Satellite Frequencies Mobile Satellite Services
(MSS)

• Satellite Messaging (Store Forward)
• 137138 MHz (down) 148149.9 MHz (up)
• 149.9150.05 MHz (up)
• 399.9400.5 MHz (up)
• 400.15401 MHz (down) and 432 MHz
• Typical application is for store and forward
  messaging to support tracking of vehicles,
  trains, ships at sea, updates on pipeline flow or
  commands to SCADA (Supervisory Control and Data
  Acquisition) terminals at power plants etc. Many
  Security applications

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Satellite Frequencies

• Broadcast Satellite Services
• 17.318.1 FSS-Uplink Feeders
• for BSS Downlinks
• 12.212.7 GHz (Reg. 2-Americas)
• 11.712.45 GHz (Reg. 1 3 Europe, Africa Asia)
• (Plus other allocations at 700 MHz,
• at 2.6 GHz, 22GHz and 42 GHz bands.
• (2.6 GHz used for direct audio broadcasting)
• Space Navigation Satellite Services
• 1.6 GHz (i.e. GPS)

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Basic Terms and Concepts

• The field of Satellite Communications is based on
  large number of basic terms, concepts and
  mathematics and physical theorems. Most of these
  can straightforward ideas.
• These include spectrum, RF, bandwidth, Hz,
  decibles, dBm, antenna gain, G/T, Quality of
  Service, S/N, system availability, flux density,
  transponders, filters, amplifiers, analog and
  digital modulation, multiplexing, intermediate
  Frequency and Base band, carrier, etc.

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Basic Terms and Concepts

• The purpose of this lecture is to become familiar
  with these terms, their meanings and how to use
  them. We will return to these in greater depth
  later. This is just a first introduction.

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The Significance of Frequencies and Line of Sight

• VHF signals involve long enough wavelengths that
  they are not easily blocked by trees, foliage,
  power lines, etc. But as one moves up to UHF and
  SHF the systems become increasingly line of sight
  systems.
• For FSS services it is possible to line an earth
  station up with a satellite and no barriers
  intervene and thus use SHF or EHF spectrum, but
  for mobile satellite services (MSS), the
  frequencies must be low enough (and wavelengths
  long enough) to not be easily blocked. This means
  that high link margins are needed for MSS
  services, especially for cars.

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Electro-Magnetism

• Electromagnetism is one of the four basic forces
  in the universe. These are (i) Gravity, (ii)
  Electromagnetism, (iii) the strong nuclear
  force and (iv) the weak nuclear force.
• The elecro-magnetic spectrum covers a very wide
  range of frequency for very low frequency cycles
  up to those that we can hear to ultra-sonics to
  radiowaves to infrared, optical signals,
  ultra-violet, X-rays on up to the very high
  energy cosmic waves at the highest frequencies.

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Radio Frequency (RF) Spectrum

• The most often used radio wave bands that are
  used by satellites is divided into the following
  categories that have been named over time.
• HF 3 MHz to 30 MHz or 100 to 10 meters
• VHF 30 MHz to 300 MHz or 10 to 1 meters
• UHF 300 MHz to 3000 MHz or 100cm to 10 cm
• SHF 3 GHz to 30 GHz or 10cm to 1 cm
• EHF 30 GHz to 300 GHz or 10mm to 1 mm

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Hertz

• Hertz Cycles per second. kHz or kiloHertz
  1000 Cycles per second. MHz or MegaHertz
  1,000,000 Cycles per second GHz or GigaHertz 1
  billion cycles per second.
• Speed of light or C 3 x 108 m/second
• CFrequency x Wavelength
• Thus a frequency of 3 MHz or 3 million
  cycles/second is C (or the speed of light which
  is 3 x 108 m/second divided by 100 meters 3 x
  106 cycles/second. Thus 300 MHz represents a
  wavelength of 1 meter and 3GHz represents a
  wavelength of 10cm. What would be wavelength of
  6GHz in cm?

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Decibels

• A decibel is a logarithmic scale measure that is
  used in communications and particularly for
  satellite communications because it allows for a
  dramatic range of power variations. Due to the
  high orbit of Geo Satellites path loss represents
  effective power reduction by many, many orders of
  magnitude.
• A decibel range on the basis of a logarithmic
  scale of 10. A 3 dB gain means that a power level
  has doubled. 6 dB means a gain of 4, a 10 dB gain
  means a gain of 10, 20 dB means a gain of 100 and
  30 dB means a gain of 1000 and 60 dB means a gain
  of 1 million times. It also works the same way in
  terms of decreases. A -3 dB shift means power is
  reduced by half. A -6 dB means power is reduced
  by 4, a -10 dB reduction is shown by 10. Thus -30
  dB is a reduction of 1000 times. This is also a
  known as a dBm or a thousandth of a dB.
• What would a gain of 1,000,000 be expressed in
  dB? What would a million times reduction in gain
  be in terms of the decibel scale?

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Antenna Gain

• An omni antenna has a gain of 1 or 0 dB.
• Any time you focus a signal to concentrate its
  radiation pattern you are increasing its gain.
  This means that the flux density of the radiated
  signal will increase at the earths surface if
  you use a higher gain antenna on a satellite.
• The history of satellite development has been
  largely linked to using higher gain space
  antennas. The larger the aperture of an antenna
  the more concentrated the beam and the higher the
  gain. The formula for antenna gain is Gµ(pi x
  d)2/lambda2 in this case µ is the efficiency of
  the reflector, dthe diameter of the parabolic
  antenna reflector and lambda the wavelength.

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E.I.R.P.

• This terms that refers to satellite irradiated
  power stands for Effective Isotropic Radiated
  Power.
• Isotropic refers to a signal sent in all
  directions equally from a single point.
• With a high gain antenna the power of the
  satellite can be radiated within specific beam
  coverage areas to create increased power flux
  density in this traffic catchment area and thus
  improve the communications throughput to earth
  stations on the ground in a particular area.

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G/T, C/N and Eb/No

• G on T or Gain to Thermal Noise is a measure of
  the effective gain or performance of a ground
  station. For larger antennas this might be 32.9
  dB/K for large 30m antenna to 22.9 dB/K for
  multi-meter antenna and for a VSAT about 8 to 12
  dB/K.
• Carrier Signal to Noise is a measure of the
  transmitted power of a carrier in relation to the
  noise or interference in the carrier band.
• Eb/No is the ratio of the power per data bit to
  the noise power density per Hz. This is the basis
  for determining the quality of a digital channel.

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System Availability and BER

• The calculation of system availability is simply
  the ratio of the time a service or circuit is
  available for service to when it is not. The
  Integrated Services Digital Network (ISDN)
  standard for this is 99.98 or outage of about an
  hour and a half out of year.
• Bit Error Rate is the determination of Quality of
  Service QoS in a digital system. Again the ISDN
  Standard for BER in a simple sense is 10-6.

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Power Flux Density

• Power Flux Density of a radio wave or signal that
  is used to measure satellite communications
  links. The power from the antenna radiates
  outwards to an ever expanding sphere until a
  signal is received. Thus flux density is the
  power flow per unit surface area. The greater the
  distance travel the flux density decreases by the
  square of the distance traveled. This is why LEO
  with the same antenna gain as a GEO satellite can
  have up to 1600 time greater flux density because
  it is 40 times closer to the Earth.
• The power flux density is thus a vector
  quantity determined by how little of a spheres
  surface it illuminates. The tighter the antenna
  beam the higher the received power flux density.

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Transponders and Filters

• A typical transponder bandwidth is 36 MHz but it
  may be 54 MHz, 72 MHz or even wider.
• A transponders function is to receive the signal,
  filter out noise, shift the frequency to a
  downlink frequency and then amplify it for
  retransmission to the ground. The main amplifier
  may be a Traveling Wave Tube (TWT) or Klystron
  Tube (now usually used for higher frequencies
  above 20 GHz and at very high power levels (i.e.
  100 to 200 watts) or it may be a Solid State
  Power Amplifier (SSPA) that would be used at
  lower L, C or Ku band frequencies. If the
  transponder is a regenerative transponder then
  the signal will be converted to base band
  frequencies and processed there rather than
  handled at RF bands.
• The transponder is the device that provide the
  connection between the satellites transmit and
  receive antennas.

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Intermediate and Base band Frequencies

• The baseband is the frequency that is in the
  original source of the information such as a
  spoken voice.
• Baseband signaling involves transmission of
  information at its original range of frequencies.
• Intermediate frequencies are sometime needed too
  shift the baseband information through to the
  much higher RF signaling where satellite
  transmissions occur in the SHF and EHF bands.

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Assignment

• Assignment 3
• Solve all the mathematical questions asked in the
  presentation and send the answers with the
  calculations steps performed to get the result.
• Summarize the Frequency Spectrum Diagram (on
  Slide 3) in terms of following table columns
• Frequency Band, Operating Frequency,
  Commercial/Military, Satellite/Component using
  this frequency, Description of Application/Service