Download Advanced Telecom Research Center

Basic Satellite Communication
(2)
Frequency Allocation, Spectrum
and Key Terms
Dr. Joseph N. Pelton
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.
Satellite Frequencies &
Spectrum
VHF
UHF
SHF
EHF
• Very High Frequency
• 30 MHz to 300 MHz : 10 to 1 meters
• Ultra High Frequency
• 300 MHz to 3000 MHz : 100 to 10 meters
• Super High Frequency
• 3 GHz to 30 GHz :
10cm to 1 cm
• Extremely High Frequency
• 30 GHz to 300 GHz : 10mm to 1 mm
Satellite Frequencies
Fixed Satellite Services (FSS)*
Name of Band
Up & Down
Links
Available Usable
Band
Status
C-Band
6GHz-Up
4GHz-Down
500MHz
500MHz
Virtually saturated
band
Ku-Band
14 GHz-Up
11/12 GHz-Down
500MHz+250MHz Very heavily used
500MHz+250MHz band
Ka-Band
27-30 GHz-Up
17-20 GHz-Down
3000 MHz
2500 MHz
Just beginning to
be used
Q/V Band
48-50 GHz-Up
38-40 GHz-Down
2000 MHz
2000 MHz
Largely
experimental
* Note: Other allocations in X band 8/7 GHz for government services
Satellite Frequencies
Mobile Satellite Services (MSS)*

Major MSS Assigned Bands*







1525~1559 MHz (L-Band)
1610~1626.5 MHz (L-Band)
1626.5~1660.5 MHz (L-Band)
1980~2025 MHz (L-Band)
2160~2200 MHz (S-Band)
2483~2500 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.
Satellite Frequencies
Mobile Satellite Services (MSS)*

Satellite Messaging (Store & Forward)*




137~138 MHz (down) 148~149.9 MHz (up)
149.9~150.05 MHz (up)
399.9~400.5 MHz (up)
400.15~401 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
Satellite Frequencies

Broadcast Satellite Services
17.3~18.1 FSS-Uplink Feeders
for BSS
Downlinks
 12.2~12.7 GHz (Reg. 2-Americas)
 11.7~12.45 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)

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.
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.
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.
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.
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
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
C=Frequency 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?
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?
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 earth’s
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
G=µ(pi x d)2/lambda2 in this case µ is the efficiency of the
reflector, d=the diameter of the parabolic antenna reflector
and lambda the wavelength.
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.
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.
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.
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 sphere’s surface it
illuminates. The tighter the antenna beam the higher the
received power flux density.
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
satellite’s transmit and receive antennas.
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.
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