This document discusses key parameters that influence satellite communication link design, including operating frequency selection, propagation considerations, and interference issues. It covers topics like how frequency selection impacts bandwidth and attenuation, how the atmosphere affects propagation, factors related to propagation like rain attenuation and multipath signals, noise sources, and problems related to interference between satellite and terrestrial links.
GENERAL CONDITIONS FOR CONTRACTS OF CIVIL ENGINEERING WORKS
Satellite link design part iii
1. Arpan Deyasi
Dept of ECE, RCCIIT, Kolkata, India
Course: MCE203A
Satellite Link Design:
Part-III
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Satellite Link Parameters
Influential parameters for satellite communication link design are:
Choice of operating frequency
Propagation considerations
Noise considerations
Interference-related problems
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Choice of Operating Frequency
Use of lower frequency bands
Economical
Interference-related problems
Lower bandwidth –
Reduced transmission capability
Use of higher frequency bands
Higher bandwidth
Severe rain-induced
Attenuation if f>10 GHz
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Propagation Considerations
Effect of atmosphere on propagation is decided by
1. Operating frequency
2. Polarization
Atmospheric effects are in the form of
1. Attenuation caused by atmospheric scattering
2. Scintillation
3. Depolarization caused by
rain in troposphere and Faraday Rotation in ionosphere
Severe if f>10 GHz Severe if f<10 GHz
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Different Factors related with Propagation
[i] Free-space loss
[ii] Gaseous absorption
[iii] Rain attenuation
[iv] Signal fading due to refraction
[v] Ionosphere-related effects
[vi] Fading due to multipath signals
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Different Factors related with Propagation
Free-space loss
Loss of signal strength due to distance from transmitter
2
2
4 4
20logFS
dB
R R
L
π π
λ λ
= =
( ) ( )32.4 20log 20log dB
R f= + +
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Different Factors related with Propagation
Gaseous absorption
primarily due to molecular
oxygen and uncondensed
water vapor
insignificant if 1<f<15 GHz
atmospheric N2 --insignificant
CO2 – significant
if f≈300 GHz
free electron absorption
significant if f<500 MHz
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Different Factors related with Propagation
Rain attenuation
caused by absorption
and scattering of em
energy by rain drops
[i] rain drop size
[ii] drop size distribution
[iii] operating wavelength
[iv] refractive index
Depends on
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Different Factors related with Propagation
Rain attenuation
Specific attenuation is given by
b
aRα = ‘a’ & ‘b’ depend on frequency and polarization
If rain rate is constant over effective path length ‘L’ , then total attenuation
b
A aR L=
Since rain rate changes on satellite path with position and time
( ) ( )
( )
0
,
L t
b
dB
A t aR y t dy= ∫
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Different Factors related with Propagation
Rain attenuation
Rain attenuation and depolarization occurs due to
[i] Individual rain drops absorb energy from radio waves
[ii] some part of energy is scattered out from propagation path
These interactions depend on rain rate,
their distribution of shapes and sizes
Drop size distributions are given by
( ) 0 exp
m
D
N D N
D
= −
Dm: median drop diameter
N(D): number of drops per cubic
volume with diameters
between ‘D’ and ‘D+dD’
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Different Factors related with Propagation
Rain attenuation
By increasing Earth station antenna noise temperature, rain
degrades performance of a satellite communication system
280 1 exp
4.34
A
A
T
= − −
effective temperature of rain
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Different Factors related with Propagation
Signal fading due to refraction
bending of em wave leads to
virtual position of the satellite
slightly different from the true
position
bending occurs due to
[i] temperature variation
[ii] cloud
[iii] fog
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Different Factors related with Propagation
Ionosphere-related effects
1. Faraday Effect -- plane of polarization of progressing em wave
gets rotated due to the interaction with
Earth’s magnetic field
depends on [i] state of ionosphere
[ii] solar activity
[iii] direction of incident wave
[iv] time of the day
2. Scintillation -- rapid fluctuation of signal amplitude, phase,
polarization, incidence angle
occurs due to small-scale refractive index variation
caused by local ion concentration
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Different Factors related with Propagation
Faraday rotation in ionosphere
For a path length ‘Zm’ in ionosphere, rotation angle ‘Φ’ is given by
( )
4
02
23.6 10
cosZNB dz
f
θ
×
Φ =
∫
θ: angle between geometric field and direction of propagation
N: electron density
B0: geomagnetic flux density
f: operating frequency
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Different Factors related with Propagation
Faraday rotation in ionosphere
Polarization loss is given by
( )1020log cosLP= ∆Φ
Cross-polarization discrimination is
( )1020log cotXPD= ∆Φ
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Different Factors related with Propagation
Fading due to multipath signals
Multipath signals
are caused by
[i] scintillation
[ii] reflection and
scattering from
obstacles
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Noise Considerations
1. Man-made noise arises from electrical equipments
insignificant if f>1 GHz
2. Natural sources
of noise
. solar radiation
. sky noise
. background radiation due to Earth
galactic noise emanating form stars
insignificant if f>1 GHz
. atmospheric noise by lightning flashes
insignificant at high frequencies
. absorption and re-emission of O2 and
water vapor
can be avoided by
antenna design
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Interference-related Problems
Major sources of
interference
interference between satellite links
and terrestrial microwave links
sharing same frequency band
interference between two satellites
sharing same frequency band
interference between two Earth stations
accessing different satellites operating in
same frequency band
cross-polarization in frequency
re-use system
adjacent channel interference
intermodulation
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Different Problems related to Interference
[i] Intermodulation distortion
[ii] Interference between satellite and terrestrial link
sharing the same frequency band
[iii] Interference between two satellites sharing the
same frequency band
[iv] Interference arising out of cross-polarization in
frequency reuse system
[v] Adjacent channel interference
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Different Problems related to Interference
Intermodulation distortion
Occurs due to
generation and interference of intermodulation products
within the satellite transponder
arises due to amplitude and phase nonlinearities
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Different Problems related to Interference
Interference between satellite and terrestrial
link sharing the same frequency band
[i] carrier power
[ii] carrier power spectral density
[iii] frequency offset between two carriers
[iv] bandwidth of satellite signal transmitted/received by
Earth station
This type of
interference
depends on
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Different Problems related to Interference
Interference between two satellites
sharing the same frequency band
Occurs due to presence of side lobes
in the radiation pattern of Earth station antenna
[i] Keep angular separations between adjacent satellites
as large as permissible
[ii] Use highly directed antenna
To avoid
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Different Problems related to Interference
Interference arising out of cross-
polarization in frequency reuse system
Occurs in frequency reuse satellite systems
Due to coupling of energy between one polarization state
to another orthogonally polarized state
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Different Problems related to Interference
Adjacent channel interference
Occurs when
transponder bandwidth is simultaneously shared
by multiple carrier frequencies
having closely spaced center frequencies
within the
transponder bandwidth
A part of carrier power
in the adjacent channel of the desired one
gets captured by the receiver
due to overlapping amplitude characteristics of the channel filters
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E-band technology. (2012). Retrieved from http://www.e-
band.com/index.php?id=86
A. K. Maini, V. Agarawal, “Satellite Communications”, Wiley, 1st Ed.,
2019
References
T. Pratt, C. Bostian, J. Allnutt, “Satellite Communications”, John
Wiley & Sons, 2nd Ed., 2003