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Propagation for Space Applications by
Bertram Arbesser-Rastburg Chairman ITU-R SG3
Invited talk at LAPC 2014 , Loughborough, [email protected]
Abstract:The presentation covers the key propagation impairments for fixed and mobile satellite communications as well as for satellite navigation. This includes rain attenuation, cloud attenuation, shadowing and multipath. Specifically for satellite navigation systems the group delay introduced by the troposphere and by the ionosphere is also addressed. For the propagation prediction methods presented a reference is made to the models recommended by ITU-R.
Keywords: Slant path propagation, attenuation, depolarization, group delay, scintillations, troposphere, ionosphere.
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Typewritten Text
Forum for Electromagnetic Research Methods and Application Technologies (FERMAT)
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 2 of 18
Outline
Propagation issues for Fixed SatCom Services
– Clear Air attenuation, Rain attenuation, Cloud attenuation
– Depolarization by rain and ice
Propagation issues for Mobile Satellite Services
– Shadowing, blockage, multipath
Propagation issues for Satellite Navigation Services
– Ionospheric delay, Tropospheric delay, Ionospheric scintillations
– Shadowing, blockage, multipath
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 3 of 18
Propagation Effects
Environment
•Shadowing
•Blockage
•Multipath
Ionosphere
•Scintillations
•Faraday Rotation
•Delay
Troposphere
•Rain attenuation
•Cloud attenuation
•Scintillations
•XPD reduction
•Delay
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 4 of 18
Fixed SatCom Systems
The first satellite communications were using 6 / 4 GHz
WHY?
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 5 of 18
Fixed SatCom Systems – main propagation effects
For fixed Earth-space links at f > 5 GHz,
the main propagation impairments are:
Rain attenuation
Depolarization due to rain and ice
Cloud attenuation
Gaseous absorption
Frozen Precipitation
Rain
Melting layer
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 6 of 18
Gaseous Attenuation
The plot shows the atmospheric
absorption lines
Water vapour
Oxygen
Communication systems use the
frequencies below and between
the lines; the lines themselves
are used for remote sensing of
the atmosphere.
Line-by-line models are good but
computationally intensive
ITU-R Rec. P.676-10
H2O
H2O
O2 O2 H2O
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 7 of 18
Slant Path Propagation Measurements – what is needed?
Beacon receiver (copolar and crosspolar reception) good dynamic range, hydrophobic antenna, may need blowing device
for feed window, may need emergency power supply, may require
tracking
Radiometer Precision calibration, good retrieval algorithm
Meteorological Equipment rain gauge, distrometer, anemometer, radiosonde, WV-GPS Rx)
HIGH UPTIME !
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 8 of 18
Cumulative Distribution of Attenuation
Total AttenuationGreen: 30 GHzBlue: 20 GHzRed: 12 GHz
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 9 of 18
Cloud Attenuation
ITU-R Rec
P. 840-5 *
sin
lcloud
LKA [dB]
Where: L is the total columnar Liquid Water
Content [kg/m2] (reduced to 0 ˚C)
Kl is the specific attenuation
coefficient (function of frequency &
temperature) is the elevation angle
* Kl in Rec P. 840-6 (in force) is slightly different
Frequency (GHz)
Spec
ific
att
enu
atio
n c
oef
fici
ent,
((dB
/km
) / (g
/m³)
)K
l
0.01
0.02
0.05
0.1
0.2
0.5
1
2
5
10
5 10 20 50 100 200
0° C
20° C
10° C
– 8° C
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 10 of 18
Cloud Map
Annual Mean Cloud Cover ( 0 – 1)
Source: ECMWF ERA 15 Database
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 11 of 18
Mobile SatCom Systems
For Mobile Earth-space links the main
propagation impairments are:
Blockage (buildings, underpasses)
Shadowing (trees etc.)
Multipath (reflections)
Semi-Markov Model
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 12 of 18
Roadside Shadowing Model
0681-01
0
4
6
8
10
12
14
16
18
20
22
24
26
28
30
2
10 15 20 25 30 35 40 45 50 55 60
1%
2%
5%
10%
20%
30%
50%
Fading at 1.5 GHz due to roadside shadowing versus
elevation angle
Fad
e ex
ceed
ed (
dB
)
Path elevation angle (degrees)
Fade distribution at 1.5 GHz, valid
for percentages of distance traveled
of 20% p 1%, at the desired path
elevation angle, 60° 20°:
ITU-R Rec P. 681-7
where:
M() = 3.44 + 0.0975 – 0.002 2
N() = – 0.443 + 34.76
AL( p,) = – M() ln ( p) + N() [dB]
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 13 of 18
Channel characterization
• A channel sounder is used to characterize the
multipath environment for land mobile and
aeronautical mobile environments. For proper
modelling, azimuth and elevation of the
incoming components need to be measured
Channel Sounder:
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 14 of 18
Channel characterization
Delay spread in a multipath-rich environment.
The peak on the left (0 delay) is the Line-of-sight signal, showing shadowing and
blockage. The delayed components are multipath contributions.
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 15 of 18
Aeronautical Multipath Model
Model used in ITU-R Rec
P. 682-3 was established
using a flying channel
sounder
1: Line of Sight (LoS): del = 0, P = 0, Doppler BW = 0 Hz
2: Flat fading of LoS: del = 0, P = -14.2 dB, Doppler BW = <0.10 Hz
3: Fuselage multipath: del = 1.5 ns, P = -14.2 dB, Doppler BW = <0.1 Hz
4: Ground reflections: del = 900 – 10 ns, P = -15 to -25 dB, Dopp BW <20 Hz
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IONOSPHERIC PROPAGATION EFFECTS
ON SATNAV SYSTEMS
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 17 of 18
Ionospheric Electron Density and Group Delay
For calculating ionospheric effects, the Electron Density along the
propagation path has to be integrated (Total Electron Content)
1 TECU = 10 16 el / m2
s = 40.3 TEC / f 2 [m] At 1.575 GHz 1 TECu causes 16 cm of group delay
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 18 of 18
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 19 of 18
Trans-Ionospheric propagation
Effects:
• Refractive index Group delay & Ray bending
• Irregularities Scintillations
• Magnetic field and electron density Faraday rotation
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 20 of 18
Ionospheric Scintillations
20
One of the most severe disruptions along a trans-ionospheric propagation path
for signals below 3 GHz is caused by ionospheric scintillation. Small-scale
irregular structures in the ionization density cause scintillation phenomena in
which the signal is fluctuating in amplitude and phase.
Measurement requires special
ionospheric scintillation
receivers:
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Bertram Arbesser-Rastburg | Propagation for Space Applications | LAPC Loughborough | Date: 2014-11-10 | Slide Number 21 of 18
• There is a wide range of microwave systems in
space, spanning across all space applications and
a wide frequency spectrum.
• Space applications are demanding not only in
terms of mass, power consumption, reliability and
radiation hardness but also in the handling of time
varying propagation conditions.
• Propagation Experiments are needed to validate
the propagation prediction methods.
Conclusion
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Thank you !
Bertram Arbesser-Rastburg
[email protected]