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Satellite Link Impairment due toRain and Other Climatic Factors
Syed Idris Syed Hassan
Sch of Electrical & Electronic Engineering
Engineering CampusUniversiti Sains Malaysia
Seri Ampangan, Nibong Tebal
14300 Penang, Malaysia
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Introduction
Rain attenuation is a major constraint in
microwave radio link design above 10 GHz.
Several empirical and non-empirical rainattenuation prediction models that have been
developed are based on the measured data
obtained from temperate regions . Most of these existing rain attenuation
prediction models do not appear to perform
well in high rainfall regions.
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Introduction (continuation)
The ITU-R [4] model is currently being widely used by
many researchers.
Cumulative distribution empirical evidence shows thatthe ITU-R model underestimates the measured rain
attenuation cumulative distribution when applied to
tropical regions, leading to a poor prediction.
Other impairments are due to gaseous absorption,
cloud, tropospheric refractive effects, scintillation, wet
antenna etc.
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Measurement of bit error rateduring cloudy and clear sky
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Teleconference between USM andNIME via Superbird C
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Theoretical
Rain attenuation
ScintillationCloud attenuation
Gaseous attenuation
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Rain attenuation model
ITU
Lognormal
Moupfouma SAM
Yamada
Lin
DAH
Assis
Flavin CETUC
Crane
Etc..
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ITU model
The specific attenuation, is a function of therainfall rate, R0.01 exceeded at 0.01% of time is
given by:
= k(R0.01
) dB/km
where kand are frequency and polarization
parameters, given by ITU-R recommendation
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ITU rain attenuation prediction modelat 0.01% of time exceeding
Specific Rain Attenuation
0
5
10
15
20
25
30
35
40
45
0 10 20 30 40 50 60 70 80 90 100
Frequency (GHz)
Spec.Atten.
dB/km
horizontal polization
vertical polization
Ka-bandKu-band
Spec. attenuation
For Ku-band
4-7dB/kmFor Ka-band
12-25dB/km
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Models and measurement
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Rain Rate Models(compared with measurement)
Rain rate at 0.01%
Mea =112.6 mm/h
ITU =120 mm/h
Crane/Gamma=148mm/h
Log =100mm/h
R-H=135mm/h
Bod=55mm/h
DD= 28mm/h
7.3501.0 =A
0
50
100
150
200
250
300
0.001 0.01 0.1 1
percentage,%
rainrate,mm/h
ITU
Crane
DDMoupfouma
Bodtman&Ruthroff
Rice-Holmberg
Log-normal
Gamma
USM(3 years avg)
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Worth month Vs Annual rain rate probability
Pa = 0.509(Pw)x1.2
r2 = 0.9731
Pa = 0.2965(Pw)1.1623
00.05
0.1
0.15
0.20.25
0.3
0.35
0.4
0 0.5 1
worst month average rain rate
exceedence,Pw( %)
annualaverage
rainrate
exceedence,
Pa(%)
Measured
ITU
Power (Measured)
Power (ITU)
Measurement:
Pa= 0.509(Pw)1.2
ITU :
Pa =0.2965(Pw)1.1623
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Attenuation model at 0.01%
Mea=30dB
ITU= 15.34dB
Moupfo=31dB
DAH= 27dB
Crane=23dB
Flavin=19dB
SAM=20dB
VIHT=16dB
Gracia=10dB
0
10
20
30
40
50
60
0.001 0.01 0.1 0.3 1
percentage, %
attenuation,d
B
USM(3 years avg)
DAH
VIHT
Crane
ITU
SAM
Moupfouma
Gracia-Lopez
Flavin
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Current Experimental SetupMeasurement Site USM KMITL ITB
Earth Station Location 5.170N
100.40E
13.70N
100.80E
6.50S
107.40E
Beacon Frequency,
(GHz) 12.255 12.74 12.247
Antenna Elevation (deg)40.1 54.8 64.7
Altitude (m) 57 40 700
Antenna
Diameter (m)2.4 2.4 1.8
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Developing a new Rain attenuation modelfor Ku-band
Modify ITU-R model to retain the concept of an
equivalent rain cell.
The horizontal projection of the slant path, LG
was
modified based on the rain height, elevation angle,
reduction factor, and the rainfall rate at the
measurement sites.
The model was revised, so that it can be used attropical countries with the antenna elevation angle
varying from 400 to 700 .
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Comparison ITU model with measured dataand proposed model at USM at Ku-band
0
5
10
15
20
25
30
35
40
45
50
0.001 0.01 0.1 1
Percentage of time %
Rainfalla
ttenuationd
B
USM
ITU
95% UL
95%LLproposed model
UL = Upper Limit ;
LL = Lower limit
(confidence interval)
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Comparing ITU model with measured dataand proposed model at KMITL at Ku-band
0
5
10
15
20
25
30
35
40
45
50
0.001 0.01 0.1 1
Percentage of time %
Rainfalla
ttenuation
dB
KMITL
ITU
95% UL
95%LL
proposed model
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0
5
10
15
20
25
30
35
40
0.001 0.01 0.1 1
Percentage of time %
Ra
infalla
ttenuation
dB
ITB
ITU
95% UL
95%LL
proposed model
Comparing ITU model with measured dataand proposed model at ITB at Ku-band
Comparing the errors between ITU and
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Comparing the errors between ITU and
proposed model
%rms
% error
KMITL
P% 0.001 0.003 0.01 0.03 0.1 0.3 1
% error
USM
ITU -27.9 -18.1 -6.4 0.4 6 9.1 -26.4 16.2
Proposed -5.1 -2.4 0.05 1.1 4.32 4.17 8.19 2.9
ITU -40.3 -33.4 -23 -18.1 -12 -15.1 -41.3 28.4
Proposed -6.09 -3.63 -0.49 -1.46 5.78 1.94 5.81 4.11
% error
ITB
ITU -35.5 -29 -23.3 -17.9 -22 -18.3 -48.1 29.9
Proposed 9 6.19 -0.11 -4.92 -5.4 -1.56 6.79 6.14
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Specific Attenuation contour mapping
for 12 GHz (horizontal polarization)
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Specific Attenuation contour mappingfor 12 GHz (vertical polarization)
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Scintillation at slant path of 41O
Scintillation ofabout 0.2-0.4 dB
occurred at
frequency 12GHzaccording to months
and seasons
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Comparison of the measured scintillation
spectrum with the theoretical pattern (straightline).
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Cloud attenuation
Gunn and East model
Liebe model
Staelin model
Slobin model-derived from Staelin model
Altshuler model
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Gunn and East model
Cloud attenuation is given by
( )kmdBd /21
Im
6
4343.0 1
+
=
where
= complex relative dielectric constant of water=wavelength (cm)d=density of water (g/cm3) (~0.99)
1=liquid water content of the cloud (g/m3
)Im=imaginary part
Li b d l
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Liebe model
The cloud attenuation is given by( )kmdBffN /)("182.0=
( ) ( ) ( )[ ] 121 1"29"
+= yfN
( )( )
( )
( )( )
( )2
21
2
1
11
"s
s
p
po
ff
ff
ff
fff
+
+
+
=
( ) "2' +=ywhere
f= frequency in GHz
15.273
300
+= T
( ) ( ) ( ) 2221
2
1
11'
++
++
=
sp
o
fffff
( )11500590 = sf
( ) ( )2129414.14209.20 += pf
( ) ( )13.10366.77 += To
51.32 =
48.51 =
T in Centigrade
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Staelin model
The cloud attenuation is given by
( ) ( )kmdBT
/16.110343.42
2910122.01
1
=
where 1= the liquid water density of the cloud (g/m3)
T=temperature (K)
=wavelenght (cm)
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Slobin model
Make use of Stelin model and divide the
cloud into 12 different categories such as
lightest cloud, light cloud, medium cloud,
heavy cloud and heavier cloud.
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Altshuler model
Cloud attenuation at 10oC is given by
( ) ( )kmdB /3.11403.000075.00242.0 115.1 +
++=
= wavelength in mm
1=surface absolute humidity(g/m3)
Total attenuation is obtained by multiplying the distance below
where
( ) ( ) csc=DFor >8o
( ) ( ) ( )[ ] ( ) sincos2/1222
eeee aahaD +=For< 8o
=elevation angle
e=effective radius of the earth (8497km)
he=6.35-0.302 effective cloud height (km)=surface absolute humidity (g/m3)
where
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Gaseous attenuation
Water vapor AW
Oxygen Ao
Total Gaseous absorption (dB) is
owg AAA +=
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Water vapor attenuation
o
www fordBhA 10sin/ >=
( ) oweweww fordBhRFhR
A 10/tan
cos
=
w =specific attenuation of water vapor (dB/km)R
e
=effective earth radius (8500km)
= elevation anglehw= equivalent height of water vapor
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Oxygen attenuation
o
ooo fordBhA 10sin/ >=
( ) ooeoeoo fordBhRFhR
A 10/tan
cos
=
o =specific attenuation of oxygen layer (dB/km)R
e
=effective earth radius (8500km)
= elevation angleho= equivalent height of oxygen layer
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Future research
To verify the attenuation models at Ka-band
Develop a new attenuation model for Ka-
band USAT application in teleconference and
telemedicine
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