Point – to – point
Radiocommunication
SMS4DC training seminar
1 – 10 May 2006
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
1
Content
• Technical overview
• SMS4DC Software link calculation
• Exercise
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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1
Point-to-point Radiocommunication Link
A Radio Link
f1
Terminal
repeater
Hop 1
A Hop
f2
repeater
fn
Terminal
Hop 2
Isotropic
antenna
Propagation
loss
Transmitting
antenna gain
TX antenna
cable lose
Isotropic
antenna
Receiving
antenna gain
RX antenna
cable lose
Receiver
Transmitter
Filters,
feeder, etc.
Filters,
feeder, etc.
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Definition
• Point-to-point communication
Radiocommunication between specified fixed stations
• Fading
Fluctuation of signal level respect to
stable condition for number of reasons
• Path Profile
Minimum acceptable
A vertical cut of terrain along propagation
signal level
path between transmitter and receiver
• NFD
Discrimination gained because of TX
emission and RX reception masks
• Polarization
The locus of electric field vector fluctuation
• SWR
Standing Wave Ratio ([1+| |]/[1-| |])
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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2
Link Budget
• Total Loss = [Free Space Loss]
+ [Atmospheric Gaseous Loss]
Fre
+ [Rain Attenuation]
e Sp
ac e
+ [Clear Air Fading]
Lo
ss = 4
πd 2
+ [Diffraction Loss]
λ
+ [NFD]
• Flat Receive Level = PT + GT
– [Free Space Loss]
– [Atmospheric Gaseous Loss]
– [Diffraction Loss]
– GR
– [Receiver Insertion Loss]
• Fade Margin = [Flat Receive Level] – [Receiver Threshold]
• Insertion Loss= [Cable Loss]+[Branching Loss]+[Mismatch Loss]
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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RF Signal Spectrum
2
Power Spectral Density of x(t) : | X ( f ) |
Occupied bandwidth
Normally β = 0.5 %
Out of band
emission
β
%
2
β
%
2
Necessary
bandwidth
Y dB (usually Y = 6dB to noise floor)
spectrum floor
noise floor
f 3 f1
f2 f4
frequency
f4
Px (t ) = | X ( f ) |2 df = Area of yellow color
f1
f3
f3
f4
| X ( f ) |2 df = | X ( f ) |2 df =
f2
β
Px (t )
200
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Transmitting and Receiving Masks
• The power spectral density (PSD)
Transmitter emission mask
0 dB
RF Signal
xc(t)
Spectrum floor
Noise floor
Necessary
bandwidth
Spurious
emissions
~6 dB
Assigned
Frequency
• Normally each TX has identical corresponding RX
receiving masks
• Mismatched TX & RX masks cause additional loss (NFD)
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Propagation Effects
• Diffraction fading due to obstruction of the path;
• Attenuation due to atmospheric gases;
• Fading due to atmospheric multipath or beam spreading
(commonly referred to as defocusing) associated with
abnormal refractive layers;
• Fading due to multipath arising from surface reflection;
• Attenuation due to precipitation or solid particles in the
atmosphere;
• Variation of the angle-of-arrival at the receiver terminal and
angle-of-launch at the transmitter terminal due to refraction;
• Reduction in cross-polarization discrimination (XPD) in
multipath or precipitation conditions;
• Signal distortion due to frequency selective fading and delay
during multipath propagation.
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Propagation Loss
• Attenuation due to atmospheric gases,
• Diffraction fading due to obstruction or partial
obstruction of the path,
• Fading due to multipath, beam spreading and
scintillation,
• Attenuation due to variation of the angle-ofarrival/launch,
• Attenuation due to precipitation,
• Attenuation due to sand and dust storms
9
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
Gaseous Attenuation
102
(ITU-R
(ITU-R P.676)
P.676)
5
Aa = γ a d
dB
• High attenuation
frequencies have
special usages
H 2O
2
10
Specific attenuation (dB/km)
• Considerable loss
above 10 GHz
5
2
1
5
2
10– 1
5
2
Total
Dry air
10– 2
Pressure: 1 013 hPa
Temperature: 15°C
Water vapour: 7.5 g/m3
Dry air
5
2
H 2O
10– 3
1
2
5
10
2
5
Frequency, f (GHz)
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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10
2
3.5
10
5
k-factor
•
•
•
•
•
Electromagnetic wave bends while passing through nonhomogenous medium,
Vertical profile of atmosphere is non-homogeneous,
Median effective Earth radius factor :
k50 = 157 /[157 − ∆N ]
Effective radius of Earth in km: ae = 6371× k e
See ITU-R P.453 for N (vertical refractivity gradient),
Modified
Actual
k>1
Modified
Actual
k<1
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Propagation by Diffraction (ITU-R P.526)
LOS is possible
• Diffraction over a spherical
earth for trans-horizon paths
shadow
• Diffraction by obstacles
inside Fresnel zone
• Consideration of diffraction from round, wedge
and sharp obstacles, single and multiple (in
P.452 propagation model)
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Fresnel ellipsoids
n =1
Fresnel Ellipsoids
n =2
M
B
A
AM + MB = AB + n
Wavelength
λ
2
• More than 90% of power, propagates inside first ellipsoid
• For Line – of – Sight (LOS) communication first Fresnel
ellipsoid should be enough clear
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
Fresnel zone
nth
13
Radius of
Fresnel zone
Rn
Rn
d1
Rn = 550
n d1 d 2
( d1 + d 2 ) f
1/ 2
d2
f is frequency in MHz and
all distances are in km
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Diffraction Fading
Obstruction of the Path
• No LOS
path
• Obstruction
inside
Fresnel zone
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ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
Diffraction loss and clearance
1st Fresnel zone
Positive h
h
Obstruct
•
0.6 F1 clearance is necessary
for tropical climate
B: theoretical knife-edge loss curve
D: theoretical smooth spherical Earth loss curve,
at 6.5 GHz and k = 4/3
A: empirical diffraction loss for intermediate terrain
F: radius of the first Fresnel zone
h: amount by which the radio path clears the Earth’s surface
Diffraction loss relative to free space (dB)
– 10
Negative h
0
10
B
20
A
d
30
D
40
– 1.5
–1
– 0.5
0
0.5
1
Normalized clearance h/F1
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Antenna Height Determination
(Single Antenna in tropical climate)
•
•
•
•
Step 1: Determine antenna heights for 1.0F1 clearance in median
k- factor (k50 = (157/(157- N)) or k =4/3)
Step 2: Determine antenna heights for 0.6F1 using effective k-factor
from the following figure
1.1
Step 3: Select the larger
1
antenna heights
0.9
In temperate climate
ke
step 2 will be down using
0.0F1 for single isolated
obstruction or 0.3F1 for
obstruction is extended
along a portion of the map
0.8
0.7
0.6
0.5
0.4
0.3
10
2
5
Path length (km)
10
2
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Multipath Fading
atmospheric Multipath
surface Multipath
Antenna Decoupling
Beam Spreading
(governs the minimum beamwidth)
(defocusing)
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Multipath Fading Elements
• Multipath fading depends on:
–
–
–
–
–
–
Refractivity gradient in the lowest 65m of atmosphere
Area terrain roughness
Path inclination
Exceedance time percentage
Frequency
Altitude of antennas
• Calculation method explained in ITU-R P.530
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Hydrometer Attenuation
• Can be ignored in frequencies below 5 GHz
• ITU gathered rain statistics during 15 year (ITUR P.837),
γ R = kR α
dB
• Specific attenuation γR depends on polarization
and frequency,
• Rain attenuation exceedance can be estimated
within 0.001% to 1% of the time
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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XPD Degradation
(XPD: Cross-polarization discrimination)
• XPD defined in ITU-R P.310
• A measure of polarization diversification
H
H
V
V
TX
H
V
RX
TX
XPD =
PR , CoPol
PR , XPol
RX
• Multipath occurrence and precipitation degrade XPD
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Techniques to Reduce Multipath Fading
• Using inclined path to reduce flat fading due to
atmospheric mechanisms (beam spreading, antenna
decoupling, and atmospheric multipath);
• Reducing the occurrence of significant surface
reflections;
– Using terrain shielding,
– Moving reflection point to poorer location
• Using vertical polarization over water
• Prevention of larger value of clearance
• Using diversities
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Diversity Technique
• Space diversity
– To combat specular surface reflection
– To combat surface multipath fading
• Angle diversity (two antennas in
different orientation, in same or
different heights)
• Frequency diversity, more than one frequency
used for transmission
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Interference Mechanisms
• Long-term mechanisms
• Short-term mechanisms
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Long-term Interference
Propagation Mechanisms
(P.452)
(P.452)
FIGURE 1
Long-term interference propagation mechanisms
Tropospheric scatter
Diffraction
0452-01
155471
Line-of-sight
25
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
Short-term Interference
Propagation Mechanisms
(P.452)
(P.452)
FIGURE 2
Anomalous (short-term) interference propagation mechanisms
Elevated layer
reflection/refraction
Hydrometeor scatter
Ducting
Line-of-sight with
multipath enhancements
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
0452-02
155471
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Exercising SMS4DC
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Types of RF Channel
Arrangements
• Homogeneous channel arrangement
f n = f 0 + f offset + n ⋅ XS
′ + n ⋅ XS
f n′ = f 0 + f offset
MHz, n = 0,1,2,....
MHz, n = 0,1,2,....
• Uniform channel arrangement
f n = f 0 + n ⋅ XS
MHz,
n = 0,1,2,....
• Non-uniform channel arrangement
• References:
– ITU-R Recommendations, F series,
– CEPT Recommendations,
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Homogeneous RF Channel Arrangements
YS
XS
(A)
Polarization
Alternated
RF channel
Arrangement
(F.746)
(F.746)
H(V)
1
1
3
3
Alternated pattern
Main frequencies
V(H)
XS 2
2
XS
N
4
2
YS
4
Polarization
(B)
H(V)
V(H)
Channel number
ZS
B
DS
XS
1
2
3
4
N
1r
2r
3r
4r
Nr
YS
1
2
3
4
N
1r
2r
3r
4r
Nr
A
Main frequency
pattern
Band re-use in the
co-channel mode
Channel number
ZS
B
XS
(C)
Polarization
Interleaved
RF channel
Arrangement
Co-channel
RF channel
Arrangement
A
N
H(V)
V(H)
XS
2
1
3
2
1r
2r
4
3r
1
N
4r
Nr
YS
3
2
1r
2r
4
3r
N
4r
Nr
ZS
Main frequency
pattern
Band re-use in the
interleaded mode
Channel number
XS
A
A: “go” channels
B
B: “return” channels
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Uniform Channel Arrangement
• Suitable for Simplex operation mode
• More common in the bands shared
between Fixed and Mobile
• The only choice for TDD transmission
– Transmitting and receiving will be down in
different time slots
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Exercising SMS4DC software (1)
• Link Calculation provided for following models in the menu
of Propagation Model:
– ITU-R P.370
– ITU-R P.1546
– ITU-R P.526
– ITU-R P.452, and
– ITU-R P.530
• Step 1: Lunch the SMS4DC software
• Step 2: Lunch the DEM view using
toolbar push
button
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Exercising SMS4DC software (2)
• Step 3: Establish Fixed station A using
set the
frequency to 890 MHz
• Step 4: Choose antenna “ant_ALE8603_806.ant” and
check the antenna pattern
• Step 5: Establish an other Fixed station B using
set
the frequency to 880 MHz
• Step 6: Choose antenna “ant_ALE8603_806.ant” and
check the antenna pattern
• Step 7: Open the administrative part from “Database>Licensing”
• Step 8: Select “Anonymous Station” and find station B,
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Exercising SMS4DC software (3)
•
•
•
•
•
Step 9: Open Antenna Information Table of station B
Step 10: Push the “Modify” button,
Step 11: Change the field “Class of Antenna” from “T” to “R”
Step 12: Push the “Save” button,
Step 13: Find the station A and go to the level of
“Frequency”
• Step 14: Push the “Add Receiver” button top of the
“Frequency Information” table of station A. The “Add
Receiver” dialog box will appear.
• Step 15: Select the “Point” Radio button. All the selectable
receivers will be displayed in relevant spreadsheet
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Exercising SMS4DC software (4)
• Step 16: Choose the station B from table under POINT
section and push ok
• Step 17: Close Administrative dialog box
• Step 18: Open the “Database” menu and select “Display
Link”.
• Step 19: Select the record of new established hop
• Step 20: Push OK button to display stations of selected
hop on map
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Exercising SMS4DC software (5)
• Step 21: Open the menu “Propagation Model” and select
Link item under the ITU-R P.370 propagation model
Changing
direction of
calculation
Push button to
save profile
Values with
colored
background
can be tried
respect to the
editable values
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Exercising SMS4DC software (6)
• Step 21: Repeat step 21 for P.452 and
P.526 propagation model. See the
different calculated results
• Step 22: Repeat step 21 for P.530
propagation model. See the different
calculated results
• Step 23: Use mouse drag to change
antenna height and manage reflection
points
• Step 24: Push “Reflection Points”
button to see spreadsheet of reflection
points
Profile data
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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Exercising SMS4DC software (6)
• Step 25: Push “Availability”
button to see the availability
calculation result
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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End
ITU-BDT SMS4DC Regional Seminar for African countries, Dar-Es-Salaam, Tanzania, May 2006
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