Bayesian networks, introduction Graphical models: nodes (vertices) links (edges)
Introduction to MW Links
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Transcript of Introduction to MW Links
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Introduction to Microwave Links
Micro...wave... link?
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Introduction to Microwave Links
Introduction to
MicrowaveLinks
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Introduction to Microwave LinksObjectives
To describe microwave link architectures.
To list propagation problems.
To list the characteristics of an antenna.
To identify the types of modulation.To list parameters for preparing a frequency plan.
To prepare a simplified link budget.
To describe the configurations of a transceiver.
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Introduction to Microwave LinksMicrowave link architectures
Signals to be transmitted
Optical fibre
Copper wire
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Introduction to Microwave LinksMicrowave link architectures
Signals to be transmitted
PDH: Plesiochronous Digital Hierarchy
TN1
2 Mbit/s ( E1 )
30 telephone
channelsTN2
8 Mbit/s ( E2 )
TN3
34 Mbit/s ( E3 )
Used code :
E1, E2, E3 HDB3
E4 CMI TN4
140 Mbit/s ( E4 )
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Introduction to Microwave LinksMicrowave link architectures
Signals to be transmitted
SDH: Synchronous Digital Hierarchy
The clock is carried by the signal itself which
synchronizes the equipment
The SDH frame incorporates:
- a header
- a payload (tributaries)
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Introduction to Microwave LinksMicrowave link architectures
Microwave
Link
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Introduction to Microwave LinksMicrowave link architectures
Diagram of a microwave link
F10111010110111
Tx
Rx
Tx
Rx
1011101 0110111F
Tx : transmitter
Rx : receiverF : transmission frequency
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Introduction to Microwave LinksMicrowave link architectures
Terminal station
Relay station
Relay station
Relay station
Relay station
Relay station
Relay station
Terminal station
I d i Mi Li k
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Introduction to Microwave LinksMicrowave link architectures
Point-to-point radio
Point-to-multipoint radio
I t d ti t Mi Li k
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Introduction to Microwave LinksMicrowave link architectures
Nodal point
Offices
Universities
Hospitals
Offices
Offices
I t d ti t Mi Li k
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Introduction to Microwave LinksMicrowave link architectures
Central office
SDH Ring
Offices
Heavy traffic customers
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Introduction to Microwave LinksCourse content
Radio waves
Definition
Polarization
Propagation in free space
Propagation problems
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Introduction to Microwave LinksRadio waves
Definition
= C * T = C / F
: wavelength in metres,
C : speed of light in metres per second,
F : frequency in Hertz,
T : period in seconds.(mm) = 300 / F(GHz) in mm F in GHz
150 2
42,86 7
23,08 13
13,04
23
7,89 38
In the air
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Introduction to Microwave LinksRadio waves
Polarizations
Vertical polarizationCircular polarization
VERTICAL
POLARIZATION
HORIZONTAL
POLARIZATION
CIRCULAR
POLARIZATION
PROPAGATION
DIRECTION
PRO
PAGATION
DIRECTION
PROPAGATION
DIRECTION
Horizontal polarization
not used in microwave links
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Introduction to Microwave LinksRadio waves
Polarizations
Rectangular waveguide section
E
E
E : electric field
Earth horizontal
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Introduction to Microwave LinksRadio waves
Polarizations
Waveguides with different flanges
30 dB !
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Introduction to Microwave LinksRadio waves
Propagation in free space
Free space = no solar effects
no effects induced by atmospheric conditions
Clearance of the first Fresnel ellipsoid
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Introduction to Microwave LinksRadio waves
Propagation in free space
First Fresnel ellipsoid
d
r
M
A B
AM + MB = AB + (n*/2)
n = 1, first Fresnel ellipsoid
d : axis of radio wave path,
r : radius of first ellipsoid
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Introduction to Microwave LinksRadio waves
Radius of first Fresnel ellipsoid: rmax = 0.5**d
Propagation in free space
Maximum radius of first Fresnel ellipsoid
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40
distance in km
radiusinm
F (GHz)
2 GHz
7 GHz
13 GHz
23 GHz
38 GHz
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Introduction to Microwave LinksRadio waves
Propagation in free space
Elevation
(metres)
60
80
100
120
140
160
260
240
220
200
180
40
20
0
0 5 10 15 20 25 30 35 40 45 50 55 60
Path Length (65.00 km)
Radiofrequency propagation path
First Fresnel ellipsoid
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Radio waves
Propagation in free space
Part of the transmitted energy that is
picked up by the receive antenna
Pe
Pr
d
Sr: receive antenna
equivalent surface area
Pr= Pe * Sr / (4**d2) , where Sr= 2 / (4*)
Pr= Pe * ( / 4 * * d)2
Part of the sphereof radiated
isotropic power
= 20 log (4 * * d / )
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Radio waves
Propagation in free space
Telegraphists equation:
= Pe / Pr = 20 log (4D / )
Free space losses
90
100
110
120
130
140
150
160
170
1 10 100 1000Distance in km
LossesindB
F (GHz)
2 GHz
7 GHz
13 GHz
23 GHz
38 GHz
5020
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Radio waves
Propagation problems : correction for the roundness of the earth
021000
21
R
ddh
=
COLOMBIA
PROYECTO RIC chapmari.pl3
Date 09-08-99 By DO
ALCATEL
CHAPARRALLatitude 003 43 40.00 N
Longitude 075 29 47.00 W
Azimuth 61.13 deg
Elevation 895 m ASL
Antenna CL 0.0 m AGL
LA MARIALatitude 004 14 25.00 N
Longitude 074 34 10.00 W
Azimuth 241.20 deg
Elevation 1586 m ASL
Antenna CL 0.0 m AGL
Frequency = 1440.0 MHz
K = 1.00
%F1 = 100.00
Path Length (117.50 km)
0 10 20 30 40 50 60 70 80 90 100 110
Elevation(metres
)
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
The bulging of the earth at a point on the profile is:
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Radio waves
Propagation problems :
Effect of atmospheric refraction
Gases in the atmosphere such as water vapour and oxygen
create additional attenuation over and above that produced
during propagation in free space.
13 GHz 18 GHz 23 GHz 38 GHz
0.03 dB/km 0.08 dB/km 0.19 dB/km 0.12 dB/km
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Radio waves
Propagation problems :
Effect of atmospheric refractionAccording to vertical variations in the atmospheric
refractive index, microwave signals do not propagate in a
straight line between antennas, but on a curved path whichchanges over time.
Standard conditions = 50% of thetime, and the path curves towards
the earth;
Unfavourable conditions = 0.1% ofthe time, and the path curves
towards the sky.
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Radio waves
Propagation problems :
Effect of atmospheric refraction
kmax = 4/3, R0 = 8504 km
the radiofrequency horizon
is further away and the
earth seems flatter.
kmin = 2/3, R0 = 4252 km
the radiofrequency horizon iscloser and the earth seems
rounder.
R0 kmax R0
R0 = 6378 km
kmin R0 R0
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Radio waves
60% OF RADIUS CLEARED (K=4/3)
0% OF RADIUS CLEARED (K MIN) pldemo_1.pl2
Date 09-22-99 By LBT
ALCATEL
WESTONVILLE
Latitude 049 15 12.00 N
Longitude 122 34 14.00 W
Azimuth 47.41 deg
Elevation 120 m ASL
Antenna CL 36.7 m AGL
BAKER LAKE
Latitude 049 38 49.00 N
Longitude 121 54 29.00 W
Azimuth 227.91 deg
Elevation 150 m ASL
Antenna CL 53.2 m AGL
Frequency = 2000.0 MHz
K = 1.33, 0.85%F1 = 100.00
Path Length (65.00 km)
0 5 10 15 20 25 30 35 40 45 50 55 60
Elevation
(metres)
0
2040
60
80
100
120
140
160
180
200
220
240
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Radio waves
Propagation problems : Clearance rules
F > 3 GHz:
1 - 100% of the first Fresnel ellipsoid must be cleared for
kmax = 4/3 (no attenuation for 50% of the time).
2 -Knife edge obstacle: 0% of the radius of the first ellipsoid
must be cleared (attenuation = 6 dB for 0.1% of the time),
A number of knife edge obstacles or a spherical obstacle:
30% of the radius of the first ellipsoid must be cleared (attenuation
= 6 dB for 0.1% of the time).
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Radio waves
Propagation problems: Clearance rules
F < 3 GHz:
1 - 60% of the first Fresnel ellipsoid must be cleared for
kmax = 4/3 (no attenuation for 50% of the time).
2 -Knife edge obstacle: 0% of the radius of the first ellipsoid
must be cleared (attenuation = 6 dB for 0.1% of the time),
A number of knife edge obstacles or a spherical obstacle:
30% of the radius of the first ellipsoid must be cleared (attenuation
= 6 dB for 0.1% of the time).
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Radio waves
Propagation problems: Diffraction
When one or more obstacles penetrate the first Fresnel ellipsoid,
this is called radiation by diffraction.
The received signal is affected by additional attenuation. It variesover time as a function of changes in propagation conditions and
must be calculated for different values of kmax = 4/3 (50% of the
time) and kmin (0.1% of the time)
Fresnel ellipsoid
r
ProfileObstacle
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Radio waves
Earth Radius Factor - arctan(K) (deg)
Relativ
eReceiveSignal(dB)
89.435.0 40 45 50 55 60 65 70 75 80 85-16
-14
-12
-10
-8
-6
-4
-2
0
2
4
1.00 1.33 2.00 5.00 10.00
h1=17.0, h2=9.0, freq=7000.0, H
Propagation problems: Reflection phenomena
Real earth
Variation of d1 for real earth
Variation of d1 for corrected earth
Reflection point displacement as a function of k
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Radio waves
Propagation problems: Reflection phenomena
STATION 2 Antenna Height (m)
RelativeReceiveSig
nal(dB)
50.04.6 10 15 20 25 30 35 40 45-14
-12
-10
-8
-6
-4
-2
0
2
4
h1=17.0, K=1.33, freq=7000.0, H
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Radio waves
Propagation problems: Reflection phenomena
Gain-heightcurve
Gain-height
curve
Resulting radiation
pattern
Receive Transmit
Complementary space diversity reception
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Radio waves
Propagation problems: Reflection phenomena
Water
Reflection phenomena
Water
Mask
Natural protection
Space diversity
Received signal variation
as a function of
antenna height variation
Water
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Radio waves
Propagation problems:
Attenuation due to hydrometeors
Attenuation, in dB per kilometre6 GHz 10 GHz 20 GHz 40 GHz
Fine rain 0.013 0.07
Downpour 0.012 0.08 0.45 1.5
Storm 0.22 1.2 5.5 13
Heavy storm 1.2 5.5 18 27
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Radio waves
Introduction to Microwave LinksRadio waves
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Propagation problems:
Attenuation due to hydrometeors
Per
centofTimeGradient
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Propagation problems:
Attenuation due to hydrometeors
Percen
tofTimeGradient
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AntennasGain
Radiation pattern
Aperture angle
Introduction to Microwave LinksAntennas
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Introduction to Microwave LinksAntennas
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Introduction to Microwave LinksAntennas
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Horn
G SdB = 10 42
log
S: projected surface area: antenna gain, from 50% to 70%
Gain
Frequency 2 GHz 4 GHz 8 GHz 13 GHz 23 GHz 38 GHz
Efficiency 50% 50% 60% 60% 70% 70%
Diameter 3.7 m 32 dB 38 dB 45 dB
Diameter 2.4 m 28 dB 34 dB 42 dB 46 dBDiameter 1.2 m 28 dB 36 dB 40 dB 46 dB
Diameter 0.6 m 34 dB 40 dB 44 dB
Diameter 0.3 m 34 dB 38 dB
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Radiation patterns
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Aperture angle at 3 dB
370
dB
d
.
Frequency 2 GHz 4 GHz 8 GHz 13 GHz 23 GHz 38 GHz
Diameter 3.7 m 2.8 1.4 0.7
Diameter 2.4 m 4.4 2.2 1.1 0.7Diameter 1.2 m 2.2 1.3 0.8
Diameter 0.6 m 2.7 1.5 0.9
Diameter 0.3 m 3 1.8
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Modulation
Introduction to Microwave LinksModulation
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Introduction to Microwave LinksModulation
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-1
0
1
0 1 2 3 4 5
BPSK
S ( t )
O.L.
Frequency
F0
A ( t )
x
Mixer
Modulator
-1
0
1
0 1 2 3 4 5
-1
0
1
0 1 2 3 4 5
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X
X
OL
++/2
Q sin 0t
Pcos 0t
cos 0t
P
H
A(t)
Q
F0
S(t)sin 0t
4QAM Modulator
H/2
H/2
-1
-0,5
0
0,5
1
0 1 2 3 4 5 6 7 8 9 10
-1
-0,5
0
0,5
1
0 1 2 3 4 5 6 7 8 9 10
-1,5
-1
-0,5
0
0,5
1
1,5
0 1 2 3 4 5 6 7 8 9 10
-1
-0,5
0
0,5
1
0 1 2 3 4 5 6 7 8 9 10
-1
0
1
0 1 2 3 4 5
4QAM
Introduction to Microwave LinksThe modulation
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The basic duration of a symbol cannot be indefinitely reduced but the
number of bits per symbol can be increased :
2n signal states = n bits transmitted for a symbol.
The Nyquist criterion defines the Nyquist band : minimum bandwith of a
transmission channel.
Note : The symbol is the digital signal element ready to be transmitted.
The symbol is the association of n bits that is to distinguish 2n different states (or different values
that the symbol can take).
For example : in 4 QAM, there are 4 states (=2n
= 22
) then 4 symbols of n (= 2) bits : 00, 01, 10 and11
MODULATION NYQUIST
BAND
Theorical peak
power
BER
MDP2 B P 10-n
4QAM B/2 P 10-n
16QAM B/4 P + 6,5 dB 10-n
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16-QAM Modulation drawback
Tx
1100
1110
Tx message : 1110 1100
Intersymbol distance
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16-QAM modulation drawback
Rx strong noise
Crosstalk area
Decoding Errors
1100
1110
Tx message : 1110 1100
Rx message : 1100 1100
Intersymbol distance
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Frequency plan
Organizations
Plan
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Introduction to Microwave LinksFrequency plan
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F4
F3
F2
F1 Fn
F'4
F'3
F'2
F'1 F'nVertical
polarization
Horizontalpolarization
Duplex separation = Fn - Fn
Example :CEPT T/R 13-02 Duplex separation = 1008 MHz
Fn (MHz) = F0 (MHz) + 798 + 28n
F n (MHz) = F0 (MHz) + 1806 + 28n
where F0 = 21,196 MHz and n =1,,20
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1, 3, 5 V
1 , 3 , 5 V 2, 4 V
2 , 4 V
1, 3, 5 H1 , 3 , 5 H
Example of frequency distribution
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Link budget
Introduction to Microwave LinksThe Bit Error Rate
D fi iti
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Definition :
There is an error when the noise led to an error interpretation of the symbol
The Bit Error Rate varies very quickly according to the Signal to Noise ratio
One generally retains the 3 following Bit Error Rate : 10-3 = unacceptable limit of quality for a telephone way
10-6 = correct limit of quality for a telephone way
10-8 = correct limit of quality for a digital data transmission
By the calculation, we may obtain the theorical levels of the receive signal accordingto these different Bit Error Rate
They are these values of Bit Error Rate which start the requests of :
priority switching
switching
early warning switching
Introduction to Microwave LinksThe receiver threshold calculation (1/3)
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Definitions :
User Bit Rate : tributary bit rate at the transmission equipment input
Binary bit rate : UBR + over bit rate of the transmission equipment
(engineering service channels + FEC)
Noise Factor : at the receiver input (for example : F = 1,8 dB )
C1 / N1 : Signal to Noise ratio at the receiver input
C2 / N2 : Signal to Noise ratio at the receiver output
DEMODULAT0R RECEIVER
C2 / N2BER C1 / N1
4 QAM Gain = GNoise Factor = F
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Introduction to Microwave LinksThe receiver threshold calculation (3/3)
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C2
N2x FKTBNC1 =
C1 dBm = ( C2/N2 ) dB + ( F ) dB + ( kTB1Hz ) dBm + ( BN ) dB
Example (theorical value)
UBR = 16x2 Mbit/s -> BN = 19.75 MHz
( C2/N2 ) dB at 10-3
for a 4QAM demodulator = 9.8 dB
( F ) dB = 1.8 dB
then the receiver threshold for a 10-3 bit error rate :
C1 dBm = 9.8 dB + 1.8 dB + ( -1741Hz ) dBm + ( 19,75 MHz ) dB
= 9.8 dB + 1.8 dB + ( -1741Hz ) dBm + ( 10 log 19,75x10-6 ) dB
= 9.8 dB + 1.8 dB + ( -1741Hz ) dBm + 72.95 dB
= - 89.45 dBm
Introduction to Microwave LinksSimplified link budget
dBmFrequency = 23 GHz
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Transmitted
power
Transmit
antenna gain
Received power
Free space
losses
Threshold 10-6
-87dBm
Threshold 10-3
-90dBm
Threshold 10-8
-8 5dBm
Quality
threshold
Receive antenna
gain
Margin
relative to
DCP : 40 dB
PTx= 12 dBm
PN= - 50 dBm
DCA
DC
DCP
Propagation
alarm
DCA PRx
- 75 dBm
- 80 dBm
Connection
losses
Connection
losses
Tx Rx
Free space losses = - 140 dB
Tx connection losses = - 1 dBTx antenna gain = 40 dB
Rx antenna gain = 40 dB
Rx connection losses = - 1 dB
Total losses = -62 dBThese values depend
on bit rates 2x2, 4x2,
8x2, 16x2 Mbits/s
or 34Mbits/s
q y
Distance = 10 kmBit rate = 2 tributaries
Antenna diameter = 0.6 m
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Transceiver hardwareconfigurations
Introduction to Microwave LinksHardware configurations
1+0 Configuration
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1 0 Configuration
F101110101101110
Tx
Rx
Tx
Rx
1011101 01101110F
Introduction to Microwave LinksHardware configurations
1+1 HSB Configuration
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1011101
F Rx 1
1011101
Tx 101101110
Tx x
Rx xoo
Rx 1
F
01101110
Tx 1
Tx x
Rx xoo
Introduction to Microwave LinksHardware configurations
Frequency Diversity Configuration
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q y y f g
Tx
Rx
Tx
Rx
TxF2
F
F1
F1 Tx
Rx Rx1100101 101010
011010
2
1101101
Introduction to Microwave LinksHardware configurations
Space Diversity Configuration
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Tx
Rx
01101110
Tx
Rx
01101110
1011101
1011101
F
F
Tx
Rx
F
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Microwavelink!