introduction to mw links

8/11/2019 Introduction to MW Links

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Introduction to MW Links July 2006 Page 1 / 70

Introduction to Microwave Links

Micro...wave... link?


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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





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 )





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)




Microwave

Link




Diagram of a microwave link

F10111010110111

Tx

Rx

Tx

Rx

1011101 0110111F

Tx : transmitter

Rx : receiverF : transmission frequency




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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Point-to-point radio

Point-to-multipoint radio

I t d ti t Mi Li k


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Nodal point

Offices

Universities

Hospitals

Offices

Offices

I t d ti t Mi Li k


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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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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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Polarizations

Rectangular waveguide section

E

E

E : electric field

Earth horizontal



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Polarizations

Waveguides with different flanges

30 dB !



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Free space = no solar effects

no effects induced by atmospheric conditions

Clearance of the first Fresnel ellipsoid



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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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Radius of first Fresnel ellipsoid: rmax = 0.5**d


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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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


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


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


Azimuth 241.20 deg

Elevation 1586 m ASL


Frequency = 1440.0 MHz

K = 1.00

%F1 = 100.00


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

Introduction to Microwave LinksR di


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Radio waves


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


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


Azimuth 47.41 deg

Elevation 120 m ASL


BAKER LAKE

Latitude 049 38 49.00 N


Azimuth 227.91 deg

Elevation 150 m ASL


Frequency = 2000.0 MHz

K = 1.33, 0.85%F1 = 100.00


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


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


Gain-heightcurve

Gain-height

curve

Resulting radiation

pattern

Receive Transmit

Complementary space diversity reception



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Radio waves


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



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Per

centofTimeGradient



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Percen

tofTimeGradient



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AntennasGain

Radiation pattern

Aperture angle

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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-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

Introduction to Microwave LinksFrequency plan


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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


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


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


Space Diversity Configuration


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Tx

Rx

01101110

Tx

Rx

01101110

1011101

1011101

F

F

Tx

Rx

F



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introduction to mw links

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