01 microwave communication principles 38

7/30/2019 01 Microwave Communication Principles 38

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Microwave Principles


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Contents

Microwave Equipments Application

PART 2

PART 3

PART 1

Microwave Communication Principles

Network Planning


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Microwave Equipment Application

Ethernet Application

Mobile Network Application

Cellular Network Application

Application/Solution


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Application/Solution

Point to Point Digital Microwave transmission system

MUX

Satellite

Fiber optic cable

Microwave link

Coaxial cable

MUX


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Mobile Network Application

BSC

MSCPSTNBSC

.....

MSC

SDH

BSC

BSC

BTS

BTS

BTS

BTS

BTS

BTS

BTS

BTSBTS

BTS BTS

BTS

BTS

BTS

BTS

BTS PDH

PDH

BTS

PDHBTS

BTS

BTS

BTS

BTS

BTS

SDH

SDH

SDH

SDH

PDH

PDH

PDH

PDH

PDH

PDH

PDH

SDH SDH

SDH

Microwave

PDH

Microwave

PSTN: Public Switched

Telephone Network

MSC:Mobile Switching Center

BSC: Base Station ControllerBTS: Base Transceiver Station


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Cellular Network Application1

UMTS: Universal Mobile

Telecommunication System


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Cellular Network Application2

RNC: Regional Network Centre

ADM: Add/Drop Multiplexer

MUX: Multiplexer

STM: Synchronous Transport Module


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Ethernet Application(1)LAN to LAN Bridge


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Ethernet Application(2)


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Ethernet Application(3)


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Review

What are the main transmission methodsnowadays?

What are the main applications for microwave

equipments?


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Microwave Communication Principles

System Structure

Introduction to Microwave Principles


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Introduction to Microwave Principles

Radio Frequency Spectrum Utilization

Features of Radio Transmission

Microwave Frequency

Different Transmission Systems

Microwave Radio Link

Fading

Interference

Radio Wave Propagation

Relay station (Passive)


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MUX

Satellite

Fiber optic cable

Microwave link

Coaxial cable

MUX

Different Transmission Systems


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10Km 1Km 100m 10m 1m 10cm 1cm 1mm

f 30KHz 300KHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz

LF MF HF VHF UHF SHF EHF

microwave

Frequency: 300MHZ 300GHZ Wavelength: 1m~1mm

Frequency band: UHF: 0.3-1.12G X: 8.2-12.4G L: 1.12-1.7G

KU: 12.4-18G LS: 1.7-2.6 G K: 18-26G

S: 2.6-3.95 G Ka: 26.5-40G C: 3.95-5.85G

U: 40-60G XC: 5.85-8.2G

Microwave Frequency


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Wavelength is short while frequency is high.

Wide frequency band

Line of sight propagation, reflection, diffraction and scattering

Free space loss

Fading caused by other types of path loss.

Interference

1

2

3

4

5

6

Features of Radio transmission


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85432 10 201 30 40 50

1.5 2.5

Regional network

National backbone network

Regional and local network

2

8

34Mbit/s

34

140

155

Mbit/s

28

34140155

Mbit/s

3.3 11 GHz

GHz

Radio Frequency Spectrum Utilization1


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Channel number

Frequency

F3

F1F2

Fo

1 2 n 1' n'

Low frequency band High frequency band

Band width

Fo: Center frequency

2'

Radio Frequency Spectrum Utilization2


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The radio link propagation follows the line of sight: it requires a perfect clearing between

transmitting and receiving antennas. The propagation medium is made of the lower layers

of the atmosphere (a few meters to a few hundred of meters above ground)

The non homogeneity of the atmosphere influences the waves propagation:

1) Path curvature

2) Reflecting, diverging, focusing intermittent events

Free space loss (Lfs)=92.4+20log(fd) (dB)

f:GHz, d:km

Radio Wave Propagation1


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AbsorptionPartial reflection

Almost horizontal

DiffusionRefraction

Atmosphere influence

i.1

i.2

n1

n2

n1

n2

Diffusion

volume

500Km

n1sin i.1 = n2sin i.2

Gaz and watervapor

Frequ. < 15 GHz :

insignificant

20 GHz : 0.1 dB / kmRain

Freq > 10

GHz



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Ground influence

Reflection

Diffraction

Spherical diffraction

Diffraction on a ridge



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An imaginary earth with the radius of 8500km, allows to simplify analysis on

Refraction propagation of radio wave.

R

Imaginary EarthReal Earth

Ro

Standard atmosphere N = - 39 N.units Km

K = R/Ro = 4/3h

h

N : Gradient of air refraction index

N may reach more extreme values than + 250 or - 350, during short percentage of time

N = 315 N units

Air refraction index at sea level: n = 1.000 315

N



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Fading

Causes

Types

Selective Fading

Rain and Snow Fading

Anti-Fading Measures


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Causes

Causes of fading

Reflection

Changes of transmitting media

Atmosphere

Rain

1

2

3

4


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Types

Fast fading and slow fading

Up fading and down fading

Frequency selective fading and flat fading

1

2

3


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Selective Fading

Refraction

ReceiverTransmitter

A max

A minFrequency

Radio channel

> 1 non-minimal phase fading

A

F0

F

A

AA

For A1 = A2 A max dB = + 6A min dB = -

A

F =1

1

1

1

2

- A+ A

2

2

8

= T

=A

A

2

2

1

- T 1

Reflection

A ,T2 2A ,T11

< 1 minimal-phase fading

Cause Multi-path propagation

The direct signal is larger than the reflected signal


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Rain and Snow Fading

Transmitter

FI

-80 < Pr < -20 dBm

Receiver Demodulator

Digital

signal

IF

A B

CAG

A

Time

dBm

W0

Noise

W

B

dBm

Time

IF Level 0 dBr 2dB

CN

Main cause frequencies > 10 GHz

Signal

Noise


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Anti-Fading Measures

H

Frequency Diversity

1

2

3

Techniques without diversity

Diversity techniques

Space Diversity

Reduce ground reflection

Increase path consistency

Various equalizers

1

2

10.2/F0/2


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Interference

Types

Anti-Interference Measures


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Sort

A

B

Co-channel interference

Adjacent channel interference


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Anti-Interference Measures

A

B

Increase transmit power

Improve band pass filter performance


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TX/R

x

HopNO.1

Or

TX/Rx

HopNO.2

HopNo.n

TX/Rx TX/R

x

Distance between the transmitter and the receiver, a few km < D < 100km

Availability and quality depends on the distance recommended by ITU-R.

Terminal

Station

Cable

Relay station

(Passive)

Terminal

StationRelay station

(Active)

CableRadio Link

Microwave Radio Link


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Parabolic reflectorsPlane reflectors

Relay station (Passive)


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System hierarchy

Transmission Rate Levels

Digital System Hierarchy


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2400/19200 bit/sData VF

TN 1

64 kbit/s

2.048 Mbit/s

8.448 Mbit/s

34.268 Mbit/s

139.264 Mbit/s

TN 2

TN 3

TN 4

4 x 480 channels

1920 channels

4 x 120 channels

480 channels

4 x 30 channels

120 channels

+ frame + stuffing

30 channels 64 kbit/s + 64 kbit/s signalling + 64 kbit/s frame

32 x 64 = 2048 kbit/s

Data

MUX PCM

Digital System Hierarchy


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Tx/RxCMI

Tx/RxHDB3

Tx/RxHDB3

Tx/RxHDB3

1

4

32

1

4

3

2

TN2

1

4

3

2

1

30

140 Mbit/s34,268 Mbit/s

8,448 Mbit/s

2,048 Mbit/s

64 kbit/s

34 Mbit/s

8 Mbit/s

2 Mbit/s

Tx/Rx

TN4

2/34 Mbit/s PDHADM

155

155 Mbit/s

CMI

4x2 Mbit/s

or 4x2 Mbit/s

or 16x2 Mbit/s

TN3

TN1

Transmission Rate Levels


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Review

1.What are the frequency rang of microwave?2. Describe the features of the microwave transmission?

3. What are the influences of the atmosphere on

microwave transmission?

4. What are the causes of fading?

5. What are the main causes of selective fading?

6. What are the two types of counter-fading measures?

What are the main measures?

7. How many kinds of passive relay stations are there?


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01 microwave communication principles 38

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