digital microwave communication principles-zte.pdf

MICROWAVEMICROWAVEMICROWAVEMICROWAVE PRINCIPLEPRINCIPLEPRINCIPLEPRINCIPLE

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LearningLearningLearningLearning GuideGuideGuideGuide

Microwave communication is developed on the basis of the electromagnetic

field theory.

Therefore, before learning this course, you are supposed to have mastered

the following knowledge:

Network communications technology basics

Electromagnetic field basic theory

Objectives

AfterAfterAfterAfter thisthisthisthis course,course,course,course, youyouyouyou should know:

Concept and characteristics of digital microwave communications

Functions and principles of each component of digital microwave

equipment

Common networking modes and application scenarios of digital

microwave equipment

Propagation principles of digital microwave communication and various

types of fading

Anti-fading technologies

Procedure and key points in designing microwave transmission link

ContentsContentsContentsContents

1.1.1.1. DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave CommunicationCommunicationCommunicationCommunication OverviewOverviewOverviewOverview

2. Digital Microwave Communication Equipment

3. Digital Microwave Networking and Application

4. Microwave Propagation and Anti-fading Technologies

5. Designing Microwave Transmission Links

TransmissionTransmissionTransmissionTransmission MethodsMethodsMethodsMethodsinininin ModernModernModernModern CommunicationsCommunicationsCommunicationsCommunications NetworksNetworksNetworksNetworks

Coaxial cable communication

Optical fiber communication

MUX/DEMUX Microwavecommunication

MUX/DEMUX

Satellite communication

MicrowaveMicrowaveMicrowaveMicrowave CommunicationCommunicationCommunicationCommunicationvs.vs.vs.vs. OpticalOpticalOpticalOptical FiberFiberFiberFiber CommunicationCommunicationCommunicationCommunication

Microwave Communication Optical Fiber CommunicationPowerful space cross ability, little landoccupied, not limited by land privatization

Small investment, short constructionperiod, easy maintenance

Optical fiber burying and landoccupation required

Large investment ,long construction period

Strong protection ability against naturaldisaster and easy to be recover

Outdoor optical fiber maintenance requiredand hard to recover from natural disaster

Limited frequency resources (frequencylicense required)

Not limited by frequency, license notrequired

Transmission quality greatly affected byclimate and landform

Stable and reliable transmission qualityand not affected by external factors

Limited transmission capacity Large transmission capacity

DefinitionDefinitionDefinitionDefinition ofofofof MicrowaveMicrowaveMicrowaveMicrowave MicrowaveMicrowaveMicrowaveMicrowave

Microwave is a kind of electromagnetic wave. In a broad sense, the

microwave frequency range is from 300 MHz to 300 GHz. But In

microwave communication, the frequency range is generally from 3 GHz

to 30 GHz.

According to the characteristics of microwave propagation, microwave

can be considered as plane wave.

The plane wave has no electric field and magnetic field longitudinal

components along the propagation direction. The electric field and

magnetic field components are vertical to the propagation direction.

Therefore, it is called transverse electromagnetic wave and TEM wave for

short.

DevelopmentDevelopmentDevelopmentDevelopment ofofofof MicrowaveMicrowaveMicrowaveMicrowave CommunicationCommunicationCommunicationCommunication

155M

34/140M

Transmissioncapacitybit/s/ch)

PDH digital microwavecommunication

system

SDH digital microwavecommunication

system

2/4/6/8M

480 voicechannels Analog microwave

communication system

Small and mediumcapacity digital microwavecommunication system

1980s1980s1980s1980s

LatLatLatLateeee 1990199019901990ssss ttttoooo nownownownow

1970s1970s1970s1970s

1950s1950s1950s1950sNote:Note:Note:Note:

Small capacity: < 10M

Medium capacity: 10M to 100M

Large capacity: > 100M

ConceptConceptConceptConcept ofofofof DigitalDigitalDigitalDigitalMicrowaveMicrowaveMicrowaveMicrowave CommunicationCommunicationCommunicationCommunication Digital microwave communication is a way of transmitting digital information in

atmosphere through microwave or radio frequency (RF).

Microwave communication refers to the communication that use microwave as carrier .

Digital microwave communication refers to the microwave communication that adopts the

digital modulation.

The baseband signal is modulated to intermediate frequency (IF) first . Then the intermediate

frequency is converted into the microwave frequency.

The baseband signal can also be modulated directly to microwave frequency, but only phase

shift keying (PSK) modulation method is applicable.

The electromagnetic field theory is the basis on which the microwave communication theory is

developed.

MicrowaveMicrowaveMicrowaveMicrowave FrequencyFrequencyFrequencyFrequency BandBandBandBandSelectionSelectionSelectionSelection andandandand RFRFRFRF ChannelChannelChannelChannel ConfigurationConfigurationConfigurationConfiguration (1)(1)(1)(1)

Generally-usedGenerally-usedGenerally-usedGenerally-used frequencyfrequencyfrequencyfrequency bandsbandsbandsbands inininin digitaldigitaldigitaldigital microwavemicrowavemicrowavemicrowave transmission:transmission:transmission:transmission:

7G/8G/11G/13G/15G/18G/23G/26G/32G/38G (defined by ITU-R Recommendations)

1.5 GHz 2.5 GHzRegional network

3.3 GHz

2/8/34Mbit/s

Long haultrunk network

11 GHz

Regional network, local network,and boundary network

34/140/155 Mbit/s

2/8/34/140/155 Mbit/s

GHz

1 2 3 4 5 8 10 20 30 40 50


In each frequency band, subband frequency ranges, transmitting/receiving spacing (T/R

spacing), and channel spacing are defined.

FrequFrequFrequFrequeeeennnnccccyyyy rangerangerangerange

f0 (center frequency)Low frequency band High frequency band

Protectionspacing

T/R spacingT/R spacing

Channelspacing

Adjacent channelT/R spacing

Channelspacing

f1f2 fn f1 f2 fn


Frequency range (7425M7725M)

T/R spacing: 154Mf0 (7575M)

28M

f =7470 =7596 f f f1=7442 2 f5 f1 2 5

7G7G7G7G FrequFrequFrequFrequeeeencyncyncyncy

RangeRangeRangeRange

74257725

71107750

72507550

FFFF0000 ((((MMMMHz)Hz)Hz)Hz)

7575

7575

7275

7597

7400

T/RT/RT/RT/R SpacSpacSpacSpaciiiinnnngggg

(MHz)(MHz)(MHz)(MHz)

154

161

196

196

161

CCCChhhhaaaannnnnelnelnelnel SpacingSpacingSpacingSpacing

(MHz)(MHz)(MHz)(MHz)

28

7

28

28

3.5

PrimaryPrimaryPrimaryPrimary andandandand Non-Non-Non-Non-

primaryprimaryprimaryprimary StatStatStatStatiiiioooonsnsnsns

Fn=f0-161+28n,

Fn=f0- 7+28n,

(n: 15)

DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowaveCommunicationCommunicationCommunicationCommunication ModulationModulationModulationModulation (1)(1)(1)(1)

Digital baseband signal is the unmodulated digital signal. The baseband signal cannot

be directly transmitted over microwave radio channels and must be converted into carrier

signal for microwave transmission.

ModulaModulaModulaModulattttionionionion

DigitalDigitalDigitalDigital basebandbasebandbasebandbaseband signalsignalsignalsignal IFIFIFIF signalsignalsignalsignal

Service signaltransmitted

DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowaveCommunicationCommunicationCommunicationCommunication ModulationModulationModulationModulation (2)(2)(2)(2)

The following formula indicates a digital baseband signal being converted into a digitalfrequency band signal.

A*COS(Wc*tA*COS(Wc*tA*COS(Wc*tA*COS(Wc*t++++))))

Amplitude Frequency Phase

PSK and QAM aremost frequently usedin digital microwave.

ASK: Amplitude Shift Keying. Use the digital baseband signal to change the carrieramplitude (A). Wc and remain unchanged.

FSK: Frequency Shift Keying. Use the digital baseband signal to change the carrierfrequency (Wc). A and remain unchanged.

PSK: Phase Shift Keying. Use the digital baseband signal to change the carrier phase ().Wc and A remain unchanged.

QAM: Quadrature Amplitude Modulation. ). Use the digital baseband signal to change thecarrier phase () and amplitude (A). Wc remains unchanged.

sMicrowaveMicrowaveMicrowaveMicrowave FrameFrameFrameFrame StructureStructureStructureStructure (1)(1)(1)(1) RFCOH

171.072 Mbit/s

15.552 Mbit/s STM-1 155.52Mbit/s

RFCOH SOH Payload

MLCM DMY XPIC ATPC WS RSC INI ID FA11.84 Mbit/s 64 kbit/s 16 kbit/s 64 kbit/s 2.24 Mbit/s 864 kbit/ 144 kbit/s 32 kbit/s 288 kbit/s

RFCOH: Radio Frame Complementary OverheadRSC: Radio Service ChannelMLCM: Multi-Level Coding ModulationINI: N:1 switching commandDMY: DummyID: IdentifierXPIC: Cross-polarization Interference CancellationFA: Frame AlignmentATPC: Automatic Transmit Power ControlWS: Wayside Service

MicrowaveMicrowaveMicrowaveMicrowave FrameFrameFrameFrame StructureStructureStructureStructure (2)(2)(2)(2) RFCOH is multiplexed into the STM-1 data and a block multiframe is formed. Each

multiframe has six rows and each row has 3564 bits. One multiframe is composed of

two basic frames. Each basic frame has 1776 bits. The remaining 12 bits are used for

frame alignment.

6 bitsFS Basic frame 1

Multiframe 3564 bits

FS Basic frame 2

6 bits 1776 bits148 words 6 bits 1776 bits (148 words)

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12 bits (the 1st word) 12 bits (the 148th word)

I: STM-1 information bitC1/C2: Two-level correction coding monitoring bitsFS: Frame synchronizationa/b: Other complementary overheads

QuestionsQuestionsQuestionsQuestions

What is microwave?

What is digital microwave communication?

What are the frequently used digital microwave frequency bands?

What concepts are involved in microwave frequency setting?

What are the frequently used modulation schemes? Which are the most

frequently used modulation schemes?


1. Digital Microwave Communication Overview

2.2.2.2. DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave CommunicationCommunicationCommunicationCommunication EquipmentEquipmentEquipmentEquipment




MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment CategoryCategoryCategoryCategory

System Digital microwave Analog microwave

MUX/DEMUXMode PDH SDH

CapacitySmall and medium

capacity (216E1, 34M)Large capacity

(STM-0, STM-1, 2xSTM-1)

(Discontinued)

Trunk radio

StructureSplit-mount radio

All outdoor radio

TrunkTrunkTrunkTrunk MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment

High cost, largetransmission capacity,more stable performance,applicable to long hauland trunk transmission

RF, IF, signal processing,and MUX/DEMUX unitsare all indoor. Only theantenna system isoutdoor.

P

M1

M2

SDH microwave equipment

BRU: Branch RF Unit

MSTU: Main SignalTransmission Unit(transceiver, modem, SDHelectrical interface, hitlessswitching)

SCSU: Supervision, Controland Switching Unit

BBIU: Baseband InterfaceUnit (option) (STM-1optical interface, C4 PDHinterface)

AllAllAllAll OutdoorOutdoorOutdoorOutdoor MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment

All the units areoutdoor.

RF processing unit

Installation is easy.IF cable

The equipment roomcan be saved.

IF and basebandprocessing unit

Service and power cable

All outdoor microwave equipment

)Split-MountSplit-MountSplit-MountSplit-Mount MMMMicrowaveicrowaveicrowaveicrowave EquipmentEquipmentEquipmentEquipment (1)(1)(1)(1)

The RF unit is an outdoor unit (ODU).

The IF, signal processing, and

MUX/DEMUX units are integrated in the

indoor unit (IDU). The ODU and IDU are

connected through an IF cable.

The ODU can either be directly mounted

onto the antenna or connected to the

antenna through a short soft waveguide.

Although the capacity is smaller

than the trunk, due to the easy

installation and maintenance, fast

network

construction, its the most widely used

Antenna

ODU(Outdoor Unit

IF cable

IDU(Indoor Unit)

microwave equipment. Split-mount microwaveequipment

Split-MountSplit-MountSplit-MountSplit-Mount MMMMicrowaveicrowaveicrowaveicrowave EquipmentEquipmentEquipmentEquipment (2)(2)(2)(2)

Unit Functions

Antenna: Focuses the RF signals transmitted by ODUs and increases the signal gain.

ODU: RF processing, conversion of IF/RF signals.

IF cable: Transmitting of IF signal, management signal and power supply of ODU.

IDU: Performs access, dispatch, multiplex/demultiplex, and modulation/demodulation for

services.

Split-MountSplit-MountSplit-MountSplit-Mount MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment IIIInstallationnstallationnstallationnstallation

SepSepSepSepaaaaraterateraterate MountMountMountMount DirectDirectDirectDirect MountMountMountMount

antenna(direct mount)

antenna (separatemount)

ODU

Soft waveguide

ODU IF cable IF cable

IDU IF portIDU IF port

MicrowaveMicrowaveMicrowaveMicrowave AntennaAntennaAntennaAntenna (1)(1)(1)(1)

Parabolic antenna Cassegrainian antenna

Antennas are used to send and receive microwave signals.

Parabolic antennas and cassegrainian antennas are two common types of microwave antennas.

Microwave antenna diameters includes: 0.3m, 0.6m, 1.2m, 1.8m,2.0m, 2.4m, 3.0m, 3.2metc.

MicrowaveMicrowaveMicrowaveMicrowave AntennaAntennaAntennaAntenna (2)(2)(2)(2)

Different frequency channels in same frequency band can share one antenna.

ChannelChannelChannelChannel CCCChannelhannelhannelhannel

TxTxTxTx

RxRxRxRx

1111

1111

1111

1111

TxTxTxTx

RxRxRxRx

nnnn

nnnn

nnnn

nnnn

AntennaAntennaAntennaAntenna AdjustmentAdjustmentAdjustmentAdjustment (1)(1)(1)(1)

Half-power angle Main lobe

Side lobeSide view

Tail lobe

Half-power angle Main lobe

Side lobeTop view

Tail lobe

AntennaAntennaAntennaAntenna AdjustmentAdjustmentAdjustmentAdjustment (2)(2)(2)(2) During antenna adjustment, change the direction vertically or

horizontally. Meanwhile, use a multimeter to test the RSSI at

the receiving end. Usually, the voltage wave will be displayedas shown in the lower right corner. The peak point of the

voltage wave indicates the main lobe position in the vertical or

horizontal direction. Large-scope adjustment is unnecessary.

Perform fine adjustment on the antenna to the peak voltagepoint.

When antennas are poorly aligned, a small voltage may be

detected in one direction. In this case, perform coarse

adjustment on the antennas at both ends, so that the antennasare roughly aligned.

AGCVoltage

detection point

VAGC

The antennas at both ends that are well aligned face a little

bit upward. Though 12 dB is lost, reflection interference willbe avoided.

Side lobe positionMain lobe position

Angle

AntennaAntennaAntennaAntenna AdjustmentAdjustmentAdjustmentAdjustment (3)(3)(3)(3)

During antenna adjustment, the two

wrong adjustment cases are show here.

One antenna is aligned to another antenna

through the side lobe. As a result, the RSSI

cannot meet the requirements.

Wrong Wrong Correct

Split-MountSplit-MountSplit-MountSplit-Mount MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment AAAAntennantennantennantenna (1)(1)(1)(1) AntAntAntAnteeeennannannanna gaingaingaingain

Definition: Ratio of the input power of an isotropic antenna Pio to the input power of a parabolic

antenna Pi when the electric field at a point is the same for the isotropic antenna and the

parabolic antenna.P D

2 Calculating formula of antenna gain:

G = io =

* P

i

Half-powerHalf-powerHalf-powerHalf-power anganganganglllleeee

Usually, the given antenna specifications contain the gain in the largest radiation (main lobe)

direction, denoted by dBi. The half-power point, or the 3 dB point is the point which is deviated

from the central line of the main lobe and where the power is decreased by half. The angle

between the two half-power points is called the half-power angle.

Calculating formula of half-power angle: 0.5 = (650 ~

700 )

D

Half-power angle

Split-MountSplit-MountSplit-MountSplit-Mount MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment AAAAntennantennantennantenna (2)(2)(2)(2) Cross polarization discrimination

Suppression ratio of the antenna receiving heteropolarizing waves, usually, larger than 30 dB.

XdB10lgPo/Px

Po: Receiving power of normal polarized wave

Px: Receiving power of abnormal polarized wave

Antenna protection ratio

Attenuation degree of the receiving capability in a direction of an antenna compared with that

in the main lobe direction. An antenna protection ratio of 180 is called front-to-back ratio.

ODU system architecture

Split-MountSplit-MountSplit-MountSplit-Mount MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment OOOODUDUDUDU ((((1111))))

Uplink IF/RF conversion

IFamplificat

ion

Frequencymixing

Sidebandfiltering

Poweramplification

RFattenuation

Localoscillation

(Tx) ATPCPower

detection

Localoscillation

(Rx)RF loop

Supervision and

IFamplification

Filtering Frequencymixing

Low-noiseamplification

Bandpassfiltering

controlsignal

Alarm and control

Downlink RF/IF conversion


SpecificationsSpecificationsSpecificationsSpecifications ofofofof TransmitterTransmitterTransmitterTransmitter

WorkingWorkingWorkingWorking frequencyfrequencyfrequencyfrequency bandbandbandband

Generally, trunk radios use 6, 7, and 8 GHz frequency bands. 11, 13 GHz and

higher frequency bands are used in the access layer (e.g. BTS access).

OutOutOutOutpppputututut powerpowerpowerpower

The power at the output port of a transmitter. Generally, the output power is 15 to

30 dBm.

Split-MountSplit-MountSplit-MountSplit-Mount MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment OOOODUDUDUDU ((((3333)))) LocalLocalLocalLocal frequencyfrequencyfrequencyfrequency stabilitystabilitystabilitystability

If the working frequency of the transmitter is unstable, the demodulated effectived

signal ratio will be decreased and the bit error ratio will be increased. The value

range of the local frequency stability is 3 to 10 ppm.

TransmTransmTransmTransmiiiitttt FrequencyFrequencyFrequencyFrequency SpectrumSpectrumSpectrumSpectrum FrFrFrFraaaammmmeeee

The frequency spectrum of the transmitted signal must meet specified

requirements, to avoid occupying too much bandwidth and thus causing too much

interference to adjacent channels. The limitations to frequency spectrum is

called transmit frequency spectrum frame.

CopyrightCopyrightCopyrightCopyright 2006200620062006 HuaweiHuaweiHuaweiHuawei TTTTeeeechnologieschnologieschnologieschnologies Co.,Co.,Co.,Co., LLLLttttd.d.d.d. AllAllAllAll rightsrightsrightsrights reserved.reserved.reserved.reserved. PagePagePagePage 35353535


SpecificationsSpecificationsSpecificationsSpecifications ofofofof ReceiverReceiverReceiverReceiver

WorkingWorkingWorkingWorking frequencyfrequencyfrequencyfrequency bandbandbandband

Receivers work together with transmitters. The receiving frequency on the local

station is the transmitting frequency of the same channel on the opposite station.

LocalLocalLocalLocal frequencyfrequencyfrequencyfrequency stabilitystabilitystabilitystability

The same as that of transmitters: 3 to 10 ppm

NoiseNoiseNoiseNoise figurefigurefigurefigure

The noise figure of digital microwave receivers is 2.5 dB to 5 dB.


PassbandPassbandPassbandPassband

To effectively suppress interference and achieve the best transmission quality, the

passband and amplitude frequency characteristics should be properly chosen. The

receiver passband characteristics depend on the IF filter.

SelectivitySelectivitySelectivitySelectivity

Ability of receivers of suppressing the various interferences outside the passband,

especially the interference from adjacent channels, image interference and the

interference between transmitted and received signals.

AutomaticAutomaticAutomaticAutomatic gaingaingaingain controlcontrolcontrolcontrol (AGC)(AGC)(AGC)(AGC) rangerangerangerange

Automatic control of receiver gain. With this function, input RF signals change within a

certain range and the IF signal level remains unchanges.


Frequency range (7425M7725M)

T/R spacing: 154Mf0(7575M) ODUs are of rich

types and smallvolume. Usually,ODUs are produced

Subband A Subband B Subband C Subband A Subband B Subband C by smallmanufacturers andintegrated by bigmanufacturers.

7442 7498

Non-primary station Primary station

ODU specifications are related to radio frequencies.As one ODU cannot cover an entire frequency band,usually, a frequency band will be divided into severalsubbands and each subband corresponds to oneODU. Different T/R spacing corresponds to differentODUs. Primary and non-primary stations have differentODUs.

Types of ODUs = Number offrequency bands x Number of

T/R spacing x Number ofsubbands x 2

(ODUs of some manufacturersare also classified by capacity.

Split-MountSplit-MountSplit-MountSplit-Mount MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment IIIIDDDDUUUU

Tributaryunit

Line unit

Cross-connection

Servicechannel

Microwaveframe

multiplexing

Microwaveframe

demultiplexing

IF unit

Modulation

Demodulation

Tx IF

Rx IF From/to ODU

O&Minterface

Supervision and control

Servicechannel

Powerinterface DC/DC conversion


What types are microwave equipment classified into?

What units do the split-mount microwave equipment have? And whatare their functions??

How to adjust antennas?

What are the key specifications of antennas?

What are the key specifications of ODU transmitters and receivers?

Can you describe the entire signal flow of microwave transmission?

SummarySummarySummarySummary

Classification of digital microwave equipment

Components of split-mount microwave equipment and their

functions

Antenna installation and key specifications of antennas

Functional modules and key performance indexes of ODU

Functional modules of IDU

Signal flow of microwave transmission




3.3.3.3. DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave NetworkingNetworkingNetworkingNetworking andandandand ApplicationApplicationApplicationApplication



CommonCommonCommonCommon NetworkingNetworkingNetworkingNetworking ModesModesModesModes ofofofofDigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave

Ring network Chain network

Add/Dropnetwork

Hub network

TypesTypesTypesTypes ofofofof DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave StationsStationsStationsStations

Digital microwave stations are classified into Pivotal stations, add/drop relay stations,relay stations and terminal stations.

Terminal station

Relaystation

Add/Droprelay station

Pivotal station Terminalstation

Terminalstation

TypesTypesTypesTypes ofofofof RelayRelayRelayRelay StationsStationsStationsStations

Passive Back-to-back antenna Plane reflector

Relay station

Active Regenerative repeater IF repeater RF repeater

ActiveActiveActiveActive RelayRelayRelayRelay StationStationStationStation RadioRadioRadioRadio FrequencyFrequencyFrequencyFrequency relayrelayrelayrelay stationstationstationstation

An active, bi-directional radio repeater system without frequency shift. The RF

relay station directly amplifies the signal over radio frequency.

RegeneratorRegeneratorRegeneratorRegenerator relayrelayrelayrelay stationstationstationstation

A high-frequency repeater of high performance. The regenerator relay station isused to extend the transmission distance of microwave communication systems, or

to deflect the transmission direction of the signal to avoid obstructions and ensurethe signal quality is not degraded. After complete regeneration and amplification, thereceived signal is forwarded.

PassivePassivePassivePassive RelayRelayRelayRelay StationStationStationStation

ParabolicParabolicParabolicParabolic rrrreeeeflectorflectorflectorflector passivepassivepassivepassive rrrreeeelaylaylaylay stationstationstationstation

The parabolic reflector passive relay station is composed of two parabolic

antennas connected by a soft waveguide back to back.

The two-parabolic passive relay station often uses large-diameter antennas.

Meters are necessary to adjust antennas, which is time consuming.

The near end is less than 5 km away.

PlanePlanePlanePlane RRRReflectoreflectoreflectoreflector PassivePassivePassivePassive RelayRelayRelayRelay StationStationStationStation

Plane reflector passive relay station: A metal board which has smooth surface,proper effective area, proper angle and distance with the two communication points.It is also a passive relay microwave station.

Full-distance free space loss:

L

s

= 142.1+ 20logd1d2 20loga

(km)1

d

(km)2

a = A c o 2a is the effective area (m2) of the flat reflector.

PassivePassivePassivePassive RelayRelayRelayRelay StationStationStationStation (Photos)(Photos)(Photos)(Photos)

Passive relay station(plane reflector)

Passive relay station(parabolic reflectors)

ApplicationApplicationApplicationApplication ofofofof DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave

Complementarynetworks to opticalnetworks (access the

services from the last 1km)

Special transmissionBTS backhaultransmission

conditions (rivers, lakes,islands, etc.)

Redundancy backupof important links

Microwaveapplication

Emergencycommunications

(conventions, activities,danger elimination,disaster relief, etc.)

VIP customer access


What are the networking modes frequently used for digital microwave?

What are the types of digital microwave stations?

What are the types of relay stations?

What is the major application of digital microwave?





4.4.4.4. MicrowaveMicrowaveMicrowaveMicrowave PropagationPropagationPropagationPropagation andandandand Anti-fadingAnti-fadingAnti-fadingAnti-fading TechnologiesTechnologiesTechnologiesTechnologies




4.14.14.14.1 FactorsFactorsFactorsFactors AffectingAffectingAffectingAffecting EleEleEleElecccctrictrictrictric WaveWaveWaveWave PropagationPropagationPropagationPropagation

4.2 Various Fading in Microwave Propagation

4.3 Anti-fading Technologies for Digital Microwave

KeyKeyKeyKey ParametersParametersParametersParameters ininininMicrowaveMicrowaveMicrowaveMicrowave PropagationPropagationPropagationPropagation (1)(1)(1)(1)

FresnelFresnelFresnelFresnel ZoneZoneZoneZone andandandand FresnelFresnelFresnelFresnel ZoneZoneZoneZone RadiusRadiusRadiusRadius

Fresnel zone: The sum of the distance from P to T and the distance from P to R

complies with the formula, TP+PR-TR= n/2 (n=1,2,3, ). The elliptical region encircled

by the trail of P is called the Fresnel zone.

T O

F 1

R

d 1P

d 2

Fresnel zone radius: The vertical distance from P to the TR line in the Fresnel zone. The

first Fresnel zone radius is represented by F1 (n=1).


d (km) d (km) Formula of the first Fresnel zone radius:

F = 17.32 1 21f (GHz) d (km)

The first Fresnel zone is the region where the microwave transmission energy is the

most concentrated. The obstructionobstructionobstructionobstruction inininin thethethethe FresnelFresnelFresnelFresnel zonezonezonezone shouldshouldshouldshould bebebebe asasasas littlelittlelittlelittle asasasas possible.possible.possible.possible.

With the increase of the Fresnel zone serial numbers, the field strength of the receiving

point reduces as per arithmetic series.


ClearClearClearClearaaaancencencence

h1

h3

h

A

hphc

M

hs

Bh5

h24

d1 d2d

h6

Along the microwave propagation trail, the obstruction from buildings, trees, and mountain

peaks is sometimes inevitable. If the height of the obstacle enters the first Fresnel zone,

additional loss might be caused. As a result, the received level is decreased and the transmission

quality is affected. Clearance is used to avoid the case described previously.

The vertical distance from the obstacle to AB line segment is called the clearance of the

obstacle on the trail. For convenience, the vertical distance hc from the obstacle to the ground

surface is used to represent the clearance. In practice, the error is not big because the line

segment AB is approximately parallel to the ground surface. If the first Fresnel zone radius of the

obstacle is F1, then hc/ F1 is the relative clearance.

FactorsFactorsFactorsFactors AffectingAffectingAffectingAffecting ElectricElectricElectricElectric WaveWaveWaveWave PropagationPropagationPropagationPropagation TeTeTeTerrrrrarararaiiiinnnn

The reflected wave from the ground surface is the major factor that affects the received level.

Straight lineStraight line

Reflection Reflection

Smooth ground or water surface can reflect the part of the signal energy transmitted by the antenna to

the receiving antenna and cause interference to the main wave (direct wave). The vector sum of the

reflected wave and main wave increases or decreases the composite wave. As a result, the transmission

becomes unstable. Therefore, when doing microwave link design, avoid reflected waves as much as

possible. If reflection is inevitable, make use of the terrain ups and downs to block the reflected waves.

FactorsFactorsFactorsFactors AffectingAffectingAffectingAffecting ElectricElectricElectricElectric WaveWaveWaveWave PropagationPropagationPropagationPropagation TeTeTeTerrrrrarararaiiiinnnn

Different reflection conditions of different terrains have different effects on electric wave

propagation. Terrains are classified into the following four types:

Type A: mountains (or cities with dense buildings)

Type B: hills (gently wavy ground surface)

Type C: plain

Type D: large-area water surface

The reflection coefficient of mountains is the smallest, and thus the mountain terrain is

most suitable for microwave transmission. The hill terrain is less suitable. When designing

circuits, try to avoid smooth plane such as water surface.

FactorsFactorsFactorsFactors AffectingAffectingAffectingAffecting ElectricElectricElectricElectric WaveWaveWaveWavePropagationPropagationPropagationPropagation AAAAtmospheretmospheretmospheretmosphere

Troposphere indicates the low altitude atmosphere within 10 km from the ground.

Microwave antennas will not be higher than troposphere, so the electric wave

propagation in aerosphere can be narrowed down to that in troposphere. Main effects of

troposphere on electric wave propagation are listed below:

Absorption caused by gas resonance. This type of absorption can affect the

microwave at 12 GHz or higher.

Absorption and scattering caused by rain, fog, and snow. This type of absorption

can affect the microwave at 10 GHz or higher.

Refraction, absorption, reflection and scattering caused by inhomogeneity of

atmosphere. Refraction is the most significant impact to the microwave propagation.



4.1 Factors Affecting Electric Wave Propagation

4.24.24.24.2 VariousVariousVariousVarious FadingFadingFadingFading inininin MicrowaveMicrowaveMicrowaveMicrowave PropagationPropagationPropagationPropagation

4.3 Anti-fading Technologies for Digital Microwave

FadingFadingFadingFading inininin MicrowaveMicrowaveMicrowaveMicrowave PropagationPropagationPropagationPropagation

Fading: Random variation of the received level. The variation is irregular and thereasons for this are various.

Fadingmechanism

Fading time Receivedlevel

Influence offading on signal

FreeFreeFreeFree SpaceSpaceSpaceSpace TransmissionTransmissionTransmissionTransmission LossLossLossLoss

Free space loss: A = 92.4 + 20 log ddd + 20 log f

(d:d:d: km, f: GHz). If d or f is doubled, the loss will increase by 6 dB.

ddddGTX GRX

PTX = Transmit power

PRX = Receive power

Power level

PTX

G

Receiving threshold

ffff

A0

G

G = Antenna gain

A0 = Free space loss

M = Fading margin

PRX

M

Distance

AbsorptionAbsorptionAbsorptionAbsorption FadingFadingFadingFading

Molecules of all substances are composed of charged particles. These particles have their

own electromagnetic resonant frequencies. When the microwave frequencies of these

substances are close to their resonance frequencies, resonance absorption occurs to the

microwave.

Statistic shows that absorption to the microwave frequency lower than 12 GHz is smaller

than 0.1 dB/km. Compared with free space loss, the absorption loss can be ignored.

10dB

1dB

0.1dB

0.01dB60GHz 23GHz 12GHz 7.5GHz 1GHz

Atmosphere absorption curve (dB/km)

RainRainRainRain FadingFadingFadingFading

For frequencies lower than 10 GHz, rain loss can be ignored. Only a few db may be

added to a relay section.

For frequencies higher than 10 GHz, repeater spacing is mainly affected by rain loss.

For example, for the 13 GHz frequency or higher, 100 mm/h rainfall causes a loss of 5

dB/km. Hence, for the 13 GHz and 15 GHz frequencies, the maximum relay distance is

about 10 km. For the 20 GHz frequency and higher, the relay distance is limited in few

kilometres due to rain loss.

High frequency bands can be used for user-level transmission. The higher the

frequency band is, the more severe the rain fading.

K-TypeK-TypeK-TypeK-Type FadingFadingFadingFading (1)(1)(1)(1)

AtmosphereAtmosphereAtmosphereAtmosphere refractionrefractionrefractionrefraction

As a result of atmosphere refraction, the microwave propagation trail is bent. It is

considered that the electromagnetic wave is propagated along a straight line above the

earth with an equivalent earth radius ofRe

,R

e

= KR (R: actual earth radius.)

The average measured K value is about 4/3. However, the K value of a specific

section is related to the meteorological phenomena of the section. The K value may

change within a comparatively large range. This can affect line-of-sight propagation.

R

e R


MicrowaveMicrowaveMicrowaveMicrowave propagationpropagationpropagationpropagation

k > 1: Positive refraction

k = 1: No refraction

k < 1: Negative refraction


EEEEqqqquivalentuivalentuivalentuivalent earthearthearthearth radiusradiusradiusradius

In temperate zones, the refraction when the K value is 4/3 is regarded as

the standard refraction, where the atmosphere is the standard atmosphere andRe which is 4R/3 is the standard equivalent earth radius.

k =

4/31

2/3Ground surface

Actual earth radius (r)

2/314/3

k =

Ground surface

Equivalent earth radius (rk)

MultipathMultipathMultipathMultipath FadingFadingFadingFading (1)(1)(1)(1)

Multipath fading: Due to multipath propagation of refracted waves, reflected

waves, and scattered waves, multiple electric waves are received at the receivingend. The composition of these electric waves will result in severe interference fading.

Reasons for multipath fading: reflections due to non-uniform atmosphere, water

surface and smooth ground surface.

Down fading: fading where the composite wave level is lower than the free

space received level. Up fading: fading where the composite wave level is higherthan the free space received level.

Non-uniform atmosphere

Water surface

Smooth ground surface. Ground surface

MultipathMultipathMultipathMultipath FadingFadingFadingFading (2)(2)(2)(2)

Multipath fading is a type of interference fading caused by multipath transmission.

Multipath fading is caused by mutual interference between the direct wave and reflected

wave (or diffracted wave on some conditions) with different phases.

Multipath fading grows more severe when the wave passes water surface or smooth

ground surface. Therefore, when designing the route, try to avoid smooth water and

ground surface. When these terrains are inevitable, use the high and low antenna

technologies to bring the reflection point closer to one end so as to reduce the impact of

the reflected wave, or use the high and low antennas and space diversity technologies or

the antennas that are against reflected waves to overcome multipath fading.

MultiMultiMultiMulti----pathpathpathpath FadingFadingFadingFading FFFFrequencyrequencyrequencyrequency SelectiveSelectiveSelectiveSelective FadingFadingFadingFading

Flat Selective fading

Normal

Frequency (MHz)

MultiMultiMultiMulti----pathpathpathpath FadingFadingFadingFading FFFFlatlatlatlat FadingFadingFadingFading

Up fading

Received levelin free space

Threshold level(-30 dB)

1hSignal

interruption

DuctDuctDuctDuct TypeTypeTypeType FadingFadingFadingFading

Due to the effects of the meteorological conditions such as ground cooling in the night,burnt warm by the sun in the morning, smooth sea surface, and anticyclone, a non-uniform structure is formed in atmosphere. This phenomenon is called atmospheric duct.

If microwave beams pass through the atmospheric duct while the receiving point isoutside the duct layer, the field strength at the receiving point is from not only the directwave and ground reflected wave, but also the reflected wave from the edge of the ductlayer. As a result, severe interference fading occurs and causes interruption to thecommunications.

Duct type fading

ScintillationScintillationScintillationScintillation FadingFadingFadingFading

When the dielectric constant of local atmosphere is different from the ambient due to the

particle clusters formed under different pressure, temperature, and humidity conditions,scattering occurs to the electric wave. This is called scintillation fading. The amplitude and

phase of different scattered waves vary with the atmosphere. As a result, the composite fieldstrength at the receiving point changes randomly.

Scintillation fading is a type of fast fading which lasts a short time. The level changes little

and the main wave is barely affected. Scintillation fading will not cause communicationsinterruption.

Scintillation fading

SummarySummarySummarySummary

The higher the frequency is and the longer the hop distance is, the more severe the fading

is. Fading is more severe at night than in the daylight, in summer than in winter. In the

daylight, sunshine is good for air convection. In summer, weather changes frequently. In sunny days without wind, atmosphere is non-uniform and atmosphere subdivision easily

forms and hardly clears. Multipath transmission often occurs in such conditions. Fading is more severe along water route than land route, because both the reflection

coefficient of water surface and the atmosphere refraction coefficient above water surface

are bigger. Fading is more severe along plain route than mountain route, because atmosphere

subdivision often occurs over plain and the ground reflection factor of the plain is bigger. Rain and fog weather causes much influence on high-frequency microwave.



4.1 Factors Affecting Electric Wave Propagation

4.2 Various Fading in Microwave Propagation

4.34.34.34.3 Anti-fadingAnti-fadingAnti-fadingAnti-fading TechnologiesTechnologiesTechnologiesTechnologies forforforfor DigitalDigitalDigitalDigital MiMiMiMiccccrrrrowaveowaveowaveowave

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesforforforfor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (1)(1)(1)(1)

CategoryCategoryCategoryCategory EffectEffectEffectEffect

Adaptive equalization Waveform distortion

EquipmentEquipmentEquipmentEquipment levellevellevellevelcountermeasurecountermeasurecountermeasurecountermeasure

Automatic transmit powercontrol (ATPC)

Power reduction

Forward error correction (FEC) Power reduction

SystemSystemSystemSystem levellevellevellevelcountermeasurecountermeasurecountermeasurecountermeasure

Diversity receiving technologyPower reduction andwaveform distortion

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesforforforfor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (2)(2)(2)(2) FrequencyFrequencyFrequencyFrequency domaindomaindomaindomain equalizationequalizationequalizationequalization

Signal frequencyspectrum

Multipath fadingSlope equalization

Frequency spectrum afterequalization

The frequency domain equalization only equalizes the amplitude frequency response

characteristics of the signal instead of the phase frequency spectrum characteristics.

The circuit is simple.


Time domain equalization

Time domain equalization directly counteracts the intersymbolinterference.

T T T

C-n C0 CnAfter

-2Ts -Ts Ts -2Ts -Ts Ts

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesForForForFor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (4)(4)(4)(4) Automatic transmit power control (ATPC)

Under normal propagation conditions, the output power of the transmitter is always at a

lower level, for example, 10 to 15 dB lower than the normal level. When propagation

fading occurs and the receiver detects that the propagation fading is lower than the

minimum received level specified by ATPC, the RFCOH is used to let the transmitter to

raise the transmit power.

Working principle of ATPC

Modulator Transmitter Receiver Demodulator

ATPC ATPC

Demodulator Receiver Transmitter Modulator

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesForForForFor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (5)(5)(5)(5)

ATPC: The output power of the transmitter automatically traces and changes with the

received level of the receiver within the control range of ATPC.

The time rate of severe propagation fading is usually small (

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesForForForFor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (6)(6)(6)(6) ATPCATPCATPCATPC adjustmadjustmadjustmadjustmeeeentntntnt processprocessprocessprocess (gradual(gradual(gradual(gradual change)change)change)change)

-25

-35High level

31

-45 Low level21

-55

-72ATPC dynamic range

45

Link loss (dB)

75 85 102


Cross-polarization interference

cancellation (XPIC)

In microwave transmission, XPIC is

30MHz

680MHz

340MHz80MHz 60MHz

used to transmit two different signals

over one frequency. The utilization ratio of

the frequency spectrum is doubled. To

avoid severe interference between two

different polarized signals, the

V (H)

H (V)

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

680 MHz

interference compensation technology

must be used.30MHz 80MHz

340MHz60MHz

V (H)

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

Horizontal polarizationH (V)

Vertical polarization1X 2X 3X 4X 5X 6X 7X 8X 1X 2X 3X' 4X 5X 6X

7X 8X

ShapeShapeShapeShape ofofofof waveguiwaveguiwaveguiwaveguiddddeeee iiiinnnntttterfaceerfaceerfaceerfaceFrequency configuration of U6 GHz frequency band (ITU-R F.384-5)


Diversity technologies

For diversity, two or multiple transmission paths are used to transmit the same information and the

receiver output signals are selected or composed, to reduce the effect of fading.

Diversity has the following types, space diversity, frequency diversity, polarization diversity, andangle diversity.

Space diversity and frequency diversity are more frequently used. Space diversity is economical and

has a good effect. Frequency diversity is often applied to multi-channel systems as it requires a wide

bandwidth. Usually, the system that has one standby channel is configured with frequency diversity.

Hf1

f2

Space diversity (SD) Frequency diversity (FD)


Frequency diversity

Signals at different frequencies have different fading characteristics. Accordingly,

two or more microwave frequencies with certain frequency spacing to transmit and

receive the same information which is then selected or composed, to reduce the

influence of fading. This work mode is called frequency diversity.

Advantages: The effect is obvious. Only one antenna is required.

Disadvantages: The utilization ratio of frequency bands is low.

f1f1f1f1

f2f2f2f2

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesForForForFor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (10)(10)(10)(10) Space diversity

Signals have different multipath effect over different paths and thus have different fading

characteristics. Accordingly, two or more suites of antennas at different altitude levels to

receive the signals at the same frequency which are composed or selected. This work mode iscalled space diversity. If there are n pairs of antennas, it is called n-fold diversity.

Advantages: The frequency resources are saved.

Disadvantages: The equipment is complicated, as two or more suites of antennas are

required.

Antenna distance: As per experience, the distance between the diversity antennas is 100 to

200 times the wavelength in frequently used frequency bands.f1f1f1f1

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesforforforfor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (11)(11)(11)(11) Dh calculation in space diversity

Tx

h1

Rx

Dh

d Approximately, Dh can be calculated according to this formula:

(nll/2)d

l: wavelengthd: path distance

Dh =2h1

h1: height of the antenna at the transmit end

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesforforforfor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (12)(12)(12)(12) Apart from the anti-fading technologies introduced previously, here are two frequently

used tips:

Method I: Make use of some terrain and ground objects to block reflected waves.

Anti-fadingAnti-fadingAnti-fadingAnti-fading TTTTechnologiesechnologiesechnologiesechnologiesforforforfor DigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave SystemSystemSystemSystem (13)(13)(13)(13) Method II: high and low antennas

ProtectionProtectionProtectionProtection ModesModesModesModes ofofofofDigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment (1)(1)(1)(1)

Hybrid coupler

With one hybrid coupler added between two

ODUs and the antenna, the 1+1 HSB can berealized in the configuration of one antenna.Moreover, the FD technology can also be adopted.

The 1+1 HSB can also be realized in the

configuration of two antennas. In this case,the FD and SD technologies can both be

adopted, which improves the system

availability.

ProtectionProtectionProtectionProtection ModesModesModesModes ofofofofDigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment (2)(2)(2)(2) N+1 (N3, 7, 11) Protection

In the following figure, Mn stands for the active channel and P stands for the standbychannel. The active channel and the standby channel have their independentmodulation/demodulation unit and signal transmitting /receiving unit.

When the fault or fading occurs in the active channel, the signal is switched to the standbychannel. The channel backup is an inter-frequency backup. This protection mode (FD) is mainlyused in the all indoor microwave equipment.

ProductsProductsProductsProducts ofofofof differdifferdifferdiffereeeentntntnt vvvveeeennnnddddorsorsorsors ssssuuuupportpportpportpport differentdifferentdifferentdifferent specspecspecspeciiiiffffiiiiccccaaaattttions.ions.ions.ions.

ch1ch2ch3

chP

Switchingcontrol unit

M1M2M3

P

RFSOH

M1M2M3

P

Switchingcontrol unit

ch1ch2ch3

chP

ProtectionProtectionProtectionProtection ModesModesModesModes ofofofofDigitalDigitalDigitalDigital MicrowaveMicrowaveMicrowaveMicrowave EquipmentEquipmentEquipmentEquipment (3)(3)(3)(3)

ConfigurationConfigurationConfigurationConfiguration

1+0 NP

ProteProteProteProteccccttttiiiioooonnnn ModeModeModeMode

Non-protection

ReReReRemmmmaaaarksrksrksrks ApplicationApplicationApplicationApplication

Terminal of the network

1+1

1+1

1+1

N+1

FD

SD

FD+SD

FD

Channel protection

Equipment protection andchannel protection



Inter-frequency

Intra-frequency

Inter-frequency

Inter-frequency

Select the proper modedepending on the

geographical conditionand requirements of the

customer

Large-capacity backbonenetwork


What factors can affect the microwave propagation?

What types of fading exists in the microwave propagation?

What are the two categories is the anti-fading technology?

What protection modes are available for the microwave?

SummarySummarySummarySummary Importance parameters affecting microwave propagation

Various factors affecting microwave propagation

Various fading types in the microwave propagation (free space propagation fading,

atmospheric absorption fading, rain or fog scattering fading, K type fading, multipath

fading, duct type fading, and scintillation type fading)

Anti-fading technologies

Anti-fading measures adopted on the equipment: adaptive equalization, ATPC, and

XPIC

Anti-fading measures adopted in the system: FD and SD

Protection modes of the microwave equipment






5.5.5.5. DesigningDesigningDesigningDesigning MicrowaveMicrowaveMicrowaveMicrowave TransmissionTransmissionTransmissionTransmission LinksLinksLinksLinks


5.5.5.5. DesigningDesigningDesigningDesigning MicrowaveMicrowaveMicrowaveMicrowave TransmissionTransmissionTransmissionTransmission LinksLinksLinksLinks

5.15.15.15.1 BasisBasisBasisBasis ofofofof DesigningDesigningDesigningDesigning aaaa MicrowaveMicrowaveMicrowaveMicrowave TransmissiTransmissiTransmissiTransmissioooonnnn LineLineLineLine

5.2 Procedures for Designing a Microwave Transmission Line

BasisBasisBasisBasis ofofofof DesigningDesigningDesigningDesigning aaaa MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission LineLineLineLine

Requirement on the point-to-point line-of-sight communication

Objective of designing a microwave transmission line

Transmission clearance

Meanings of K value in the microwave transmission planning

RequirementRequirementRequirementRequirement onononon aaaa MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission LineLineLineLine Because the microwave is a short wave and has weak ability of diffraction, the normal

communication can be realized in the line-of-sight transmission without obstacles.

Line propagation Irradiated waveAntenna

D

RequirementRequirementRequirementRequirement onononon aaaa MicrowaveMicrowaveMicrowaveMicrowave TransmissionTransmissionTransmissionTransmissionLineLineLineLine

In the microwave transmission, the transmit power is very small, only the antenna in the

accurate direction can realize the communication. For the communication of long

distance, use the antenna of greater diameter or increase the transmit power.

Direction demonstration of the microwave antenna

Microwave antenna

Half power angle of themicrowave antenna 3 dB

ObjectiveObjectiveObjectiveObjective ofofofof DesigningDesigningDesigningDesigning aaaa MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission LineLineLineLine

In common geographical conditions, it is recommended that there be no

obstacles within the first Fresnel zone if K is equal to 4/3.

When the microwave transmission line passes the water surface or the desert

area, it is recommended that there are no obstacles within the first Fresnel zoneif K is equal to 1.

The first Fresnel zone

k = 4/3

TransmissionTransmissionTransmissionTransmission ClearanceClearanceClearanceClearance (1)(1)(1)(1) The knife-edged obstacle blocks partial of the Fresnel zone. This also causes the

diffraction of the microwave. Influenced by the two reasons, the level at the actual

receive point must be lower than the free space level. The loss caused by the knife-

edged obstacle is called additional loss.

TransmissionTransmissionTransmissionTransmission ClearanceClearanceClearanceClearance (2)(2)(2)(2)

When the peak of the obstacle is in the line

connecting the transmit end and the receive end, that is,

the HC is equal to 0, the additional loss is equal to 6 dB.

When the peak of the obstacle is above the line

connecting the transmit end and the receive end, the

additional loss is increased greatly.

When the peak of the obstacle is below the line

connecting the transmit end the receive end, the additional

loss fluctuates around 0 dB. The transmission loss in the

path and the signal receiving level approach

the values in the free space transmission.

8

642

0-2

-4

-6-8-10-12-14

-16-18-20-22-24

-26-28

-2.5-2.0-1.5-1.0-0.5 0 0.51.0 1.5 2.0 2.5

Loss caused by block of knife-edged obstacle

HC/F1


Clearance calculation

Calculation formula for path clearance

h1d2 + h2d1h

c

=d

hb hs

h

cThe value of clearance isrequired greater than thatof the first Fresnel Zonesradius.

h1h

s

h2

hb

stands for the projectingd1

h

b

d2

height of the earth. d

h

b

= 0.0785d1d2

K

K stands for the atmosphere refraction factor.

TransmissionTransmissionTransmissionTransmission ClearanceClearanceClearanceClearance (4)(4)(4)(4) To present the influence of various factors on microwave transmission, the field strength

fading factor V is introduced. The field strength fading factor V is defined as the ratio of the

combined field strength when the irradiated wave and the reflected wave arrive at the

receive point to the field strength when the irradiated wave arrives at the receive point in

the free space transmission.

E 2 h

ce

V =

E

= 1+ 2

cos F

0

1

E

: Combined field strength when the irradiated wave and reflected wavearrive at the receive point

E0: Field strength when the irradiated wave arrives at the received point inthe free space transmission: Equivalent ground reflection factor


The relation of the V and canberepresented by the curve in the figure on the

right.

In the case that is equal to 1, with the

influence of the earth considered, HC/F1 is equal

to 0.577 when the signal receiving level is equal

to the free space level the first time.

In the case that is smaller than 1, HC/F1 is

approximately equal to 0.6 when the signal

receiving level is equal to the free space level the

first time.

When the HC/F1 is equal to 0.577, the

clearance is called the free space clearance,

represented by H0 and expressed in the following

formula:

H0 = 0.577F 1 = (d1d2/d)1/2

VdB10

5

0

-5

-10

-15

-20

-25

-30

-35

-40

Relation curve of V and Hc/F1

0.2

0.5

0.8

1

HC/F1=N

MeaningMeaningMeaningMeaning ofofofof KKKK ValueValueValueValue inininin MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission PlanningPlanningPlanningPlanning (1)(1)(1)(1)

To make the clearance cost-effective and reasonable in the engineering, the height of

the antenna should be adjusted according to the following requirements.

In the case that is not greater than 0.5, that is, for the circuit that passes the area

of small ground reflection factor like the mountainous area, city, and hilly area, to

avoid over great diffraction, the height of the antenna should be adjusted according

to the following requirements:

When K = 2/3, HC 0.3F1 (for common obstacles)HC 0 (for knife-shaped obstacles)

The diffraction fading should not be greater than 8 dB in this case.

MeaningMeaningMeaningMeaning ofofofof KKKK ValueValueValueValue inininin MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission PlanningPlanningPlanningPlanning (2)(2)(2)(2)

In the case that is greater than 0.7, that is, for the circuit that passes the area of great

ground reflection factor like the plain area and water reticulation area, to avoid over great

reflection fading, the height of the antenna should be adjusted according to the following

requirements

When K = 2/3, HC 0.3F1 (for common obstacles)HC 0 (for knife-edged obstacles)

When K = 4/3, HC F1When K = , HC 1.35F1 (The deep fading occurs when HC = 21/2 F1.)

If these requirements cannot be met, change the height of the antenna or the route.

ProcedureProcedureProcedureProcedure forforforfor DesigningDesigningDesigningDesigning aaaa MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission LineLineLineLine Step 1 Determine the route according to the engineering map.

Step 2 Select the site of the microwave station.

Step 3 Draw the cross-sectional chart of the terrain.

Step 4 Calculate the parameters for site construction.

ProcedureProcedureProcedureProcedure forforforfor DesigningDesigningDesigningDesigning aaaa MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission LineLineLineLine (1)(1)(1)(1)

Step 1 Determine the route according to engineering map.

We should select the area that rolls as much as possible, such as the hilly area.

We should avoid passing the water surface and the flat and wide area that isnot suitable for the transmission of the electric wave. In this way, the strong

reflection signal and the accordingly caused deep fading can be avoided.

The line should avoid crossing through or penetrating into the mountainousarea.

The line should go along with the railway, road and other areas with theconvenient transportation.


Step 2 Select the site of the microwave station.

The distance between two sites should not be too long. The distance between

two relay stations should be equal, and each relay section should have the

proper clearance.

Select the Z route to avoid the over-reach interference.

Avoid the interference from other radio services, such as the satellite

communication system, radar site, TV station, and broadcast station.

f1f1f1f1 f1f1f1f1 f1f1f1f1

f2f2f2f2 f2f2f2f2 f2f2f2f2

Over-reachinterference

The signal from the firstmicrowave station

interferes with the signalof the same frequency

from the third microwavestation.


Step 3 Draw the cross-sectional chart of the terrain.

Draw the cross-sectional chart of the terrain based on the data of each site.

Calculate the antenna height and transmission situation of each site. For the line

that has strong reflection, adjust the mounting height of the antenna to block

the reflected wave, or have the reflection point fall on the earth surface with

small reflection factor.

Consider the path clearance. The clearance in the plain area should not be over

great, and that in the mountainous area should not be over small.

ProcedureProcedureProcedureProcedure forforforfor DesigningDesigningDesigningDesigning aaaa MicrowaveMicrowaveMicrowaveMicrowaveTransmissionTransmissionTransmissionTransmission LineLineLineLine (4)(4)(4)(4)Step 4 Calculate the parameters for site construction.

Calculate the terrain parameters when the route and the site are alreadydetermined.

Calculate the azimuth and the elevation angles of the antenna, distancebetween sites, free space transmission loss and receive level, rain fadingindex, line interruption probability, and allocated values and margin of theline index.

When the margin of the line index is eligible, plan the equipment andfrequencies, make the approximate budget, and deliver the constructionchart.

Input

There is special networkplanning software, and thecommonly used is CTEPathloss.

Input


What are the requirements for microwave communication?

What is the goal of microwave design?

What extra factors should be taken into consideration for microwave planning?

Can you tell the procedure for designing a microwave transmission line?

digital microwave communication principles-zte.pdf

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