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CELLULARAND

MOBILE

COMMUNICATIONS

SOURCE:

MOBILECELLULAR

TELECOMMUNICATIONS

BYWILLIAMC.Y.LEE

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IntroductiontoCellularMobile

Systems

WhyCellularMobileTelephoneSystems?

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LimitationsofConventionalMobileTelephoneSystems

operationallimitations

limitedservicecapability

poorservice

performance

inefficientfrequencyspectrumutilization.

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LimitedServiceCapability

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PoorServicePerformance

Inthepast,atotalof33channelswereallocatedtothree

mobiletelephonesystems:

MobileTelephoneService(MTS),

ImprovedMobileTelephoneService(IMTS)MJsystems,and

Improved

Mobile

Telephone

Service

(IMTS)

MK

systems.

Thelargenumberofsubscriberscreatedahighblocking

probabilityduringbusyhours.

A

high

capacity

system

for

mobile

telephones

was

needed.

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InefficientFrequencySpectrum

Utilization

theconventionalsystemdoesnotutilizethespectrum

efficientlysince

each

channel

can

only

serve

one

customer

atatimeinawholearea.

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SpectrumEfficiencyConsiderations limitation availableradiofrequencyspectrum

minimalbandwidth

but

provide

high

usage

andconsumersatisfaction.

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Threemajorapproachestoachieve

theideal

are

1.Singlesideband(SSB),whichdividesthe

allocated

frequency

band

into

maximum

numbersofchannels

2.Cellular,whichreusestheallocated

frequencyband

in

different

geographic

locations

3.

Spread

spectrum

or

frequency

hopped,

whichgeneratesmanycodesoverawidefrequencyband

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ABasicCellularSystem

amobileunit,

acellsite,and

amobile

telephone

switching

office

(MTSO)

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1.Mobileunits.Amobiletelephoneunitcontainsacontrolunit,atransceiver,andanantennasystem.

2.Cellsite.ThecellsiteprovidesinterfacebetweentheMTSOandthemobileunits.Ithasacontrolunit,radiocabinets,antennas,a

powerplant,anddataterminals.

3.MTSO.Theswitchingoffice,thecentralcoordinatingelementfor

all

cell

sites,

contains

the

cellular

processor

and

cellular

switch.

It

interfaceswith

telephone

company

zone

offices,

controls

call

processing,andhandlesbillingactivities.

4.Connections.Theradioandhighspeeddatalinksconnectthethreesubsystems.Eachmobileunitcanonlyuseonechannelatatime

for

its

communication

link.

TheMTSOistheheartofthecellularmobilesystem.Itsprocessorprovidescentralcoordinationandcellularadministration.

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OperationofCellularSystems

Mobileunitinitialization. selflocationprocedure Mobileoriginatedcall. Arequestforserviceissentona

selectedsetupchannelobtainedfromaselflocationscheme

Networkoriginatedcall. Alandlinepartydialsamobileunitnumber.

Calltermination. Handoffprocedure.

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PerformanceCriteria

VoiceQuality a

set

value

xat

which

ypercent

of

customers

ratethesystemvoicequality(fromtransmitter

to

receiver)

as

good

or

excellent,

the

top

two

circuitmerits(CM)ofthefivelistedbelow.

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PerformanceCriteria

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PerformanceCriteria

ServiceQuality 1.Coverage.

2.Requiredgradeofservice.

3.Numberofdroppedcalls.

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ServiceQuality Thesystemshouldserveanareaaslargeas

possible. Thetransmittedpowerwouldhavetobevery

high

to

illuminate

weak

spots

with

sufficient

reception,asignificantaddedcostfactor.

Thehigherthetransmittedpower,theharder

itbecomes

to

control

interference.

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Numberofdroppedcalls. Ahighdropratecouldbecausedbyeither

coverageproblemsor

handoffproblems

related

to

inadequate

channelavailability.

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PerformanceCriteria

SpecialFeatures callforwarding,

call

waiting,

voicestored(VSR)box,

automaticroaming,ornavigationservices

NOEXTRACOST

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UniquenessofMobileRadio

Environment

Mobile radio transmission model.

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ThePropagationAttenuation

thepropagationpathlossincreasesnotonlywithfrequencybutalsowithdistance

Thepropagation

path

loss

would

be

40

dB/dec

Thismeansthata40dBlossatasignalreceiverwillbeobservedbythemobileunitasitmovesfrom1to10

km.

whereC=

received

carrier

power

R=distancemeasuredfromthetransmittertothereceiver

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Thedifferenceinpowerreceptionattwo

differentdistances

R1 and

R2 will

result

in

andthedecibelexpressionis

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WhenR2 =2R1,DC=12dB;whenR2 =10R1,

DC=40

dB.

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A typical fading signal received while the mobile unit is moving(SevereFading)ww.jntuworld.com

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MobileFadingCharacteristicsww.jntuworld.com

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DelaySpread thesignaltransmittedfromacellsiteandarriving

atamobile

unit

will

be

from

different

paths

eachpathhasadifferentpathlength

thetimeofarrivalforeachpathisdifferent.

Foranimpulsetransmittedatthecellsite,bythe

timethisimpulseisreceivedatthemobileunitit

isno

longer

an

impulse

but

rather

apulse

with

a

spreadwidththatwecallthedelayspread.

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CoherenceBandwidth bandwidthinwhicheithertheamplitudesor

thephases

of

two

received

signals

have

ahigh

degreeofsimilarity

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NoiseLevelinCellularFrequencyBand TheIgnitionNoise thevehicleignitionnoise

800MHz

Emission

Noise

AmplifierNoise

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MarketingImageofHexagonalshaped

Cells

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AnalogCellularSystems

DigitalCellular

Systems

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