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Chapter2

ElementsofCellularMobileRadio

SystemDesign

SOURCE:

MOBILECELLULAR

TELECOMMUNICATIONS

BYWILLIAMC.Y.LEE

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GeneralDescriptionoftheProblem

Aim efficientspectrumutilization

ElementsofCellularMobileRadioSystemDesign

(1)theconceptoffrequencyreusechannels

(2)thecochannelinterferencereductionfactor

(3)thedesiredcarriertointerferenceratio

(4)thehandoffmechanism

(5)

cell

splitting.

Challengetoservethegreatestnumberofcustomerswithaspecifiedsystemquality

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1.Howmanycustomerscanweserveina

busyhour?

2.Howmanysubscriberscanwetakeintoour

system?

3.Howmanyfrequencychannelsdoweneed?

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Maximum

Number

of

Calls

Per

Hour

Per

Cell Thesizeofthecell

Thetraffic

conditions

in

the

cell

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Maximum

Number

of

Frequency

Channels

Per

Cell Averagecallingtimeinthesystem

Chargingrate

of

the

system

Thegeneralincomeprofileoftheusers

Offeredload=A=Qi*T(hours)erlangs

averagecalling

time

T

maximumcallsperhourpercellQi

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LetthemaximumcallsperhourQiinonecell

be3000

and

an

average

calling

time

Tbe

1.76

min.TheblockingprobabilityBis2percent.

Find

the

offered

load

and

number

of

channels.

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ConceptofFrequencyReuseChannels

Inthisfrequencyreusesystem,usersin

differentgeographic

locations

(different

cells)

maysimultaneouslyusethesamefrequency

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increasethespectrumefficiency

Interferencedue

to

the

common

use

of

the

samechanneliscalledcochannelinterference

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FrequencyReuseSchemes

Frequencyreuseinthetimedomainresultsinthe

occupation

of

the

same

frequency

in

different

timeslots

Frequencyreuseinthespacedomain

1.Same

frequency

assigned

in

two

different

geographicareas,suchasAMorFMradiostationsusingthesamefrequencyindifferentcities.

2.

Same

frequency

repeatedly

used

in

asame

general

areainonesystemtheschemeisusedincellularsystems.

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Handoffmechanism

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Cellsplitting

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ConsiderationoftheComponentsof

CellularSystems

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Cochannel InterferenceReduction

Factor q=D/R

D=f(KI,

C/I)

whereKIisthenumberofcochannel

interferingcells

in

the

first

tier

and

C/Iisthereceivedcarriertointerferenceratio

atthedesiredmobilereceiver

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whereqkis

the

cochannel interference

reduction

factor

with

kth cochannel interferingcell

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Thepropagationpathlossis40dB/dec

Hence,

q=(6*C/I)^1/r

=(6

*63.1)

^1/6

=4.41

C/I=18dB ismeasuredbytheacceptanceof

voicequality

from

the

present

receivers.

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ThemaximumnumberofKIinthefirsttier

canbe

shown

as

six

(i.e.,

2piD/D

6).

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