无线通信系统

会计学1无线通信系统Cellular

Networks第1页/共46页2023-01-052Cell

shape:iCrcleirrtlaelgnaEquilate:

nogaxeH::erauqS第2页/共46页2023-01-053Cellular

coverage

representation2023-01-054第3页/共46页lMacrocell

large,

covering

a

wide

arerange

of

several

hundred

kilometres

(km)

to

ten

kmmostly

deployed

in

rural

and

sparsely

populated

areaslMicrocell

medium

cell,

coverage

are

a

smaller

than

in

macro

cellsrange

of

several

hundred

metres

to

a

couple

of

metresdeployed

mostly

in

crowdedareas,stadiums,

shoppingmallslPicocell

small,

covering

a

very

small

arearange

of

several

tens

of

metreslow

power

antennas,

indoor2023-01-055The

size

of

a

cell第4页/共46页第5页/共46页2023-01-056Base

station

transmittersareeithe:rblInhexagonalcells,asestationstransmitters–reofthecellcentre-excited,basestationisatthecent–ellverticeeedge-excitsd,basestationat3ofthe6ctdecentre-exci2023-01-057cxe-egdeited第6页/共46页Cellular

coverage

representationofcapaciytCcanbeusedasameasure2023-01-058第7页/共46页A

mobile

communication

system

uses

a

frequency

reusefactor

of

1/7

and

416

channels

available.

If

21

channels

areallocated

as

control

channels,

compute

its

system

capacity.Assume

achannel

supports

8

usersChannels

available

for

allocation

=

416

-

21

=

395Channel

Number

of

a

cell

=

395

/

7

=

57Number

of

simultaneous

users

per

cell

=

8

x

57

=

456Number

of

simultaneous

users

in

system

=

7

x

456

=

31922023-01-059Example

1第8页/共46页If

a

total

of

33

MHz

of

bandwidth

is

allocated

to

a

particular

FDDcellular

telephone

system

which

uses

two

25

kHz

simplex

channels

toprovide

full

duplex

voice

and

control

channels,

compute

the

numberof

channels

available

per

cell

if

a

system

uses

four-cellreuse.

If

1

MHzof

the

allocated

spectrum

is

dedicated

to

control

channels,

determine

an

equitable

distribution

of

control

channels

and

traffic

channels

ineach

cell

for

each

of

the

system.2023-01-0510Example

2第9页/共46页Method

of

locating

co-channel

cells第10页/共46页2023-01-0511Channel

Assignment

Strategies2023-01-0512sThree

assignment

approacheslFixed

and

static

(most

common)lDynamic

l

HybridsFixed

channel

assignmentlall

channels

in

a

cell

could

be

in

use

all

the

time–new

calls

are

then

blocked

(no

channels

left)–may

be

solved

by

borrowing

spare

channels

from

nearbycells第11页/共46页elassignmnnDynamicchatne2023-01-0513nformationonTodothisitneedsreal-timei––––––nacllismadeaMSCallocatesfrequencieswhe

lutilisationProvideshighchannenyeloccupancchan

ributionandftraficdist

cation(RSSI)radiosignalstrengthindi

iaercniodnadhaghcomputationallsedstorage第12页/共46页Handover(Handoff)Provides

continuity

of

communication

across

cellsDifficultydropping

a

call

before

reconnecting

is

unacceptabledifferent

cells

use

different

frequencies

mobile

phone

users

usually

move

from

place

to

place

and

veryquickly

too2023-01-0514第13页/共46页HandoverProcessParties

in

communication

share

the

same

channelsReceived

signal

weakens

as

mobile

moves

out

of

cell

Cell

site

at

some

point

requests

handover

to

cell

with

strongersignal

strengthMSC

switches

call

to

new

cell

after

allocating

channels.2023-01-0515第14页/共46页Handover

Process第15页/共46页2023-01-0516Handover

ProcessHandover

must

not

be

too

frequent

or

system

is

kept

busy

servicinghandover

requestshandover

threshold

is

set

slightly

stronger

Minimum

usable

signal

level

is

normally

set

to

be

between

-90dBm

and

-100

dBm2023-01-0517第16页/共46页Choosing

Handover

MarginsHandover

margin=

P

r

handover

-

Pr

minimumusableIf

is

too

large

unnecessary

handover

will

occur,

burdening

the

MSC

If

is

too

small,

there

maybe

insufficient

time

to

complete

thehandover

before

a

call

is

lost

due

to

weak

signalsTherefore

is

chosen

carefully2023-01-0518第17页/共46页Setting

Handover

Thresholds第18页/共46页2023-01-0519Handoff

in

different

system2023-01-05201G

signal

strength

measurements

are

made

bythe

base

stations

and

supervised

by

the

MSCGSM

MAHO

handoff

decisions

are

mobileassistedCDMA

pilot

channel,

soft

handoff第19页/共46页Interference

and

System

Capacity第20页/共46页2023-01-0521Six

Effective

Interfering

Cells

of

Cell

12023-01-0522第21页/共46页Co-channel

reuse

ratio

Q第22页/共46页2023-01-0523Co-channel

reuse

ratio

vs.frequency

reuse

pattern2023-01-0524第23页/共46页7-cell

reuse

pattern2023-01-0525第24页/共46页12-cell

reuse

pattern2023-01-0526第25页/共46页19-cell

reuse

pattern2023-01-0527第26页/共46页Co-channel

reuse

ratio

vs.frequency

reuse

pattern2023-01-0528第27页/共46页Propagation

model2023-01-0529第28页/共46页Co-channel

interferenceratio第29页/共46页2023-01-0530Example

32023-01-0531第30页/共46页More

exact

geometry

layout2023-01-0532第31页/共46页Closely

approximately

as第32页/共46页2023-01-0533Trunking

and

Grade

of

Service(GOS)第33页/共46页2023-01-0534Grade

of

Service

(GOS)第34页/共46页2023-01-0535About

Erlang2023-01-0536第35页/共46页Erlang

B

formulaeredtraffic.whereCisthenumberoftrunkedchannelsofferedbyatrunkedradiosystemandAisthetotaloff2023-01-0537第36页/共46页TPTPrrrruouonbnbkakaebebdidimlmloioibtbtiyiyloloefefnbnbeleltootwccwkokoirirnknkpgpgr=r=o2o2v%v%i=i=d0d0e.e.c0c0e22elllluullaarrsseerrvviicceeiinntthhiissaarreeaa..SSyysstteemmhhaass339944cceellllsswwiitthh1199cchhaannnneellsseeaacchh..FFiinnddtthheennuummbbeerrooffuusseerrsstthhaattccaannbbeessuuppppoorrtteeddaatt22%%bblloocckkiinnggiiffeeaacchhuusseerraavveerraaggeessttwwooccaallllssppeerrhhoouurraattaannaavveerraaggeeccaalllldduurraattiioonnoofftthhrreeeemmiinnuutteess..CCoommppuutteetthheettoottaallnnuummbbeerrooffssuubbssccrriibbeerrsstthhaattccaannbbeessuuppppoorrtteeddbbyytthhiissssyysstteemm..2023-01-0538NTNTururmamabfbfefefririococfificncnhttheaaennnnsnsneieiltltsysyppppeeeerrrrucucseseelelrllru,,usAsAeueud=d=iHiHn=n=t2t2hxxhe(e(s3s3y/y/s6s6t0t0e)e)m=m=,0,0C.C.=1=11E1E9r9rllaannggssλfTfTrhrhoeoemrmrtetehfhfeoeoErrEerer,l,ltaatnhnhgegeBnBncucuhmhmababreretrtr,o,otfftuhuhesesteterorosttsatatlhlhcaacatatrcrcraraininebebdedetstsruruappapfpfofforiritccte,,eAdAd,p,pieiesrsrcoocbebetltlalaliiiinssneeddaass1122EErrllaannggss..USUS=i=iAnAnIcIcAeAeutut=h=h1e1e2rr2e/e/a0a0r..r1e1e=3=3191924240c0ceellllss,,tthheettoottaallnnuummbbeerrooffssuubbssccrriibbeerrsstthhaattccaannbbeessuuppppoorrtteeddbbyySSyysstteemmAAiisseeqquuaallttoo112200xx339944==4477228800Example4第37页/共46页sOften

large

cells

need

to

be

split

into

smaller

ones

because

thepopulation

of

users

in

the

big

cell

has

increased

beyond

what

it

cansupportlCell

splitting

increases

system

capacitylIs

used

in

high

density

subscriber

areaslResults

to

increased

costs

(eg.

new

base

stations)2023-01-0539Improving

Capacity

in

Cellular

System第38页/共46页第39页/共46页2023-01-0540第40页/共46页2023-01-0541Cell

Splitting2023-01-0542第41页/共46页Sectoring第42页/共46页2023-01-0543nn1%Acellularsystem:anaveragecalllaststwomi.utes,andtheprobabilityofblockingistobenomorethachanEverysubscribermakesonecallperhour,onaverage.Ifthereareatotalof395trafficchannelsforaseven-cellreusesystem,therewillbeabout57traffic°annetna3/75(rotcesanneFnarepslennahc91ylnoetaereht,gnirotces.)srsysehtniresuhcaerofI/Sehtgnivorpmielihwycneiciffegniknurtehtsesaercedgnirotces,suhT.met2023-01-0544Example

5第43页/共46页.ns.1.Wir