2.1 introduction to cellular architecture

2.1 introduction to cellular architecture

1. INTRODUCTION
TO CELLULAR
ARCHITECTURE

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3. Fundamental architecture of Cellular System
MOBILE STATION BASE STATION
MOBILE
SWITCHING
CENTRE (MSC)
PUBLIC SWITCHED
TELEPHONE
NETWORK (PSTN)Astationinthe
cellularradioservice
intendedforuse
whileinmotionat
unspecifiedlocations.
Mobilestationmay
behand held
personal units
(Portables) or
installedinvehicles
(Mobiles)
Afixedstationina
mobileradiosystemused
forradiocommunication
withmobilestations.
Basestationsarelocated
atthecentreoronthe
edgeofacoverageregion
andconsistsofradio
channels and
transmitter and
receiver antennas
mountedonatower.
Switchingcentrewhich
coordinatetherouting
ofcallsinalarge
servicearea.Incellular
radiosystemtheMSC
connectthecellularbase
stationandthemobiles
tothePSTN.AnMSCis
alsocalledaMobile
Telephone Switching
Office(MTSO).
PSTN (publicswitched
telephonenetwork)isthe
world’s collectionof
interconnectedvoice-oriented
publictelephonenetworks.
PTSNcomprisesallthe
switched telephone
networksaroundtheworld
thatareoperatedbylocal,
nationalorinternational
carriers.

4. Cellular System to cover a geographical area
BASE STATION
MOBILE STATION
CELL
Acellisthegeographicareathat
iscoveredbyasinglebase
stationinacellularnetwork.

5. Detailed View of GSM Architecture
Abasetransceiverstation(BTS)isapieceofequipmentthat
facilitateswirelesscommunicationbetweenuserequipment(UE)anda
network.UEsaredeviceslikemobilephones(handsets),WLLphones,
computerswithwirelessInternetconnectivity.
Abasestationcontroller(BSC)isanetworkelementthatcontrolsand
monitorsanumberofbasestationsandprovidestheinterface
betweenthecellsitesandthemobileswitchingcenter(MSC).
TheHomeLocationRegisterisadatabasefromamobilenetworkin
whichinformationfromallmobilesubscribersisstored.TheHLR
containsinformationaboutthesubscribersidentity,histelephone
number,theassociatedservicesandgeneralinformationaboutthe
locationofthesubscriber.
TheVisitorLocationRegister(VLR)isadatabasecontainstheexact
locationofallmobilesubscriberscurrentlypresentintheservicearea
oftheMSC.Thisinformationisnecessarytorouteacalltotheright
basestation.Thedatabaseentryofthesubscriberisdeletedwhenthe
subscriberleavestheservicearea.
TheAuthenticationCentre(AUC)isafunctioninaGSMnetworkused
fortheauthenticationamobilesubscriberthatwantstobeconnected
tothenetwork.Authenticationisdonebyidentificationand
verificationofthevalidityoftheSIM.Oncethesubscriberis
authenticated,theAUCisresponsibleforthegenerationofthe
parametersusedfortheprivacyandthecipheringoftheradiolink.
OperationMaintenanceCenter(OMC)isusedtomonitorandmaintainthe
performanceofeachMobileStation(MS),BaseStation(BS),BaseStation
Controller(BSC)andMobileSwitchingCenter(MSC)withinaGSMsystem.
IntegratedServicesDigitalNetwork(ISDN)isasetofcommunication
standardsforsimultaneousdigitaltransmissionofvoice,video,data,andother
networkservicesoverthetraditionalcircuitsofthepublicswitchedtelephone
network.

6. GSM Channels
MOBILE STATION BASE STATION
MOBILE SWITCHING
CENTRE (MSC)
PUBLIC SWITCHED
TELEPHONE NETWORK
(PSTN)
Wireless Access through Radio Channels Wired Communication –Back Bone Networks
ThecommunicationbetweentheMSand
BSaredefinedbyCAI(CommonAir
Interface)Standard.
VOICE AND
DATA
CHANNEL
CONTROL
CHANNEL
FORWARD VOICE
CHANNEL
REVERSE VOICE
CHANNEL
FORWARD CONTROL
CHANNEL
REVERSE CONTROL
CHANNEL
Used for voice transmission
from BS to MS
Used for voice transmission
from MS to BS
Used for setting up the calls
and exchanging the control
messages

7. Channel Access Mechanisms
In real time scenario a single Base
Station will serve several Mobile
Stations simultaneously. This gives
raise to 2 important questions
1.How Full duplexing is
achieved?
2.How mobile users share the
available finite amount of
spectrum
FullDuplexcanbeachievedby
FrequencyDivisionDuplexing(FDD):
Frequency-divisionduplexing(FDD)isamethodforestablishingafull-duplex
communicationslinkthatusestwodifferentradiofrequenciesfortransmitterand
receiveroperation.FDDoperationnormallyassignsthetransmitterandreceiver
todifferentcommunicationchannels.Onefrequencyisusedtocommunicatein
onedirection,andtheotherfrequencyisrequiredtocommunicateintheopposite
direction.Thetransmitdirectionandreceivedirectionfrequenciesareseparated
byadefinedfrequencyoffset.
TimeDivisionDuplexing(TDD):
Timedivisionduplex(TDD)referstoduplexcommunicationlinkswhereuplinkis
separatedfromdownlinkbytheallocationofdifferenttimeslotsinthe
samefrequencyband.

8. HowMobileUsersSharetheAvailable
Spectrum:
TheBasicResourceforWireless
CommunicationisRadioSpectrum.Thisis
tobesharedamongmultipleusers.
MultipleAccessschemesareusedtoallow
many mobileuserstoshare
simultaneouslyafiniteamountofradio
spectrum.
Thesharingofspectrumisrequiredto
achievehighcapacitybysimultaneously
allocatingtheavailablebandwidthor
channeltomultipleusers
Duplexingisneededtoallowsubscribers
send and receiveinformation
simultaneously.Ex:MobileSystems
Note:
This must be done without severe degradation
in the performance of the system

9. Summary
•Basic Components and definition
•Architecture of Cellular Systems
•CAI Standards for GSM channels
•Concepts of Duplexing
•Concepts of Multiple Access Techniques