In Depth Basics of GSM for beginner (Telecom)

INTRODUCTION TO GSM

INTRODUCTION
•TheGlobalSystemforMobileCommunications(GSM)isasetof
recommendationsandspecificationsforadigitalcellulartelephone
network(knownasaPublicLandMobileNetwork,orPLMN).
•Theserecommendationsensurethecompatibilityofequipmentfrom
differentGSMmanufacturers,andinterconnectivitybetweendifferent
administrations,includingoperationacrossinternationalboundaries.
•GSMnetworksaredigitalandcancaterforhighsystemcapacities.
•Theyareconsistentwiththeworld-widedigitizationofthetelephone
network,andareanextensionoftheIntegratedServicesDigital
Network(ISDN),usingadigitalradiointerfacebetweenthecellular
networkandthemobilesubscriberequipment.
INTRODUCTION TO GSM

CELLULAR TELEPHONY
•Acellulartelephonesystemlinksmobilesubscribersintothepublic
telephonesystemortoanothercellularsubscriber.
•Informationbetweenthemobileunitandthecellularnetworkuses
radiocommunication.Hencethesubscriberisabletomovearound
andbecomefullymobile.
•Theserviceareainwhichmobilecommunicationistobeprovided
isdividedintoregionscalledcells.
•Eachcellhastheequipmenttotransmitandreceivecallsfromany
subscriberlocatedwithinthebordersofitsradiocoveragearea.
Radio
Mobile subscriber
Cell
INTRODUCTION TO GSM

GSMFREQUENCIES
•GSMsystemsuseradiofrequenciesbetween890-915MHzfor
receiveandbetween935-960MHzfortransmit.
•RFcarriersarespacedevery200kHz,allowingatotalof124
carriersforuse.
•AnRFcarrierisapairofradiofrequencies,oneusedineach
direction.
•Transmitandreceivefrequenciesarealwaysseparatedby45MHz.
890 960935915
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ
INTRODUCTION TO GSM

UPLINK FREQUENCIES DOWNLINK FREQUENCIES
890 915 935 960880 925
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 45MHZ
ExtendedGSM(EGSM)
•EGSMhas10MHzofbandwidthonbothtransmitandreceive.
•Receivebandwidthisfrom880MHzto890MHz.
•Transmitbandwidthisfrom925MHzto935MHz.
•TotalRFcarriersinEGSMis50.
INTRODUCTION TO GSM

1710 MHz 1880 MHz1805 MHz1785 MHz
UPLINK FREQUENCIES DOWNLINK FREQUENCIES
UPLINK AND DOWNLINK FREQUENCY SEPARATED BY 95MHZ
DCS1800FREQUENCIES
•DCS1800systemsuseradiofrequenciesbetween1710-1785MHz
forreceiveandbetween1805-1880MHzfortransmit.
•RFcarriersarespacedevery200kHz,allowingatotalof373
carriers.
•Thereisa100kHzguardbandbetween1710.0MHzand1710.1
MHzandbetween1784.9MHzand1785.0MHzforreceive,and
between1805.0MHzand1805.1MHzandbetween1879.9MHz
and1880.0MHzfortransmit.
•Transmitandreceivefrequenciesarealwaysseparatedby95MHz.
INTRODUCTION TO GSM

FEATURES OF GSM

INCREASEDCAPACITY
•TheGSMsystemprovidesagreatersubscribercapacitythananalogue
systems.
•GSMallows25kHzperuser,thatis,eightconversationsper200kHz
channelpair(apaircomprisingonetransmitchannelandonereceive
channel).
•Digitalchannelcodingandthemodulationusedmakesthesignal
resistanttointerferencefromcellswherethesamefrequenciesarere-
used(co-channelinterference);aCarriertoInterferenceRatio(C/I)level
of12dBisachieved,asopposedtothe18dBtypicalwithanalogue
cellular.
•Thisallowsincreasedgeographicreusebypermittingareductioninthe
numberofcellsinthereusepattern.
FEATURES OF GSM

AUDIOQUALITY
•Digitaltransmissionofspeechandhighperformancedigitalsignal
processorsprovidegoodqualityspeechtransmission.
•SinceGSMisadigitaltechnology,thesignalspassedoveradigitalair
interfacecanbeprotectedagainsterrorsbyusingbettererror
detectionandcorrectiontechniques.
•Inregionsofinterferenceornoise-limitedoperationthespeechquality
isnoticeablybetterthananalogue.
USEOFSTANDARDISED OPENINTERFACES
•StandardinterfacessuchasC7andX25areusedthroughoutthe
system.Hencedifferentmanufacturerscanbeselectedfordifferent
partsofthePLMN.
•ThereisahighflexibilityinwheretheNetworkcomponentsare
situated.
FEATURES OF GSM

IMPROVEDSECURITYANDCONFIDENTIALITY
•GSMoffershighspeechanddataconfidentiality.
•Subscriberauthenticationcanbeperformedbythesystemtocheckif
asubscriberisavalidsubscriberornot.
•TheGSMsystemprovidesforhighdegreeofconfidentialityforthe
subscriber.Callsareencodedandcipheredwhensentoverair.
•Themobileequipmentcanbeidentifiedindependentlyfromthemobile
subscriber.Themobilehasaidentitynumberhardcodedintoitwhenit
ismanufactured.Thisnumberisstoredinastandarddatabaseand
wheneveracallismadetheequipmentcanbecheckedtoseeifithas
beenreportedstolen.
FEATURES OF GSM

CLEANERHANDOVERS
•GSMusesMobileassistedhandovertechique.
•Themobileitselfcarriesoutthesignalstrengthandquality
measurementofitsserverandsignalstrengthmeasurementofits
neighbors.
•ThisdataispassedontheNetworkwhichthenusessophisticated
algorithmstodeterminetheneedofhandover.
SUBSCRIBERIDENTIFICATION
•InaGSMsystemthemobilestationandthesubscriberare
identifiedseparately.
•Thesubscriberisidentifiedbymeansofasmartcardknownasa
SIM.
•Thisenablesthesubscribertousedifferentmobileequipmentwhile
retainingthesamesubscribernumber.
FEATURES OF GSM

ENHANCEDRANGEOFSERVICES
•Speechservicesfornormaltelephony.
•ShortMessageServiceforpointotpointtransmissionoftext
message.
•Cellbroadcastfortransmissionoftextmessagefromthecelltoall
MSinitscoveragearea.Messageliketrafficinformationor
advertisingcanbetransmitted.
•Faxanddataservicesareprovided.Dataratesavailableare2.4
Kb/s,4.8Kb/sand9.6Kb/s.
•Supplementaryserviceslikenumberidentification,callbarring,call
forwarding,chargingdisplayetccanbeprovided.
FEATURES OF GSM

FREQUENCY REUSE
•Therearetotal124carriersinGSM(additional50carriersare
availableifEGSMbandisused).
•Eachcarrierhas8timeslotsandif7canbeusedfortrafficthena
maximumof868(124X7)callscanbemade.Thisisnotenough
andhencefrequencieshavetobereused.
•ThesameRFcarriercanbeusedformanyconversationsinseveral
differentcellsatthesametime.
6
4
3
7
2
•Theradiocarriersavailableareallocated
accordingtoaregularpatternwhichrepeatsover
thewholecoveragearea.
•Thepatterntobeuseddependsontraffic
requirementandspectrumavailability.
•Sometypicalrepeatpatternsare4/12,7/21etc.
5
1
2
1
FEATURES OF GSM

NETWORK COMPONENTS

MSC
EC
PSTN
AUC HLREIR VLRNMC
OMC-S
OMC-R
IWF
XCDR
BTS BTS
BSC NETWORK COMPONENTS
UM
UM
ABIS
A
BC
D
F
H

Mobile Switching Centre (MSC)
•TheMobileservicesSwitchingCentre(MSC)co-ordinatesthesettingup
ofcallstoandfromGSMusers.
•ItisthetelephoneswitchingofficeforMSoriginatedorterminatedtraffic
andprovidestheappropriatebearerservices,teleservicesand
supplementaryservices.
•ItcontrolsanumberofBaseStationSites(BSSs)withinaspecified
geographicalcoverageareaandgivestheradiosubsystemaccessto
thesubscriberandequipmentdatabases.
•TheMSCcarriesoutseveraldifferentfunctionsdependingonitsposition
inthenetwork.
•WhentheMSCprovidestheinterfacebetweenPSTNandtheBSSinthe
GSMnetworkitiscalledtheGatewayMSC.
•SomeimportantfunctionscarriedoutbyMSCareCallprocessing
includingcontrolofdata/voicecallsetup,interBSS&interMSC
handovers,controlofmobilitymanagement,Operation&maintenance
supportincludingdatabasemanagement,trafficmeteringandman
machineinterface&managingtheinterfacebetweenGSM&PSTNN/W.
NETWORK COMPONENTS

Mobile Switching Centre (MSC) –Lucent MSC
NETWORK COMPONENTS

MobileStation(MS)
•TheMobileStationconsistsoftheMobileEquipment(ME)andthe
SubscriberIdentityModule(SIM).
MobileEquipment
•TheMobileEquipmentisthehardwareusedbythesubscriberto
accessthenetwork.
•ThemobileequipmentcanbeVehiclemounted,withtheantenna
physicallymountedontheoutsideofthevehicleorportablemobile
unit,whichcanbehandheld.
•Mobilesareclassifiedintofiveclassesaccordingtotheirpower
rating.CLASSPOWER OUTPUT
1 20W
2 8W
3 5W
4 2W
5 0.8W
NETWORK COMPONENTS

SIM
•TheSIMisaremovablecardthatplugsintotheME.
•Itidentifiesthemobilesubscriberandprovidesinformationaboutthe
servicethatthesubscribershouldreceive.
•TheSIMcontainsseveralpiecesofinformation
–InternationalMobileSubscribersIdentity(IMSI)-Thisnumber
identifiesthemobilesubscriber.Itisonlytransmittedovertheair
duringinitialising.
–TemporaryMobileSubscriberIdentity(TMSI)-Thisnumberalso
identifiesthesubscriber.Itcanbealternativelyusedbythesystem.
Itisperiodicallychangedbythesystemtoprotectthesubscriber
frombeingidentifiedbysomeoneattemptingtomonitortheradio
interface.
–LocationAreaIdentity(LAI)-Identifiesthecurrentlocationofthe
subscriber.
–SubscribersAuthenticationKey(Ki)-Thisisusedtoauthenticate
theSIMcard.
–MobileStationInternationalStandardDataNumber(MSISDN)-
Thisisthetelephonenumberofthemobile.
NETWORK COMPONENTS

SIM
•MostofthedatacontainedwithintheSIMisprotectedagainstreading
(egKi)oralterationsaftertheSIMisissued.
•Someoftheparameters(eg.LAI)willbecontinouslyupdatedto
reflectthecurrentlocationofthesubscriber.
•TheSIMcardcanbeprotectedbyuseofPersonalIdentityNumber(
PIN)password.
•TheSIMiscapableofstoringadditionalinformationsuchas
accumulatedcallcharges.
G S M
FULL SIZE SIM CARD MINI SIM CARD
NETWORK COMPONENTS

98 XXX 12345
CC
NDC
SN
CC NDC SN
= Country code
= National Destination Code
= Subscriber Number
Mobile Station International Subscribers Dialling Number( MSISDN ) :
•Human identity used to call a MS
•The Mobile Subscriber ISDN (MSISDN) number is the telephone
number of the MS.
•This is the number a calling party dials to reach the subscriber.
•It is used by the land network to route calls toward the MSC.
NETWORK COMPONENTS

MCC MNC MSIN
404 XX 12345..10
MCC
MNC
MSIN
= Mobile Country Code ( 3 Digits )
= Mobile Network Code ( 2 Digits )
= Mobile Subscriber Identity Number
International Mobile Subscribers Identity ( IMSI ) :
•Network Identity Unique to a MS
•The International Mobile Subscriber Identity (IMSI) is the primary
identity of the subscriber within the mobile network and is
permanently assigned to that subscriber.
•The IMSI can be maximum of 15 digits.
NETWORK COMPONENTS

TemporaryMobileSubscribersIdentity(TMSI):
•TheGSMsystemcanalsoassignaTemporaryMobileSubscriber
Identity(TMSI).
•Afterthesubscriber'sIMSIhasbeeninitializedonthesystem,the
TMSIcanbeusedforsendingmessagesbackwardsandforwards
acrossthenetworktoidentifythesubscriber.
•ThesystemautomaticallychangestheTMSIatregularintervals,thus
protectingthesubscriberfrombeingidentifiedbysomeone
attemptingtomonitortheradiochannels.
•TheTMSIisalocalnumberandisalwaysallocatedbytheVLR.
•TheTMSIismaximumof4octets.
NETWORK COMPONENTS

Equipment Identity Register ( EIR )
•TheEquipmentIdentityRegister(EIR)containsacentralized
databaseforvalidatingtheinternationalmobilestationequipment
identity,theIMEI.
•Thedatabasecontainsthreelists:
–Thewhitelistcontainsthenumberseriesofequipmentidentities
thathavebeenallocatedinthedifferentparticipatingcountries.
Thislistdoesnotcontainindividualnumbersbutbutarangeof
numbersbyidentifyingthebeginningandendoftheseries.
–ThegreylistcontainsIMEIsofequipmenttobemonitoredand
observedforlocationandcorrectfunction.
–TheblacklistcontainsIMEIsofMSswhichhavebeenreported
stolenoraretobedeniedservice.
•TheEIRdatabaseisremotelyaccessedbytheMSC’sinthe
NetworkandcanalsobeaccessedbyanMSCinadifferentPLMN.
.
NETWORK COMPONENTS

Equipment Identity Register ( EIR )
White List
All Valid
assigned ID’s
Range 1
Range 2
Range n
Black List
Service denied
MS IMEI 1
MS IMEI 2
MS IMEI n
Grey List
Service allowed
but noted
MS IMEI 1
MS IMEI 2
MS IMEI n
EIR
NETWORK COMPONENTS

TAC FAC SNR
6 2 6 1
TAC
FAC
SNR
SP
SP
= Type Approval Code
= Final Assembly Code
= Serial Number
= Spare
InternationalMobileEquipmentIdentity(IMEI):
•IMEIisaserialnumberuniquetoeachmobile
•EachMSisidentifiedbyanInternationalMobilestationEquipment
Identity(IMEI)numberwhichispermanentlystoredintheMobile
Equipment.
•Onrequest,theMSsendsthisnumberoverthesignallingchanneltothe
MSC.
•TheIMEIcanbeusedtoidentifyMSsthatarereportedstolenor
operatingincorrectly.
NETWORK COMPONENTS

HOMELOCATIONREGISTER(HLR)
•TheHLRcontainsthemasterdatabaseofallsubscribersinthePLMN.
•ThisdataisremotelyaccessedbytheMSC´´sandVLRsinthenetwork.
ThedatacanalsobeaccessedbyanMSCoraVLRinadifferent
PLMNtoallowinter-systemandinter-countryroaming.
•APLMNmaycontainmorethanoneHLR,inwhichcaseeachHLR
containsaportionofthetotalsubscriberdatabase.Thereisonlyone
databaserecordpersubscriber.
•ThesubscribersdatamaybeaccessedbytheIMSIortheMSISDN.
•TheparametersstoredinHLRare
–SubscribersID(IMSIandMSISDN)
–CurrentsubscriberVLR.
–Supplementaryservicessubscribedto.
–Supplementaryservicesinformation(eg.Currentforwarding
address).
–AuthenticationkeyandAUCfunctionality.
–TMSIandMSRN
NETWORK COMPONENTS

VISITOR LOCATION REGISTER ( VLR )
•TheVisitedLocationRegister(VLR)isalocalsubscriberdatabase,
holdingdetailsonthosesubscriberswhoentertheareaofthenetwork
thatitcovers.
•ThedetailsareheldintheVLRuntilthesubscribermovesintothearea
servicedbyanotherVLR.
•ThedataincludesmostoftheinformationstoredattheHLR,aswellas
morepreciselocationandstatusinformation.
•TheadditionaldatastoredinVLRare
–Mobilestatus(Busy/Free/Noansweretc.)
–LocationAreaIdentity(LAI)
–TemporaryMobileSubscribersIdentity(TMSI)
–MobileStationRoamingNumber(MSRN)
•TheVLRprovidesthesystemelementslocaltothesubscriber,with
basicinformationonthatsubscriber,thusremovingtheneedtoaccess
theHLReverytimesubscriberinformationisrequired.
NETWORK COMPONENTS

•TheAUCisaprocessorsystemthatperformauthenticationfunction.
•Itisnormallyco-locatedwiththeHLR.
•Theauthenticationprocessusuallytakesplaceeachtimethe
subscriberinitialisesonthesystem.
•Eachsubscriberisassignedanauthenticationkey(Ki)whichis
storedintheSIMandattheAUC.
•Arandomnumberof128bitsisgeneratedbytheAUC&senttothe
MS.
•TheauthenticationalgorithmA3usesthisrandomnumberand
authenticationkeyKitoproduceasignedresponseSRES(Signed
Response).
•AtthesametimetheAUCusestherandomnumberand
AuthenticationalgoritmA3alongwiththeKikeytoproduceaSRES.
•IftheSRESproducedbyAUCmatchestheoneproducedbyMSis
thesame,thesubscriberispermittedtousethenetwork.
Authentication Centre ( AUC )
NETWORK COMPONENTS

AUTHENTICATION PROCESS
HLR AUC
TRIPLES
RAND, Kc , SRES
VLR
RAND Kc SRES
RAND
SRES
SRES
SRES = SRES
BTS
A5 ,
HYPERFRAME NUM
Kc
AIR INTERFACE
ENCRYPTION
MS
A3 , A8 , A5 , Ki
SRES =
A3 (RAND , Ki )
Kc =
A8 (RAND , Ki )
Ki, A3, A8
A3 ( RAND, Ki ) = SRES
A8 ( RAND, Ki ) = Kc
Triples
Generated
NETWORK COMPONENTS

Base Station Sub-System ( BSS ) :
•TheBSSisthefixedendoftheradiointerfacethatprovidescontrol
andradiocoveragefunctionsforoneormorecellsandtheir
associatedMSs.
•ItistheinterfacebetweentheMSandtheMSC.
•TheBSScomprisesoneormoreBaseTransceiverStations(BTSs),
eachcontainingtheradiocomponentsthatcommunicatewithMSsin
agivenarea,andaBaseSiteController(BSC)whichsupportscall
processingfunctionsandtheinterfacestotheMSC.
•Digitalradiotechniquesareusedfortheradiocommunicationslink,
knownastheAirInterface,betweentheBSSandtheMS.
•TheBSSconsistsofthreebasicNetworkElements(NEs).
–Transcoder(XCDR)orRemotetranscoder(RXCDR).
–BaseStationController(BSC).
–BaseTransceiverStations(BTSs)assignedtotheBSC..
NETWORK COMPONENTS

Transcoder( XCDR )
•Thespeechtranscoderistheinterfacebetweenthe64kbit/sPCM
channelinthelandnetworkandthe13kbit/svocoder(actually22.8
kbit/safterchannelcoding)channelusedontheAirInterface.
•ThisreducestheamountofinformationcarriedontheAirInterfaceand
hence,itsbandwidth.
•Ifthe64kbits/sPCMistransmittedontheairinterfacewithout
occupation,itwouldoccupyanexcessiveamountofradiobandwidth.
Thiswouldusetheavailableradiospectruminefficiently.
•Therequiredbandwidthisthereforereducedbyprocessingthe64
kbits/sPCMdatasothattheamountofinformationrequiredtotransmit
digitisedvoicefallsto13kb/s.
•TheXCDRcanmultiplex4trafficchannelsintoasingle64kbit/s
timeslot.ThusaE1/T1seriallinkcancarry4timesasmanychannels.
•ThiscanreducethenumberofE1/T1leasedlinesrequiredtoconnect
remotelylocatedequipment.
•WhenthetranscoderisbetweentheMSCandtheBSCitiscalleda
remotetranscoder(RXCDR).
NETWORK COMPONENTS

TRANSCODER(XCDR) -Siemens
NETWORK COMPONENTS

TRANSCODING
30 Timeslots
1 traffic channel / TS
64 Kbps / TS
4 E1 lines = 30 X 4
=120 Timeslots
Each Timeslot =16 X 4
= 64 Kb/s
30 timeslots = 30 x 4
=120 traffic channels
MSC XCDR BSC
012 3116
Transcoded information from four calls
NETWORK COMPONENTS

BaseStationController(BSC)
•TheBSCnetworkelementprovidesthecontrolfortheBSS.
•ItcontrolsandmanagestheassociatedBTSs,andinterfaceswith
theOperationsandMaintenanceCentre(OMC).
•ThepurposeoftheBSCistoperformavarietyoffunctions.The
followingcomprisethefunctionsprovidedbytheBSC:
–ControlstheBTScomponents.-
–PerformsCallProcessing.
–PerformsOperationsandMaintenance(O&M).
–ProvidestheO&Mlink(OML)betweentheBSSandtheOMC.
–ProvidestheAInterfacebetweentheBSSandtheMSC.
–Managestheradiochannels.
–TransferssignallinginformationtoandfromMSs.
NETWORK COMPONENTS

BaseStationController(BSC)–SiemensBSC
NETWORK COMPONENTS

BaseTransceiverStation(BTS)
•TheBTSnetworkelementconsistsofthehardwarecomponents,
suchasradios,interfacemodulesandantennasystemsthat
providetheAirInterfacebetweentheBSSandtheMSs.
•TheBTSprovidesradiochannels(RFcarriers)foraspecificRF
coveragearea.
•TheradiochannelisthecommunicationlinkbetweentheMSs
withinanRFcoverageareaandtheBSS.
•TheBTSalsohasalimitedamountofcontrolfunctionalitywhich
reducestheamountoftrafficbetweentheBTSandBSC.
NETWORK COMPONENTS

BaseTransceiverStation(BTS)
NETWORK COMPONENTS

MSC BSC BTS12
BTS1
BTS2
BTS4
BTS3BTS11
BTS13 BTS14
BTS5
BTS6
BTS7
BTS8
BTS9
BTS11
Open ended Daisy Chain
Daisy Chain with
a fork. Fork has a
return loop back
to the chain
Star
Daisy Chain with
a fork. Fork has a
return loop back
to the chain
BTS Connectivity
NETWORK COMPONENTS

•TheOMCcontrolsandmonitorstheNetworkelementswithina
region.
•TheOMCalsomonitorsthequalityofservicebeingprovidedbythe
Network.
•ThefollowingarethemainfunctionsperformedbytheOMC-R
–TheOMCallowsnetworkdevicestobemanuallyremovedforor
restoredtoservice.Thestatusofnetworkdevicescanbe
checkedfromtheOMCandtestsanddiagnosticsinvoked.
–ThealarmsgeneratedbytheNetworkelementsarereported
andloggedattheOMC.TheOMC-REngineercanmonitorand
analysethesealarmsandtakeappropriateactionlikeinforming
themaintenancepersonal.
–TheOMCkeepsoncollectingandaccumulatingtrafficstatistics
fromthenetworkelementsforanalysis.
–Softwareloadscanbedownloadedtonetworkelementsor
uploadedtotheOMC.
Operation And Maintenance Centre For Radio (OMC-R)
NETWORK COMPONENTS

Operation And Maintenance Centre For Radio (OMC-R)
NETWORK COMPONENTS

•BSIC allows a mobile station to distinguish between neighboring base
stations.
•It is made up of 8 bits.
NCC = National Colour Code( Differs from operator to operator )
BCC = Base Station Colour Code, identifies the base station to help
distinguish between Cell’s using the same BCCH frequencies
Base Station Identity Code
BCC00 BCCNCC
7 6 5 4 3 2 1 0
NETWORK COMPONENTS

•TheMSisidentifiedbyit’sclassmarkwhichthemobilesendsduring
it’sinitialmessage.
•Theclassmarkcontainsthefollowinginformation
–Revisionlevel-IdentifiesthephaseoftheGSMspecificationsthe
mobilescomplieswith.
–RFPowerCapabilities-Themaximumpowerthemobilecan
transmit.ThisinformationisheldintheMSPowerClassNumber.
–CipheringAlgorithm-Indicatesthecipheringalgorithm
implementedinthemobile.Thereisonlyonealgorithm(A5)in
GSMphase1,howeverGSMphase2specifiesdifferent
algorithms(A5/0toA5/7)
–FrequencyCapability-IndicatesthefrequencybandstheMScan
receiveandtransmiton.
–ShortMessageCapability-IndicateswhethertheMSisableto
receiveshortmessagesornot.
MS ClassMark
NETWORK COMPONENTS

MOBILE MAXIMUM RANGE
RANGE=
TIMING ADVANCE = DELAY OF BITS (0-63)
BIT PERIOD= 577/156.25 = 3.693sec =3.693 * 10e-6 sec
VELOCITY= 3 * 10e5 Km/sec
RANGE= 34.9 Km
TIMIMG ADVANCE * BIT PERIOD* VELOCITY
2

MULTIPLE ACCESS TECHNIQUES
•Inorderforseverallinkstobeinprogresssimultaneouslyinthe
samegeographicalareawithoutmutualinterference,multiple
accesstechniquesaredeployed.
•Thecommonlyusedmultipleaccesstechniquesare
–FrequencyDivisionMultipleAccess(FDMA)
–TimeDivisionMultipleAccess(TDMA)
–CodeDivisionMultipleAccess(CDMA)

TERRESTERIALINTERFACE
•Theterrestrialinterfacescomprisesalltheconnectionsbetween
theGSMsystementities,apartfromtheUmorairinterface.
•Theterrestrialinterfacestransportthetrafficacrossthesystem
andallowsthepassageofthousandsofdatamessagestomake
thesystemfunction.
•Thestandardinterfacesusedare
–2Mb/s
–SignallingSystem(C7orSS7
–PacketSwitchedData
–AbisusingtheLAPDprotocol(LinkAccessProcedureD)
•

INTERFACE NAMES
Each interface specified in GSM has a name associated with it.
NAME INTERFACE
Um MS -----BTS
Abis BTS -----BSC
A MSC ------BSC
B MSC ------VLR
C MSC ------HLR
D VLR -----HLR
E MSC ------MSC
F MSC ------EIR
G VLR ------VLR
H HLR ------AUC

2Mbits/sTrunk30-channelPCM
ThisinterfacecarriesthetrafficfromthePSTNtotheMSC,
betweenMSC’s,fromtheMSCtotheBSC’sandfromtheBSC’sto
theBTS’s.
ItrepresentsthephysicallayerintheOSImodel.
Each2Mb/slinkprovides30trafficchannelsavailabletocarry
speech,dataorcontrolinformation.
TypicalConfiguration
TS 0 TS 1-15 TS 16 TS 17 -31
TS 0 -Frame allignment/ Error checking/ Signalling/ Alarms
TS 1-15 , 17-31 -Traffic
TS 16 -Siganlling

BSS CONNECTIONS
MSC
XCDR
BSC
BTS BTSBTS
OMC
CBC
MTL
(C7 )
OML (X.25)
RSL
( LAPD)
CBL

Cell Global Identity ( CGI ) :
MCC
MNC
LAC
CI
MCC MNC LAC CI
LAI
CGI
= Mobile Country Code
= Mobile Network Code
= Location Area Identity
= Cell Identity

Physicalchannel-Eachtimeslotonacarrierisreferredtoasaphysical
channel.Percarrierthereare8physicalchannels.
Logicalchannel-VarietyofinformationistransmittedbetweentheMSand
BTS.Therearedifferentlogicalchannelsdependingontheinformation
sent.Thelogicalchannelsareoftwotypes
•Trafficchannel
•Controlchannel
Downlink
Uplink
CHANNELS
CHANNEL CONCEPT

GSM Traffic Channels
Traffic Channels
TCH/F
Full rate 22.8kbits/s
TCH/H
Half rate 11.4 kbits/s
CHANNEL CONCEPT

GSM Control Channels
BCH ( Broadcast channels)
Downlink only
Control Channels
DCCH(Dedicated Channels)
Downlink & Uplink
CCCH(Common Control Chan)
Downlink & Uplink
Synch.
Channels
RACH
Random
Access Channel
CBCH
Cell Broadcast
Channel
SDCCH
Standalone
dedicated
control channel
ACCH
Associated
Control Channels
SACCH
Slow associated
Control Channel
FACCH
Fast Associated
Control Channel
PCH/
AGCH
Paging/Access grant
FCCH
Frequency
Correction channel
SCH
Synchronisation
channel
BCCH
Broadcast
control channel
CHANNEL CONCEPT

BCH Channels
BCCH( Broadcast Control Channel )
•Downlinkonly
•BroadcastsgeneralinformationoftheservingcellcalledSystem
Information
•BCCHistransmittedontimeslotzeroofBCCHcarrier
•Readonlybyidlemobileatleastonceevery30secs.
SCH( Synchronisation Channel )
•Downlinkonly
•Carriesinformationforframesynchronisation.ContainsTDMA
framenumberandBSIC.
FCCH( Frequency Correction Channel )
•Downlink only.
•Enables MS to synchronise to the frequency.
•Also helps mobiles of the ncells to locate TS 0 of BCCH carrier.
CHANNEL CONCEPT

CCCH Channels
RACH( Random Access Channel )
•Uplink only
•Used by the MS to access the Network.
AGCH( Access Grant Channel )
•Downlink only
•Used by the network to assign a signalling channel upon
successfull decoding of access bursts.
PCH( Paging Channel )
•Downlink only.
•Used by the Network to contact the MS.
CHANNEL CONCEPT

DCCH Channels
SDCCH( Standalone Dedicated Control Channel )
•Uplink and Downlink
•Used for call setup, location update and SMS.
SACCH( Slow Associated Control Channel )
•Used on Uplink and Downlink only in dedicated mode.
•Uplink SACCH messages -Measurement reports.
•Downlink SACCH messages -control info.
FACCH( Fast Associated Control Channel )
•Uplink and Downlink.
•Associated with TCH only.
•Is used to send fast messages like handover messages.
•Works by stealing traffic bursts.
CHANNEL CONCEPT

NORMAL BURST
0123456701234567
57 bits 57 bits26 bits 33
FRAME1(4.615ms)
FRAME2
Training
sequence
Data Data
Tail
Bits
Tail
Bits
Flag
Bit
Flag
Bit
Guard
Period
Guard
Period
0.546ms
0.577ms
CarriestrafficchannelandcontrolchannelsBCCH,PCH,AGCH,SDCCH,
SACCHandFACCH.
CHANNEL CONCEPT

Data-Twoblocksof57bitseach.Carriesspeech,dataorcontrolinfo.
Tailbits-Usedtoindicatethestartandendofeachburst.Threebitsalways
000.
Guardperiod-8.25bitslong.Thereceivercanonlyreceiveanddecodeif
theburstisreceivedwithinthetimeslotdesignatedforit.SincetheMSare
moving.Exactsynchronizationofburstisnotpossiblepractically.Hence
8.25bitscorrespondingtoabout30usisavailableasguardperiodforasmall
marginoferror.
Flagbits-Thisbitisusedtoindicateifthe57bitsdatablockisusedas
FACCH.
TrainingSequence-Thisisasetsequenceofbitsknownbyboththe
transmitterandthereceiver(BCCofBSIC).Whenaburstofinformationis
receivedtheequalisersearchesforthetrainingsequencecode.The
receivermeasuresandthenmimicsthedistortionwhichthesignalhasbeen
subjectedto.Thereceiverthencomparesthereceiveddatawiththe
distortedpossibletransmittedsequenceandchoosesthemostlikelyone.
NORMAL BURST
CHANNEL CONCEPT

FREQUENCY CORRECTION BURST
0123456701234567
142 bits 33
FRAME1(4.615ms) FRAME2
Fixed Data
Tail
Bits
Tail
Bits
Guard
Period
Guard
Period
0.546ms
0.577ms
•Carries FCCH channel.
•Made up of 142 consecutive zeros.
•Enables MS to correct its local oscillator locking it to that of the BTS.
CHANNEL CONCEPT

SYNCHRONISATION BURST
0123456701234567
39 bits 33
FRAME1(4.615ms) FRAME2
Synchronisation
Sequence
Tail
Bits
Tail
Bits
Guard
Period
Guard
Period
0.546ms
0.577ms
64 bits 39 bits
Encrypted
Bits
Encrypted
Bits
•Carries SCH channel.
•Enables MS to synchronise its timings with the BTS.
•Contains BSIC and TDMA Frame number.
CHANNEL CONCEPT

DUMMY BURST
0123456701234567
57 bits 57 bits26 bits 33
FRAME1(4.615ms) FRAME2
Training
sequence
Data Data
Tail
Bits
Tail
Bits
Flag
Bit
Flag
Bit
Guard
Period
Guard
Period
0.546ms
0.577ms
•TransmittedontheunusedtimeslotsoftheBCCHcarrierinthe
downlink.
CHANNEL CONCEPT

ACCESS BURST
0123456701234567
41 bits 68.25 bits8
FRAME1(4.615ms) FRAME2
Tail
Bits
Tail
Bits
Guard
Period
0.577ms
36 bits
Synchronisation
Sequence
Encrypted
Bits
3
•CarriesRACH.
•Hasabiggerguardperiodsinceitisusedduringinitialaccessand
theMSdoesnotknowhowfaritisactuallyfromtheBTS.
CHANNEL CONCEPT

NEED FOR TIMESLOT OFFSET
0123456701234567
0123456701234567
•IfUplinkandDownlinkarealignedexactly,thenMSwillhaveto
transmitandreceiveatthesametime.Toovercomethisproblema
offsetof3timeslotsisprovidedbetweendownlinkanduplink
BSS Downlink
MS Uplink
CHANNEL CONCEPT

0123456701234567
5670123456701234
•AsseentheMSdoesnothavetotransmitandreceiveatthesame
time.ThissimplifiestheMSdesignwhichcannowuseonlyone
synthesizer.
BSS Downlink
MS Uplink
5
0
3 timeslot
offset
CHANNEL CONCEPT
NEED FOR TIMESLOT OFFSET

T
15
T
5
T
9
T
10
T
11
S
12
T
13
T
14
T
6
T
7
T
8
T
0
T
1
T
2
T
3
T
4
T
16
T
17
T
18
T
19
T
20
T
21
T
22
T
23
T
24
I
25
012345670123456701234567
120 msec
4.615 msec
26 FRAME MULTIFRAME STRUCTURE
•MSondedicatedmodeonaTCHusesa26-framemultiframe
structure.
•Frame0-11and13-24usedtocarrytraffic.
•Frame12usedasSACCHtocarrycontrolinformationfromandtoMS
toBTS.
•Frame25isidleandisusedbymobiletodecodetheBSICofneighbor
cells.
CHANNEL CONCEPT

BCCH
CCCH
BCCH
CCCH
BCCH
CCCH
BCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH
CCCH 0
10
20
30
40
50 50
40
30
20
10
0
IDLE
CCCH BLOCK
BCCH BLOCK
SCH BLOCK
FCCH BLOCK
BCCH/CCCH NON -COMBINED MULTIFRAME
RACH BLOCK
Downlink Uplink

0
10
20
30
40
50 50
40
30
20
10
0
IDLE
CCCH BLOCK
BCCH BLOCK
SCH BLOCK
FCCH BLOCK
BCCH/CCCH COMBINED MULTIFRAME
51
101 101
51BCCH
CCCH
BCCH
CCCH
CCCH
BCCH
CCCH
CCCH
CCCH
SACCH
SACCH
CCCH
CCCH
CCCH
CCCHSDCCH
SDCCH
SDCCH
SDCCH BCCH
CCCH
BCCH
CCCH
CCCH
BCCH
CCCH
CCCH
CCCH
SACCH
SACCH
CCCH
CCCH
CCCH
CCCHSDCCH
SDCCH
SDCCH
SDCCH BCCHCCCHSDCCH
CCCHSACCH
CCCHSACCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCH BCCHCCCHSDCCH
CCCHSACCH
CCCHSACCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCH
CCCHCCCHCCCHSDCCH
RACH BLOCK
SDCCH/4
SACCH/4
Downlink Uplink

0
10
20
30
40
50 50
40
30
20
10
0
IDLE
DCCH/8 MULTIFRAME
51
101 101
51
SDCCH/8
SACCH/C8BCCH
CCCH
A2
A3
BCCH
CCCH
A0
A1
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0 BCCH
CCCH
A6
A7
BCCH
CCCH
A4
A5
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0 BCCHA0
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0
BCCH
CCCH
A6
A7
CCCHA5 BCCHA4
CCCHCCCHCCCHD7
CCCHCCCHCCCHD6
CCCHCCCHCCCHD5
CCCHCCCHCCCHD4
CCCHCCCHCCCHD3
CCCHCCCHCCCHD2
CCCHCCCHCCCHD1
CCCHCCCHCCCHD0
BCCH
CCCH
A2
A3
CCCHA1
Downlink Uplink

01
0 1 2 2045 2046 2047
1 Hyperframe = 2048 superframes = 2,715,648 TDMA frames3h 28min 53s 760ms
1 Superframe = 1326 TDMAframes = 51(26 fr) 0r 26(51 fr) multiframes
1 2 3 494847 50
0 1 24 25
0 1 2 232425 0 481 2 4950
234567
6.12s
0
235.38ms120ms
Control 51 -Frame MultiframeTraffic 26 -Frame Multiframe
4.615ms
TDMA Frame
HYPERFRAME AND SUPERFRAME STRUCTURE
CHANNEL CONCEPT

SPEECH
CODING
CHANNEL
CODING
INTERLEAVING
BURST
ASSEMBLING
CIPHERING
MODULATION DEMODULATION
DECIPHERING
BURST
DISASSEMBLING
DEINTERLEAVING
CHANNEL
DECODING
SPEECH
DECODING
Transmission
CODING, INTERLEAVING CIPHERING

•Thetransmissionofspeechisoneofthemostimportantserviceofa
mobilecellularsystem.
•TheGSMspeechcodec,whichwilltransformtheanalogsignal(voice)
intoadigitalrepresentation,hastomeetthefollowingcriterias
•Agoodspeechquality,atleastasgoodastheoneobtainedwith
previouscellularsystems.
•Toreducetheredundancyinthesoundsofthevoice.Thisreduction
isessentialduetothelimitedcapacityoftransmissionofaradio
channel.
•Thespeechcodecmustnotbeverycomplexbecausecomplexityis
equivalenttohighcosts.
•ThefinalchoicefortheGSMspeechcodecisacodecnamedRPE-
LTP(RegularPulseExcitationLong-TermPrediction).
SPEECH CODING
CODING

•Thiscodecusestheinformationfromprevioussamples(this
informationdoesnotchangeveryquickly)inordertopredictthecurrent
sample.
•Thespeechsignalisdividedintoblocksof20ms.Theseblocksare
thenpassedtothespeechcodec,whichhasarateof13kbps,inorder
toobtainblocksof260bits.
SPEECH CODING
CODING

CHANNEL CODING
•Channel coding adds redundancy bits to the original information in
order to detect and correct, if possible, errors ocurred during the
transmission.
•The channel coding is performed using two codes: a block code and
a convolutional code.
•The block code receives an input block of 240 bits and adds four
zero tail bits at the end of the input block. The output of the block
code is consequently a block of 244 bits.
•A convolutional code adds redundancy bits in order to protect the
information. A convolutional encoder contains memory. This property
differentiates a convolutional code from a block code.
•A convolutional code can be defined by three variables : n, k and K.
•The value n corresponds to the number of bits at the output of the
encoder, k to the number of bits at the input of the block and K to the
memory of the encoder.
CODING

CHANNEL CODING ( Cont )
•The ratio, R, of the code is defined as R = k/n.
Example-Let'sconsideraconvolutionalcodewiththefollowing
values:kisequalto1,nto2andKto5.Thisconvolutionalcodeuses
thenarateofR=1/2andadelayofK=5,whichmeansthatitwill
addaredundantbitforeachinputbit.Theconvolutionalcodeuses5
consecutivebitsinordertocomputetheredundancybit.Asthe
convolutionalcodeisa1/2rateconvolutionalcode,ablockof488bits
isgenerated.These488bitsarepuncturedinordertoproduceablock
of456bits.Thirtytwobits,obtainedasfollows,arenottransmitted:
C(11+15j)forj=0,1,...,31
•Theblockof456bitsproducedbytheconvolutionalcodeisthen
passedtotheinterleaver
Convolution code R = k/n = 1/2k=1
1 bit input
n=2
2 bit input
CODING

CHANNEL CODING FOR GSM SPEECH CHANNELS
•Beforeapplyingthechannelcoding,the260bitsofaGSMspeech
framearedividedinthreedifferentclassesaccordingtotheirfunction
andimportance.
•Themostimportantclassistheclass1acontaining50bits.Next
importantistheclass1b,whichcontains132bits.Theleastimportant
istheclass2,whichcontainstheremaining78bits.
•Thedifferentclassesarecodeddifferently.
•Firstofall,theclass1abitsareblock-coded.Threeparitybits,used
forerrordetection,areaddedtothe50class1abits.Theresultant53
bitsareaddedtotheclass1bbits.
•Fourzerobitsareaddedtothisblockof185bits(50+3+132).A
convolutionalcode,withr=1/2andK=5,isthenapplied,obtaining
anoutputblockof378bits.
•Theclass2bitsareadded,withoutanyprotection,totheoutput
blockoftheconvolutionalcoder.Anoutputblockof456bitsisfinally
obtained.
CODING

Speech Channel Coding
Class 1a
50 bits
Class 1b
132 bits
Class 1a
50 bits
Class 1b
132 bits
378 bits
Class 2
78 bits
3 4
Parity
check
Tail
bits
260 bits
456 bits
Convolution coding
CODING

CHANNEL CODING FOR CONTROL CHANNELS
•InGSMthesignallinginformationisjustcontainedin184bits.
•Fortyparitybits,obtainedusingafirecode,andfourzerobitsare
addedtothe184bitsbeforeapplyingtheconvolutionalcode(r=1/2
andK=5).Theoutputoftheconvolutioncodeisthenablockof456
bitswhichdoesnotneedtobepunctured.
184 bits
184 bits
456 bits
Fire
code
Tail
bits
Convolution coding
40 bits4
Parity
bits
CODING

CHANNEL CODING FOR DATA CHANNELS
•Indatainformationiscontainedin240bits.
•Fourtailsbitsareaddedtothe240bitsbeforeapplyingthe
convolutionalcode(r=1/2andK=5).Theoutputofthe
convolutionalcodeisthenablockof488bitswhichwhenpunctuated
yields456bits.
240 bits
240 bits
488 bits
Tail
bits
Convolution coding
4
456 bits
Punctuate
CODING

INTERLEAVING
•Aninterleavingrearrangesagroupofbitsinaparticularway.
•ItisusedincombinationwithFECcodes(ForwardErrorCorrection
Codes)inordertoimprovetheperformanceoftheerrorcorrection
mechanisms.
•Theinterleavingdecreasesthepossibilityoflosingwholebursts
duringthetransmission,bydispersingtheerrors.
•Astheerrorsarelessconcentrated,itistheneasiertocorrectthem.
INTERLEAVING

GSM SPEECH CHANNEL INTERLEAVING
•AburstinGSMtransmitstwoblocksof57databitseach.
•Thereforethe456bitscorrespondingtotheoutputofthechannelcoder
fitinto8‘57data’bits(8*57=456).The456bitsaredividedintoeight
blocksof57bits.
•Thefirstblockof57bitscontainsthebitnumbers(0,8,16,.....448),the
secondonethebitnumbers(1,9,17,.....449),etc.
•Thelastblockof57bitswillthencontainthebitnumbers(7,15,.....455).
•Thefirstfourblocksof57bitsareplacedintheeven-numberedbitsof
fourconsecutivebursts.
•Theotherfourblocksof57bitsareplacedintheodd-numberedbitsof
thenextfourbursts.
•TheinterleavingdepthoftheGSMinterleavingforspeechchannelsis
eight.
•Anewdatablockalsostartseveryfourbursts.Theinterleaverfor
speechchannelsiscalledablockinterleaver.
INTERLEAVING

4
GSM SPEECH CHANNEL INTERLEAVING ( Diagram )
1 2 3 5 601234567012345670123456701234567
4
456 bits
5
456 bits
6
456 bits
Full rate encoded speech blocks
from a single conversation
Bursts
TDMA
Frames Frame 1 Frame 2 Frame 3 Frame 4
INTERLEAVING

CONTROL CHANNEL INTERLEAVING
•AburstinGSMtransmitstwoblocksof57databitseach.
•Thereforethe456bitscorrespondingtotheoutputofthechannelcoder
fitintofourbursts(4*114=456).
•The456bitsaredividedintoeightblocksof57bits.Thefirstblockof57
bitscontainsthebitnumbers(0,8,16,.....448),thesecondonethebit
numbers(1,9,17,.....449),etc.Thelastblockof57bitswillthencontain
thebitnumbers(7,15,.....455).
•Thefirstfourblocksof57bitsareplacedintheeven-numberedbitsof
fourbursts.
•Theotherfourblocksof57bitsareplacedintheodd-numberedbitsof
thesamefourbursts.
•ThereforetheinterleavingdepthoftheGSMinterleavingforcontrol
channelsisfourandanewdatablockstartseveryfourbursts.
•Theinterleaverforcontrolchannelsiscalledablockrectangular
interleaver.
INTERLEAVING

DATA INTERLEAVING
•Aparticularinterleavingscheme,withaninterleavingdepthequalto22,
isappliedtotheblockof456bitsobtainedafterthechannelcoding.
•Theblockisdividedinto16blocksof24bitseach,2blocksof18bits
each,2blocksof12bitseachand2blocksof6bitseach.
•Itisspreadover22burstsinthefollowingway:
•thefirstandthetwenty-secondburstscarryoneblockof6bits
each
•thesecondandthetwenty-firstburstscarryoneblockof12bits
each
•thethirdandthetwentiethburstscarryoneblockof18bitseach
•fromthefourthtothenineteenthburst,ablockof24bitsisplaced
ineachburst
•Aburstwillthencarryinformationfromfiveorsixconsecutivedata
blocks.Thedatablocksaresaidtobeinterleaveddiagonally.
•Anewdatablockstartseveryfourbursts.
INTERLEAVING

CIPHERING
•Cipheringisusedtoprotectsignalinganduserdata.
•AcipheringkeyiscomputedusingthealgorithmA8storedonthe
SIMcard,thesubscriberkeyandarandomnumberdeliveredbythe
network(thisrandomnumberisthesameastheoneusedforthe
authenticationprocedure).
•A114bitsequenceisproducedusingthecipheringkey,analgorithm
calledA5andtheburstnumbers.
•ThisbitsequenceisthenXORedwiththetwo57bitblocksofdata
includedinanormalburst.
•Inordertodeciphercorrectly,thereceiverhastousethesame
algorithmA5forthedecipheringprocedure.
MODULATION
•Modulation is done using 0.3 GMSK
MODULATION

SIGNALLING
Other Networks

•Thetermsignalingisusedinmanycontexts.
•Intechnicalsystems,itveryoftenreferstothecontrolofdifferent
procedures.
•Withreferencetotelephony,signalingmeansthetransferof
informationandtheinstructionsrelevanttocontrolandmonitor
telephonyconnections.
SIGNALLING SYSTEM
WHAT IS SIGNALLING ?

GENERALINTRODUCTION
•Today’sglobaltelecomnetworksareincludedinverycomplex
technicalsystems.
•Naturally,asystemofthistyperequiresextensivesignaling,both
internallyindifferentnodes(forexample,exchanges)andexternally
betweendifferenttypesofnetworknodes.
•Duringthistrainingwewillfocusonexternalsignaling.
•Thus,thetermsignalinginthefollowingslidesalwaysrefersto
externalsignalingtraffic.
•Themainpurposeofusingsignalinginmoderntelecomnetworks–
wheredifferentnetworknodesmustcooperateandcommunicatewith
eachother–istoenabletransferofcontrolinformationbetween
nodesinconnectionwith:
–Trafficcontrolproceduresasset-up,supervision,andrelease
oftelecommunicationconnectionsandservices
SIGNALLING SYSTEM C7

GENERALINTRODUCTION
•Databasecommunication,forexample,databasequeriesconcerning
specificservices,roamingincellularnetworks,etc.
•Networkmanagementprocedures,forexample,blockingor
deblockingtrunks.
•Traditionally,externalsignalinghasbeendividedintotwobasictypes
–Accesssignaling(forexample,SubscriberLoopSignaling)This
meanssignalingbetweenasubscriberterminal(telephone)and
thelocalexchange.
–Trunksignaling(thatis,Inter-ExchangeSignaling)Thisisused
forsignalingbetweenexchanges.

SIGNALING IN TELECOMMUNICATION NETWORK
DIGITAL SUBSCRIBER SIG.
SUBSCRIBER LINE SIG.
ACCESS SIG
SIGNALLING
TRUNK SIGNALLING
CHANNEL ASSOCIATED SIG.
COMMON CHANNEL SIG.

AccessSignaling
•Therearemanytypesofaccesssignaling,forexample,PSTNanalogue
subscriberlinesignaling,ISDNDigitalSubscriberSignalingSystem
(DSS1),andsignalingbetweentheMSandthenetworkintheGSM
system.
•Signalingontheanaloguesubscriberlinebetweenatelephony
subscriberandtheLocalExchange(LE)isperformedbymeansof
on/offhooksignals,dialeddigits,informationtones(dialtone,busy
tone,etc.),recordedannouncements,andringingsignals.
•Thedialeddigitscanbesentintwodifferentways:asdecadicpulses
(usedforold-typerotary-dialtelephones),orasacombinationoftwo
tones(usedformodernpushbuttontelephones).Thelattersystemis
knownastheDualToneMultiFrequency(DTMF).
•Theinformationtones(dialtone,ringingtone,busytone,etc.)areaudio
signalsusedtokeepthecallingparty(theA-subscriber)informedabout
whatisgoingoninthenetworkduringtheset-upofacall.

AccessSignaling
•DigitalSubscriberSignalingSystemNo.1(DSS1)isthestandard
accesssignalingsystemusedinISDN.ItisalsocalledaD-channel
signalingsystem
•D-channelsignalingisdefinedfordigitalaccesslinesonly.
•ThesignalingprotocolsarebasedontheOSI(OpenSystem
Interconnection)referencemodel,layers1to3.
•Consequently,thesignalingmessagesaretransferredasdata
packetsbetweentheuserterminalandthelocalexchange.
•DuetothemuchmorecomplexserviceenvironmentattheISDN
user’ssite,theamountofsignalinginformationandthenumberof
variations

TrunkSignaling
•TheInter-exchangeSignalinginformationisusuallytransportedon
oneofthetimeslotsinaPCMlink,eitherinassociationwiththe
speechchannelorindependently.
•TherearetwocommonlyusedmethodsforInterExchangeSignaling.
ChannelAssociatedSignaling(CAS)
–InCAS,thespeechchannel(in-band),orachannelclosely
associatedwithaspeechchannel(out-band),isusedfor
signaling.
CommonChannelSignaling(CCS)
–Inthiscaseadedicatedchannel,completelyseparatefromthe
speechchannel,isusedforsignaling.Duetothehighcapacity,
onesignalingchannelinCCScanservealargenumberof
speechchannels.
•InaGSMnetwork,CCITTSignalingSystemNo.7isused.
•SignalingSystemNo.7isaCommonChannelSignalingsystem.

CHANNELASSOCIATEDSIGNALING(CAS)
•ChannelAssociatedSignaling(CAS)meansthatthesignalingis
alwayssentonthesameconnection(PCMlink)asthetraffic.
•Thesignalingisassociatedwiththetrafficchannel.
•Ina2Mb/sPCMlink,30timeslotsareusedforspeech,whereasTS
0isusedforsynchronizationandTS16isusedforthelinesignaling.
•All30trafficconnectionsshareTS16inamultiframeconsistingof16
consecutiveframes.
•OnTS16,eachtrafficchannelhasapermanentlyallocatedrecurring
locationforlinesignaling,wheretwotrafficchannelsshareTS16in
oneframe.

COMMONCHANNELSIGNALING(CCS)
•InCCS,signalingmessages(ordatapackets)aretransmittedovertime
slotsinaPCMlinkreservedforthepurposeofsignaling.
•Thesystemisdesignedtouseacommondatachannel(orsignaling
link)asthecarrierofallsignals,requiredbyalargenumberoftraffic
channels.
•In1968,CCITTspecifiedaCommonChannelSignalingsystemcalled
CCSSystemNo.6,whichwasdesignedespeciallyforinternational
analoguetelephonynetworks.
•However,veryfewinstallationsofthissystemremaintoday.Ithas,as
alreadymentioned,beenreplacedbySignalingSystemNo.7.
•ThefirstversionofSS7(1980)wasdesignedfortelephonyanddata.
•Inthe80’sthedemandfornewservicesdramaticallyincreasedandthe
SS7wasthereforedevelopedtomeetthesignalingrequirements,
specifiedforallthesenewservices.
•TodaySS7isusedinmanydifferentnetworksandrelatedservices
typicallybet
n
PSTN,ISDN,PLMN&INservicesthroughouttheworld.

OSIREFERENCEMODEL
•TheSignalingSystemNo.7,whichisatypeofpacketswitcheddata
communicationsystem,isstructuredinamodularandlayeredway.
•SuchadesignofSS7issimilartotheOpenSystemInterconnection
model.
•OpenSystemsaresystemsthatusestandardizedcommunication
proceduresdevelopedfromthereferencemodel.
•Thus,allsuchopensystemsareabletocommunicatewitheach
other.
•Theword“system”canrefertocomputers,exchanges,data
networks,etc.

PHYSICAL
LINK
NETWORK
TRANSPORT
SESSION
PRESENTATION
OSI MODEL REFERENCE DIAGRAM
APPLICATION
PHYSICAL
LINK
NETWORK
TRANSPORT
SESSION
PRESENTATION
APPLICATION

COMMUNICATION PROCESS
•Eachlayerhasitsownspecifiedfunctionsandprovidesspecific
servicesforthelayersabove.
•Itisimportanttodefinetheinterfacesbetweendifferentlayersandthe
functionswithineachlayer.
•Thewayafunctionisrealizedwithinalayerisnotpredicted.
•Logically,thecommunicationbetweenfunctionsalwaystakesplace
onthesamelevelaccordingtotheprotocolsforthatlevel.
•Onlyfunctionsonthesamelevelcan“talktoeachother”.
•Inthetransmittingsystem,theprotocolforeachlayeradds
informationtothedatareceivedfromthelayerabove.
•Theadditionusuallyconsistsofaheaderand/oratrailer.
•Inthereceivingsystem,theadditionsareused,forexample,to
identifybitsordatafieldscarryinginformationforthatspecificlayer
only.
•Thesefieldsaredecodedbylayerfunctionalityandareremoved
whendeliveringthemessagetotheapplicationsorlayersabove.

•Whenthedatareachestheapplicationlayeronthereceivingside,
itconsistsofonlythedatathatoriginatedintheapplicationlayerof
thesendingsystem.
•Logically,eachlayercommunicateswiththecorrespondinglayer
intheothersystem.
•ThiscommunicationiscalledPeer-to-Peercommunicationandis
controlledbythelayer’sprotocol.
DESCRIPTIONOFLAYERS
ApplicationLayer
•Thislayerprovidesservicesforsupportoftheuser’sapplication
processandforcontrolofallcommunicationbetweenapplications.
•Examplesoflayer7functionsarefiletransfer,messagehandling,
directoryservices,andoperationandmaintenance.

PresentationLayer
•Thislayerdefineshowdataistoberepresented,thatis,thesyntax.
•Thepresentationlayertransformsthesyntaxusedintheapplication
intothecommonsyntaxneededforthecommunicationbetween
applications.
•Layer6containsdatacompression.
SessionLayer
•Thislayerestablishesconnectionsbetweenpresentationlayersin
differentsystems.
•Italsocontrolstheconnection,thesynchronizationandthe
disconnectionofthedialogue.
•Itallowsthepresentationlayertodeterminecheckpoints,fromwhich
theretransmissionwillstartwhenthedatatransmissionhasbeen
interrupted.

TransportLayer
•Thislayerguaranteesthatthebearerservicehasthequality
requiredbytheapplicationinquestion.
•Examplesoffunctionsareerrordetectionandcorrection(end-to-
end),andflowcontrol.
•Thetransportlayeroptimizesthedatacommunication,forexample
bymultiplexingorsplittingdatastreamsbeforetheyreachthe
network.

NetworkLayer
•Thebasicnetworklayerserviceistoprovideatransparentchannel.
•Thismeansthattheapplicationrequestingachannelignoresnetwork
problemsandtherelatedsignalexchangebecausethatisthetaskof
thelowerlevels.
•Itjustrequiresanopenchannel,transparentforthetransmissionof
data,betweentransportlayersindifferentsystems.
•TheNetworkLayerestablishes,maintains,andreleasesconnections
betweenthenodesinthenetworkandhandlesaddressingand
routingofcircuits.
DataLinkLayer
•Thislayerprovidesanessentiallyerror-freepoint-to-pointcircuit
betweennetworklayers.
•Thelayercontainsresourcesforerrordetection,errorcorrection,flow
control,andretransmission.

PhysicalLayer
•Thislayerprovidesmechanical,electrical,functional,and
proceduralresourcesforactivating,maintaining,andblocking
physicalcircuitsforthetransmissionofbitsbetweendatalink
layers.
•Thephysicallayercontainsfunctionsforconvertingdatainto
signalscompatiblewiththetransmissionmedium.
•Forthecommunicationbetweenonlytwoexchanges,layers1and
2aresufficient.
•Forthecommunicationbetweenallexchangesinthenetwork,layer
3mustbeaddedbecauseitprovidesaddressingandrouting.

SIGNALING SYSTEM NO. 7 INTRODUCTION
•TheSignalingSystem(SS)No.7isanelaboratesetof
recommendationsdefiningprotocolsfortheinternalmanagementof
digitalnetworks.
•Theserecommendationswereintroducedin1980andrevisedin1984
and1988indifferent-coloredbooks(yellow,red,andblue).
•CCITTSSNo.7isintendedprimarilyfordigitalnetworks,both
nationalandinternational,wherethehightransmissionrates(64
kbps)canbeexploited.
•Itmayalsobeusedonanaloguelinesespeciallyoninternational
trunks(CCITTSSNo6).
•CCSwasinitiallymeantfortelephonyonly,buthasnowevolvedinto
non-telephonyandnon-connectionrelatedapplications(forexample,
locationupdatingofamobilesubscriber).
•Adialoguewithadatabaseorbetweentwodatabasesisatypical
applicationforCSinGSM.

•Thus,thereisaneedforagenericsystemthatisabletosupporta
widevarietyofapplicationsintelecommunication.
•Thevarietyofapplicationsisincreasingasnewtypesoftelephony
systemsandawideruseofdatabasesinthenetworkbecome
necessary(mobiletelephonynetworks,ISDN,IN,etc.).
•EventhoughthestandardizationofSS7isnowtheresponsibilityof
ITU-T,fortraditionalandhistoricalreasons,thesystemisoften
called“CCITTNo.7signalingsystem”.
•ThesignalingsystemusedinGSMfollowstheCCITT
recommendations.
•Themodularlayerstructureallowsflexibleusageofthe
specifications.

USERPARTS
•TheUserParts(UPs)containfunctionsdealingwiththeprocessingof
signalinformationbeforeandafteritistransmittedthroughthe
signalingnetwork.
•TheMTPprovidesthemeansofreliabletransportanddeliveryofUP
informationacrosstheSS7network.
•Italsohastheabilitytoreacttosystemandnetworkfailuresthat
affecttheinformationfromtheUPsandtakenecessaryactionto
ensurethattheinformationissafelyconveyed.
•TheUserdoesnotmeanthesubscriberinvolvedinthecall,butthe
useroftheMTP.
•TheMTPisacommontransportsystemdevelopedtoserveoneor
moreUserPartsinthesamenode.
•EverySignalingPoint(SP)consistsofMTP&anumberofitsusers.
•OnlyUPsofthesametypecancommunicatewitheachother.
•ToforwardsignalingmessagesbetweenUPs,locatedindifferent
nodes,theMTPisused.
.

USERS OF SIGNALING SYSTEM CCITT NO 7
MAP CAP BSSAP ISUP TUP
TCAP
MTP
SCCP CCITT SS NO. 7 PROTOCOLS IN GSM

MTPuserparts
ISUP(ISDNUserPart)
•Itprovidescontrol-functionsandsignaling,neededinanISDN,todeal
withISDNsubscribercallsandrelatedfunctions.
TUP(TelephonyUserPart)
•Itprovidesallnecessaryfunctionsandsignalingfordealingwitha
telephonyuser.
•TUPisbeingreplacedbyISUPintelecommunicationnetworks.
DUP(DigitalUserPart)
•ThisUPisusedforpurposessuchasfiletransferandrelated
signaling.

SCCP
•TheMTPwasdesignedforthereal-timeapplicationsoftelephony.
•TheconnectionlessnatureoftheMTPprovidesalow-overheadfacility
suitingtherequirementsoftelephony.
•RegardingGSM,otherapplicationssuchasnetworkmanagement
needservicessuchasexpandedaddressingcapabilityandreliable
messagetransfer.
•TheSCCPwasdevelopedtomeettheserequirements.
•TheSCCPalsosendsitsmessagesthroughtheMTP.
•TheSCCPprovidesfunctionsforcompletelynewservices,for
example,non-circuit-relatedsignaling.
•Somefunctions,notdirectlyrelatedtousers,butnecessaryfor
networkcontrol,areused.
•Themainreasonisthattheyarenecessaryforservingapplicationsin
higherlayersandformaintenancepurposes.

SCCP
•ThesefunctionsuseSCCPservices:
TransactionCapabilities(TC)
–Firstintroducedin1984,TCprovidesthemechanismsfor
transaction-orientedapplicationsandfunctions.
OperationandMaintenanceApplicationPart(OMAP)
–Specifiesnetworkmanagementfunctionsandmessagesrelated
tooperationandmaintenance.

PHYSICAL
LINK
NETWORK
TRANSPORT
SESSION
PRESENTATION
APPLICATION
SIGNALLING DATA LINK
SIGNALLING LINK
SIGNALLING NETWORK
SCCP
TCAP
USER PARTS
ASE
OSI Model CCITT SS NO 7 Model
MTP NSP

CALL FLOW

Mobile originated call
MS
Channel Request (RACH)
BSS MSC
SDCCH Seizure
Immediate Assignment [ Reject ] (AGCH)
CM Service Request + Connection Request < CMSREQ >
Connection [ Confirmed / Refused ]
Link Establishment
Authentication Request
Authentication Response
DT1 <CICMD>
Ciphering Mode Command
Ciphering Mode Complete
DT1 <CICMP>
Identity Request
Identity Response
Setup
Call Proceeding
Connection Management
Assignment Request
Assignment Request [ Failed ]
Assignment Command
Assignment [ Complete / Failure ]
Assignment [ Complete / Failure ]
TCH Seizure
S
D
C
C
H
T
C
H

MS BSS MSC
Paging
SDCCH Seizure
Link Establishment
Paging Request (PCH)
UDT < PAGIN >
Paging
Channel Request (RACH)
Immediate Assignment [ Reject ] (AGCH)
Paging Response + Connection Request < PAGRES >
Connection [ Confirmed / Refused ]
Authentication Request
Authentication Response
S
D
C
C
H
Ciphering Mode Command
Ciphering Mode Complete
DT1 <CICMD>
DT1 <CICMP>
Identity Request
Identity Response
Setup
Call Confirmed
Connection Management
Assignment Request
Assignment Request [ Failed ]
Assignment Command
Assignment [ Complete / Failure ]
T
C
H TCH Seizure
Assignment [ Complete / Failure ]
Mobile terminated call

POWER CONTROL

RF POWER CONTROL
•RFpowercontrolisemployedtominimisethetransmitpower
requiredbyMSorBSwhilemaintainingthequalityoftheradiolinks.
•Byminimisingthetransmitpowerlevels,interferencetoco-channel
usersisreduced.
•PowercontrolisimplementedintheMSaswellastheBSS.
•PowercontrolontheUplinkalsohelpstoincreasethebatterylife.

•TheRFpowerlevelemployedbytheMSisindicatedbymeansofthe
5bitTXPWRfieldsenteitherinthelayer1headerofeachdownlink
SACCHmessageblock,orinadedicatedsignallingblock.
•TheMSconfirmsthepowerlevelthatitiscurrentlyemployingby
settingtheMS_TXPWR_CONF fieldintheuplinkSACCHL1header
toitscurrentpowersetting.Thevalueofthisfieldisthepowersetting
actuallyusedbythemobileforthelastburstofthepreviousSACCH
period.
•TheMSemploysthemostrecentlycommandedRFpowerlevel
appropriatetothechannelforalltransmittedburstsoneitheraTCH
(includinghandoveraccessburst),FACCH,SACCHorSDCCH.
•WhenaccessingacellontheRACH(randomaccess)andbefore
receivingthefirstpowercommandduringacommunicationona
DCCHorTCH(afteranIMMEDIATEASSIGNMENT),theMSuses
eitherthepowerleveldefinedbytheMS_TXPWR_MAX_CCH
parameterbroadcastontheBCCHofthecell,orthemaximum
TXPWRoftheMSasdefinedbyitspowerclass,whicheveristhe
lower.
POWER CONTROL IN THE MS

POWER CONTROL MS
•TherangeoverwhichaMSiscapableofvaryingitsRFoutput
powerisfromitsmaximumoutputdownto20mW,instepsof
nominally2dB.
•0-43dBm…….15-13dBm.8 7 6 5 4 3 2 1
Octet 1
Octet 2
Ordered MS Power LevelSpare
Ordered Timing AdvanceSpare
1111111 indicates this field does not have any TA value

TIMING OF POWER CHANGE BY MS
•UponreceiptofacommandontheSACCHtochangeitsRFpower
level(TXPWRfield)theMSchangestothenewlevelatarateof
onenominal2dBpowerstepevery60ms(13TDMAframes),i.e.a
fullrangechangeof15stepsshouldtakeabout900ms.
•ThechangecommencesatthefirstTDMAframebelongingtothe
nextreportingperiod.TheMSchangesthepoweronenominal2
dBstepatatime,atarateofonestepevery60msfollowingthe
initialchange,irrespectiveofwhetheractualtransmissiontakes
placeornot.
•Incaseofchannelchangethecommandedpowerlevelisapplied
onthenewchannelimmediately.

BSS POWER CONTROL
•PowercontrolatBSSisoptional.
•TherangeoverwhichtheBSiscapableofreducingitsRFoutput
powerfromitsmaximumlevelisnominally30dB,in15stepsof
nominally2dB.

RADIO LINK FAILURE
•The criterion for determining Radio Link Failure in the MS is based on
the success rate of decoding messages on the downlink SACCH.
•The radio link failure criterion is based on the radio link counter S.
•If the MS is unable to decode a SACCH message, S is decreased by 1.
•If a SACCH message is decodedsuccessfully,S is increased by 2.
•If S reaches 0 a radio link failure is assumed & the MS aborts the conn.
•The RADIO_LINK_TIMEOUT parameter is transmitted by each BS in the
BCCH data.4
Decoded
3
Not Decoded
2
1
0
SACCH Blocks

RADIO LINK FAILURE
•TheMScontinuestransmittingasnormalontheuplinkuntilS
reaches0.
•Thealgorithmwillstartaftertheassignmentofadedicatedchannel
andSisinitializedtoRADIO_LINK_TIMEOUT.
•TheaimofdeterminingradiolinkfailureintheMSistoensurethat
callswithunacceptablevoice/dataquality,whichcannotbeimproved
eitherbyRFpowercontrolorhandover,areeitherre-establishedor
releasedinadefinedmanner.
•Ingeneraltheparametersthatcontroltheforcedreleaseshouldbe
setsuchthattheforcedreleasewillnotnormallyoccuruntilthecall
hasdegradedtoaqualitybelowthatatwhichthemajorityof
subscriberswouldhavemanuallyreleased.Thisensuresthat,for
example,acallontheedgeofaradiocoveragearea,althoughof
badquality,canusuallybecompletedifthesubscriberwishes.

CELL SELECTION AND RE -SELECTION
•InIdlemode(i.e.notengagedincommunicatingwithaBS),anMSwill
dothecellselectionandre-selectionprocedures.
•TheproceduresensurethattheMSiscampedonacellfromwhichit
canreliablydecodedownlinkdataandwithwhichithasahigh
probabilityofcommunicationsontheuplink.Thechoiceofcellis
determinedbythepathlosscriterion.OncetheMSiscampedona
cell,accesstothenetworkisallowed.
•AnMSissaidtobecampedonacellwhenithasdeterminedthatthe
cellissuitableandstaystunedtoaBCCH+CCCHofthatcell.While
campedonacell,anMSmayreceivepagingmessagesorunder
certainconditionsmakerandomaccessattemptsonaRACHofthat
cell,andreadBCCHdatafromthatcell.
•TheMSwillnotusethediscontinuousreception(DRX)modeof
operation(i.e.poweringitselfdownwhenitisnotexpectingpaging
messagesfromthenetwork)whileperformingtheselectionand
reselectionalgorithm.Howeveruseofpoweringdownispermittedat
allothertimesinidlemode.

CELL SELECTION AND RE -SELECTION
•Forthepurposesofcellselectionandreselection,theMSisrequired
tomaintainanaverageofreceivedsignalstrengthsforallmonitored
frequencies.Thesequantitiestermedthe"receivelevelaverages”is
theaveragesofthereceivedsignalstrengthsmeasuredindBm.
•Thecellselectionandreselectionproceduresmakeuseofthe"BCCH
Allocation"(BA)list.ThereareintwoBAlistswhichmayormaynotbe
identical,dependingonchoicesmadebythePLMNoperator.
•(i)BA(BCCH)-ThisistheBAsentinSystemInformationMessages
ontheBCCH.ItisthelistofBCCHcarriersinusebyagivenPLMNin
agivengeographicalarea.ItisusedbytheMSincellselectionand
reselection.
•(ii)BA(SACCH)-ThisistheBAsentinSystemInformationMessages
ontheSACCHandindicatestotheMSwhichBCCHcarriersaretobe
monitoredforhandoverpurposes.
•WhentheMSgoesontoaTCHorSDCCH,itstartsmonitoringBCCH
carriersinBA(BCCH)untilitgetsitsfirstBA(SACCH)message.

CELL SELECTION -NO BCCH DATA AVAILABLE
•TheMSsearchesall124RFchannelsintheGSMsystem,takes
readingsofRSSoneachRFchannel,andcalculatethereceived
levelaverageforeach.
•Theaveragingisbasedonatleastfivemeasurementsamplesper
RFcarrierspreadover3to5secs.
•TheMStunestothecarrierwiththehighestaverageRSS&
determineswhetherornotthiscarrierisaBCCHcarrier.
•IfitisaBCCHcarrier,theMSattemptstosynchronisetothiscarrier
andreadtheBCCHdata.TheMScampsonthecellprovideditcan
successfullydecodetheBCCHdataandthisdataindicatesthatitis
partoftheselectedPLMN,thatthecellisnotbarred
(CELL_BAR_ACCESS =0)&thattheparameterC1isgreaterthan
0.
•IfthecellispartoftheselectedPLMNbutisbarredorC1islessthan
zero,theMSusestheBCCHAllocationobtainedfromthiscelland
subsequentlyonlysearchestheseBCCHcarriers.OtherwisetheMS
tunetothenexthighestcarrierandsoon.

CELL SELECTION -NO BCCH DATA AVAILABLE
•CELL_BAR_ACCESS maybeemployedtobaracellthatisonly
intendedtohandlehandovertrafficetc.Forexampleofthiscouldbe
anumbrellacellwhichencompassesanumberofmicrocells.
•Ifatleastthe30strongestRFchannelshavebeentried,butno
suitablecellhasbeenfound,providedtheRFchannelswhichhave
beensearchedincludeatleastoneBCCHcarrier,theavailable
PLMN'sshallbepresentedtotheuser,otherwisemoreRFchannels
shallbesearcheduntilatleastoneBCCHcarrierisfound.
•30RFchannelsarespecifiedtogiveahighprobabilityoffindingall
suitablePLMN's,withoutmakingtheprocesstaketoolong.

CELL SELECTION -BCCH INFORMATION AVAIL.
•TheMSstorestheBCCHcarriersinusebythePLMNselectedwhenit
waslastactiveintheGSMnetwork.AMSmayalsostoreBCCH
carriersformorethanonePLMNwhichithasselectedpreviously(e.g.
atnationalbordersorwhenmorethanonePLMNservesacountry).
•IfanMSincludesaBCCHcarrierstorageoptionitsearchesonlyfor
BCCHcarriersinthelist.
•IfanMSdecodesBCCHdatafromacelloftheselectedPLMNbutis
unabletocamponthatcell,theBAofthatcellisexamined.AnyBCCH
carriersintheBAwhicharenotintheMS'slistofBCCHcarrierstobe
searchedisaddedtothelist.
•IfnosuitablecellhasbeenfoundafteralltheBCCHcarriersinthelist
havebeensearched,theMSactsasiftherewerenostoredBCCH
carrierinformation.Sinceinformationconcerninganumberofchannels
isalreadyknowntotheMS,itmayassignhighpriorityto
measurementsonthoseofthe30strongestcarriersfromwhichithas
notpreviouslymadeattemptstoobtainBCCHinformation,andomit
repeatedmeasurementsontheknownones.

PATH LOSS CRITEREON( C1)
•ThisparameterisusedtoensurethattheMSiscampedonthecell
withwhichithasthehighestprobabilityofsuccessfulcommunication
onuplinkanddownlink.
•ThepathlosscriterionparameterC1usedforcellselectionand
reselectionisdefinedby:
C1=(A-Max(B,0))
whereA=ReceivedLevelAverage-RXLEV_ACCESS_MIN
B=MS_TXPWR_MAX_CCH -P
RXLEV_ACCESS_MIN =MinimumreceivedlevelattheMS
requiredforaccesstothesystem.
MS_TXPWR_MAX_CCH =MaximumTXPWRlevelanMSmay
usewhenaccessingthesystem.
P=MaximumRFoutputpoweroftheMS.
•AllvaluesareexpressedindBm.

PATH LOSS CRITEREON( C1)
A = +Good Downlink
-Poor Downlink
B = -Good Downlink
+Poor Downlink
Monitoring of Received Level and BCCH data
•InIdleModeanMScontinuestomonitorallBCCHcarriersas
indicatedbytheBCCHAllocation.
•Arunningaverageofreceivedlevelinthepreceding5to60seconds
isbemaintainedforeachcarrierintheBCCHAllocation.
•Fortheservingcellreceivelevelmeasurementsamplesistakenat
leastforeachpagingblockoftheMSandthereceivelevelaverage
isdeterminedusingsamplescollectedoveraperiodof5sorfive
consecutivepagingblocksofthatMS,whicheveristhegreater
period.

Monitoring of Received Level and BCCH data
•Atleast5receivedlevelmeasurementsamplesarerequiredper
receivelevelaveragevalue.Newsetsofreceivelevelaverage
valuesiscalculatedasoftenaspossible.
•Thesamenumberofmeasurementsamplesistakenforallnon
servingcellBCCHcarriers,andthesamplesallocatedtoeachcarrier
isasfaraspossibleuniformlydistributedovereachevaluation
period.
•Thelistofthe6strongestcarriersisupdatedatleasteveryminute
andmaybeupdatedmorefrequently.
•Inordertominimisepowerconsumption,MSsthatemployDRX(i.e.
powerdownwhenpagingblocksarenotdue)monitorthesignal
strengthsofnon-servingcellBCCHcarriersduringtheframesofthe
PagingBlockthattheyarerequiredtolistento.Receivedlevel
measurementsamplescanthusbetakenonseveralnon-serving
BCCHcarriersandontheservingcarrierduringeachPagingBlock.
•TheMSincludestheBCCHcarrierofthecurrentservingcell(i.e.the
celltheMSiscampedon)inthismeasurementroutine.

MonitoringofReceivedLevelandBCCHdata
•TheMShastodecodethefullBCCHdataoftheservingcellatleast
every30seconds.
•TheMSattemptstodecodetheBCCHdatablockthatcontainsthe
parametersaffectingcellreselectionforeachofthe6strongestnon-
servingcellBCCHcarriersatleastevery5minutes.
•WhentheMSrecognizesthatanewBCCHcarrierhasbecomeoneof
the6strongest,theBCCHdatashallbedecodedforthenewcarrier
within30seconds.
•TheMSattemptstochecktheBSICforeachofthe6strongestnon
servingcellBCCHcarriersatleastevery30seconds,toconfirmthatit
ismonitoringthesamecell.
•IfachangeofBSICisdetectedthenthecarrieristreatedasanew
carrierandtheBCCHdataredetermined.
•Whenrequestedbytheuser,theMSmonitorsthe30strongestGSM
carriertodetermine,within15seconds,whichPLMN'sareavailable.
Thismonitoringisdonesoastominimiseinterruptionstothe
monitoringofthePCH.

CALL RE-ESTABLISHMENT
•Intheeventofaradiolinkfailure,callre-establishmentmaybe
attemptedifitisenabledinthedatabase.
•Thereceivedlevelmeasurementsamplestakenonsurroundingcells
andontheservingcellBCCHcarrierinthelast5secondsisaveraged,
andthecarrierwiththehighestaveragereceivedlevelwhichispartof
apermittedPLMNistaken.
•ABCCHdatablockcontainingtheparametersaffectingcellselection
isreadonthiscarrier.
•IftheparameterC1isgreaterthanzero,itispartoftheselected
PLMN,thecellisnotbarred,andcallre-establishmentisallowed,call
re-establishmentisattemptedonthiscell.
•Iftheaboveconditionsarenotmet,thecarrierwiththenexthighest
averagereceivedlevelistaken,andtheMSrepeatstheabove
procedure.
•Ifthecellswiththe6strongestaveragereceivedlevelvaluesaretried
butcannotbeused,thecallre-establishmentattemptisabandoned.

bs_ag_blk_res
•Toensurethatsomeoftheblocksarealwaysleftclearforaccess
grantmessagestheparameterbs_ag_blk_resisusedtoinputthe
numberofblockstobereservedforthispurpose.
•Thereservedblocksisnotbeusedforpagingwhateverthedemand.
•Ifmorethanonetimeslotexistswithinacell,thisparameterwill
reservetheindicatednumberofblocksoneachtimeslot.
•ThisparameterisbroadcastontheBCCH.
•Thisparameterisusedtocalculatethenumberofpaginggroups
available.COMBINED CCCH BLOCKS AGCH BLOCKS PCH BLOCKS
No 9 0 9
No 9 1 8
No 9 2 7
No 9 3 6
No 9 4 5
No 9 5 4
No 9 6 3
No 9 7 2
Yes 3 0 3
Yes 3 1 2
Yes 3 2 1

Bs_pa_mfrms
•Usedtoindicatethenumberof51framemultiframesbetween
transmissionofpagingmessagestoMSofthesamegroup.
•IstransmittedonBCCH.
•UsedbytheMStocalculateitspaginggroup.BCCH
AGCH
1
2
3
4
5
6
7
8 BCCH
AGCH
1
2
3
4
5
6
7
8 BCCH
AGCH
9
10
11
12
13
14
15
16 BCCH
AGCH
17
18
19
20
21
22
23
24 BCCH
AGCH
25
26
27
28
29
30
31
32
Value
0=2multiframes
1=3multiframes
2=4multiframes
3=5multiframes
4=6multiframes
5=7multiframes
6=8multiframes
7=9multiframes

PAGING
Example
cch_conf = 0
bs_ag_blk_res = 1
bs_pa_mfrms = 2
If cch_conf = 1
minimum = 2
If cch_conf = 6
Maximum = 81 * 4
Min time between pages = 2 * 235.5 = 471ms
Maxtime between pages= 9 * 235.5 =2.1195 sec

max_retran
•AnMSrequestsresourcesfromthenetworkbytransmittingan
``accessburst´´containingthechannelrequestmessage.
•Forasinglerequest,channelrequestwillberepeateduptoM+
1timeswhereM=max_retran.max_retrans M
1 1
2 2
3 4
4 7

tx_integer
•Toreducethechancesofcollisionthewaitperiodis
randomisedforeachMS.
•Afterthefirstchannelrequestissentthenextisrepeatedafter
arandomwaitperiodintheset
(S,S+1,…..,S+T-1)
•Waitperiodfromthissetischosenrandomlyfromthisset.TX INTEGER
RACH SLOTS
S FOR NON-
COMB CCCH
S FOR COMB
CCCH
3, 8, 14 55 41
4, 9, 16 76 52
5, 10, 20 109 58
6, 11, 25 163 86
7, 12, 32 127 115

AVAILABLE PAGING BLOCKS ON 1 CCCH_GROUP
Maximum AGCH reservation for non-combined multiframe = 7
Available paging blocks = 2
Maximum AGCH reservation for combined multiframe = 1
Available paging blocks = 2
Minimum AGCH reservation for non-combined multiframe = 0
Available paging blocks = 9
Minimum AGCH reservation for combined multiframe = 0
Available paging blocks = 3
No of paging blocks will have a range of 2 -9

CALCULATIONOFCCCHANDPAGINGGROUPNO
CCCH_GROUP =[(IMSImod1000)mod(BS_CC_CHANS *N)]
divN
Paginggroupno=[(IMSImod1000)mod(BS_CC_CHANS *N)
]modN

HANDOVER

•TheGSMhandoverprocessusesamobileassistedtechniquefor
accurateandfasthandovers,inorderto:
–Maintaintheuserconnectionlinkquality.
–Managetrafficdistribution
•TheoverallhandoverprocessisimplementedintheMS,BSS&
MSC.
•Measurementofradiosubsystemdownlinkperformanceandsignal
strengthsreceivedfromsurroundingcells,ismadeintheMS.
•ThesemeasurementsaresenttotheBSSforassessment.
•TheBSSmeasurestheuplinkperformancefortheMSbeingserved
andalsoassessesthesignalstrengthofinterferenceonitsidle
trafficchannels.
•Initialassessmentofthemeasurementsinconjunctionwithdefined
thresholdsandhandoverstrategymaybeperformedintheBSS.
AssessmentrequiringmeasurementresultsfromotherBSSorother
informationresidentintheMSC,maybeperform.intheMSC.
HANDOVER
HANDOVER

•TheMSassiststhehandoverdecisionprocessbyperforming
certainmeasurements.
•WhentheMSisengagedinaspeechconversation,aportionofthe
TDMAframeisidlewhiletherestoftheframeisusedforuplink
(BTSreceive)anddownlink(BTStransmit)timeslots.
•Duringtheidletimeperiodoftheframe,theMSchangesradio
channelfrequencyandmonitorsandmeasuresthesignallevelof
thesixbestneighborcells.
•Measurementswhichfeedthehandoverdecisionalgorithmare
madeatbothendsoftheradiolink.
HANDOVER (Cont)
HANDOVER

•AttheMSend,measurementsarecontinuouslysignalled,viathe
associatedcontrolchannel,totheBSSwherethedecisionfor
handoverisultimatelymade.
•MSmeasurementsinclude:
–Servingcelldownlinkquality(biterrorrate(BER)estimate).
–Servingcelldownlinkreceivedsignallevel,andsixbestneighbor
cellsdownlinkreceivedsignallevel.
•TheMSalsodecodestheBaseStationIDCode(BSIC)fromthe
sixbestneighborcells,andreportstheBSICsandthe
measurementinformationtotheBSS.
MS END
HANDOVER

•TheBTSmeasurestheuplinklinkquality,receivedsignallevel,
andMStoBTSsitedistance.
•TheMSRFtransmitoutputpowerbudgetisalsoconsideredin
thehandoverdecision.
•IftheMScanbeservedbyaneighborcellatalowerpower,the
handoverisrecommended.
•Fromasystemperspective,handovermaybeconsidereddueto
loadingorcongestionconditions.Inthiscase,theMSCorBSC
triestobalancechannelusageamongcells.
BTS END
HANDOVER

•Duringtheconversation,theMSonlytransmitsandreceivesforone
eighthofthetime,thatisduringonetimeslotineachframe.
•Duringitsidletime(theremainingseventimeslots),theMSswitches
totheBCCHofthesurroundingcellsandmeasuresitssignal
strength.
•Thesignalstrengthmeasurementsofthesurroundingcells,andthe
signalstrengthandqualitymeasurementsoftheservingcell,are
reportedbacktotheservingcellviatheSACCHonceinevery
SACCHmultiframe.
•ThisinformationisevaluatedbytheBSSforuseindecidingwhen
theMSshouldbehandedovertoanothertrafficchannel.
•ThisreportingisthebasisforMSassistedhandovers.
MS IDLE TIMEREPORTING
HANDOVER

MEASUREMENT IN ACTIVE MODE012345670123456701234567012
012345670123456701234567012
Frame 24 Frame 25 Idle Frame Frame 0
Frame 24 Frame 25 Idle Frame Frame 0
1 2 3 1 2 1 2
1.MS receives and measures signal strength on serving cell(TS2).
2.MS transmits
3.MS measures signsl strength for at least one neighbor cell.
4.MS reads BSIC on SCH for one of the 6 strongest neighbor.
4
Downlink
Uplink
HANDOVER

•Maximum32averagingofRSStakesplace.
•Practicallyacellneighborscanbeequippedforacell.
•Ifhighnumbersofneighborsareequipped,thentheaccuracyof
RSSisdecreasedasshouldhave8to10neighbors.
T
15
T
5
T
9
T
10
T
11
S
12
T
13
T
14
T
6
T
7
T
8
T
0
T
1
T
2
T
3
T
4
T
16
T
17
T
18
T
19
T
20
T
21
T
22
T
23
T
24
I
25
T
15
T
5
T
9
T
10
T
11
S
12
T
13
T
14
T
6
T
7
T
8
T
0
T
1
T
2
T
3
T
4
T
16
T
17
T
18
T
19
T
20
T
21
T
22
T
23
T
24
I
25
T
15
T
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NUMBER OF NEIGHBORS
HANDOVER

NUMBER OF NEIGHBORS
•In one SACCH multiframe there are 104 TDMA frames.
•Outofthis104frames4framesareidleandareusedtodecodethe
BSIC.
•Remaining100TDMAframesareusedtomeasureRSS(Received
SignalStrength)oftheneighbor.
•If25neigborsareequipped,theninoneSACCHmultiframeeach
neigborismeasured100/25=4timesandaveragedout.This
producesalessaccuratevalue.
•If10neigborsareequipped,theninoneSACCHmultiframeeach
neigborismeasured100/10=10timesandaveragedout.This
producesamoreaccuratevalue.
HANDOVER

•GSM causes its own time interference.
•The MS has a omni-directional antenna. Much of the MS power goes
to the server but a lot is interfering with surrounding cells using the
same channel.
•The TDMA frames of adjacent cell are not aligned since they are not
synchronised. Hence the uplink in the surrounding cell suffers from
interference.
INTERFERENCE ON IDLE CHANNEL
Channel 10
Cell 1
Channel 10
Cell 2
HANDOVER

•TheBSSkeepsonmeasuringtheinterferenceontheidletimeslots.
•Ambientnoiseismeasuredandrecorded104timesinoneSACCH
multiframe.
•Thesemeasurementsareaveragedouttoproduceonefigure.
•TheBSSthendistributestheidletimeslotsintoband0toband5.
•SincetheBSSknowstheinterferencelevelonidletimeslots,ituses
thisdatatoallocatethebestchannelfirstandtheworstlast.
INTERFERENCE ON IDLE CHANNEL0 1 2 3 4 5 6 7
Inteference on idle channel measured on Idle Timeslot by BSS
HANDOVER

ThefollowingmeasurementsisbecontinuouslyprocessedintheBSS:
i)MeasurementsreportedbyMSonSACCH
-DownlinkRXLEV
-DownlinkRXQUAL
-DownlinkneighborcellRXLEV
ii)MeasurementsperformedinBSS
-UplinkRXLEV
-UplinkRXQUAL
-MS-BSdistance
-Interferencelevelinunallocatedtimeslots
EverySACCHmultiframe(480ms)anewprocessedvalueforeachof
themeasurementsiscalculated..
HANDOVER
HANDOVER

Handoverisdoneonfiveconditions
–Interference
–RXQUAL
–RXLEV
–DistanceorTimingAdvance
–PowerBudget
Interference-IfsignallevelishighandstillthereisRXQUALproblem,
thentheRXQUALproblemisbecauseofinterference.
RXQUAL-Itisthereceivequality.Itrangesfrom0to7,0beingthebest
and7theworst
RXLEV-Itisthereceivelevel.Itvariesfrom-47dBmto-110dBm.
TimingAdvance-Rangesfrom0to63.
Powerbudget-ItisusedtosavethepoweroftheMS.
HANDOVER CONDITIONS
HANDOVER

•Handovertakesplaceinthesamecellfromonetimeslottoanother
timeslotofthesamecarrierordifferentcarriers(butthesamecell).
•Intra-cellhandoveristriggeredonlyifthecauseisinterference.
•Intra-cellhandovercanbeenabledordisabledinacell.
HANDOVER TYPES
Intra-Cell Handover
BSC
BTS
Call is handed
from timeslot 3 to timeslot 501234567
HANDOVER

•Handovertakesplacebetweendifferentcellwhicharecontrolledby
thesameBSC.
HANDOVER TYPES
Intra-BSC Handover
BSC1
BTS1
Call is handed from timeslot 3
of cell1 to timeslot 1 of cell2 .
Both the cells are controlled
by the same BSC.01234567 01234567
HANDOVER

•Handovertakesplacebetweendifferentcellwhicharecontrolledby
thedifferentBSC.
HANDOVER TYPES
Inter-BSC Handover
BSS1
BTS1
Call is handed from timeslot 3
of cell1 to timeslot 1 of cell2 .
Both the cells are controlled
by the different BSC.01234567 01234567
BSS2
MSC
BTS2
HANDOVER

•Handovertakesplacebetweendifferentcellwhicharecontrolledby
thedifferentBSCandeachBSCiscontrolledbydifferentMSC.
HANDOVER TYPES
Inter-MSC Handover
BSS1
BTS1
Call is handed from timeslot 3
of cell1 to timeslot 1 of cell2 .
Both the cells are controlled
by the different BSC, each BSC
being controlled by different MSC.01234567 01234567
BSS2
MSC1
BTS2
MSC2
HANDOVER

LOCATION UPDATE

LOCATION UPDATE
•MSCshouldalwaysknowthelocationoftheMSsothatitcan
contactitbysendingpageswheneverrequired.
•ThemobilekeepsoninformingtheMSCaboutitscurrentlocation
areaorwheneveritchangesfromoneLAtoanother.
•ThisprocessofinformingtheMSCisknownaslocationupdating.
•ThenewLAisupdatedintheVLR.
•LAI=MCC+MNC+LAC
MCC MNC LAC
3 digits1-2 digitsMax 16 bits
MCC=Mobilecountrycode.
MNC=MobileNetworkCode.
LAC=Locationareacode.IdentifiesalocationareawithinaGSM
PLMNnetwork.ThemaximumlengthofLACis16bits.Thus65536
differentLAcanbedefinedinoneGSMPLMN.

•Normallocationupdate
•Periodiclocationupdate
•IMSIattach
NormalLocationUpdate
•Mobilepowersonandisidle.
•ReadstheLAIbroadcastontheBCCH.
•CompareswiththelaststoredLAIandifitisdifferentdoesa
locationupdate.
LOCATION UPDATE TYPES

LOCATION UPDATEMS MSCBSS
RACH
Imme. Assign
Location update request
Authentication request
Authentication response
DTI<CICMD>
DTI<CICMP>
Cipher mode command
Cipher mode complete
Location update accepted

IMSI ATTACH
•SavesthenetworkfrompagingaMSwhichisnotactiveinthesystem.
•WhenMSisturnedofforSIMisremovedtheMSsendsadetachsignal
totheNetwork.Itismarkedasdetached.
•WhentheMSispoweredagainitreadsthecurrentLAIandifitissame
doesalocationupdatetypeIMSIattach.
•Attach/detachflagisbroadcastontheBCCHsysinfo.
PERIODIC LOCATION UPDATE
•ManytimestheMSentersnon-coveragezone.
•TheMSwillkeeponpagingtheMSthuswastingpreciousresources.
•ToavoidthistheMShastoinformtheMSCaboutitscurrentLAIinaset
periodoftime.
•Thistimerangesfrom0to255decihours.
•PeriodiclocationtimervalueisbroadcastonBCCHsysinfomessages.

•During conversation user talks alternatively.
•In DTX mode of operation the transmitter are switched on only
for frames containing useful information.
•Helps to increase battery life and reduce interference level.
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DISCONTINOUS TRANSMISSION
SID

IMPLEMENTATION OF DTX
Voice Activity Detector ( VAD )
•Determines which specific block of 20ms from the speech coder
contains speech.
•Removes statinary noise.
•Inserts comfort noise.
•The frames containing this background noise are called SID frames
and are sent in blocks of 8 frames within every 104 frame block.
VAD Speech / No speech
20 ms speech
block

SYSTEM INFORMATION
MESSAGES

BROADCAST MESSAGES
•SysteminformationisdataaboutthenetworkwhichtheMS
needstobeabletocommunicatewiththenetworkina
appropriatemanner.
•SysteminformationmessagesaresentontheBCCHand
SACCH.
•Therearesixdifferenttypesofsysteminformationmessages.
•Systeminformationmessages1to4arebroadcastontheBCCH
andarereadbytheMSinidlemode.
•Systeminformationmessage5and6aresentontheSACCHto
theMSindedicatedmode.
•Systeminformationmessages1to4arebroadcastontheBCCH
inacyclicmodeover8BCCHmultiframes,i.e.8*51frames.
•Everymessageissentatleastafterevery1.8sec.
SYS INFORMATION MESSAGES

WhatissentisoptionalonBCCHMultiframe4and5
•Systeminformation5and6aresentontheSACCHimmediately
afterHOorwhenevernothingelseisbeingsent.
•DownlinkSACCHisusedforsysteminformationmessageswhile
UplinkSACCHisusedformeasurementreports.
BROADCAST MESSAGESSystem
Information
BCCH
Multiframe
1 0
2 1
3 2 and 6
4 3 and 7
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 1
WhenfrequencyhoppingisusedincellMSneedstoknowwhich
frequencybandtouseandwhatfrequencywithinthebanditshould
useinhoppingalgorithm.
Cell Channel Description
Cell allocation number:-Informs the band number of the
frequency channels used.
00 -Band 0 ( Current GSM band )
Cell allocation ARFCN:-ARFCN’s used for hopping. It is coded
in a bitmap of 124 bits.124123122121
016015014013012011010009
008007006005004003002001
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 1
RACHControlParameters
AccessControlClass:-Bitmapwith16bits.AllMSspreadouton
class0-9.Prioritygroupsuseclass11-15.Abitsetto1barres
accessforthatclass.Bit10isusedtotelltheMSifemergencycall
isallowedornot.
0-AllMScanmakeemergencycall.
1-MSwithclass11-15onlycanmakeemergencycalls.
Cellbarredforaccess:-
0-Yes
1-No
SYS INFORMATION MESSAGES

RACHControlParameters
Re-establishmentallowed:-
0–Yes
1-No
max_retransmissions:-NumberoftimestheMSattemptsto
accesstheNetwork[1,2,4or7].
tx_integer:-Numberofslotstospreadaccessretransmissions
whenaMSattemptstoaccessthesystem.
EmergencyCallAllowed:-Yes/No
SYSTEM INFORMATION 1
SYS INFORMATION MESSAGES

•ContainslistofBCCHfrequenciesusedinneighborcells.
•MSusesthislisttomeasuresthesignalstrengthoftheneighbors.
NeighborCellDescription
BAIndicator:-Allowstodifferentiatemeasurementresultsrelated
todifferentlistofBCCHfrequenciessenttotheMS.
BCCHAllocationnumber:-Band0isused.
BCCHARFCNnumber:-Bitmap1-124
1 = Set
0 = Not set
PLMNpermitted
RACHControlParameters
SYSTEM INFORMATION 2
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 3
LocationAreaIdentity
CellIdentity8 7 6 5 4 3 2 1
Octet A
1 1 1 1 Octet B BCD
Octet C
Octet D
Octet E
MCC DIG 1MCC DIG 2
MCC DIG 3
MNC DIG 1MNC DIG 2
LAC
LAC
Binary 8 7 6 5 4 3 2 1
Octet F
Octet G
CI
CI
Binary
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 3
ControlChannelDescription
Attach/Detach
0=Allowed
1=Notallowed
cch_conf:-Definesmultiframestruture
bs_agblk:-NumberofblockreservedforAGCH[0-7].
Ba_pmfrms:-Numberof51framemultiframesbetween
transmisiionofpagingmessagestoMSofthesamegroup.
T3212:-Periodiclocationupdatetimer[1-255decihours].cch_confPhysical ChannelsCombinedNo of CCH
0 1 timeslot (0) NO 9
1 1 timeslot (0) YES 3
2 2 timeslots (0, 2)NO 18
4 3 timeslots (0, 2, 4)NO 27
6 4 timeslots (0, 2, 4, 6)NO 36
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 3
CellOptions
dtx
pwrc:-Powercontrolonthedownlink.
0=Notused
1=Used
Radiolinktimeout:-SetsthetimerT100intheMS.
CellSelectionParameters
Rxlev_access_min:-MinimumreceivedsignallevelattheMSfor
whichitispermittedtoaccessthesystem.
0-63=-110dBmto-47dBm
mx_txpwr_cch:-MaximumpowertheMSwillusewhenaccessing
thesystem.
Cell_reselect_hysteresis:-Usedforcellreselection.
RACHControlParameters
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 4
Location Area Identification
Cell Selection Parameters
Rxlev_access_min
mx_txpwr_cch
Cell_reselect_hysteresis
RACH Control Parameters
max_retransmissions
tx_integer
Cell barred for access
Re-establishment allowed
Emergency Call Allowed
Access Control Class
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 4
ChannelDescription
Channeltype:-Indi.channeltypeSDCCHorCBCH(SDCCH/8).
Subchannelnumber:-Indicatesthesubchannel.
Timeslotnumber:-IndicatesthetimeslotforCBCH[0-7].
TrainingSequenceCode:-TheBCCpartofBSIC[0-7].
HoppingChannel(H):-InformsifCBCHchannelishoppingor
single.0-SingleRFChannel1-RFhoppingchannel
ARFCN:-IfH=0
MAIO:-IfH=1,informstheMSwheretostarthopping.Values[0
-63].
HSN:-IfH=1,informstheMSinwhatorderinwhatorderthe
hoppingshouldtakeplace.Values[0-63].HSN=0Cyclic
Hopping.
MA:-IndicateswhichRFChannelsareusedforhopping.ARFCN
numberscodedinbitmap.
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 5
Sent on the SACCH on the downlink to the MS in dedicated mode.
Neighbour Cell Description
BA-IND :-Used by the Network to discriminate measurements
results related to different lists of BCCH carriers sent by the MS(
Type 2 or 5).
Values 0 or 1 ( different from type 2).
BCCH Allocation number :-00 -Band 0 (Current GSM band).
BCCH ARFCN :-Neighboring cells ARFCN’s. Sent as a bitmap.
0 = ARFCN not used
1 = ARFCN used124123122121
016015014013012011010009
008007006005004003002001
SYS INFORMATION MESSAGES

SYSTEM INFORMATION 6
•MSindedicatedmodeneedstoknowiftheLAhaschanged.
•MSmaychangebetweencellswithdifferentRadiolinktimeout
andDTX.
Cell Identity
Location Area Identification
Cell Options
dtx
pwrc
Radio link timeout
PLMN permitted
SYS INFORMATION MESSAGES

PAGING
•WhenevertheNetworkwantstocontacttheMS,itsends
messagesonthepagingchannel.
•PagingissentonthePCHanditoccupies4bursts.
•MShastomonitorthepagingchanneltoreceivepaging
messages.
•MSdoesnotmonitorallpagingchannelbutonlyspecificpaging
channels.
•TherearethreetypesofpagingmessagesPaging
Type
No of MS
using IMSI
No of MS
using TMSI
Total no of
MS
1 2 - 2
2 1 2 3
3 - 4 4
SYS INFORMATION MESSAGES

CALCULATION OF PAGING GROUP
Following factors are used for calculation of paging group
•CCCH_group
– cch_conf in System Information 3 defines the number of
CCCH used in the cell.
– CCCH can be allocated only TN 0, 2, 4, 6.
– Each CCCH carries its own paging group of MS.
– MS will listen to paging messages of its specific group.
•bs_pa_mfrms
•bs_ag_blk_res
SYS INFORMATION MESSAGES

CALCULATION OF PAGING GROUP
Total number of paging groups on 1 CCCH_GROUP(N)
No of paging groups N =Paging blocks*Repitition of paging blocks
=[ CCCH -bs_ag_blk_res ]*bs_pa_mfrms
Range of Paging Groups on 1 CCCH_Group
Minimum available Paging Groups =Min pag blocks* min bs_pa_mfrms
=2*2
= 4
Maximum available Paging Groups =Max pag blocks* max bs_pa_mfrms
=9*9
= 81
SYS INFORMATION MESSAGES

AVAILABLE PAGING BLOCKS ON 1 CCCH_GROUP
Maximum AGCH reservation for non-combined multiframe = 7
Available paging blocks = 2
Maximum AGCH reservation for combined multiframe = 1
Available paging blocks = 2
Minimum AGCH reservation for non-combined multiframe = 0
Available paging blocks = 9
Minimum AGCH reservation for combined multiframe = 0
Available paging blocks = 3
No of paging blocks will have a range of 2 -9
SYS INFORMATION MESSAGES

CALCULATIONOFCCCHANDPAGINGGROUPNO
CCCH_GROUP =[(IMSImod1000)mod(BS_CC_CHANS *N)]
divN
Paginggroupno=[(IMSImod1000)mod(BS_CC_CHANS *N)
]modN
SYS INFORMATION MESSAGES

SOME KEY DATABASE
PARAMETERS

TIMER T3101
•TheMSrequestsforresourcesbysendingchannelrequeston
RACH.
•TheBSSallocatesaSDCCH,ifavailable,andsendsaIMMEDIATE
ASSIGNMENTmessageonthedownlink.Thismessagecontainsthe
detailsofallocatedSDCCH,TSC,TAetc.
•AssoonastheBSSallocatesandsendsmessageontheAGCH,it
startsatimerT3101.
•TheMSlogsontheSDCCHandsendsamessageontheUPLINK.
•AssoonastheBSSreceivesthismessagethetimerT3101is
stopped.
•IfnomessageisreceivedbytheBSSfromtheMSandtimerT3101
expires,thentheBSSreleasestheallocatedSDCCHresource.
•Thistimerissetinmillisecs.

TIMER T3101
MS
CELL
RACH
CL2I
IF MS SENDS CL2I ON
SDCCH STOP TIMER
T3101
IMMEDIATE ASSIGNMENT
(AGCH)
SDCCH ALLOCATED
START TIMER T3101

MS
CELL
RACH
IMMEDIATE ASSIGNMENT
(AGCH)
SDCCH ALLOCATED
START TIMER T3101
IF T3101 EXPIRES AND
BSS DOES NOT RECEIVE
CL2I ON SDCCH RELEASE
ALLOCATED RESOURCES
Successful SDCCH Access Unsuccessful SDCCH Access

Wait_indication parameter & Timer T3122
•TheMSrequestsforresourcesbysendingchannelrequestonRACH.
•TheBSSallocatesaSDCCH,ifavailable,andsendsaIMMEDIATE
ASSIGNMENTmessageonthedownlink.Thismessagecontainsthe
detailsofallocatedSDCCH,TSC,TAetc.
•IfnoSDCCH isavailable,theBSSsendsaIMMEDIATE
ASSIGNMENTREJECTmessagetotheMS.
•AssoonastheMSreceivestheIMMEDIATEASSIGNMENTREJECT
message,itstartsatimerT3122andsetesitequalto
wait_parameter_indication.
•TillthetimerT3122isrunning,nochannelrequestleavestheMS.
•ThenextchannelrequestissentonlyaftertheexpiryofT3122.
•Thiswait_indication_parametercanbesetfrom0to255secs.

Wait_indication parameter & Timer T3122

MS
CELL
RACH
IMMEDIATE ASSIGNMENT
REJECT (AGCH)
NO SDCCH AVAILABLE
IF T3122 EXPIRES,
MS CAN NOW SEND
A FRESH REQUEST
SET T3122 IN MS
EQUAL TO
WAIT_INDICATION
RACH
INACTIVE MODE

CALL QUEING
•TheMSrequestsforresourcesbysendingarequesttotheBSSon
RACH.
•TheBSSassignsaSDCCHandthecallsetuptakesplaceonthe
SDCCH.
•Itispossiblethatafterthecallsetup,theirmaynotbeaTCHavailable
fortheMSduetocongestion..
•TheNetworkisabletoplacethis
callinaqueuealongwithother
MSawaitingassignmentofa
TCH.
•Thelengthofthequeuecanbe
setinthedatabase.
•ThetimeforwhichaMScan
stayinthequeuecanbesetby
settingthevalueofT11timer.
Assig. Req
Start T11
Stop T11
Queuing Indication
Assign. Compl / Fail
T11 expires. Clr Req.

TCH RESOURCE REPORTING
•ThenumberofdedicatedtrafficchannelinusewithinaBSSmaybe
usefulinformationfortheMSC.
•ThenumberofTCHcurrentlyallocatedcanbeindicatedwithaBSSMAP
REOURCEINDICATIONMESSAGE.
•ThemessagecanbesenttotheMSCindifferentmodes.
•Inone-offmode,theMSCasksforareportandtheBSSgeneratesone.
•Intheperiodicmode,theMSCtellstheBSSthatitwantsreportsat
regularinterval.
•Inspontaneousmode,thereportisgeneratedinresponsetoTCH
demand.

TCH RESOURCE REPORTING100% TCH Usage
LWM

HWM

Traffic Usage
Resource Indication to MSC
No Handover request entertained
Resource Indication to MSC
Handover request entertained
No of TCH free

T3109
•TheMSandBSSmonitortheappearanceofSACCHmessages.
•IfanuplinkfailureoccursandthethresholdoflostSACCHmessages
isreached,theBSSwillactivatetimerT3109.
•TheBSSwillstopsendingSACCHmessagestotheMS.
•TheMSwillnotreceiveanySACCHmessagesandhenceT100will
expire.
•WhenT100expirestheMSwillreturntoidealmode.
•TheBSSwillreleasethechannelresourcesonceT3109expires.
•ForthedownlinkfailuresamepatternisfollowedexceptthatT100
expiresfirst.
•T3109shouldbesethigherthanT100ensuringthatthesystem
holdsontotheradiolinklongenoughforMStoreleaseitfirst.
OtherwiseitwillbepossibletohavetwoMSonthesameTCH.

T3109 LADDER DIAGRAM
MS
BSS
SACCH
LINK_FAIL EXCEEDED
DEACTIVATE D/L SACCH
START TIMER T3109
SACCH NOT DECODED
START TIMER T100
SACCH DEACTIVATED ON D/L
T100 EXPIRES. RELEASE
RADIO RESOURCES
TIMER T3109 STILL RUNNING
TIMER T3109 EXPIRES
BSS RELEASES RADIO RESOURCE

T3110 AND T3111 -Normal Release
•Thesysteminitiatesthereleaseofachannelbysendingachannel
releasemessagetotheMSandwillstarttimerTT3109.
•SACCHmessagesonthedownlinkaredisconnected.
•Onthereceiptofthechannelrelease,theMSstartsinternaltimer
T3110anddisconnectsthemainsignallinglink.
•WhenT3110timesoutorwhenthesignallingisdisconnect
confirmed,theMSdeactivatesallRFlinksandreturnstoBCCHidle
mode.
•WhentheBSSreceivesdisconnectmessage,itstopstimerT3109
andstartsT3111.
•WhenT3111hasexpiredallRFlinksareterminated.
•IfT3109timesoutallRFchannelsaredeactivatedandarethenfree
tobeallocated.
•T3109shouldbegreaterthanT3110.

T3110 AND T3111 -Normal Release
Channel Release
Start timer T3109
Start timer T3110
Disconnect
Stop timer T3109
Start timer T3111
UA
Stop T3110 on the
receipt of UA
T3111 expired
Release Radio
Resources

FREQUENCY HOPPING

Information is
transmitted
by different frequencies
at
different timeslot
Voice
Modulated
RF signal
f1
f2
f3
f4
f1
INTRODUCTION TO FREQUENCY HOPPING

IntroductiontoFrequencyHopping
•Canbeusedtoimprovethequalityofthenetwork
•AlsocanbeusedtoincreasethecapacityoftheNetworkthereby
reducingthenumberofsitesrequiredforCAPACITY.
Thewayitworks
•Eachburstistransmittedonadifferentfrequency
•Bothmobileandbasestationfollowthesamehoppingsequence

IntroductiontoFrequencyHopping
•Fading
–Causesqualitydeterioration
–Isfrequencydependent
•FHdiversifiestheimpactoffadingandimprovesquality.
•Theimmunitytofadingincreasesbyexploitingitsfrequency
selectivity,becauseusingdifferentfrequenciestheprobabilityofbeing
continuouslyaffectedbyfadingisreduced,sothetransmissionlink
qualityisimproved.
•Thisimprovementismuchmorenoticeableforslowmovingmobiles.
•

IncreasedImmunitytofading
•Inacellularurbanenvironmentinmostcasesmultipathpropagation
willbepresentand,asaconsequenceofthat,importantshortterm
variationsinthereceivedlevelarefrequent.ThisiscalledRayleigh
fadingwhichresultsinqualitydegradationbecausesomeofthe
informationwillbecorrupted.
•Forafastmovingmobile,thefadingsituationcanbeavoidedfrom
onebursttoanotherbecauseitalsodependsonthepositionofthe
mobilesotheproblemisnotsoserious.
•Forastationaryonethereceptionmaybepermanentlyaffected
resultinginaverybadquality,evenadropcall.
•Oncetheinformationisreceivedbythemobileorthebasestation,the
onlywaytocopewiththedisturbanceproducedbythefading(errors
intheinformationbits)arethedecodinganddeinterleaving
processes,withaneffectivenesslimitedbythenumberoferrorsthey
havetodealwith.

IncreasedImmunitytofading
•Interference
•Aresultoffrequencyreuse&irregularterrainandsites
•FHdiversifiestheimpactofinterferenceandimprovesquality
•Thesituationofpermanentinterferencecomingfromneighbourcells
transmittingthesameoradjacentfrequenciesisavoidedusing
FrequencyHoppingbecausethecallswillspendthetimemoving
throughdifferentfrequenciesnotequallyaffectedbyinterfering
signals.ThiseffectiscalledInterferenceAveraging.

IncreasedImmunitytofading
•Consideringanonhoppingsystem,thesetofcallsontheinterferer
cellswhichcaninterferewiththewantedcallisfixedforthedurationof
thosecallsandsomecallswillbefoundwithverygoodquality(no
interferenceproblems)whereassomeotherswithverybadquality
(permanentinterferenceproblems).
•Withhopping,thatsetofinterferingcallswillbecontinuallychanging
andtheeffectisthatcallstendtoexperienceanaveragequalityrather
thanextremesituationsofeithergoodorbadquality(allthecallswill
sufferfromacontrolledinterferencebutonlyforshortanddistant
periodsoftime,notforallthedurationofthecall).
•Thisinterferenceaveragingmeansagainspreadingtherawbiterrors
(BERcausedbytheinterference)inordertohavearandomdistribution
oftheminsteadofburstsoferrors,andthereforeenhancethe
effectivenessofdecodinganddeinterleavingprocessestocopewiththe
BERandleadtoabettervalueofFER.

TYPESOFHOPPING
BaseBandHopping(BBH)
•Theradiounitstransmitalwaysthesamefrequency
•Numberoffrequenciesforhopping=Numberofcarriers
•Theradiounitsarealwaystransmittingafixedfrequencyandfrequency
hoppingisperformedbymovingtheinformationforeverycallamong
theavailableradiounitsinacellonaperburstbasis.
•Inreceptionthecallisalwaysprocessedbythesameradiounit(the
onewherethecallstarted).
•Thenumberoffrequenciestohopoverislimitedbythenumberofradio
unitsequippedinthecell.
•TheBCCHcarriercanhopintimeslots1to7(withoutpower
control/DTX).

TYPESOFHOPPING
SynthesiserFrequencyHopping(SFH)
•Theradiounitschange(retune)thefrequencyeveryburst.
•Thecallalwaysstaysinthesameradiounit.
•Numberoffrequenciesforhopping>Numberofcarriers.
•Theradiounitscanhopoverarangeofdifferentfrequencies(64in
caseofMotorola).
•Hybridcombinersarerequiredinthebasestation(CavityCombiners
cannotbeusedwithSFH).
•TheBCCHcarriercanneverhop.

HoppingParameters
Forfrequencyhoppingoperability,GSMdefinesthefollowingsetof
parameters:
•MobileAllocation(MA):Setoffrequenciesthemobileisallowedtohop
over.MAisasubsetofallthefrequenciesallocatedbythesystem
operatortothecell(cellallocation)althoughitcanbethesame.Eg:-If
theoperatorhasfrequenciesfrom1-32,thenhecanuse1-15forBCCH
and17-32forhopping(MA).
•HoppingSequenceNumber(HSN):Determinesthehoppingorderused
inthecell.64differentHSNscanbeassigned,whereHSN=0providesa
cyclichoppingsequenceandHSN=1to63providevarious
pseudorandomhoppingsequences.
•MobileAllocationIndexOffset(MAIO):Determinesinsidethehopping
sequencewhichfrequencythemobilestartstotransmiton.
•FrequencyHoppingIndicator(FHI):Definesahoppingsystemmadeup
byanassociatedsetoffrequencies(MA)tohopoverandahopping
sequence(HSN).

INTRODUCTION
TO
RF PLANNING

•Designingacellularsystem-particularlyonethatincorporatesboth
MacrocellularandMicrocellularnetworksisadelicatebalancing
exercise.
•Thegoalistoachieveoptimumuseofresourcesandmaximum
revenuepotentialwhilstmaintainingahighlevelofsystemquality.
•Fullconsiderationmustalsobegiventocostandspectrumallocation
limitations.
•Aproperlyplannedsystemshouldallowcapacitytobeadded
economicallywhentrafficdemandincreases.
•Aseveryurbanenvironmentisdifferent,soiseverymacrocelland
microcellnetwork.Henceinformedandaccurateplanningisessential
inordertoensurethatthesystemwillprovideboththeincreased
capacityandtheimprovementinnetworkqualitywhererequired,
especiallywhendeployingMicrocellularsystems.
INTRODUCTION TO RF PLANNING

•RFplanningplaysacriticalroleintheCellulardesignprocess.
•BydoingaproperRFPlanningbykeepingthefuturegrowthplanin
mindwecanreducealotofproblemsthatwemayencounterinthe
futureandalsoreducesubstantiallythecostofoptimization.
•On the other hand a poorly planned network not only leads to many
Network problems , it also increases the optimization costs and still
may not ensure the desired quality.

TOOLS USED FOR RF PLANNING
•Network Planning Tool
•CW Propagation Tool
•Traffic Modeling Tool
•Project Management Tool
INTRODUCTION TO RF
PLANNING

Network Planning Tool
•Planningtoolisusedtoassistengineersindesigningandoptimizing
wirelessnetworksbyprovidinganaccurateandreliablepredictionof
coverage,doingfrequencyplanningautomatically,creatingneighbor
listsetc.
•Withadatabasethattakesintoaccountdatasuchasterrain,clutter,
andantennaradiationpatterns,aswellasanintuitivegraphical
interface,thePlanningtoolgivesRFengineersastate-of-the-arttoolto:
–Designwirelessnetworks
–Plannetworkexpansions
–Optimizenetworkperformance
–Diagnosesystemproblems
•ThemajortoolsavailableinthemarketarePlanet,Pegasos,CellCad.
•AlsomanyvendorshavedevelopedPlanningtoolsoftheirownlike
NetplanbyMotorola,TEMSbyEricssonandsoon.
INTRODUCTION TO RF
PLANNING

Network Planning Tool(PLANET)
INTRODUCTION TO RF
PLANNING

Propagaton Test Kit
•Thepropagationtestkitconsistsof
–Testtransmitter.
–Antenna(generallyOmni).
–ReceivertoscantheRSS(Receivedsignallevels).Thereceiver
scanningrateshouldbesettablesothatitsatisfiesLee’slaw.
–Alaptoptocollectdata.
–AGPStogetlatitudeandlongitude.
–Cablesandaccessories.
–WattmetertocheckVSWR.
•A single frequency is transmitted a predetermined power level from the
canditate site.
•These transmitted power levels are then measured and collected by the
Drive test kit. This data is then loaded on the Planning tool and used for
tuning models.
•Commonly Graysons or CHASE prop test kits are used.
INTRODUCTION TO RF
PLANNING

Propagaton Test Kit
INTRODUCTION TO RF
PLANNING

Traffic Modeling Tool
•TrafficmodellingtoolisusedbytheplanningengineerforNetwork
modellinganddimensioning.
•Ithelpstheplanningengineertocalculatethenumberofnetwork
elementsneededtofulfilcoverage,capacityandqualityneeds.
•NetdimbyNokiaisanexampleofaTrafficmodellingtool.
INTRODUCTION TO RF
PLANNING

Project Management Tool
•Though not directly linked to RF Design Planning, it helps in scheduling
the RF Design process and also to know the status of the project
•Site database : This includes RF data, site acquisition,power, civil ,etc.
•Inventory Control
•Fault tracking
•Finance Management
INTRODUCTION TO RF
PLANNING

RF PLANNING
PROCEDURES

Propagation tool setup
Setuptheplanningtoolhardware.Thisincludestheserver
andorclientswhichmaybeUNIXbased.
Setuptheplotterandprintertobeused.
Terrain,Clutter,Vectordataacquisitionandsetup
Procuretheterrain,clutterandvectordataintherequired
resolution.
Setupthesedataontheplanningtool.
Testtoseeiftheyaredisplayedproperlyandprintedcorrectly
ontheplotter.
PRELIMINARY WORK

Setup site tracking database
ThisisdoneusingProjectmanagementorsitemanagement
databases.
Thisisthecentraldatabasewhichisusedbyallrelevant
department,viz.RF,Siteacquisition,Power,Civilengineeringetc,
andavoidsdatamismatch.
Load master lease site locations in database
Ifpredeterminedfriendlysitesthatcanbeusedareavailable,
thenloadthisdataintothesitedatabase.
PRELIMINARY WORK

Marketing Analysis and GOS determination
Marketing analysis is mostly done by the customer.
Growthplanisprovidedwhichliststheprojectedsubscriber
growthinphases.
GOSisdeterminedinagreementwiththecustomer(generallythe
GOSistakenas2%)
Basedonthemarketinganalysis,GOSandnumberofcarriersas
inputs,thenetworkdesigniscarriedout.
Zoning Analysis
Thisinvolvesstudyingtheheightrestrictionsforantennaheights
inthedesignarea.
PRELIMINARY WORK

SetInitialLinkBudget
LinkBudgetAnalysisistheprocessofanalyzingallmajorgains
andlossesintheforwardandreverselinkradiopaths.
Inputs
Basestation&mobilereceiversensitivityparameters
Antennagainatthebasestation&mobilestation.
Hardwarelosses(Cable,connector,combinersetc).
Targetcoveragereliabilty.
Fademargins.
Output
Maximumallowablepathloss.
PRELIMINARY WORK

Initialcellradiuscalculation
Usinglinkbudgetcalculation,themaximumallowablepathlossis
calculated.
UsingOkumurahataempricalformula,theinitialcellradiuscan
becalculated.
Initialcellcountestimates
Oncethecellradiusisknown,theareacoveredbyonesitecan
beeasilycalculated.
Bydividingthetotalareatobecoveredbytheareaofeachcell,a
initialestimateofthenumberofcellscanbemade.
PRELIMINARY WORK

INITIAL SURVEY
MorphologyDefinition
Morphologydescribesthedensityandheightofmanmadeor
naturalobstructions.
Morphologyisusedtomoreaccuratelypredictthepathloss.
SomemorphologyareadefinitionsareUrban,Suburban,rural,
openetc.
Densityalsoappliestomorphologydefinitionslikedenseurban,
lightsuburban,commercialetc.
Thisbasicallyleadstoanumberofsub-areaformationwherethe
linkbudgetwilldifferandhencethecellradiusandcellcountwill
differ.

MorphologyDriveTest
Thisdrivetestisdonetopreparegenericmodelsfornetwork
design.
Drivetestisdonetocharacterizethepropagationandfading
effects.
Theobjectiveistocollectfielddatatooptimizeoradjustthe
predictionmodelforpreliminarysimulations.
Atesttransmitterandareceiverisusedforthispurpose.
Thereceivedsignalsaretypicallysampled(around50samples
in40).

PropagationToolAdjustment
Thedatacollectedbydrivetestingisusedtopreparegeneric
models.
Foragivennetworkdesigntheremaybemorethanonemodel
likedense-urban,urban,suburban,rural,highwayetc.
Thepredictedandmeasuredsignalstrengthsarecomparedand
themodeladjustedtoproduceminimumerror.
Thesemodelsarethenusedforinitialdesignofthenetwork.

INITIAL DESIGN
CompleteInitialCellPlacement
Planningofcellsitessub-areadependingoncluttertypeand
trafficrequired.
RunPropagationAnalysis
Usinggenericmodelspreparedbydrivetesting&proptest,run
predictionsforeachcelldependingonmorphologytypetopredict
thecoverageinthegivensub-areas.
Planningtoolcalculatesthepathlossandreceivedsignal
strengthusingCo-ordinatesofthesitelocation,Groundelevation
abovemeansealevel,Antennaheightaboveground,Antenna
radiationpattern(vertical&horizontal)&antennaorientation,
Powerradiatedfromtheantenna.

ResetCellPlacement(IdealSites)
Accordingtothepredictionschangethecellplacementstodesign
thenetworkforcontigiouscoverageandappropriatetraffic.
SystemCoverageMaps
Preparepresentationsasfollows
BackgroundonpapershowingareaMAPwhichinclude
highways,mainroadsetc.
Phase1siteslayoutontransparency.
Phase1sitescompositecoverageprediction.
Phase2siteslayouttransparency.
Phase2compositecoveragepredictionontransparency.
Ifmorephasesfollowthesameprocedure.
INITIAL DESIGN

DesignReviewWithTheClient
Initialdesignreviewhastobecarriedoutwiththeclientsothathe
agreestothebasicdesignofthenetwork.
Duringdesignreview,firstputonlythebackgroundmapwhichis
onpaper.Thenstepbystepputthesitelayoutandcoverage
prediction.
Displaymayshowsomecoverageholesinphase1whichshould
getsolvedinphase2.
INITIAL DESIGN

PrepareInitialSearchRing
Notethelatitudeandlongitudefromplanningtool.
Gettheaddressoftheareafrommappingsoftware.
Releasethesearchringwithdetailslikeradiusofsearchring,
heightofantennaetc.
Release search rings to project management
Visit friendly site locations
Iftherearefriendlysitesavailablethatcanbeused(infrastructure
sharing),thenthesesitesaretobegivenpreference.
Ifthesesitessuitethedesignrequirements,thenvisitthesesites
first.
SELECTION OF SITES

SelectInitialAnchorSites
Initialanchorsitesarethesiteswhichareveryimportantforthe
networkbuildup,Eg-SitesthatwillalsoworkasaBSC.
Enter Data In Propagation Tool
Enter the sites exact location in the planning tool.
Perform Propagation Analysis
Now since the site has been selected and the lat/lon of the actual
site ( which will be different from the designed site) is known, put
this site in the planning tool and predict coverage.
Check to see that the coverage objectives are met as per
prediction.
SELECTION OF SITES

Reset/ReviewSearchRings
Ifthepredictionshowsacoveragehole(astheactualsitemay
beshiftedfromthedesignedsite),thesurroundingsearchrings
canberesettedandreviewed.
CandidatesiteVisit(Average3perring)
For each proposed location, surveys should carried out and at
least 3 suitable site candidates identified.
Details of each candidate should be recorded on a copy of the
Site Proposal Form for that site. Details must include:
»SitenameandoptionletterSitelocation(Lat./Long)
»Building Height
»Site address and contact number
»Height of surrounding clutter
»Details of potential coverage effecting obstructions or
other comments(A, B, C,...)
SELECTION OF SITES

DriveTestAndReviewBestCandidate
Inordertoverifythatacandidatesite,selectedbasedonits
predictedcoveragearea,isactuallycoveringallobjectiveareas,
drivetesthastobeperformed.
Drivetestalsopointstopotentialinterferenceproblemsor
handoverproblemsforthesite.
Thetesttransmitterhastobeplacedattheselectedlocationwith
allparametersthathavebeendeterminedbasedonsimulations.
Drivetestallmajorroadsandcriticalareaslikeconvention
centers,majorbusinessareas,roadsetc.
Takeaplotofthedataandcheckforsufficientsignalstrength,
sufficientoverlapsandsplashes(leastinteferencetoothercells).
SELECTION OF SITES

DriveTestIntegration
Thedataobtainedfromthedrivetesthastobeloadedonthe
planningtoolandoverlappedwiththeprediction.Thisgivesa
ideaofhowclosethepredictionandactualdrivetestdatamatch.
Iftheydonotmatch(say80to90%)thenforthatsitethemodel
mayneedtuning.
VisitSiteWithAllDisciplines(SA,Power,Civiletc)
Ameetingattheselectedsitetakesplaceinwhichallconcerned
departmentslikeRFEngineering,Siteacquisition,Power,Civil
Engineer,Civilcontractorandthesiteownerispresent.
Anyobjectionsaretakencareoffatthispointitself.
SELECTION OF SITES

SelectEquipmentTypeForSite
Selectequipmentforthecelldependingonchannelrequirements
Selectionofantennatypeandaccessories.
LocateEquipmentOnSiteForConstructionDrawing
Planofthebuilding(ifsitelocatedonthebuilding)tobemade
showingequipmentplacement,cableruns,batterybackup
placementandantennamountingpositions.
Antennamountingpositionstobeshownseparatelyandclearly.
DrawingstobecheckedandsignedbythePlanner,site
acquisition,powerplannerandprojectmanager.

PerformLinkBalanceCalculations
Linkbalancecalculationpercelltobedonetobalancetheuplink
andthedownlinkpath.
Basicallylinkbalancecalculationisthesameaspowerbudget
calculation.Theonlydifferenceisthatonapercellbasisthe
transmitpoweroftheBTSmaybeincreasedordecreased
dependingonthepathlossonuplinkanddownlink.
EMIStudies
StudyofRFRadiationexposuretoensurethatitiswithinlimits
andcontrolofhazardousareas.
DatasheettobepreparedpercellsignedbyRFPlannerand
projectmanagertobesubmittedtotheappropriateauthority.

RadioFrequencyPlan/PNPlan
Frequencyplanninghastobecarriedoutontheplanningtool
basedonrequiredC/IandC/Aandinterferenceprobabilities.
SystemInterferencePlots
C/I,C/A,Bestserverplotsetchastobeplotted.
Theseplotshavetobereviewedwiththecustomertogetthe
frequencyplanpassed.
FinalCoveragePlot
Thispresentationshouldbethesameasdesignreview
presentation.
Thisplotiswithexactlocationsofthesiteinthenetwork.

Identificationofcoverageholes
Coverageholescanbeidentifiedfromtheplotsandsubsequent
actioncanbetaken(likeputtinganewsite)tosolvetheproblem.

RADIO WAVE
PROPAGATION

BASIC DEFINITIONS
Isotropic RF Source
ApointsourcethatradiatesRFenergyuniformlyinalldirections
(I.e.:intheshapeofasphere)
Theoreticalonly:doesnotphysicallyexist.
HasapowergainofunityI.e.0dBi.
Effective Radiated Power (ERP)
Hasapowergainofunityi.e.0dBi
Theradiatedpowerfromahalf-wavedipole.
Alosslesshalf-wavedipoleantennahasapowergainof0dBdor
2.15dBi.
Effective Isotropic Radiated Power (EIRP)
Theradiatedpowerfromanisotropicsource
EIRP = ERP + 2.15 dB

BASIC DEFINITIONS
•Radio signals travel through space at the Speed of Light
C = 3 * 10
8
meters / second
•Frequency (F) is the number of waves per second (unit: Hertz)
•Wavelength () (length of one wave) = (distance traveled in one second)
(waves in one second)
= C / F
If frequency is 900MHZ then
wavelength = 3 * 10
8
900 * 10
6
= 0.333 meters

BASIC DEFINITIONS
dB
•dB is a a relative unit of measurement used to describe power gain or
loss.
•The dB value is calculated by taking the log of the ratio of the measured
or calculated power (P2) with respect to a reference power (P1). This
result is then multiplied by 10 to obtain the value in dB.
dB = 10 * log
10(P
1/P
2)
•The powers P
1ad P
2must be in the same units. If the units are not
compatible, then they should be transformed.
•Equal power corresponds to 0dB.
•A factor of 2 corresponds to 3dB
If P1 = 30W and P2 = 15 W then
10 * log
10(P
1/P
2) = 10 * 10 * log
10(30/15)
= 2

BASIC DEFINITIONS
dBm
•Themostcommon"definedreference"useofthedecibelisthedBm,or
decibelrelativetoonemilliwatt.
•ItisdifferentfromthedBbecauseitusesthesamespecific,measurable
powerlevelasareferenceinallcases,whereasthedBisrelativeto
eitherwhateverreferenceaparticularuserchoosesortonoreferenceat
all.
•AdBhasnoparticulardefinedreferencewhileadBmisreferencedtoa
specificquantity:themilliwatt(1/1000ofawatt).
•TheIEEEdefinitionofdBmis"aunitforexpressionofpowerlevelin
decibelswithreferencetoapowerof1milliwatt."
•ThedBmismerelyanexpressionofpowerpresentinacircuitrelativeto
aknownfixedamount(i.e.,1milliwatt)andthecircuitimpedanceis
irrelevant.}

BASIC DEFINITIONS
dBm
•dBm = 10 log (P) (1000 mW/watt)
where dBm = Power in dB referenced to 1 milliwatt
P = Power in watts
•If power level is 1 milliwatt:
Power(dBm) = 10 log (0.001 watt) (1000 mW/watt)
= 10 log (1)
= 10 (0)
= 0
•Thus a power level of 1 milliwatt is 0 dBm.
•If the power level is 1 watt
1 watt Power in dBm = 10 log (1 watt) (1000 mW/watt)
= 10 (3)
= 30

BASIC DEFINITIONS
dBm
•dBm = 10 log (P) (1000 mW/watt)
•The dBm can also be negative value.
•If power level is 1 microwatt
Power in dBm = 10 log (1 x 10E-6 watt) (1000 mW/watt)
=-30dBm
•Since the dBm has a defined reference it can be converted back to
watts if desired.
•Since it is in logarithmic form it may also be conveniently combined
with other dB terms.

BASIC DEFINITIONS
dBv/m
•To convert field strength in dbv/m to received power in dBm with a
50optimum terminal impedance and effective length of a half wave
dipole /
0dBu=10log[(10
-6
)
2
(1000)(/)
2
/(4*50)]dBm
At850MHZ
0dBu=-132dBm
39dBu=-93dBm

FREE SPACE PROPAGATION
•Friis Formula
P
r = P
t G
tG
r
2
(4d)
2
•Propagation Loss
L
p = 10log [4d / ]
2
Thesquaretermisthepropagationexponent.Itisgreaterthan2
whenobstructionsexist.
• Propagation Loss in dB:
L
p = 32.44 + 20Log(d) +20Log(f)
f = MHz
d = km
P
t
G
t G
r
P
rL
p
d

PROPAGATION MECHANISMS
Reflection
•Occurswhenawaveimpingesuponasmoothsurface.
•Dimensionsofthesurfacearelargerelativeto.
•Reflectionsoccurfromthesurfaceoftheearthandfrombuildingsand
walls.
Diffraction(Shadowing)
•Occurswhenthepathisblockedbyanobjectwithlargedimensions
relativetoandsharpirregularities(edges).
•Secondary“wavelets”propagateintotheshadowedregion.
•Diffractiongivesrisetobendingofwavesaroundtheobstacle.
Scattering
•Occurswhenawaveimpingesuponanobjectwithdimensionsonthe
orderoforless,causingthereflectedenergytospreadout
or“scatter”inmanydirections.
•Smallobjectssuchasstreetlights,signs,&leavescausescattering

MULTIPATH
•Multiple Waves Create “Multipath”
•Due to propagation mechanisms, multiple waves arrive at the
receiver
•Sometimes this includes a direct Line-of-Sight (LOS) signal

MULTIPATH
Multipath Propagation
•Multipath propagation causes large and rapid fluctuations in a signal
•These fluctuations are not the same as the propagation path loss.
Multipathcausesthreemajorthings
•Rapidchangesinsignalstrengthoverashortdistanceortime.
•RandomfrequencymodulationduetoDopplerShiftsondifferent
multipathsignals.
•Timedispersioncausedbymultipathdelays
•Thesearecalled“fadingeffects
•Multipathpropagationresultsinsmall-scalefading.

WHAT IS FADING ?
•Thecommunicationbetweenthebasestationandmobilestationin
mobilesystemsismostlynon-LOS.
•TheLOSpathbetweenthetransmitterandthereceiverisaffectedby
terrainandobstructedbybuildingsandotherobjects.
•Themobilestationisalsomovingindifferentdirectionsatdifferent
speeds.
•TheRFsignalfromthetransmitterisscatteredbyreflectionand
diffractionandreachesthereceiverthroughmanynon-LOSpaths.
•Thisnon-LOSpathcauseslong-termandshorttermfluctuationsin
theformoflog-normalfadingandrayleighandricianfading,which
degradestheperformanceoftheRFchannel.

WHAT IS FADING ?
Signal Power (dBm)
Large scale fading component
Small scale fading
component

LONG TERM FADING
•Terrainconfiguration&manmadeenvironmentcauseslong-term
fading.
•Duetovariousshadowingandterraineffectsthesignallevel
measuredonacirclearoundbasestationshowssomerandom
fluctuationsaroundthemeanvalueofreceivedsignalstrength.
•Thelong-termfadesinsignalstrength,r,causedbytheterrain
configurationandmanmadeenvironmentsformalog-normal
distribution,i.ethemeanreceivedsignalstrength,r,varieslog-
normallyindBifthesignalstrengthismeasuredoveradistanceof
atleast40.
•Experimentallyithasbeendeterminedthatthestandarddeviation,,
ofthemeanreceivedsignalstrength,r,liesbetween8to12dBwith
thehighergenerallyfoundinlargeurbanareas.

RAYLEIGH FADING
•Thisphenomenonisduetomultipathpropagationofthesignal.
•TheRayleighfadingisapplicabletoobstructedpropagationpaths.
•AllthesignalsareNLOSsignalsandthereisnodominantdirectpath.
•Signalsfromallpathshavecomparablesignalstrengths.
•Theinstantaneousreceivedpowerseenbyamovingantennabecomes
arandomvariabledependingonthelocationoftheantenna.

RICEAN FADING
•Thisphenomenonisduetomultipathpropagationofthesignal.
•Inthiscasethereisapartiallyscatteredfield.
•Onedominantsignal.
•Othersareweaker.

DIVERSITY ANTENNA
SYSTEMS

Diversity Antenna Systems
NEED OF DIVERSITY
Building
Building
Building

Diversity Antenna Systems
NEEDOFDIVERSITY
•Inatypicalcellularradioenvironment,thecommunicationbetweenthe
cellsiteandmobileisnotbyadirectradiopathbutviamanypaths.
•Thedirectpathbetweenthetransmitterandthereceiverisobstructed
bybuildingsandotherobjects.
•Hencethesignalthatarrivesatthereceiveriseitherbyreflectionfrom
theflatsidesofbuildingsorbydiffractionaroundmanmadeornatural
obstructions.
•Whenvariousincomingradiowavesarriveatthereceiverantenna,
theycombineconstructivelyordestructively,whichleadstoarapid
variationinsignalstrength.
•Thesignalfluctuationsareknownas‘multipathfading’.

Diversity Antenna Systems
Multipath Propagation
•Multipath propagation causes large and rapid fluctuations in a signal
•These fluctuations are not the same as the propagation path loss.
Multipathcausesthreemajorthings
•Rapidchangesinsignalstrengthoverashortdistanceortime.
•RandomfrequencymodulationduetoDopplerShiftsondifferent
multipathsignals.
•Timedispersioncausedbymultipathdelays
•Thesearecalled“fadingeffects
•Multipathpropagationresultsinsmall-scalefading.

Diversity Antenna Systems
DIVERSITY TECHNIQUE
•Diversitytechniqueshavebeenrecognisedasaneffectivemeans
whichenhancestheimmunityofthecommunicationsystemtothe
multipathfading.GSMthereforeextensivelyadoptsdiversity
techniquesthatinclude
Diversity techniques
Interleaving
In time domain
Frequency Hopping
In Frequency domain
Spatial diversity
In spatial domain
Polarisation diversity
In polarisation domain

Diversity Antenna Systems
CONCEPTOFDIVERSITYANTENNASYSTEMS
•Spatialandpolarisationdiversitytechniquesarerealisedthrough
antennasystems.
•Adiversityantennasystemprovidesanumberofreceivingbranches
orportsfromwhichthediversifiedsignalsarederivedandfedtoa
receiver.Thereceiverthencombinestheincomingsignalsfromthe
branchestoproduceacombinedsignalwithimprovedqualityin
termsofsignalstrengthorsignal-to-noiseratio(S/N).
•Theperformanceofadiversityantennasystemprimarilyrelieson
thebranchcorrelationandsignalleveldifferencebetweenbranches.

Diversity Antenna Systems
Transmission
media 1
Transmission
Tmedia 2
Peak
Fade
Receiver
Information
CONCEPT OF DIVERSITY ANTENNA SYSTEMS

Diversity Antenna SystemsTime
Signal Strength
Combined signal
Signal 1
Signal 2
Combining
Combined signal
fed to receiver
Signal 2
Signal 1

Diversity Antenna Systems
SPATIALDIVERSITYANTENNASYSTEMS
•Thespatialdiversityantennasystemisconstructedbyphysically
separatingtworeceivingbasestationantennas.
•Oncetheyareseparatedfarenough,bothantennasreceive
independentfadingsignals.Asaresult,thesignalscapturedbythe
antennasaremostlikelyuncorrelated.
•Thefurtherapartaretheantennas,themorelikelythatthesignals
areuncorrelated.
• ThetypesoftheconfigurationusedinGSMnetworksare:
horizontalseparation
verticalseparation
compositeseparation.

Diversity Antenna Systems
TYPICALSPATIALANTENNADIVERSITYCONFIGURATIONS
Horizontal Separation Vertical Separation

Diversity Antenna Systems
THREEANTENNASPATIALCONFIGURATION
10Separation
Receive 1 Transmit Receive 2

Diversity Antenna Systems
TWOANTENNASPATIALCONFIGURATION
10Separation
Receive 2
TxRx
Transmit Receive 1
Duplexer

Diversity Antenna Systems
POLARISATIONDIVERSITYANTENNASYSTEMS
•Asingle(sayvertical)polarisedelectromagneticwaveisconvertedto
awavewithtwoorthogonalpolarisedfieldswhileitispropagating
throughscatteringenvironment.
•Ithasalsobeenfoundthatthetwofieldsexhibitsomeextentof
decorrelation.

Diversity Antenna Systems
DUALPOLARISEDANTENNAS
•Adual-polarisationantennaconsistsoftwosetsofradiatingelements
whichradiateor,inreciprocal,receivetwoorthogonalpolarised
fields.
•Theantennahastwoinputconnectorswhichseparatelyconnectsto
eachsetoftheelements.
•Theantennahasthereforetheabilitytosimultaneouslytransmitand
receivetwoorthogonallypolarisedfields.
H / V Slant 45

Diversity Antenna Systems
ADVANTAGESOFDUALPOLARISEDANTENNAS
•Thebestadvantageofusingthedualpolarisationantennaisthe
reductioninthenumberofantennaspersector.
•Reducedsizeoftheheadframeofthesupportingstructure
•Reducedwindloadandweight.
•Reduceddifficultyinsiteacquisitionandinstallation.
•Costsaving
–Requiringslimtower
–Requiringlessinstallationtime.
–Costofonedualpolarisationantennaisgenerallylowerthanthat
oftwo
–Singlepolarisedantennas

Diversity Antenna Systems
DUALPOLARISEDANTENNACONFIGURATIONS
DUAL POLE ANTENNA
TR
TX RX RX
DUAL POLE ANTENNA
SINGLE POLE ANTENNA
RX RX
TX
DUAL POLE ANTENNA
T TR R
TX RXTX RX

INTERFERENCE

WHAT IS INTERFERNCE ?
•Interferenceisthesumofallsignalcontributionsthatareneithernoise
notthewantedsignal.

EFFECTS OF INTERFERENCE
•Interferenceisamajorlimitingfactorintheperformanceofcellular
systems.
•Itcausesdegradationofsignalquality.
•Itintroducesbiterrorsinthereceivedsignal.
•Biterrorsarepartlyrecoverablebymeansofchannelcodinganderror
correctionmechanisms.
•Theinterferencesituationisnotreciprocalintheuplinkanddownlink
direction.
•Mobilestationsandbasestationsareexposedtodifferentinterference
situation.

SOURCES OF INTERFERENCE
•Anothermobileinthesamecell.
•Acallinprogressintheneighboringcell.
•Otherbasestationsoperatingonthesamefrequency.
•Anynon-cellularsystemwhichleaksenergyintothecellularfrequency
band.

TYPES OF INTERFERENCE
•Therearetwotypesofsystemgeneratedinterference
–Co-channelinterference
–Adjacentchannelinterference
Co-ChannelInterference
•Thistypeofinterferenceistheduetofrequencyreuse,i.e.several
cellsusethesamesetoffrequency.
•Thesecellsarecalledco-channelcells.
•Co-channelinterferencecannotbecombatedbyincreasingthepower
ofthetransmitter.Thisisbecauseanincreaseincarriertransmitpower
increasestheinterferencetoneighboringco-channelcells.
•Toreduceco-channelinterference,co-channelcellsmustbephysically
separatedbyaminimumdistancetoprovidesufficientisolationdueto
propagationorreducethefootprintofthecell.

Co-ChannelInterference
•Somefactorsotherthenreusedistancethatinfluenceco-channel
interferenceareantennatype,directionality,height,sitepositionetc,
•GSMspecifiesC/I>9dB.
Carrier f1 Interferer f1
dB
Distance
C
I

Co-ChannelInterference
•Inacellularsystem,whenthesizeofeachcellisapproximatelythe
same,co-channelinterferenceisindependentofthetransmittedpower
andbecomesafunctionofcellradius(R)andthedistancetothecentre
ofthenearestco-channelcell(D).
C1
C2
C3
C1
C2
C3
D

Co-ChannelInterference
•Q=D/R=3N
•ByincreasingtheratioofD/R,thespatialseperationbetweentheco-
channelcellsrelativetothecoveragedistanceofacellisincreased.In
thiswayinterferenceisreducedfromimprovedisolationofRFenergy
fromtheco-channelcell.
•TheparameterQ,calledtheco-channelreuseratio,isrelatedtothe
clustersize.
•AsmallvalueofQprovideslargercapacitysincetheclustersizeNis
smallwhereasalargevalueofQimprovesthetransmissionquality.

Adjacent-ChannelInterference
•Interferenceresultingfromsignalswhichareadjacentinfrequencyto
thedesiredsignaliscalledadjacentchannelinterference.
•Adjacentchannelinterferenceresultsfromimperfectreceiverfilters
whichallownearbyfrequenciestoleakintothepassband.
•Adjacentchannelinterferencecanbeminimizedthroughcareful
filteringandchannelassignments.
•Bykeepingthefrequencyseparationbetweeneachchannelinagiven
cellaslargeaspossible,theadjacentinterferencemaybereduced
considerably.

Adjacent-ChannelInterference
Carrier f1 Interferer f2
dB
A
C
Distance

COUNTERING INTERFERENCE
POWERCONTROL
•RFpowercontrolisemployedtominimisethetransmitpowerrequired
byMSorBSwhilemaintainingthequalityoftheradiolinks.
•Byminimisingthetransmitpowerlevels,interferencetoco-channel
usersisreduced.
•PowercontrolisimplementedintheMSaswellastheBSS.
•PowercontrolontheUplinkalsohelpstoincreasethebatterylife.
•PowerreceivedbytheMSiscontinouslysentinthemeasurement
report.
•SimilarlyuplinkpowerreceivedfromtheMSbytheBTSismeasured
bytheBTS.
•Complexalgorithmevaluatethismeasurementsandtakeadecision
subsequentlyreducingorincreasingthepowerintheUplinkorthe
downlink.

COUNTERING INTERFERENCE
SECTORIZATION
•For120degreessectoredsiteascomparedtoanomnisitealmost
1/3rdinterferenceisreceivedintheuplink.
•Themoreselectiveanddirectionalistheantenna,thesmalleristhe
interference.
•Reductionininterferenceresultsinhighercapacityinbothlinks.

REPEATERS

REPEATERS
•Repeaterunitsaredesignedtoreceivesignalsfromadonorsite,
amplifyandrebroadcastthedonorsitessignalsintopoorcoverage
areasortoextendthecoveragerangeofthedonorsite.
•Theserepeaterarebi-directionalanddonottranslatefrequencyand
subsequentlyarelimitedinoutputpowerandgain.
•Repeatersprovidebetween50to80dBofgain.
Donor Cell
INTRODUCTION
Donor side antenna Mobile side antenna
Poor Coverage area
Repeater receives
Donor signal at
~ -90dBm
Repeater amplifies
the signal and
rebroadcasts the
signal

REPEATERS
INTRODUCTION
•Therearetwotypesofrepeaterbandselectiveandchannel
selective.
•Bandselectiverepeateramplifiesabandoffrequency.Henceit
amplifiesanyfrequencythatfallswithinitsband.
•Channelselectiverepeaterallowsselectionofanumberof
individualchannelstoamplifyandrebroadcast.
•Typicallyachannelselectiverepeaterallowsselectionof2to4
channels.
•IftheGSM900orDCS1800networkincorporatesfrequency
hopping,thenonlybandselectiverepeatersshouldbeused.

TRANSMISSION
SYSTEMS
Other Networks

Introduction To Transmission Systems
•Transmissionsystemsformthebackboneofanynetworks.
•NormallytransmissionsystemsincludeSDH,PDH,ATM,
Microwaves,leasedlines.
•InGSMnormallythecorenetworkislocatedinthesamepremises
andaremostlyinterconnectedbyfixedwireline.Inhugenetwork
consistingofmanyMSClocatedatdifferentplacesthe
interconnectionmaybethroughanyofthetransmissionsystems
mentionedabove.
•TheAccessnetworkconsistsofBSC’swithmanyBTS’sconnected
totheminvarioustransmissiontopologies.Normalpracticeisto
connectvariousBSC’ctotheMSCviafiberanddifferentBTS’s
connectedtoBSCviamicrowaveinDaisychain,staroranyother
topology.Howevertherecanbemanydifferentwaysof
implementation.

E1
•2.048Mbpscircuitprovideshighspeed,digitaltransmissionfor
voice,data,andvideosignalsat2.048Mbps.
•2.048MbpstransmissionsystemsarebasedontheITU-T
specificationsG.703,G.732andG.704,andarepredominantin
Europe,Australia,Africa,SouthAmerica,andregionsofAsia.
•Theprimaryuseofthe2.048Mbpsisinconjunctionwith
multiplexersforthetransmissionofmultiplelowspeedvoiceand
datasignalsoveronecommunicationpathratherthenovermultiple
paths.
•Themostcommonlinecodeusedtotransmitthe2.048Mbps
signalisknownasHDB3(HighDensityBipolar3)whichisa
bipolarcodewithaspecificzerosuppressionschemewhereno
morethenthreeconsecutivezerosareallowedtooccur.

Typical implementation of a E1

The2.048MbpsFramingFormat
•The2.048Mbpssignaltypicallyconsistsofmultiplexeddataand/or
voicewhichrequiresaframingstructureforreceivingequipmentto
properlyassociatetheappropriatebitsintheincomingsignalwith
theircorrespondingchannels.
•The2.048Mbpsframeisbrokenupinto32timeslotsnumbered0-
31.
•Eachtimeslotcontains8bitsinaframe,andsincethereare8000
framespersecond,eachtimeslotcorrespondstoabandwidthof8
x8000=64kbps.
•Timeslot0isallocatedentirelytotheframealignmentsignal(FAS)
pattern,aremotealarm(FASDistantAlarm)indicationbit,and
othersparebitsforinternationalandnationaluse.

Framing Format

E1
•TheFASpattern(0011011)takesup7bits(bits2-8)intimeslot0of
everyotherframe.
•InthoseframesnotcontainingtheFASpattern,bit3isreservedfor
remotealarmindication(FASDistantAlarm)whichindicateslossof
framealignmentwhenitissetto1.
•Theremainingbitsintimeslot0areallocatedasshowninthe
followingFigure.
•Ifthe2.048Mbpssignalcarriesnovoicechannels,thereisno
needtoallocateadditionalbandwidthtoaccommodatesignaling.
•Hence,timeslot1-31areavailabletotransmitdatawithan
aggregatebandwidthof2.048Mbps-64kbps(TSO)=1.984
Mbps.

E1
TS 16 Multiframe Format

E1
•Iftherearevoicechannelsonthe2.048Mbpssignal,itisnecessary
totakeupadditionalbandwidthtotransmitthesignalling
information.
•ITU-TRecommendationG.704allocatestimeslot16forthe
transmissionofthechannel-associatedsignallinginformation.
•The2.048Mbpscancarryuptothirty64kbpsvoicechannelsin
timeslot1-15and17-31.
•Voicechannelsarenumbered1-30;voicechannels16-30are
carriedintimeslot17-31.
•However,the8bitsintimeslot16arenotsufficientforall30
channelstosignalinoneframe.Therefore,amultiframestructureis
requiredwherechannelscantaketurnsusingtimeslot16.

E1
•SincetwochannelscansendtheirABCDsignallingbitsineach
frame,atotalof15framesarerequiredtocyclethroughallofthe30
voicechannels.
•Oneadditionalframeisrequiredtotransmitthemultiframe
alignmentsignal(MFAS)pattern,whichallowsreceivingequipment
toaligntheappropriateABCDsignallingbitswiththeir
correspondingvoicechannels.
•ThisresultsintheTS-16multiframestructurewhereeach
multiframecontainsatotalof162.048Mbps,numbered0-15.
•FigureonthepreviousslideshowstheTS-16multiframeformatfor
the2.048MbpssignalasdefinedbytheITU-TRecommendation
G.704.

E1
•AscanbeseeninFigure,timeslot16offrame0containsthe4-bit
longmultiframealignmentsignal(MFAS)pattern(0000)inbits1-4.
The“Y”bitisreservedfortheremotealarm(MFASDistantAlarm)
whichindicateslossofmultiframealignmentwhenitissetto1.
•Timeslot16offrames1-15containstheABCDsignallingbitsofthe
voicechannels.
•Timeslot16ofthenthframecarriesthesignallingbitsofthenthand
(n+15)thvoicechannels.Forexample,frame1carriesthesignalling
bitsofvoicechannels1and16,frame2carriesthesignallingbitsof
channels2and17etc.
•Itisalsoimportanttonotethattheframealignmentsignal(FAS)is
transmittedintimeslot0oftheevennumberedframes.

T1Introduction
•T1isadigitalcommunicationslinkthatenablesthetransmission
ofvoice,data,andvideosignalsattherateof1.544millionbitper
second(Mb/s).
•Introducedinthe1960s,itwasinitiallyusedbytelephone
companieswhowishedtoreducethenumberoftelephonecables
inlargemetropolitanareas.
•T1simplifiesthetaskofnetworkingdifferenttypesof
communicationsequipmentsinceitcancarrzbothvoiceanddata
onthesamelink.

T1Introduction
•Toillustrate,Figure1onthenextpageshowswhatacompany’s
communicationsnetworkmightlooklikewithoutT1
•Figure1showsthattelephone,facsimile,andcomputer
applicationswouldallrequireseparatelines.
•Typically,voiceandlow-speeddataapplicationsareservicedby
analoglines,whilehigh-speeddataapplicationsareservicedby
digitalfacilities.
•Figure2onthenextpagedepictsthesamenetworkwithaT1link
installed.

T1
FIGURE 1

T1
FIGURE 2

PDHOverview
•Long-establishedanalogtransmissionsystemsthatproved
inadequateweregraduallyreplacedbydigitalcommunications
networks.
•Inmanycountries,digitaltransmissionnetworksweredeveloped
baseduponstandardscollectivelyknowntodayasthe
PlesiochronousDigitalHierarchy(PDH).
•Althoughithasnumerousadvantagesoveranalog,PDHhas
someshortcomings:provisioningcircuitscanbelabor-intensive
andtime-consuming,automationandcentralizedcontrol
capabilitiesoftelecommunicationnetworksarelimited,and
upgradingtoemergingservicescanbecumbersome.
•Amajordisadvantageisthatstandardsexistforelectricalline
interfacesatPDHrates,butthereisnostandardforopticalline
equipmentatanyPDHrate,whichisspecifictoeach
manufacturer.

PDHOverview
•Thismeansthatfiberoptictransmissionequipmentfromone
manufacturermaynotbeabletointerfacewithother
manufacturers’equipment.
•Asaresult,serviceprovidersareoftenrequiredtoselecta
singlevendorfordeploymentinareasofthenetwork,andare
lockedintousingthenetworkcontrolandmonitoring
capabilitiesofthatvendor.
•ReconfiguringPDHnetworkscanbedifficultandlabor-intensive
-resultingincostly,time-consumingmodificationstothe
networkwhenevernewservicesareintroducedorwhenmore
bandwidthisrequired.

SDHOverview
•Bellcore(theresearchaffiliateoftheBelloperatingcompaniesin
theUnitedStates)proposedanewtransmissionhierarchyin1985.
•Bellcore’smajorgoalwastocreateasynchronoussystemwithan
opticalinterfacecompatiblewithmultiplevendors,butthe
standardizationalsoincludedaflexibleframestructurecapableof
handlingeitherexistingornewsignalsandalsonumerousfacilities
builtintothesignaloverheadforembeddedoperations,
administration,maintenanceandprovisioning(OAM&P)purposes.
•ThenewtransmissionhierarchywasnamedSynchronousOptical
Network(SONET).
•TheInternationalTelecommunicationUnion(ITU)establishedan
internationalstandardbasedontheSONETspecifications,known
astheSynchronousDigitalHierarchy(SDH),in1988.

SDHOverview
•TheSDHspecificationsdefineopticalinterfacesthatallow
transmissionoflower-rate(e.g.,PDH)signalsatacommon
synchronousrate.
•AbenefitofSDHisthatitallowsmultiplevendors’optical
transmissionequipmenttobecompatibleinthesamespan.
•SDHalsoenablesdynamicdrop-and-insertcapabilitiesonthe
payload;PDHoperatorswouldhavetodemultiplexand
remultiplexthehigher-ratesignal,causingdelaysandrequiring
additionalhardware.
•Sincetheoverheadisrelativelyindependentofthepayload,
SDHeasilyintegratesnewservices,suchasAsynchronous
TransferMode(ATM)andFiberDistributedDataInterface
(FDDI),alongwithexistingEuropean2,34,and140Mbit/s
PDHsignals,andNorthAmerican1.5,6.3,and45Mbit/s
signals.

SDHOverviewSTM1dataratecalculation
•SDHmultiplexingcombineslow-speeddigitalsignalssuchas2,
34,and140Mbit/ssignalswithrequiredoverheadtoformaframe
calledSynchronousTransportModuleatlevelone(STM-1).
•Figure1showstheSTM-1frame,whichiscreatedby9segments
of270byteseach.
•Thefirst9bytesofeachsegmentcarryoverheadinformation;the
remaining261bytescarrypayload.
•Whenvisualizedasablock,theSTM-1frameappearsas9rows
by270columnsofbytes.
•TheSTM-1frameistransmittedrow#1first,withthemost
significantbit(MSB)ofeachbytetransmittedfirst.

SDHOverviewSTM1dataratecalculation
•Thisformulacalculatesthebitrateofaframeddigitalsignal:
•bitrate=frameratexframecapacity
•InorderforSDHtoeasilyintegrateexistingdigitalservicesintoits
hierarchy,itoperatesatthebasicrateof8kHz,or125
microsecondsperframe,sotheframerateis8,000framesper
second.
•Theframecapacityofasignalisthenumberofbitscontainedwithin
asingleframe.
•Figure2shows:framecapacity=270bytes/rowx9rows/framex8
bits/byte=19,440bits/frame
•ThebitrateoftheSTM-1signaliscalculatedasfollows:
bitrate=8,000frames/secondx19,440bits/frame=155.52Mbit/s

SDHOverview
FIGURE 1 1 2 3 4 5 6 7 8 9
OVERHEAD PAYLOAD
9 BITS 261 BITS
FRAME PERIOD 125 MICRO SEC.

SDHOverview
FIGURE 2 1 2 3 4 5 6 7 8 9
1
2
3
4
5
6
7
8
9
OVERHEAD PAYLOAD
270 BITS

SDHOverviewMultiplexingofSTMframes
•AstheFigurecomingonthenextslideshows,theITUhas
specifiedthatanSTM-4signalshouldbecreatedbybyte
interleavingfourSTM-1signals.
•Thebasicframerateremains8,000framespersecond,butthe
capacityisquadrupled,resultinginabitrateof4x155.52
Mbit/s,or622.08Mbit/s.
•TheSTM-4signalcanthenbefurthermultiplexedwiththree
additionalSTM-4stoformanSTM-16signal.
•Table1liststhedefinedSDHframeformats,theirbitrates,and
themaximumnumberof64kbit/stelephonychannelsthatcan
becarriedateachrate.

SDHOverviewMultiplexingofSTMframes
STM1 A
STM1 B
STM1 C
STM1 D
4:1
STM4

SDHOverviewMultiplexingofSTMframesFRAME BIT MAX NUMBER OF
FORMAT RATE TELEPHONY CHANNELS
STM - 1 155.52 Mbits/S 1920
STM - 4 622.08 M bits/S 7680
STM - 16 2.488 Gbits/S 30720

MicrowaveOverview
•Normallyusedforpointtopointtransmission
•UsedmainlyintheGHzrange.
•Normallydistancebetweenradiosislessthan50Kms.

In Depth Basics of GSM for beginner (Telecom)

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In Depth Basics of GSM for beginner (Telecom)

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