Slides of First Day

A THREE DAYS WORKSHOP ON

ADVANCE MOBILE TECHNOLOGY (GSM)

ICIT GOMAL UNIVERSITY

D.I.KHAN

Resource Person: ASIF QAYUM

MS (Telecom & Networks)

Organized By: M.KHALID HAMID

A.Q.Khan aA.Q.Khan aqkhan@gu.edu.pkqkhan@gu.edu.pk

START WITH THE NAME OF START WITH THE NAME OF ALLAHALLAH THE MOST MERCIFULL & MIGHTY THE MOST MERCIFULL & MIGHTY

Day 1 (section 1)Day 1 (section 1)

Cellular Networks Cellular Networks Cell shapeCell shapeHexagonal CellHexagonal CellCell areaCell areaFrequency spectrumFrequency spectrumFrequency spectrum divisionFrequency spectrum divisionNew standardNew standardFrequency Re-UseFrequency Re-UseCell clusterCell clusterAny QuestionAny Question

Cellular NetworksCellular Networks

The essential difference between a The essential difference between a cellular and fixed telephony network is cellular and fixed telephony network is that the subscriber’s terminal (the that the subscriber’s terminal (the Mobile Station - MS) is not linked by a Mobile Station - MS) is not linked by a fixed physical connection to the networkfixed physical connection to the network Connection is a radio based wireless Connection is a radio based wireless

connectionconnection

Cell shapeCell shapeEach cell is serviced by a fixed radio Each cell is serviced by a fixed radio transmitter\receiver known as a “base station” transmitter\receiver known as a “base station” (BS) which is commonly located in the centre (BS) which is commonly located in the centre or corner of a cellor corner of a cell

While often drawn as hexagonal in shape, While often drawn as hexagonal in shape, real cells have no defined shape. The actual real cells have no defined shape. The actual area a cell covers depends on many area a cell covers depends on many parameters:parameters: Transmitter powerTransmitter power WeatherWeather Antenna directivityAntenna directivity

Hexagonal Cell Cell

7(Site)X 1(Cell) Re-use

Hexagonal cell

Cell areaCell area

The area a cell covers typically varies from The area a cell covers typically varies from a very small region in urban areas to quite a very small region in urban areas to quite large regions (around 35 km radius in GSM) large regions (around 35 km radius in GSM) in rural areasin rural areas

Cells are often classified as being:Cells are often classified as being: MicrocellsMicrocells MacrocellsMacrocells Umbrella cellsUmbrella cells Selective (directional) cellsSelective (directional) cells

Frequency SpectrumFrequency Spectrum

Cellular networks operate within defined Cellular networks operate within defined frequency bands of the spectrumfrequency bands of the spectrum

For example, GSM-900 utilises two 25 MHz For example, GSM-900 utilises two 25 MHz bandsbands 890-915 MHz (Uplink - MS to BS)890-915 MHz (Uplink - MS to BS) 935-960 MHz (Downlink - BS to MS)935-960 MHz (Downlink - BS to MS)

These 25 MHz bands are subdivided into These 25 MHz bands are subdivided into 124 carrier frequencies each spaced at 124 carrier frequencies each spaced at approximately 200 kHz (FDMA)approximately 200 kHz (FDMA)

Frequency Spectrum divisionFrequency Spectrum division

Not all countries utilise the full 25 MHz and Not all countries utilise the full 25 MHz and within a country the full GSM band must be within a country the full GSM band must be subdivided among several network operatorssubdivided among several network operators

Additional frequency spectrum is allocated in Additional frequency spectrum is allocated in most countries around 1800 MHz (GSM-most countries around 1800 MHz (GSM-1800)1800)

In US, certain operators implement GSM In US, certain operators implement GSM standard on a frequency band around 1900 standard on a frequency band around 1900 MHz (GSM-1900)MHz (GSM-1900)

New standardNew standardGSM 900

876 880 890 915 921 925 935 960

GSM 900EGSM RGSM RGSM EGSM

EGSM – Extra 10MHz, therefore total available ARFCN become 174.

RGSM – Extra 15MHz, therefore total available ARFCN become 199.

Frequency Re-useFrequency Re-use

In a given country with, say, two different In a given country with, say, two different GSM networks will each use half the 124 GSM networks will each use half the 124 (i.e. 62) GSM-900 carriers(i.e. 62) GSM-900 carriers

Clearly, even using TDMA technology this Clearly, even using TDMA technology this is an extremely small number of carrier is an extremely small number of carrier frequencies to support a GSM network in a frequencies to support a GSM network in a complete countrycomplete country

All cellular networks address this problem All cellular networks address this problem by what is termed “frequency re-use”by what is termed “frequency re-use”

Frequency Re-useFrequency Re-useFrequency re-use means that the same set of Frequency re-use means that the same set of carrier frequencies being used in one cell can be carrier frequencies being used in one cell can be re-used in the network in a different cellre-used in the network in a different cell

However, the cells re-using the same carriers However, the cells re-using the same carriers must not be adjacent as they would interfere with must not be adjacent as they would interfere with one anotherone another

In practice, these cell must be distant from one In practice, these cell must be distant from one another another Typical “re-use distance” is 2.5 to 3 times the cell Typical “re-use distance” is 2.5 to 3 times the cell

“radius”“radius”

Frequency ReuseFrequency ReuseHow can we reuse frequency?How can we reuse frequency?

Cell ClustersCell Clusters

Cells in a cellular network are generally Cells in a cellular network are generally “grouped” together into cell clusters“grouped” together into cell clusters

Cellular networks are generally designed as Cellular networks are generally designed as a repeated cluster patterna repeated cluster pattern

The number of cells in a cluster (typically 4,7, The number of cells in a cluster (typically 4,7, 12 or 21) is a trade-off between the traffic 12 or 21) is a trade-off between the traffic capacity in the cluster and its interference capacity in the cluster and its interference with the adjacent cluster of cells (where the with the adjacent cluster of cells (where the same frequencies will be re-used)same frequencies will be re-used)

Cluster Cluster Cluster of 3,4,7,9 & 12Cluster of 3,4,7,9 & 12

Larger cluster size

Longer distance between interferers

1112 1

Less interferenceBUT

Reduced capacity

ANY QUESTIONANY QUESTION

DAY1 (SECTION 2)DAY1 (SECTION 2)GSM Cellular StandardGSM Cellular StandardJustification for GSMJustification for GSMMeeting these CriteriaMeeting these CriteriaGSM Network ArchitectureGSM Network ArchitectureMobile Station (MS)Mobile Station (MS)Base station subsystem (BSS)Base station subsystem (BSS)Network Subsystem (NSS)Network Subsystem (NSS)HLR & VLRHLR & VLRAuC & EIRAuC & EIROther Network functionOther Network functionGSM Air InterfaceGSM Air Interface

GSM Cellular StandardGSM Cellular StandardAll GSM networks and equipment conform to a All GSM networks and equipment conform to a defined GSM standard issued by ETSI (European defined GSM standard issued by ETSI (European Telecommunications Standard Institute)Telecommunications Standard Institute)

GSM is a second generation or digital cellular GSM is a second generation or digital cellular technologytechnology All transmissions (signalling as well as traffic - speech) All transmissions (signalling as well as traffic - speech)

between MS and BS is by digital modulation of between MS and BS is by digital modulation of frequency carrierfrequency carrier

Currently, the most widely used of several second Currently, the most widely used of several second generation digital cellular telephony standardsgeneration digital cellular telephony standards

Justification for GSMJustification for GSM

GSM development started in the early 1980s GSM development started in the early 1980s to replace first generation (analogue) cellular to replace first generation (analogue) cellular technologytechnology

The proposed system had to meet certain The proposed system had to meet certain criteriacriteria Good subjective speech qualityGood subjective speech quality Low terminal and network equipment costsLow terminal and network equipment costs Support of international roamingSupport of international roaming Efficient use of available spectrumEfficient use of available spectrum

Meeting these CriteriaMeeting these CriteriaGSM has been very successful in meeting all of GSM has been very successful in meeting all of these criteriathese criteria Widely used in well over 100 countriesWidely used in well over 100 countries Equipment costs are lowEquipment costs are low Voice, data and new services availableVoice, data and new services available

However,However, Still not a single “global” standardStill not a single “global” standard MS to BS bearer rates are still very slow for non-MS to BS bearer rates are still very slow for non-

voice servicesvoice services

Third generation “global” standard UMTSThird generation “global” standard UMTS

Internet

GSM Network ArchitectureGSM Network Architecture

- PPP session termination (learn wireless-specific info. while establishing PPP session. Security and policy are linked.- QoS management - wireless-TCP- Personalization of Content Services depending on the device- PUSH and PULL services for Wireless advertisements- Wireless-Specific Policy Gateway- Wireless-VPNs

AUCAUC

MEME SIMSIM

OMCOMC

HLRHLR

MSC/VLRMSC/VLR

BTSBTS BSCBSC

EIREIR

GSM Network ComponentsGSM Network Components

Mobile Station—MSMobile Station—MS

ME = Mobile EquipmentME = Mobile Equipment

MS=ME+SIMMS=ME+SIM

SIM = Subscriber SIM = Subscriber Identity Identity

ModuleModule

Subscriber Identity Module – Subscriber Identity Module – SIMSIM

• International Mobile International Mobile Subscriber Identity (IMSI)Subscriber Identity (IMSI)

• Temporary Mobile Temporary Mobile Subscriber Identity Subscriber Identity (TMSI)(TMSI)

• Authentication Key (Ki)Authentication Key (Ki)• Algorithms A3,A5,A8Algorithms A3,A5,A8

• International Mobile International Mobile Subscriber Identity (IMSI)Subscriber Identity (IMSI)

• Temporary Mobile Temporary Mobile Subscriber Identity Subscriber Identity (TMSI)(TMSI)

• Authentication Key (Ki)Authentication Key (Ki)• Algorithms A3,A5,A8Algorithms A3,A5,A8

The Base Station

Controller – BSC The Base Transceiver

Station – BTS TRAU

The Base Station

Controller – BSC The Base Transceiver

Station – BTS TRAU

BTSBTS

BSCBSC

TRAUTRAUBSS

Base Station Subsystem – BSSBase Station Subsystem – BSS

BTSBTS

The BTS provide the physical connection The BTS provide the physical connection of an MS to the Network inform of Air of an MS to the Network inform of Air interface “Uinterface “Um m

On the other side towards NSS ,the BTS is On the other side towards NSS ,the BTS is connected to the BSC via the Air interface connected to the BSC via the Air interface “Abis” “Abis” Size of BTS = Today the size is Size of BTS = Today the size is comparable to a mailbox comparable to a mailbox

BTS Block DiagramBTS Block Diagram

Base Station Controller (BSC)Base Station Controller (BSC)BSC forms the center of BSSBSC forms the center of BSS

BSC connect to many BTSs over Abis BSC connect to many BTSs over Abis interfaceinterface

Technically BSC is a small digital Technically BSC is a small digital exchange with mobile-specific extensionexchange with mobile-specific extension

Architecture of BSCArchitecture of BSC

Switch MatrixSwitch MatrixIts function is to switch the incoming traffic Its function is to switch the incoming traffic channels (A-interface from MSC) to the channels (A-interface from MSC) to the correct Abis-interface channelscorrect Abis-interface channels

It take care of the relay functionalityIt take care of the relay functionality

It is also used as the internal control bussIt is also used as the internal control buss

Terminal Control Elements (TCE)Terminal Control Elements (TCE)Abis- interfaceAbis- interface

The connection to the BTSs is establish The connection to the BTSs is establish via the TCEsvia the TCEs

The connection is establish independently The connection is establish independently from BSC central Unitfrom BSC central Unit

The number of TCE depends on the The number of TCE depends on the number of BTSs connected with BSCnumber of BTSs connected with BSC

A-interface Terminal Control A-interface Terminal Control ElementsElements

The connection of a BSC to the MSC is The connection of a BSC to the MSC is establish via the A-TCEsestablish via the A-TCEsRemember that every BSC is connected Remember that every BSC is connected to only one MSCto only one MSCSo large number of A-TCEs is needed to So large number of A-TCEs is needed to support the A-interface becoz all the support the A-interface becoz all the payload and signaling data of the entire payload and signaling data of the entire BSC have to be conveyed over this BSC have to be conveyed over this interface interface

Data Base (DB)Data Base (DB)

The BSC database contain the The BSC database contain the maintenance status of the whole BSSmaintenance status of the whole BSS

It contain the complete BTS operations It contain the complete BTS operations software for all attached BTSs software for all attached BTSs

Central Module (CM)Central Module (CM)The main task of CM is the Handover The main task of CM is the Handover decisiondecisionIt decide when a Handover should take It decide when a Handover should take placeplaceFor both intra BTS and intra BSC For both intra BTS and intra BSC Handover decision BSC do not required Handover decision BSC do not required the permission of MSCthe permission of MSCOnly for external Handover BSC needs to Only for external Handover BSC needs to involve of MSCinvolve of MSCPower control is also the main task of CM Power control is also the main task of CM

TRAUTRAU

The task of TRAU is to compress or The task of TRAU is to compress or decompress speechdecompress speech

It compress speech from 64kbps to It compress speech from 64kbps to 16kbps16kbps

Typically it is located between the BSC Typically it is located between the BSC and MSC but it can be placed between and MSC but it can be placed between BTS and BSCBTS and BSC

Possible installation site of Possible installation site of TRAUTRAU

The speech compression is intended The speech compression is intended mainly to save resources over the Air-mainly to save resources over the Air-interfaceinterface

It is also suitable to save line costIt is also suitable to save line cost

So to get the most benefit from the So to get the most benefit from the compression,the TRAU would be install at compression,the TRAU would be install at the site of the MSC.the site of the MSC.

The GSM specification also allow the The GSM specification also allow the installation of TRAU b/w the BTS & BSC installation of TRAU b/w the BTS & BSC

Mobile Switching Center – MSC Home Location Register – HLR Visitor Location Register – VLR Equipment Identity Register – EIR Authentication Center – AUC Inter-Working Function – IWFEcho Cancellor – EC

AUCAUCHLRHLR

MSC/VLRMSC/VLR

EIREIROMC

IWFIWF

The Network Switching SystemThe Network Switching System

NSS HierarchyNSS Hierarchy

NSS ArchitectureNSS Architecture

Mobile Service Switching Mobile Service Switching Center – MSC Center – MSC

Call ProcessingCall Processing Operations and Operations and

Maintenance SupportMaintenance Support Inter-network & Inter-Inter-network & Inter-

workingworking BillingBilling

Call ProcessingCall Processing Operations and Operations and

Maintenance SupportMaintenance Support Inter-network & Inter-Inter-network & Inter-

workingworking BillingBilling

Home Location Register – HLR Home Location Register – HLR

Subscriber ID (IMSI and Subscriber ID (IMSI and MSISDN)MSISDN)

Current subscriber VLR (current Current subscriber VLR (current location)location)

Supplementary service Supplementary service informationinformation

Subscriber status Subscriber status (registered/deregistered)(registered/deregistered)

Authentication key and AuC Authentication key and AuC functionalityfunctionality

Subscriber ID (IMSI and Subscriber ID (IMSI and MSISDN)MSISDN)

Current subscriber VLR (current Current subscriber VLR (current location)location)

Supplementary service Supplementary service informationinformation

Subscriber status Subscriber status (registered/deregistered)(registered/deregistered)

Authentication key and AuC Authentication key and AuC functionalityfunctionality

Visitor Location Register – VLR Visitor Location Register – VLR

Mobile Status(IMSI detached/ Mobile Status(IMSI detached/

attached)attached)

Location Area Identity(LAI)Location Area Identity(LAI)

Temporary Mobile Subscriber Temporary Mobile Subscriber

Identity(TMSI)Identity(TMSI)

Mobile Station Roaming Mobile Station Roaming

Number(MSRN)Number(MSRN)

Mobile Status(IMSI detached/ Mobile Status(IMSI detached/

attached)attached)

Location Area Identity(LAI)Location Area Identity(LAI)

Temporary Mobile Subscriber Temporary Mobile Subscriber

Identity(TMSI)Identity(TMSI)

Mobile Station Roaming Mobile Station Roaming

Number(MSRN)Number(MSRN)

IMEIIs Checked against White List

IMEIIs Checked against Black/Grey List

If NOT found, checked against Grey/Black List

Equipment Identity Register – Equipment Identity Register – EIR EIR

AuthenticationAuthentication

RANDRANDKi Ki

MSMS NetworkNetworkUm interface

Accept / reject?

Ki = authentication key

RAND = random number

SRES = Signal Response

Any QuestionAny Question

Short BreakShort Break

15 minutes15 minutes

Day1 (section 3)Day1 (section 3)

GSM ChannelsGSM Channels

GSM BurstGSM Burst

The physical channel is the medium over which the information is carriedThe logical channels consist of the information carried over the physical channel

00 1 2 3 4 5 6 7

TDMA FRAME

Timeslot

The information carried in one time slot is called a “burst”

Physical and Logical ChannelsPhysical and Logical Channels

Traffic ChannelTraffic Channel

TCHTraffic Channels

Speech

TCH/FS

TCH/HSTCH/9.6 TCH/2.4

TCH/4.8

Normal Burst

TCH Traffic ChannelTCH/FS Full rate Speech Channel TCH/HS Half rate Speech Channel TCH/9.6 Data Channel 9.6kb/sTCH/4.8 Data Channel 4.8kb/sTCH/2.4 Data Channel 2.4Kb/s

FCCHSCH

CCH Control Channels

BCCH Synch. CH.ACCH

SACCHFACCH CCCH

RACHCBCH

PCH/AGCH

Broadcast Control Channel – BCCHCommon Control Channel – CCCHDedicated Control Channel – DCCHAssociated Control Channel – ACCH

Control ChannelControl Channel

GSM MultiframeGSM MultiframeTDMA Frames

0 1 2 43 21 22 23 2524

26 – Frame Multiframe (120ms)

0 1 10

TRAFFIC CHANNELS

2 3 4 5 6 7 2 3 5 764

TDMA Frames

0 1 2 43 46 47 48 5049

51 – Frame Multiframes (235.3ms)

0 1 10

CONTROL CHANNELS

2 3 4 5 6 7 2 3 5 764

GSM MultiframeGSM Multiframe

Timeslots and TDMA FramesTimeslots and TDMA Frames

Higher Capacity Cell

Broadcast TrafficDedicated

Traffic00 1 2 3 4 5 6 7

00 1 2 3 4 5 6 7

Low Capacity Cell

Combined Traffic00 1 2 3 4 5 6 7

GSM BurstGSM BurstThe timeslots are termed burst periods The timeslots are termed burst periods because the GSM transmitter must transmit because the GSM transmitter must transmit its data in a short “burst” within the time slotits data in a short “burst” within the time slot

Random Access burst (RACH): Used in MS Random Access burst (RACH): Used in MS initial accessinitial accessFrequency correction burst (FCH): Used in Frequency correction burst (FCH): Used in frequency synchronization between MS and frequency synchronization between MS and BTSBTS

• Synchronous burst (SCH): Used in timing Synchronous burst (SCH): Used in timing synchronization between MS and BTSsynchronization between MS and BTS

BURST Frame FormatBURST Frame Format

8bit 41 synchronous bits

36 encrypted bits 3bit 68.25bit

Tail bit Tail bit Guard intervalData

• Random Access burst (RACH): Used in MS initial access

Guard interval

3bit 142bit 3bit 8.25bit

Tail bit Tail bitData

• Frequency correction burst (FCH): Used in frequency synchronization between MS and BTS

3bit 39 encrypted bits

39 encrypted bits

3bit 8.25bit

Tail bit Tail bit Guard intervalDataData

64 synchronous bits

• Synchronous burst (SCH): Used in timing synchronization between MS and BTS

Burst Mapping on physical Burst Mapping on physical channelchannel

Burst (148 bits)Burst (148 bits)Guard

Interval

(8.25 bits)

Interval

(8.25 bits)

TDMA frame = 4.615 ms

f s7 0

577µs (156.25 bits)

Any QuestionAny Question

Day 1 (Section 4)Day 1 (Section 4)

GSM ModulationGSM Modulation

Battery Life Battery Life

IMSIIMSI

TMSITMSI

IMEIIMEI

Modulation TechniquesModulation Techniques

Amplitude Modulation (AM)

Frequency Modulation (FM)

Phase Modulation (PM)

Phase modulation can be implemented easily

for digital signals, this is the method which is

Used for the GSM air interfaces. Phase

Modulation is known as Phase Shift Keying when

applied to Digital signals.

Gaussian Minimum Shift Keying (GMSKGaussian Minimum Shift Keying (GMSK))

1 0 0 1 1

Gaussian Digital Filter

GMSK Modulator

Gaussian Minimum Shift Keying

(GMSK)

Battery LifeBattery Life

Power Power ControlControl

Voice Activity Detection – VAD

Discontinuous Transmission – DTX

Discontinuous Reception – DRX

MCC ： Mobile Country Code ， It consists of 3 digits . For example: The MCC of China is "460"。MNC ： Mobile Network Code ， It consists of 2 digits . For example: The MNC of China Telecom is "00"。MSIN ： Mobile Subscriber Identification Number. H1H2H3 S ABCDEF For example: 666-9777001NMSI ： National Mobile Subscriber Identification ， MNC and MSIN form it

together. For Example of IMSI : 460-00-666-9777001

MCC ： Mobile Country Code ， It consists of 3 digits . For example: The MCC of China is "460"。MNC ： Mobile Network Code ， It consists of 2 digits . For example: The MNC of China Telecom is "00"。MSIN ： Mobile Subscriber Identification Number. H1H2H3 S ABCDEF For example: 666-9777001NMSI ： National Mobile Subscriber Identification ， MNC and MSIN form it

together. For Example of IMSI : 460-00-666-9777001

Not more than 15 digits

3 digits 2 digits

MCC MNC MSIN

IMSI IMSI

The TMSI is assigned only after successful The TMSI is assigned only after successful subscriber authentication. subscriber authentication.

The VLR controls the allocation of new TMSI The VLR controls the allocation of new TMSI numbers and notifies them to the HLR.numbers and notifies them to the HLR.

TMSI is used to ensure that the identity of the TMSI is used to ensure that the identity of the mobile subscriber on the air interface is kept mobile subscriber on the air interface is kept secret.secret.

The TMSI consists of 4 bytes( 8 HEX numbers) The TMSI consists of 4 bytes( 8 HEX numbers) and determined by the telecom operator.and determined by the telecom operator.

The TMSI is assigned only after successful The TMSI is assigned only after successful subscriber authentication. subscriber authentication.

The VLR controls the allocation of new TMSI The VLR controls the allocation of new TMSI numbers and notifies them to the HLR.numbers and notifies them to the HLR.

TMSI is used to ensure that the identity of the TMSI is used to ensure that the identity of the mobile subscriber on the air interface is kept mobile subscriber on the air interface is kept secret.secret.

The TMSI consists of 4 bytes( 8 HEX numbers) The TMSI consists of 4 bytes( 8 HEX numbers) and determined by the telecom operator.and determined by the telecom operator.

TMSITMSI

TMSI: Temporary Mobile Subscriber Identification)

IMEI (15 digits)IMEI (15 digits)

TAC FAC SNR SP

TAC ： Type approval code. It is administered by the type approval center.

FAC ： Final assembly code.It is administered by the manufacturer.

SNR ： Serial number.It is issued by the manufacturer of the MS.SP ： Not used.

TAC ： Type approval code. It is administered by the type approval center.

FAC ： Final assembly code.It is administered by the manufacturer.

SNR ： Serial number.It is issued by the manufacturer of the MS.SP ： Not used.

IMEI: International Mobile Station Equipment Identification

THANKSTHANKS

END OF THE DAYEND OF THE DAY

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