Download pdf - GSM DETAILS

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Global System for Mobiles

GSM

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TOPICS

• GSM CONCEPTS• GSM SYSTEM ARCHITECTURE• IDENTITIES USED IN GSM• GSM CHANNELS• GSM RADIO LINK• MOBILITY MANAGEMENT• CALL MANAGEMENT• RADIO RESOURCE MANAGEMENT

3

TOPICS


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Telecom Basics

• Communication– Voice and Data– Analog and Digital– Circuit Switched and Packet Switched– Media - Copper Wire, Co-axial cable, Air, Optical

Fibre– Networks -PSTN, ISDN, PDN and Mobile

Networks

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Background to GSM

• 1G : Advanced Mobile Phone Service (AMPS)• Analog, Circuit Switched, FDMA, FDD

• 2G : Digital Advanced Mobile Phone Service (D-AMPS)• Digital, Circuit Switched, FDMA, FDD

• 2G : Global System for Mobile (GSM)• Digital, Circuit Switched, FDMA and TDMA, FDD

• 2G : Code Division Multiple Access (CDMA)• Digital, Circuit Switched, FDMA, SS, FDD

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GSM History

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1982: Groupe Spécial Mobile (GSM) created

1984: Description of GSM features

1985: List of recommendations settled

1987: Initial MoU (Memorandum of Understanding) aside the drafting of technical specifications was signed by network operators of 13 countries:

1988: Validation and trials, of the radio interface.

1991: First system trials are demonstrated at the Telecom 91 exhibition.

1992: Official commercial launch of GSM service in Europe. First Launch in Finland

1993: The GSM-MoU has 62 signatories in 39 countries worldwide.

1995: Specifications of GSM phase 2 are frozen.

1999: GSM MoU joins 3GPP (UMTS)GPRS Trials begins

2000: 480M GSM subscribers WorldwideFirst GPRS Networks roll out

End 2002: 792M GSM subscribers Worldwide

Development of the GSM Standard

12 SERIESOPERATION ANDMAINTENANCE

01 SERIESGENERAL 02 SERIES

SERVICE ASPECTS

03 SERIESNETWORK ASPECTS

04 SERIESMS-BSS INTERFACE AND

PROTOCOLS

05 SERIESPHYSICAL LAYER ON THE

RADIO PATH.

06 SERIESSPEECH CODINGSPECIFICATIONS

07 SERIESTERMINAL ADAPTERS

FOR MOBILE STATIONS

11 SERIESEQUIPMENT AND TYPE

APPROVAL SPECIFICATIONS

10 SERIESSERVICE INTERWORKING

09 SERIESNETWORK

INTERWORKING

08 SERIESBSS TO MSC INTERFACES

GSM Specifications

Increasing GSM Data Rates

Transmission Time

GPRS = General Packet Radio ServiceHSCSD = High Speed Circuit Switched DataEDGE = Enhanced Data rate for GSM EvolutionUMTS = Universal Mobile Telecommunication System

10 sec 1 min 10 min 1 hour0

UMTS

E/GPRS

ISDN

PSTN

GSM

webe-mail photo

web photoe-mail

web photo

videoclipreportphoto

web photoe-mail

videoclipreport

videoclipreport

videoclipreport

videoclipreport

10

thro

ughp

ut k

bps

10 k

100 k64 k

1 M

2 M

1 k1998 1999 2000 2001 2002

Time frame

UMTSUMTS

GPRSGPRS

HSCSDHSCSD

9.69.614.414.4

packet

GPRS = General Packet Radio ServiceHSCSD = High Speed Circuit Switched DataEDGE = Enhanced Data rate for GSM EvolutionUMTS = Universal Mobile Telecommunication System

EDGEcircuit

Wireless Data Technology Options

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Circuit mode

Packet mode

A→FD→H

C→G

C→G

C→G

C→G

C→G

D→H

D→H

A→FD→H

D→H

A→F

A→F

A→F

A

B

C

D

E

F

G

H

Circuit-Switched or Packet-Switched

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Multiple Access Technique

• Multiple Access – Achieved by dividing the available radio frequency spectrum, so that multiple users can be given access at the same time.

• FDMA - Frequency Division Multiple Access– ( eg: GSM each Frequency channel is 200KHz)

• TDMA - Time Division Multiple Access– ( eg: GSM each frequency channel is divided into

8 timeslots)• CDMA - Code Division Multiple Access

– (eg: IS95- Each User data is coded with a unique code)

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Duplex Technique

• Duplex - How the up link and Down link of a user is separated

• FDD - Frequency Division Duplex– (eg:In GSM the up link and down link of a user is

separated by 45MHz )• TDD - Time Division Duplex

– (the up link and down link of a user will be at the same frequency but at different Time )

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CellularNetworking technology that breaks geographic area into cells shaped like honey comb

Cellis the radio coverage area of one base transceiver station

1

234

56

76

72

1

5

GSM Concepts -Cellular Structure

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What are the types in GSM Network?

• GSM-900 (Channels 125 operating band 900Mhz carrier spacing 200khz spacing 45Mhz)

• GSM -1800 (Channels 374 spacing 95Mhz)

• GSM -1900(Used in USA)

GSM Band Allocations (MHz)

Carrier frequency = ARFCN = Absolute Radio Frequency Channel Number

Frequencies are in MHz

374299

9580

2x75 2x60

1805-1880 1930-1990

1710-1785 1850-1910

GSM 1800GSM 1900

12417440

454541

2x25 2x35 2x04

935-960 925-960 921-925

890-915 880-915 876-880

GSM 900E-GSM (900)R-GSM (900)

3535124

101045

2x7.22x7.22x25

460.4-467.6488.8-496869-894

450.4-457.6 478.8-486 824-849

GSM 450GSM 480GSM 850

Duplexchannels

DuplexSpacing

BandDownlinkUplinkGSM systems

GSM Family Radio Band Spectrum

Uplink

Downlink

880 890 915 1710 1785

925 935 960 1805 1880MHz

P-GSM

GSM 1800 GSM 1900

1850 1910

1930 1990

R-GSM

876

921

960960

915915

E-GSM

Uplink

Downlink

824 849

869 894 MHz

GSM 850

478.8 486

488.8 496

450.4 457.6

460.4 467.6

GSM 450 GSM 480

Traffic/Signaling

Signaling

«bla bla bla...»

« RING ! »

riiiiing

Network

Traffic

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AuC

MS

MS

BTS

BTS

BTS

BSC

BSC

MSC

MSC

VLR

VLR

GMSC

HLR

PSTN

EIR

Um

Abis

AbisA

A

OMC Server

Um

GSM - Network Structure

B

E

E

X.25

C

F

H

X.25

20

Frequency band Uplink 890 - 915 MHzDownlink 935 - 960MHz

Duplex Frequency Spacing 45MHzCarrier separation 200KHzFrequency Channels 124Time Slots /Frame(Full Rate) 8Voice Coder Bit Rate 13KbpsModulation GMSKAir transmission rate 270.833333 KbpsAccess method FDMA/TDMASpeech Coder RPE-LTP-LPC

GSM System specifications

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890 MHz 915 MHz 935 MHz 960 MHz

Uplink Downlink

Example:Channel 48

0 124channel # 0 124channel #

Frequency Frequency

Duplex spacing = 45 MHzFrequency band spectrum = 2 x 25 MHzChannel spacing = 200 kHz

BTS

Paired Radio Channels in GSMCase of GSM 900

GSM Time Division Multiplex Frame and Physical Channels

TS TS TS TS TS TS TS TS

0 1 2 3 4 5 6 7

Time4.615 ms

TDMA frame

Physical channel # 2 = recurrence of time-slot # 2

TDMA frame

0 9.23 ms

Time-slot

(frames repeat continuously)

TS TS TS TS TS TS TS TS

0 1 2 3 4 5 6 7

Physical Channel

MS3

////ARFCN1 2 124FDMA

BTSWithout FH

0

TDMAs

TS7

n

n-1

n+1

MS2

MS1

timeBTSWith FH

Radio Link Aspects• From Speech to RF Signal

Blah… Blah… Blah...Blah... Blah... Blah...

Digitizing andSource Coding

Channel Coding

Interleaving

Ciphering

Burst Formatting

Modulating Demodulating

Burst De-formatting

Deciphering

De-interleaving

Channel Decoding

Source Decoding

Functions of the Radio Interface

BTS-1 BTS-2

BTS

• Speech and user's data• Signaling

Communication modeIdle mode

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Uplink 890 MHz to 915 MHzDown Link 935 MHz to 960 MHz25 MHz divided into 125 channels of 200 KHz bandwidth

890.0 890.2 890.4 914.8 915.0

935.0 935.2 935.4 959.8 960.0

UP

DOWN

Access Techniques

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Time Division Multiple AccessEach carrier frequency subdivided in time domain into 8 time slots Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs.8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs

0 1 2 3 4 5 6 7

4.616 ms

0.577 ms

Access Techniques ...

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GSM utilizes two bands of 25 MHz. 890-915 MHz band is used for uplink while the 935-960 MHz is used for downlink.

The frequency bands are divided into 200 KHz wide channels called ARFCNs (Absolute Radio Frequency Channel Numbers) i.e. there are 125 ARFCNs out of which only 124 are used.

Each ARFCN supports 8 users with each user transmitting / receiving on a particular time slot (TS).

Fundamentals

1

2

……

…….

123

124

1

2

……

…….

123

124

7654321 0

76543210

Data burst = 156.25 bit periods = 576.9μs

960 MHz

959.8MHz

200KHz

935 MHz

935.2 Mhz

915 MHz

200KHz

45 MHz

Downlink (TDMA frame) = 8 TS

Uplink (TDMA frame)

Delay

TS: Time slot

914.8 MHz

890.2 MHz

890 MHz

DOWNLINK

UPLINK

Therefore Therefore 1 TDMA1 TDMA frame = 156.25 x 8 = 1250 bits frame = 156.25 x 8 = 1250 bits and has a duration of 576.92and has a duration of 576.92μμs x 8 = 4.615 mss x 8 = 4.615 msThe technology

GSM Delays Uplink TDMA Frames

Downlink TDMA

T T T T T T T T

R TMS1

R TMS2

Downlink

Uplink

Fixed transmitdelay of three

time-slots

R R R R R R R R

0 1 2 3 4 5 6 7

The start of the uplink TDMAis delayed of three time-slots

BTS side

MSs side

BTS

TDMA Frame (4.615 ms)

Timing Advance1 - Propagation Delay

M2 M1d1>>d2d2

BTS Frame reference

MSs transmit

Propagation Delay τp

TS0 TS1 TS2 TS3 TS4 TS6TS5 TS7

Bits Overlapping

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TX BTS CAN WHAT GSM HOW WHEN WHATRX BTS yes the ms-isdn

RX MS1 CANTX MS1 yes

RX MS2 WHATTX MS2 the

RX MS3 GSMTX MS3 ms-isdn

RX MS4 HOWTX MS4

RX MS5 WHENTX MS5

RX MS6 WHATTX MS6

RX MS7TX MS7

RX MS8TX MS8

Propagation Delay

DD

+3TS

TA

Timing Advance2 - Without Timing Advance: Collision

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CAN WHAT HOW WHEN WHAT

CAN

WHAT

HOW

WHEN

WHAT

TX BTSRX BTS

RX MS1TX MS1

RX MS2TX MS2

RX MS3TX MS3

RX MS4TX MS4

RX MS5TX MS5

RX MS6TX MS6

RX MS7TX MS7

RX MS8TX MS8

yes

the

Propagation Delay

DD

+3TS - TA

yes the

Timing Advance = 2 * Propagation Delay

GSMms-isdn

ms-isdnGSM

Timing Advance3 - With Timing Advance: No Collision

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GSM in comparison with other Standards• GSM gives mobility without any loss in Audio quality • Encryption techniques used gives high security in the

air Interface and also use of SIM.• Bit Interleaving for high efficiency in Transmission.• Variable Power (Power budgeting- extend battery life)• Minimum Interference.• Features-CCS7 Signaling

– SMS (Short Message Services)– Emergency Calls– CELL Broadcast

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TOPICS


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AuC

MS

MS

BTS

BTS

BTS

BSC

BSC

MSC

MSC

VLR

VLR

GMSC

HLR

PSTN

EIR

Um

Abis

AbisA

A

OMC Server

Um

GSM - Network Structure

B

E

E

X.25

C

F

H

X.25

37

GSM Network

OMC

AUC

HLR

MSC

EIRVLR

BSC

BTS

MS

ExternalPSTN &PDN N/W

SS

BSS

SwitchingSystem

Base StationSystem

MS Mobile Station

BTS Base transceiver System

BSC Base Station Controller

MSC Mobile Switching Center

HLR Home Location Register

VLR Visitor Location Register

EIR Equipment Identity Register

AUC Authentication Center

OMC Operation And Maintenance Center

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GSM Architecture

HLR

VLR

EIR

AUC

MSC

BSC

BSC

SMSC

PSTN

VMSC

MobileStation

GSM Air interface

OMCR

TRAU

Base Station System

Network and switching subsystem

A interface SS7 / speech

SS7X.25

BTSBTS

BTS

BTS

BTSBTS

Abisinterface

Ainterface

OMCS

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Mobile Equipment(ME)

• Frequency and Time Synchronization• Voice encoding and transmission• Voice encryption/decryption functions• Power measurements of adjacent cells• Display of short messages• International Mobile Equipment Identifier (IMEI)

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SIM• Portable Smart Card with memory (ROM-6KB to

16KB-A3/A8 algorithm, RAM- 128KB TO 256KB, EEPROM- 3KB to 8KB )

• Static Information– International Mobile Subscriber Identity(IMSI)– Personal Identification Number (PIN)– Authentication Key (Ki)

• Dynamic Information– Temporary Mobile Subscriber Identity(TMSI)– Location Area Identity (LAI)– Phone memories, billing information– Ability to store Short Messages received

SIM-Card and GSM Mobile Equipment

G S M

Global GSM MobilityCardThe Smart Card to use +

SIM-Card

Contains:- IMSI

=

The SIM-Card Functions

Microchip with storeduser information

Credit Card Size

Permanent data:- Unique mobile subscriber identitythrough IMSI number and PIMSI for Packet Mode

- Authentication parameter Ki,- Authentication algorithm A3,- Generating encryption key Kcalgorithm A8,

- PIN code.

Removable data:- Temporary Mobile Subscriber Number,- Location Area Identification - Routing Area Identification (Packet mode)

µ SIM-Card

G S M

Global GSM MobilityCardThe Smart Card to use

25 mm

15 mm

Subscriber Identification

NatureInternational Mobile Subscriber Identity

Conformity with E212

Mobile Station -Integrated Services Digital Network Nb

Similar to ISDN, Conformity with E164/E213

Nb. digits 3 2 max 10 1 to 3 2 to 4 total max 15

*This code does not identify a geographical areabut an operator

MS - ISDN

Format MCC MNC MSINH1 H2 x x x ......... x x x CC NDC SN

M1 M2 x x x x x x x x

MeaningMobile

CountryCode

MobileNetwork

Code

Mobile SubscriberIdent. Nb

H1 H2 = Identity of HLR within the home PLMN

CountryCode

(where subscription

has been made)

NationalDestination

Code *

Mobile Subscriber(national definition)

M1 M2 = nbr of logical HLR

IMSI

National Significant Mobile NumberIdentify a PLMNworldwide

Identify the subscriberof a PLMN

Description Stored in SIM Card

MobileCountryCode

3 digits

MobileNetworkCode

2 digits

Mobile Subscriber Identification Number (MSIN)

H1 H2 X X X X X X10 digits max

Location Area CodeLAC

Temporary MobileSubscriber Identity

4 octets

G S M

Global GSM MobilityCardThe Smart Card to useMCC

= 208 (France)

234 (G-B)262 (Germany)404,405(India)

MNC=

71(APBSNL)72(TNBSNL)

20 (Bytel) IMSI = 15 digits max

NMSI

LAI

MobileCountryCode

3 digits

MobileNetworkCode

2 digits

Routing Area CodeRAC

RAI

45

CountryCode

3 digits max

NationalDestinationCode2 or 3 digits

Subscriber Number (SN)

Roaming Number (RN)

HO-number

Must be dialed to make a call to mobile subscriber

Is a PSTN-like number to track the MS that hands over to another MSC during call-in-state

Is a PSTN-like number used to reach a roamingMS

CC = 33 (France)091(India)001(US)

NDC = 9448(BSNL-karnataka)9845,9880(Airtel)

9886(Hutch)

= 660, 661, 618 (Bytel)

M1 M2 X X X X X X X X X X X X X10 digits max

CountryCode

NationalDestinationCode

CountryCode

NationalDestinationCode

MS-ISDN (15 digits max)

MSRN

Description Stored in the Network

Descriptor Embodied in the Mobile Equipment

Type ApprovalCode

TAC FAC SNR SP

Final AssemblyCode

Serial NumbeR (SPare)

TYPE

APPROVED

IMEI enables the operator to check the Mobile Equipment Identityat call setup and make sure that no stolen or unauthorized MS is used in the GSM network

International Mobile Equipment Identity (IMEI)

Type ApprovalCode

TAC FAC SNR SP

Final AssemblyCode

Serial number (SPare)

TYPE

APPROVED

IMEI: * # 0 6 #351475 60 926514 4

MS Classmark

Revision level

RF power

Encryption algorithm

Frequency

Short message

LoCation Services

MS Positioning Method

8-PSK modulation

Multi-slot class

Multi-band

ClassmarkPower classes

Class GSM400/850/900

12345

8 W*5 W2 W**

0.8 W

GSM1800

GSM1900

1 W**0.25 W

4 W

1 W**0.25 W

2 W

* Typical value for car mounted** Typical value for handheld

Class GSM400/850/900

GSM1800

GSM1900

E1E2E3

2 W0.5 W0.2 W

1 W0.4 W

0.16 W

1 W0.4 W

0.16 W

For GMSK modulation

For 8-PSK modulation

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Base Transceiver Station (BTS)• Handles the radio interface to the mobile station.• Consists of one or more radio terminals for

transmission and reception• Each Radio terminal represents an RF Channel• TRX and MS communicates over Um interface• Received data transcoding• Voice encryption/decryption• Signal processing functions of the radio interface• Uplink Radio channel power measurements

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Base Station Controller (BSC)• Provides all the control functions and physical links

between the MSC and BTS • External Interfaces

– ‘Abis’ interface towards the BTS– ‘A’ interface towards the MSC

• Monitors and controls several BTSs• Management of channels on the radio interface• Alarm Handling from the external interfaces• Performs inter-cell Handover• Switching from ‘Abis’ link to the ‘A’ link• Interface to OMC for BSS Management

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Mobile Switching Center (MSC)

• Performs call switching • Interface of the cellular network to PSTN• Routes calls between PLMN and PSTN• Queries HLR when calls come from PSTN to mobile

user• Inter-BSC Handover• Paging• Billing

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Home Location Register (HLR)• Stores user data of all Subscribers related to the

GMSC– International Mobile Subscriber Identity(IMSI)– Users telephone number (MS ISDN)– Subscription information and services– VLR address– Reference to Authentication center for key (Ki)

• Referred when call comes from public land network

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Visitor Location Register (VLR)

• Database that contains Subscriber parameters and location information for all mobile subscribers currently located in the geographical area controlled by that VLR

• Identity of Mobile Subscriber• Copy of subscriber data from HLR• Generates and allocates a Temporary

Mobile Subscriber Identity(TMSI)• Location Area Code• Provides necessary data when mobile

originates call

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Authentication Center (AuC)

• Stores Subscriber authentication data called Ki, a copy of which is also stored in in the SIM card

• Generates security related parameters to authorize a subscriber (SRES-Signed RESponse)

• Generates unique data pattern called Cipher key (Kc) for user data encryption

• Provides triplets - RAND, SRES & Kc, to the HLR on request.

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EIR (Equipment Identity Register)

• EIR is a database that contains a list of all valid mobile station equipment within the network,

where each mobile station is identified by its International Mobile Equipment Identity(IMEI).

• EIR has three databases.,– White list - For all known,good IMEI’s– Black list - For all bad or stolen handsets– Grey list - For handsets/IMEI’s that are

on observation

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Location Area Identity• LAI identifies a location area which is a group of

cells..• It is transmitted in the BCCH. • When the MS moves into another LA (detected by

monitoring LAI transmitted on the BCCH) it must perform a LU.

• LAI = MCC + MNC + LAC – MCC= Mobile Country Code(3 digits), identifies the country– MNC= Mobile Network Code(1-2 digits), identifies the GSM-

PLMN– LAC= Location Area Code, identifies a location area within a

GSM PLMN network. The maximum length of LAC is 16 bits,enabling 65536 different location areas to be defined in one GSM PLMN.

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Interfaces and Protocols

Um

Abis A

CB

E

D

F

Digital Networks

POTS

TUP

ISUP

MAP

MAPMAP

BSSAPLAPD

LAPDm

G

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GSM Entities and Signaling Architecture

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GSM Protocols• CM - Connection Management• MM - Mobility Management• RR - Radio resource • LAPDm - LAPD for mobile• LAPD - Link Access Procedure for D channel• BTSM - BTS Management Part• BSSAP - BSS Application Part (BSC - MSC)• DTAP - Direct Transfer Application Part (MS - MSC)• MAP - Mobile Application Part• MTP - Message Transfer part of SS7• SCCP - Signalling Connection Control Part of SS7• TCAP - Transaction Capabilities Application Part• ISUP - ISDN User Part

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Functional Plane of GSM

MS BTS BSC MSC/ HLR GMSCVLR

MS BTS BSC MSC/VLR HLR GMSC

CC

MM

RR

Trans

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TOPICS• GSM CONCEPTS• GSM SYSTEM ARCHITECTURE• IDENTIFIERS USED IN GSM• GSM CHANNELS• GSM RADIO LINK• MOBILITY MANAGEMENT• CALL MANAGEMENT• RADIO RESOURCE MANAGEMENT

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TOPICS• GSM CONCEPTS• GSM SYSTEM ARCHITECTURE• IDENTITIES USED IN GSM• GSM CHANNELS• GSM RADIO LINK• MOBILITY MANAGEMENT• CALL MANAGEMENT• RADIO RESOURCE MANAGEMENT

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Channels : differentiating between Physical and Logical channelsPhysical channels : The combination of an ARFCN and a time slot defines a physical channel.

Logical channels : These are channels specified by GSM which are mapped on physical channels.

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Physical channel:One timeslot of a TDMA-frame on one carrieris referred to as a physical channel.There are 8 physical channels per carrier inGSM,channel 0-7(timeslot 0-7)

Logical channel:A great variety of information must be transmitted between BTS and the MS,for e.g.user data and control signaling.Dependingon the kind of information transmitted we refer to different logical channels.These logicalchannels are mapped on physical channel.

Channel concept

65

Logical Channels on Air interfaceLOGICAL

CHANNELS

COMMONCHANNELS

DEDICATED CHANNELS

BROADCAST CHANNELS

COMMONCONTROLCHANNELS

DEDICATED CONTROL CHANNELS

TRAFFIC CHANNELS

FCCH BCCHSCH SDCCH SACCH FACCH

PCH AGCHRACH TCH/F TCH/EFRTCH/H

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FCCH

Logical channelsLogical channels

Control channels Traffic channels

BCH CCCH DCCHHalfrate

Fullrate

SCH BCCH PCH AGCH RACH SDCCH SACCHFACCHCBCH

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Broadcast channels BCH • Broadcast Channel-BCH

– Alloted one ARFCN & is ON all the time in every cell. Present in TS0 and other 7 TS used by TCH.

• Frequency correction channel-FCCH – To make sure this is the BCCH carrier.– Allow the MS to synchronize to the frequency.– Carries a 142 bit zero sequence and repeats once in every

10 frames on the BCH.

• Synchronization Channel-SCH– This is used by the MS to synchronize to the TDMA frame

structure within the particular cell.– Listening to the SCH the MS receives the TDMA frame

number and also the BSIC ( in the coded part- 39 bits).– Repeats once in every 10 frames.

68

Broadcast channels BCH ...• BCCH

– The last information the MS must receive in order to receive calls or make calls is some information concerning the cell. This is BCCH.

– This include the information of Max power allowed in the cell.– List of channels in use in the cell.– BCCH carriers for the neighboring cells,Location Area

Identity etc.– BCCH occupies 4 frames (normal bursts) on BCH and

repeats once every Multiframe.– This is transmitted Downlink point to multipoint.

• Cell Broadcast Channel - CBCH– Used for the Transmission of generally accessible

information like Short Message Services(SMS)

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Common Control Channels CCCH• CCCH-

– Shares TS-0 with BCH on a Multiframe.

• Random access channel-RACH:– Used by Mobile Station for requesting for a channel. When

the mobile realizes it is paged it answers by requesting a signaling channel (SDCCH) on RACH. RACH is also used by the MS if it wants to originate a call.

– Initially MS doesn’t know the path delay (timing advance), hence uses a short burst (with a large guard period = 68.25 bits).

– MS sends normal burst only after getting the timing advance info on the SACCH.

– It is transmitted in Uplink point to point.

70

Common Control Channels CCCH ..• Access Grant Channel-AGCH

– On request for a signaling channel by MS the network assigns a signaling channel(SDCCH) through AGCH. AGCH is transmitted on the downlink point to point.

• Paging Channel-PCH– The information on this channel is a paging message

including the MS’s identity(IMSI/TMSI).This is transmitted on Downlink, point-to-multipoint.

71

Dedicated Control Channels-DCCH• Stand alone dedicated control channel(SDCCH)• AGCH assigns SDCCH as signaling channel on

request by MS.The MS is informed about which frequency(ARFCN) & timeslot to use for traffic.

• Used for location update, subscriber authentication, ciphering information, equipment validation and assignment of TCH.

• This is used both sides, up and Downlink point-point.

72

Dedicated Control Channels-DCCH• Slow associated control channel-SACCH

– Transmission of radio link signal measurement, power control etc.

– Average signal strengths(RXLev) and quality of service (RXQual) of the serving base station and of the neighboring cells is sent on SACCH (on uplink).

– Mobile receives information like what TX power it has to transmit and the timing advance. It is associated with TCH or SDCCH

• Fast associated control channel-FACCH– Used for Hand over commands and during call setup and

release. FACCH data is sent over TCH with stealing flag set

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Traffic Channels-TCH

• TCH carries the voice data.• Two blocks of 57 bits contain voice data in the normal

burst.• One TCH is allocated for every active call.• Full rate traffic channel occupies one physical

channel(one TS on a carrier) and carries voice data at 13kbps

• Two half rate (6.5kbps) TCHs can share one physical channel.

74

GSM Channels

Control ChannelsTraffic Channels(TCHs)

Fullrate

Halfrate

Dedicated ControlChannels(DCCHs)

SlowFastDownlink

BroadcastChannels(BCHs)

Common ControlChannels(CCCHs)

Downlink Uplink

TCH /F TCH /H FCCH SCH BCCH PCH CBCH RACHAGCH SDCCH SACCHFACCH

Traffic Multiframing Signaling Multiframing Traffic Multiframing

(down uplink)

GSM Channels

75FACCH

BTS

0 1 2 3 4 5 6 7TS

MS

FCCH

SCH

BCCH

PCH

AGCH

CBCH

SDCCH

SACCH

TCH

TCH

FACCH

SDCCHSACCH

FCCH

SCH

BCCH

RACH

PCH

AGCH

RACH

CBCH

Synchronization

Frequency correction

Broadcast control

Access request

Subscriber paging

Answer to Access request

Broadcast info

Dedicated Signaling

Sys InFo 5, 6 + SMS

Traffic (speech data)

Associated Signaling

Associated Signaling

Traffic (speech-data)

Radio Measurement + SMS

Dedicated Signaling

Broadcast info

M.S. Pre-synchronization

Access request

Subscriber paging

Answer to Access request

The Logical Channels on Radio Interface

76

FACCH MESSAGES• Connection establishment from

SDCCH to TCH

• End validation of a SDCCH-TCH commutation

• Characteristics of the future used BS after handover

• Connection establishment to BS after handover

• Validation of an handover

SACCH MESSAGESMeasures:

- power level of the communication

- quality level of the communication

- level on the beacon frequency of the neighboring cells

• Timing Advance

• Power Control

• SMS

TCH MESSAGES

• Speech

• Data

• Handover Access message (uplink)

SDCCH MESSAGES• Request for a SDCCH assignment

• Request for the end of channel assignment

• Order of commutation from SDCCH to TCH

• SMS

Logical Channel Description (1/2)

77

FCCH MESSAGES

• no message is sent (all bits 0)

BCCH MESSAGES

• System Information type 1, 2, 2bis,2ter, 3, 4, 7, 8

(idle mode)

SCH MESSAGES• Frame Number

• Base Station Identity Code (BSIC)

AGCH MESSAGES• For dedicated channel assignment:

-frequency number-slot number-frequency hopping description-Timing Advance (1st estimation)-MS identification

PCH MESSAGES

• messages containing a mobileidentity for a call, a short messageor an authentication

RACH MESSAGES• Service request:

- emergency call - answer to an incoming call- outgoing call- short message- call re-establishment- inscription

CBCH MESSAGES• Specific information

(weather, road information

Logical Channel Description (2/2)

78

GPRS

CORE

NETWORK

BSCPCUSN

PDCH = Packet Data CHannel

PPCHPAGCHPNCH

PDTCHPACCHPTCCH

PDTCHPACCHPTCCH

PBCCH

PRACH

DL

UL

Packet Common Control

CHannels

Packet Traffic

CHannels

PBCCH

GPRS Channels

79

0 1 2 3 4 21 22 23 24 25 0 1 2 3 4 46 47 48 49 50

26 traffic frames = 120 ms

1 Hyperframe = 2,715,648 frames= 3h 28 min. 53 s 760 ms

0 1 2 3 5 2042 2043 2044 2045 2046 20474

1326 frames

0 1 2 3

46 47 48 49 500 1 3 42

22 23 2524

TS0

TS1

TS2

TS3

TS5

TS6

TS7

TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

TS4

TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

TS0

TS1

TS2

TS3

TS4

TS5

TS6

TS7

Frame4.615 ms

Control channelTraffic channel

51 x 26 traffic frames = 6.12 s

26 x 51 control frames = 6.12 s

Traffic and Control Multiframing

80

81

82

Full Rate - Downlink & Uplink

T : TCH A : SACCH : IDLETi: TCHsub-channel no. i

Ai: SACCHsub-channel no. i

time

26 frames = 120 ms

T0 A0T0 T0 T0 T0 T0 T0 T0 T0 T0 T0 T0T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 T1 A1 time

Half Rate - Downlink & Uplink

T AT T T T T T T T T T TT T T T T T T T T T T T

T

26 frames = 120 ms

Logical Channel Mapping1 - Traffic Channel Combination

83

A : SACCH D : SDCCH : IDLE

51 frames = 235 ms

A1 A2 A3A0D7D6D5D4D3D2D1D0

A5 A6 A7A4D7D6D5D4D3D2D1D0

time

Downlink

51 frames = 235 ms

A5 A6 A7 A0

A4

D7D6D5D4D3D2D1D0

D7D6D5D4D3D2D1D0A1 A2 A3

time

Uplink

AAAA

Logical Channel Mapping2 - Dedicated Signaling Channel Combination

84

51 frames = 235.38 ms Downlink

time

51 frames = 235.38 ms

RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR RRRRRRRRRRRRRRRRRR

Uplink

timeB : BCCHS : SCHF : FCCH : IDLE

: PCH /AGCHC R : RACH

BTS MSPhysical Channel

ARFCN (n) TS (s)

FCCHSCH BCCH

PCH/AGCH

Frames repeat continuously

Multiframem+1

Multiframem-1

Multiframe m

C CF SC CFSC CFSC CCBFS FS BFSC

Logical Channel Mapping3 - Common Channel Combination

85

A3A2

A1D3D2

D3D2

D1

D1

D0

D0 FSFSFSC CC FSBFS

FSFSFSC CC FSBFS

51 frames = 235 ms

A0

time

Downlink

R R

R R D2

D2

D1

D1

D0

D0A1

A3

A0

A2R

R

R

R

D3

D3

51 frames = 235 ms

time

Uplink

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

A : SACCH D : SDCCH : IDLEB : BCCHS : SCHF : FCCH : AGCH/PCHC R : RACH

Logical Channel Mapping4 - Common Channel Combination

86

87

Downlink message

Uplink message

Neighboring BTS(downlink)

Measurement Windows

C CF SC CF SC CF SC CCBF S F S F S

0 1 12 25 0 1 12 25

0 1 10 20 30 40 50 0 1

T AT T T T T T T T T T TT T T T T T T T T T T T T AT T T T T T T T T T TT T T T T T T T T T T T

Mobile activity

Rx Rx Tx Rx Rx Tx Rx Rx Tx(n) (n) (n)

Why 26 and 51 Frames per Multiframe?

88


89

Speech

Sourcedecoding

Channeldecoding

De-interleaving

Burst deformatting

Deciphering

Demodulationequalization

Digitizing andsource coding

Channelcoding

Modulation

Ciphering

Burst formatting

Interleaving

Step 1

Step 2

Step 3

Step 4

Transmission

Step 5

Step 6 Diversity

From Speech to Radio Transmission

90

GSM Radio Link

• Speech Coding -Done at Transcoder of BSC and MS– The Linear Predictive Coder uses RPE-LTP(Regular Pulse

Excitation- Long Term Prediction)– Converts 64kbps voice to 13kbps(260 bits every 20ms)

• Channel Coding - Done at BTS and MS– Uses Convolution Coding and CRC (Cyclic Redundancy

Check)– Converts 13 kbps to 22.8 kbps (456 bits per 20ms)

91

GSM Radio Link

• Bit Interleaving - Done at BTS and MS• Encryption - Done at BTS and MS

– EX OR data with cipher block, which is generated by applying A5 Algorithm to the Ciphering Key(Kc)

• Multiplexing - Done at BTS • Modulation - Done at BTS and MS

– GMSK(Gaussian filtered Minimum Shift Keying)– Phase change of +90 for 0 and -90 for 1

SPEECHTRANSMISSIONBETWEEN MOBILE

AND NETWORK BSSMS

SPEECH MUST BE DIGITIZED AND CODED

64 kbit/sBetter Quality Lower Rate

Why Digitizing and Coding the Speech?

93

Codec Type Mean Opinion Score Rate (kb/s)(MOS)

PCM A law 4.25 64GSM EFR 4.2 12.2CDMA 13 4.2 13D-AMPS 4 8GSM FR 3.8 13CDMA 8 3.4 8

Quality MOS Listening Effort Required

Excellent 5 Complete relaxation possible, no effort.Good 4 Attention necessary, no appreciable effort.Fair 3 Moderate effort.Poor 2 Considerable effort.Bad 1 No meaning understood with feasible effort.

Speech Quality – Source Coding

94

Speech Coding

BP A/D SPEECHENCODER

CHANNEL CODING

LP D/A SPEECHDECODER

CHANNEL DECODING

BAND PASS

300 Hz -3.4 kHZ

Every 125μ s value issampled from analog signal and quantised by 13 bit wordData rate = 13/125*10 -6

= 104 kbps

Every 20ms 160 samples takenData rate = 160 * 13/20ms

= 104 kbps

Linear Predictive Coding & Regular Pulse Excitation Analysis

1. Generates 160 filter coeff2. These blocks sorted in 4 sequence

1,5,9,…37 / 2,6,10----38/ 3,7,11…39/8,12,16…40

3. Selects the sequence with most energy

So data rate = 104/4 = 26 kbps

Long term prediction analysis1. Previous sequences stored in memory2. Find out the correlation between the present seq. And previous sequences3. Select the highest correlation sequence4. Find a value representing the differencebetween the two sequences.

Reduces data rate = 26 kbps/2 = 13 kbpsie 260 bits in 20ms

50 132 78

1A 1B 2

1A = Filter Coeffblock ampl, LTPparams

1B = RPE pointers &pulses2 = RPE pulse & filterparams

50 3 132 4

3 crc bits Four 0 bits for codec

378 coded bits

Conv coding rate = 1/2 delay = 4

78

456 bits in 20 ms = 22.8 kbps57 x 8 = 456

To modulator

95

C20 ms20 ms

A

A8

A7

A6

A5

B4

B3

B2

B1

B8

B7

B6

B5

C4

C3

C2

C1

57 bits

Information1 1

CRL CRL3 3

Tail Tail26 bits

Training

8 Bursts

8 Sub blocksof 57 bits

Source coding

Channel coding

Interleaving

Normalburst

20 ms

B

456 bitsA 456 bitsB 456 bitsC

57 bits

Information

A8B4

A7B3

A6B2

A5B1

B8C4

B7C3

B6C2

B5C1

Speech blocks

Codec dependent Codec dependentCodec dependent

Channel Processing in GSMOverview for Full Rate

96

97

C20 ms20 ms

A

A4

A3

A2

A1

B2

B1

B4

B3

C4

C3

C2

C1

4 Bursts

4 Sub blocksof 57 bits

Source coding

Channel coding

Interleaving

20 ms

B

228 bitsA 228 bitsB 228 bitsC

A4B2

A3B1

B4C2

B3C1

Speech blocks

Codec dependent Codec dependentCodec dependent

Normalburst 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Channel Processing in GSMOverview for Half Rate

98

0 1 2 3 4 5 6 7 8 ... ... 452 453 454 455

0 1 2 3 4 5 6 78 9 10 11 12 13 14 15• • • • • • • •• • • • • • • •• • • • • • • •

448 449 450 451 452 453 454 455

57 R

ows

Divide 456 bits in 8 sub-blocks

765432107654 0 1 2 3

reordering&

partitioningout

diagonalinterleaving

456coded bits

burstb0 b1 b56 b1 b56b0

bitinterleaving

Interleaving: TCH Full Rate

99

1 frame:4.615 ms

0 1 2 3 4 5 6 7

Guard

157 126 57

DATA

156.25 bits duration(0.577 ms)

Trainingsequence

33

DATA

8.25

S S GuardBand

Burst148 bits

Burst FormattingNormal Burst

100

Synchronization Burst(SCH)

Tail Data Extended Training Sequence Data Tail


3 bits 39 encrypted bits 64 synchronization bits 39 bits 3 bits 8.25 bits

Guard Period

Frequency Correction Burst(FCCH)

Tail Data Tail


3 bits 142 fixed bits (0) 3 bits 8.25 bits

Guard Period

Burst Formats

101

Access BurstTail

TrainingSequence Guard PeriodTail

156.25 bits (0.577 ms)

8 bits 36 encrypted bits 68.25 bits3 bits41 synch bits

Data

Dummy Burst

Tail Dummy Sequence Training Sequence Dummy Sequence Tail

3 bits 58 mixed bits 26 midamble bits 58 mixed bits 3 bits 8.25 bits

Guard Period

156.25 bits (0.577 ms)

156.25 bits (0.577 ms)

13 bits 57 encrypted bits 1 26 bits 57 encrypted bits 3 bits 8.25 bits

Tail Data Training Sequence Data Tail Guard Period

Normal BurstBurst Formats

102

Plain data: 0 1 1 1 0 0 1 0.....Ciphering sequence: 0 0 0 1 1 0 1 0.....XOR:Ciphered data (transmitted): 0 1 1 0 1 0 0 0.....Ciphered sequence: 0 0 0 1 1 0 1 0..... XOR: Recovered data: 0 1 1 1 0 0 1 0.....

Data S S DataBurst to betransmitted

Data S STrainingsequence DataReceived

burst

Ciphering

103

Interleaving

57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57

57 57 57 5757 57 57 57

57 57 57 5757 57 57 5757 57 57 57

57 57 57 57 57 57 57 5757 57 57 57

Encoded speech blocks - Diagonal Interleaving

Even bitsOdd bits

Tb 3

Coded Data 57

F 1

Training Sequence26

F 1

Coded Data 57

Tb 3

Gp8.25

Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3

57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57

57 57 57 5757 57 57 5757 57 57 57

57 57 57 5757 57 57 5757 57 57 57

Encoded control channel blocks - Rectangular Interleaving

Even bitsOdd bits

Bn-4 Bn-3 Bn-2 Bn-1 Bn Bn+1 Bn+2 Bn+3

104

Burst• The information format transmitted during one

timeslot in the TDMA frame is called a burst.• Different Types of Bursts

– Normal Burst– Random Access Burst– Frequency Correction Burst– Synchronization Burst

105

Normal Burst

T3

Coded Data57

S1

T. Seq.26

S1

Coded Data57

T3

GP8.25

Tail Bit(T) :Used as Guard TimeCoded Data :It is the Data part associated with the burstStealing Flag :This indicates whether the burst is carrying

Signaling data (FACCH) or user info (TCH).Training Seq. :This is a fixed bit sequence known both to

the BTS & the MS.This takes care of the signal deterioration.

156.25 bits 0.577 ms

106

T3

Training Sequence41

Coded Data36

T3

GP68.25

Random Access Burst

T3

Fixed Bit Sequence142

T3

GP8.25

T3

Coded Data39

Training Sequence64

CodedData 39

T3

GP8.25

Freq. Correc. Burst

Synchronization Burst

156.25 bits 0.577 ms

156.25 bits 0.577 ms

156.25 bits 0.577 ms

107

Transmission on the radio channels

• A timeslot has a duration of .577 m seconds (148 Bits)• 8 timeslots(8 x 0.577 = 4.62 ms) form a TDMA frame• If a mobile is assigned one TS it transmits only in this time slot• and stays idle for the other 7 with its transmitter off, called bursting• The start on the uplink is delayed from downlink by 3 TS periods• One TS = duration of 156.25 bits, and its physical contents is • called a burst

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

DownlinkBTS > MS

UplinkMS > BTS

Offset

108

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

MS1near

MS2far

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

AtBTS

0 1 2 3 4 5 6 7MS1near

0 1 2 3 4 5 6 7MS2far

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

AtBTS

Timing Advance

109

Frames Types On Um Interface• TDMA Frame

– 8 Time slots (Burst Period)– Length is 4.62 ms(8 * 0.577ms)

• 26-TDMA Multiframe– 26 TDMA Frames (24 TCH, SACCH, Idle)– 120 ms (26 * 4.62ms)

• 51-TDMA Multiframe– 26 TDMA Frames (FCCH, SCH, BCCH, SDCCH, CCCH)– 235.6 ms (51 * 4.62ms)

110

Frames Types On Um Interface• Super Frame

– 51* 26 TDMA Frames– 6.12 S

• Hyper Frame– 2048 * 51* 26 TDMA Frames– 3 Hours, 28 Minutes, 53 Secs and 760 ms

111


112

Mobility Management

• Mobility Management (MM)• Location updating- normal,periodic, IMSI attach• Paging• Security Management

– Preventing unauthorized users- authentication– Maintaining Privacy of users- ciphering

• Providing roaming facility• MM functionality mainly handled by MS, HLR,

MSC/VLR.

113

Network Attachment• Cell Identification

• MS scans complete GSM frequency band for highest power

• Tunes to highest powered frequency and looks for FCCH. Synchronizes in frequency domain

• Get training sequence from SCH which follows FCCH. Synchronizes in time domain.

• Accesses BCCH for network id, location area and frequencies of the neighboring cells.

• Stores a list of 30 BCCH channels

114

Network Attachment…..• PLMN Selection

• Get the operator information from SIM.• Cell Selection

• Selected cell should be a cell of the selected PLMN

• Signal strength should be above the threshold.• Cell should not be barred

• Location Update• Register with the network by means of location

updation procedures.

115

MS BTS BSC (G)MSC VLR HLR Action

Channel Request (RACH)Channel Assignment (AGCH)

Authentication Request (SDCCH)

Authentication Response (SDCCH)

Comparison of Authentication param

Accept LUP and allocTMSI (SDCCH)

Ack of LUP and TMSI (SDCCH)

Entry of new area and identity into VLR and HLR

Channel Release (SDCCH)

MS Location Update (registration)

Location Update Request (SDCCH)TMSI + old LAI

116

Security - AuthenticationAuthentication center provides RAND to MobileAuC generates SRES using Ki of subscriber and RANDMobile generates SRES using Ki and RANDMobile transmits SRES to BTSBTS compares received SRES with one generated by AuC

MSKi RAND

A3

SRES

RAND

SRES

SRES

Auth Result

AuCBTSMS

117

Security - Ciphering

Data sent on air interface ciphered for security A5 and A8 algorithms used to cipher dataCiphering Key is never transmitted on air

MSKi RAND

A8

Kc

MS NetworkUm interface

A5 A5

Kc Kc

Data DataCipheredData

118


119

Communication Management (CM)• Setup of calls between users on request• Routing function i.e. Choice of transmission

segments linking users• Point to Point Short message services

GSM Actors

PublicSwitched

TelephoneNetwork

BTS

BSS

BSC

Fixed subscriberMobile subscriber

AUC

HLRVLR

MSC

NSS

PLMN Selection

No

automaticmode

The MS selects the first PLMN from the preferred PLMNs list (if it is not in

the forbidden PLMNs list)

The user selects a PLMN from the

displayed PLMNs

manualmode

YesYes

Creation of a found PLMN list

Is there an up to date found PLMNs list?

End of PLMN selection

Yes No (automatic)

Cell Selection succeed?

Selection of the next preferred possible PLMN

No (manual)

Listen to all the frequencies of the GSM

spectrum:power level measurement

and average on these measurements

Select the best frequencies

according to the power level

(124 channels in GSM 900, 374 in GSM 1800and 299 in GSM 1900

(30 in GSM 900 and 40 in GSM 1800)

Memorize the beacon

frequencies in the precedent selection

=> Create the Found PLMN list

PLMN Selection• Constitution of the "Found PLMN list"

Suitable cell:

- cell of the selected PLMN- cell not barred- C1 > 0

Eligible cell

List of the frequencies of the

selected PLMN

IMSI Attach

Look for the cell with the best C1 in the suitable cells list

Eligible cell?

Yes

Selection of another PLMNNo

C1 Computation for eligible cells

Suitable cell?

YesNo

Initial Cell Selection

Rejected?

Yes

PLMN set in the forbiddenPLMN list

End of Cell Selection

No

Cell Selection

BTS-2

BTS-1

This cell

BTS-3

BTS-4BTS-5

1

1

1

12

3

45

Purpose: get synchronization with the GSM network prior establishing any communication.

FCCH

SCH

BCCH

1

Immediate AssignmentMS BSC MSC

CM SERVICE REQUESTSDCCH or TCH6

CHANNEL REQUESTRACH1

BTS

CHANNEL REQUIRED2

CHANNEL ACTIVATION3

IMMEDIATE ASSIGNMENTAGCH

5IMMEDIATE ASSIGNMENT

COMMAND5

CHANNEL ACTIVATIONACK.

4

ImmediateAssignment

LOCATION UPDAT. REQU.SDCCH or TCH6

OR

Registration: the Very First Location Update

LAI HLRIMSIVLR id

TMSI

IMSI

TMSI

Release

VLR

IMSITMSILAI

MSC

BTS

BSS

BSC

2

4

5

2

6

1

24

5

6

3

4TMSI 5

Intra – VLR Location Update

VLR

IMSITMSILAI

1

2

3

4

new TMSI

TMSI + old LAI 2

3

42

3TMSI

New TMSI

New LAI

MSC

BTS

BSS

BSC

IMSI not Required

128

New LAI

newTMSI

TMSI + old LAI

TMSI New TMSI

MSC

BSS

BTS

BSC

1

2

5

7

2

5

72

IMSI,TMSILAI

New VLR

IMSI, TMSIOld LAI

Old VLR

RAND, SRES,Kc

HLRnew

VLR id

subscriberdata

3

4

6

6

5

IMSI not Required

RAND, SRES,Kc

Inter – VLR Location Update

129

MSCBTS

BSS

BSC

VLR

3

45

4

6

1 CHANNELREQUEST

2IMMEDIATEASSIGNMENT

LOCATION UPDATINGREQUEST (IMSI Attach)3

5LOCATION UPDATINGACCEPT (LAC, TMSI)

4AuthenticationProcedure

IMSI Attach

130

MSC

BTS

BSS

BSC

VLR

1 CHANNELREQUEST

2IMMEDIATEASSIGNMENT

IMSI DETachINDication3

4CHANNELRELEASE

IMSI DETachINDication

3

IMSI Detach

131FT

Great Britain France Germany

Telephonenetwork

TerminatingMSC

BSCBTS

BSS

VLR

GatewayMSC

HLR

Outgoing Call

132

ACM = Address Complete Message ANM = ANswer MessageIAM = Initial Address Message

MS BSS MSCCHANNEL REQUEST

1

PSTN

CM SERVICE REQUEST2 CM SERVICE REQUEST2

CALL PROCEEDING 7CALL PROCEEDING7

Assignment procedure7

IAM6

IMMEDIATE ASSIGNMENT2

ACM8

VLR

Ring

ANM10

ALERTING 9

SETUP (basic) orEMERGENCY

4 SETUP4

CONNECT 11

CONNECT ACKnowledge11

Authentication procedure3

Ciphering procedure3

5

Dialing

Ringing

PathEstablished

Ringing

SendingNumber

Mobile Originating Call

133

PSTN

LA1

LA2

BTS11

BTS21

BTS22

BTS31

BTS12

BTS23

HLR

4

3

5

1

2

5

6

6

BSC1

BSC2

BSC3

MSC/VLR GMSC

Mobile Terminating Call1 - Paging Principle

134

VMSCBSS

VLR

Visitor PLMN

GMSC

HLR

Home PLMN

RoutingInformation

(MSRN)

6

IAM : Initial Address MessageMSISDN : Mobile Station Integrated Services Digital

network NumberMSRN : Mobile Station Roaming Number

IMSI : International Mobile Subscriber IdentityGMSC : Gateway MSCVMSC : Visitor MSCTMSI : Temporary Mobile Subscriber Identity

PN

InternationalSS7

ISDNIAM (MSRN)

7 IAM(MSISDN) 2

SendRoutingInformation(MSISDN)

3

Provide Roaming Number (IMSI) 4

PAGE(TMSI + LA)

9Send info to I/C(MSRN)

8

Roaming Number (MSRN)5

PAGINGREQUEST

(TMSI + LA)10

PAGINGREQUEST

(TMSI)

11

MSISDN

1

Mobile Terminating Call2 - Detailed Procedure

135

MS BSS VMSC

CHANNEL REQUEST(LAC, Cell ID)5

PSTN

IMMEDIATE ASSIGNMENT(SDCCH or TCH)

6

PAGING REQUEST4

PAGING REQUEST(TMSI or IMSI, LA)

3

GMSC

IAM(MSISDN)

1IAM(MSRN)

2

CM SERVICE REQUEST(Paging Response)

7 PAGING RESPONSE(TMSI or IMSI, LA)

7

Authentication procedure8

Ciphering procedure9

Address Complete Message11

ANswer Message12

Setup, Assignment, Alerting10

CONNECT12

Dialing

Ringing

PathEstablished

Mobile Terminating Call3 - End to End Procedure

136

MS BSS MSC

Call in progress1

RELEASE COMPLETE4

PSTN

DISCONNECT2 DISCONNECT2

RELEASE3RELEASE

3

RF Channel Releaseprocedure 8

Release5

RELEASE INDICATION7

CHANNEL RELEASE 6

Releasetone9

Call Release1 - Mobile Initiated

137

PSTN

On hook

Purpose:informs the mobilethen releases radio and network resources.

REL

RLC

MSC

BTS

BSS

BSC

11 1

12

334

5 5

46

2

Call Release2 - PSTN Initiated

138

Mobile Originated Call

• Request for Service• Authentication• Ciphering• Equipment Validation• Call Setup• Handovers• Call Release

139

Mobile Terminated Call

• Paging• Authentication• Ciphering• Equipment Validation• Call Setup• Handovers• Call Release

140

Mobile Terminated CallMS

MS

BTS

BTS

BTS

BSC

BSC

MSC

VLR

GMSC

HLR

PSTN

EIR

AuC

Land to Mobile call(MSISDN)

Query forVLR info

Reply(MSRN)

Routeto MSC

Query VLR for LAC andTMSIPaging

the area(+TMSI)

TMSI Pagedon PCH

Paging

Ch. REQover RACHAllocate SDCCHover AGCHPage RESP on SDCCH( TMSI + LAI)

Page RES Page RES

Authentication and Ciphering procedure done as seen in Location Updation

Assign. REQ

Assignment CMD(=TCH) on SDCCH

* MS tunes* Assgn CMP* Phone rings

Connect traffic Ch.to trunkfrees SDCCHAssgn CMP

Network Alerting

141


142

Radio Resource Management

• Establish maintain and release stable connections between MS and MSC

• Manage Limited Radio and Terrestrial resources• Handover process is the sole responsibility of the RR

Layer• Functions of RR layer are performed by MS and BSC

and partly by MSC

143

Radio Resource Management

• Power Control• Hand over Control• Discontinuous Transmission• Frequency Hopping

144

BTS commands MS at differentdistances to use different power levelsso that the power arriving at the BTS’s Rx isapproximately the same for each TS

- Reduce interference- Longer battery life

Power Control

145

HandoverMeans to continue a call even a mobile crosses the border of one cell to anotherProcedure which made the mobile station really roamHandover causes

RxLev (Signal strength , uplink or downlink)RxQual (BER on data)O & M interventionTiming AdvanceTraffic or Load balancing

146

Handover Types

• Internal Handover (Intra-BSS)

– Within same base station - intra cell

– Between different base stations - inter cell

• External Handover (Inter-BSS)

– Within same MSC -intra MSC

– Between different MSCs - inter-MSC

147

Handover Types

BSC

BSC

BSC

BSC

MSC

MSC

GMSC

C-1 C-2

C-3

C-4

148

Periodic Measurement Reports (SACCH)

Periodic MeasurementReports

HO requiredActivate TCH(facch)with HoRef#

if 1. Check for HO passed2. Channel avail in new BTS

Acknowledges and alloctes TCH (facch)

HO cmd with HoRef#Receives new BTS data(FACCH)

MS tunes into new frequency and TS and sends HO message to new BTS (facch)

Periodic Measurement Reports (SACCH)

HO performed

Release TCH

Cell 1

Cell 2

BSC

BTS 1

BTS 2

Intra BSC handover

149

Frequency plan and importance of BCCH

B3

B2

B9

B6 B4

B1

Sectored antennas

MS ( monitoring the broadcast radio B1 in ‘idle

mode’ )

…..…..SF I…..BBBBSF

F0 F50F2 F3 F4 F5 F10 F11F1

•F,S,B exist in time slot 0 of each frame

B7

B8

B5

B10

B11

B12

BPL frequency plan:

Broadcast frequencies :

15 Broadcast channels = 48-62

15 Hopping channels = 32-46

150

What information does Broadcast Control channel

(BCCH) contain?

Serves as a Beacon for the Cell

Country Code (CC) and the Network Code (NC)

Location Area Identity (LAI)

List of neighboring cells which should be monitored by MS

List of frequencies used in the cell

Cell identity

Back

151

Location Updates

Location Updates can be classified into two:

Periodic Location Updates:

This occurs as per the timer set by the network operator. If the MS does not perform this update the MSC marks the MS as ‘Detached’ on the VLR.

Location Update on a handover:

This occurs if during a handover the MS is moved into a new Location Area Code (LAC).

152Back

1. The MS is monitoring the BCCH and has all the decoded information stored on the SIM ( including the LAC)

2. As soon as the mobile is on a TCH it sends the signal strength indication on the corresponding SACCH

3. The BSC monitors the signal strengths and on analysis sends a ‘handoff request’ on FACCH. The handoff process is completed on the FACCH.

4. After the completion of call, the MS starts monitoring the BCCH again. On finding the LAC (stored on SIM) and that decoded from the BCCH to be different , the MS requests a ‘Location Update’ through SDCCH.

153

Discontinuous Transmission

• Discontinuous Transmission(DTX) allows the radio transmitter to be switched off most of the time during speech pauses.

• A Silence Indicator Block is transmitted at 500bps, which generates a comfort noise

• Down Link interference is decreased.• Up link battery is saved

154

Frequency Hopping• Frequency Hopping permits the dynamic switching of

radio links from one carrier frequency to another.

• Base Band Hopping

– At the BTS each the timeslot is shifted to another transceiver, which is transmitting at the hop frequency. User will be connected to different Transceivers depending on hop sequence.

• Synthesis Hopping

– At the BTS transceiver changes the frequencies used. The user will be connected to only one transceiver.

• Decreases the probability of interference

• Suppresses the effect of Rayleigh fading

155

Wireless Data

98 99 2000 2001

GSMDATA

GSMDATA

HSCSDHSCSD

GPRSGPRS

EDGEEDGE

UMTSUMTS

SIMToolkit

SIMToolkit

WAPWAP

Data Application

Time

Circuit Switched technology

Packet Switched technology

Technology for Applications

SMS Data: 160 α-numeric charactersUser Data Rate : 9.6kbpsOne time slot over the air interface

High Speed Circuit Switched DataUser Data Rate:14.5kbpsUse multiple timeslots (max=8), hence max rate = 115.2kbps.Needs a duplexor in MS for simultaneous Tx and Rx

Add-on to GSM network : PCU; Packet Segmentation/re-assembly and scheduling• Radio channel access control and management• Transmission error detection and retransmission.• Power controlSGSN: GPRS mobility• Encryption• Charging GGSN : Interface to the PDN, Internet

Max user data rate : 21.4 kbpsDynamic rate adaptation to suit the radio conditions at that time ( 9.05 kbps, 13.4 kbps, 15.6 kbps 21.4 kbps)

W@P Gateway W@P ServiceW@P

Fone

InternetMobile Network

Surf the Internet while on the move

W@P Gateway :• Adaptation of the information to the mobile• Compression of the data• Buffering of the information

Enhanced Data rate for GSM Evolution• EDGE is an enhancement of GPRS and CSD technologies.• Based on the current GSM technology - same TDMA frame structure, same bandwidth (200 kHz).• Uses 8-PSK modulation instead of GMSK.• Requires good propagation conditions. • Allows upto 48 kbps (EGPRS) and upto 28.8 kbps (ECSD) on everyradio channel• EDGE helps GSM-Only operators to compete with UMTS.

Universal Mobile Telecommunication Standards• Innovative Service Architecture : VHE Concept - providing the usthe same look and feel of its personalized services independent of

network and terminal.• Global Convergence : Fixed/Mobile, Telecom/Datacom, public/private• Mobile Multimedia driven market.• Wideband bearers - 2GHz band ( 5 MHz per carrier), -max. 2Mbps

156

References• Wireless and Personal Communication Systems.

Vijay.K.Garg and Wilkes • Overview of the GSM System and Protocol

Architecture, IEEE Comm. Magazine, Moe Rahnema. • The GSM System for Mobile Communications-

Michel Mouly & Marie-Bernadette Pautet• Overview of the GSM Comm- John Scourias.

157

Coverage or Traffic LimitationsTRAFFIC-LIMITED

AREA(10000

subscribersper km2)

COVERAGE-LIMITED

AREA(-75 dBm

at cell edge)

COVERAGE-LIMITED

AREA(-70 dBm

at cell edge)

158

159

Average number of busy channels during the period of observation

(usually, the peak hour).

Erlang is the unit of statistical resource use

Erlang BAt any time, more than 1 user may request the same resource simultaneously. The use of such a resource is associated with a blocking rate.

Erlang CWhen more than 1 user request at the same time, instead of rejecting the extra calls, there is a queuing system.

Erlang Concept

160

Different Types of Cells

• High sensitivity to interference

• Requires "secured" Frequency reuse pattern

• High isolation from interferences

• A few Frequencies intensively reused

MACRO-CELL:antenna radiating ‘above’ roofs---> Wide Coverage (≤ 35 km)

MICRO-CELL:Antenna ‘below’ the roofs---> small coverage

PICO-CELL:Antenna inside building---> Very small coverage

EXTENDED-CELL:macro cell with system coverageextension (≤ 120 km) for coasts...

CONCENTRIC-CELL:macro cell with system coveragelimitation inside another macro

161

Cell Patterns

Cell Sectorization

TRI OMNI BI

Omnidirectional Site Antennas

Bi and Trisectorial Site Antennas

Calculation of the maximum coverage range of each cell in a specific environment.

Definition of planning tools parameters.

Based on the path loss calculation between the MS and the BS in both ways.

This calculation considers:

• RF parameters of MS and BS,• system parameters (diversity gains...),• propagation parameters (shadowing),• physical installation parameters (antenna height),• environment classification.

Link Budgeting

- What is the maximum EIRP?- What are the losses in

transmission and reception?- Is diversity used? - What is the minimum

equivalent sensitivity?- What is the maximum

equivalent output power?- What are the body losses?

- Beyond which distance the communication will cut off?

- Is indoor coverage guaranteed?

- Is frequency hopping used?

EIRP:Equivalent Isotropic Radiated Power

DuplexerCombinerPower Amplifier

DLNA:Diversity Low Noise Amplifier

Specific Tx Cable Losses

Tx PA OutputPower

Combiner losses

Rx Sensitivity

Rx Diversity Gain

DLNA conf.Standard conf.

Base Station

Tx PA Output Power

Other factors for MSBody LossesCommon cable losses

Propagation Parameters:- Incar, Indoor penetration factors- Frequency 900, 1800, 1900 MHz- Antenna Height- Environment

Design Parameters:Overlapping margin

Rx SensitivityAntenna Gain

MS

Rx Sensitivity

Common cable Losses

Antenna Gain

Radio Link

Link Budget Parameters• Overview

Link Budget Parameters• BTS TX Power Amplifier

2.5W PA 25W PA 35W PA 20W PA 30W PA

GSM 900 S2000LS2000ES4000 IndoorS4000 Outdoor

S4000 Indoor S2000H S8000 Indoor S8000 Outdoor

DCS 1800 S2000L S4000 Indoor S2000E S2000H S4000 Outdoor

S4000 IndoorS8000 Indoor S8000 Outdoor

PCS 1900 S2000L

S2000E S2000H S4000 Indoor S4000 Outdoor

S8000 Outdoor

D

H2D

Hy/2

2-Way Hybrid Combiner with Duplexer 2-Way Hybrid Combiner with Duplexer

4.5 dB Loss4.5 dB Loss

allows Synthesized Frequency Hopping

4-Way Cavity Combiner with Duplexer

4-Way Cavity Combiner with Duplexer

allows Baseband Frequency Hopping

4.9 dB Loss4.9 dB LossC C C C

D

Link Budget Parameters• Combiners

TX TX TX TXTXTX

At the BS, for a 7/8” foam dielectric coaxial cable:

• 4 dB/100 m (900 MHz),

• 6 dB/100 m (1800 MHz),

• Common cable losses for 40 meters: 2.5 dB (900 MHz) and 3.5 dB (1800 MHz).

Jumpers (up and down the feeder)

• 0.5 dB (800 MHz),

• 1 dB (1800 MHz).

Link Budget Parameters• Cable Losses

Omnidirectional antenna

Default 6.5° V with 11 dBi gain

Directional antenna for trisectorial site

Default 65° H / 6.5° V with 18 dBi gain

Link Budget Parameters• BTS Antenna Gain

900 MHz 1800/1900 MHz

TX PA OutputPower 33 dBm (2W) 30 dBm (1W)

RX Sensitivity -102 dBm

-2 dBi for Handheld2 dBi for Car Kit

Body Loss

Antenna Gain

Common CableLoss

-100 dBm

0 dB for Handheld2 dB for Car Kit

3 dB for Handheld0 dB for Car Kit

Link Budget Parameters• Mobile Station Parameters

173

Link Budget PresentationParameters

Frequency 1800 MHzBase Height 40.0 mMobile Height 1.5 mEnvironment Urban

RX TX

Mobile

Antenna Gain-2 dB

Cable Loss 0 dB

Output Power

Sensitivity -100 dBm

30 dBm

Antenna Gain (65 °)

Jumper Loss

Feeder Loss

Sensitivity -110 dBm

18 dBi

3 dB

Options

Rx Diversity Gain: 5 dB

Overlapping Margin: 0 dB

Penetration Factor

Body Loss 3 dB

15 dB

Outdoor Minimum Field95%: -80 dBm

Coverage Range95%: 810 m

0.5 dB

Base Station

Max TX Output Power

RXm RXd

44.8 dBm

Coupling system

Tx loss4.5 dB

174

Link Budget Calculation

-2.0 dBm18.0 dBmANTENNA GAIN

0.0 dB3.0 dBCOMMON CABLE

LOSSES

None-115.0 dBmRX SENSITIVITY +

DIVERSITY

-102.0 dBm-110.0 dBmRX SENSITIVITY

None5.0 dBCOMBINER LOSSES

1.00 W (30.0 dBm)

30.00 W (44.8 dBm)TX OUTPUT POWER

MSBTS

18.0 dBINDOOR PENETRATION

FACTOR

0.0 dBOVERLAPPING MARGIN

3.0 dBBODY LOSSES

Exercise 1: S8000 INDOOR: OPERATING FREQUENCY 1800 MHz

FadingExample of Field Strength Variation for GSM 1800

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Distance (m)

Fiel

d St

reng

th (

dBm

)

MeasurementFree Space

Zoom onShort Term Fading

Long Term Fading

± 2 m

≅ λ/2

Clutters

177

178

Mobile Station (MS)

• Hand portable unit

• Contains Mobile Equipment(ME) and Subscriber Identity Module (SIM)