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GSM Global System for Mobiles 1

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 2

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 3

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

4

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

5

GSM Hi story

6

Devel opment of the GSM Standard 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 Worldwide First GPRS Networks roll out

End 2002: 792M GSM subscribers Worldwide 7

GSM Speci fi cati ons 12 SERIES OPERATION AND MAINTENANCE

01 SERIES GENERAL

02 SERIES SERVICE ASPECTS

11 SERIES EQUIPMENT AND TYPE APPROVAL SPECIFICATIONS

03 SERIES NETWORK ASPECTS

10 SERIES SERVICE INTERWORKING

04 SERIES MS-BSS INTERFACE AND PROTOCOLS

09 SERIES NETWORK INTERWORKING

05 SERIES PHYSICAL LAYER ON THE RADIO PATH.

08 SERIES BSS TO MSC INTERFACES

07 SERIES TERMINAL ADAPTERS FOR MOBILE STATIONS

06 SERIES SPEECH CODING SPECIFICATIONS

Increasi ng GSM Data Rates UMTS

photo

E/GPRS

web

video clip

report

video report clip

photo

ISDN

e-mail web

photo

PSTN

e-mail

web

e-mail

GSM 0

Transmi ssi on Ti me

10 sec

video report clip video report clip

photo

web

photo

1 min

video report clip

10 min

GPRS = General Packet Radio Service HSCSD = High Speed Circuit Switched Data EDGE = Enhanced Data rate for GSM Evolution UMTS = Universal Mobile Telecommunication System

1 hour

Wi rel ess Data Technol ogy Opti ons 2M throughput kbps

1M

p uit c r ci

100 k

64 k

10 k

1k

t e k ac

EDGE

UMTS

HSCSD

14.4

GPRS

9.6

Time frame 1998

1999

2000

2001

2002

GPRS = General Packet Radio Service HSCSD = High Speed Circuit Switched Data EDGE = Enhanced Data rate for GSM Evolution UMTS = Universal Mobile Telecommunication System 10

Ci rcui t-Swi tched or Packet-Swi tched Circuit mode

A

Packet mode

→F

A

A

→GHF →

C

D A C

→ →GHF

→G

→GHF

C D A

C D A

C

D

F

→F

B

→H

→G

C

G

→H

D

D

E

H 11

Multiple Access Technique •

Multiple Access – Achievedby 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) 12

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 )

13

GSM Concepts Cellular Structure 2 2 7

3 1

6

7

5

4

1 6 5

Cellular Networking technology that breaks geographic area into cells shaped like honey comb Cell is the radio coverage area of one base transceiver station 14

What are the types in GSM Network? •

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

•

GSM -1800 (Channels 374 spacing 95Mhz)

•

GSM -1900(Used in USA)

15

GSM Band Al l ocati ons (MHz) GSM systems

Upl i nk

Downl i nk

Band

Dupl ex Spaci ng

Dupl ex channel s

GSM 450 GSM 480

450.4-457.6 478.8-486

460.4-467.6 488.8-496

2x7.2 2x7.2

10 10

35 35

GSM 850

824-849

869-894

2x25

45

124

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

890-915 880-915 876-880

935-960 925-960 921-925

2x25 2x35 2x04

45 45 41

124 174 40

GSM 1800 GSM 1900

1710-1785 1850-1910

1805-1880 1930-1990

2x75 2x60

95 80

374 299

Frequencies are in MHz Carrier frequency = ARFCN = Absolute Radio Frequency Channel Number

GSM Fami l y Radi o Band Spectrum Uplink

450.4

457.6

478.8

GSM 450

Downlink

460.4

824

GSM 480

467.6

488.8

849

GSM 850

496

869

894

MHz

915

Uplink 876 880

486

915 890

915

1710

1785

1850

1910

P-GSM E-GSM

GSM 1800

GSM 1900

R-GSM 921 925

Downlink

935

960 960 960

1805

1880

1930

1990

MHz

Traffi c/ Si gnal i ng

Traffic

«bla bla bla...»

Signaling

« RING ! » riiiiing

Network

MS

GSM - Network Structure Um HLR

VLR

BTS BSC Abis

MSC A

B

H

C

MS

AuC

GMSC

BTS E Abis A

MSC

F EIR

E PSTN

BSC Um BTS

X.25 VLR X.25 OMC Server 19

GSM System specifications Frequency band Uplink Downlink Duplex Frequency Spacing Carrier separation Frequency Channels Time Slots /Frame(Full Rate) Voice Coder Bit Rate Modulation Air transmission rate Access method Speech Coder

890 - 915 MHz 935 - 960MHz 45MHz 200KHz 124 8 13Kbps GMSK 270.833333 Kbps FDMA/TDMA RPE-LTP-LPC 20

Pai red Radi o Channel s i n GSM Case of GSM 900 Uplink 890 MHz

Frequency

0

channel #

Downlink 915 MHz

124

935 MHz

Frequency

0

channel #

BTS

960 MHz

124

Example: Channel 48

Duplex spacing = 45 MHz Frequency band spectrum = 2 x 25 MHz Channel spacing = 200 kHz 21

GSM Ti me Di vi si on Mul ti pl ex Frame and Physi cal Channel s Time-slot

TDMA frame

TDMA frame

TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS 0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

(frames repeat continuously)

Time 0

4.615 ms

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

9.23 ms

Physi cal Channel BTS With FH

BTS Without FH

time

n+1

TDMAs n TS 0

7

MS1

n-1 MS2

MS3 1

FDMA

2

// 124

ARFCN

Radi o Li nk Aspects •

From Speech to RF Si gnal Blah... Blah... Blah...

Blah… Blah… Blah...

Digitizing and Source Coding

Source Decoding

Channel Coding

Channel Decoding

Interleaving

De-interleaving

Ciphering

Burst Formatting

Modulating

Deciphering

Burst De-formatting

Demodulating

Functi ons of the Radi o Interface • Speech and user's data Idle mode • Signaling

Communication mode

BTS

BTS-1

BTS-2

Access Techniques Uplink 890 MHz to 915 MHz Down Link 935 MHz to 960 MHz 25 MHz divided into 125 channels of 200 KHz bandwidth 890.0

890.2

890.4

914.8

915.0

DOWN 935.0

935.2

935.4

959.8

960.0

UP

26

Access Techniques ... Time Division Multiple Access Each 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 0.577 ms 0

1

2

3

4

4.616 ms

5

6

7 27

28

Fundamental s 960 MHz

TS: Time slot

124

959.8MHz

123 …….

DOWNLINK

…… 200KHz

2

0

1

935.2 Mhz

915 MHz

45 MHz

124 123

UPLINK

200KHz

……. …… 2

890.2 MHz

1

2

3

4 5

6

7

Th e fr e qu e n cy ba n ds a r e divide d in t o 2 0 0 KH z w ide ch a n n e ls ca lle d ARFCN s ( Absolu t e Ra dio FrData e qu e n=cy Ch abin n eods l N=u576.9 m be burst 156.25 t peri μsr s) i.e . t h e r e a r e 1 2 5 ARFCN s ou t of w h ich on ly 1 2 4 a r e u se d.

935 MHz

914.8 MHz

GSM u t ilize s t wDownlink o ba n ds (TDMA of 2 5 Mframe) H z. 8=9 0 915 8 -TS M H z ba n d is u se d for u plin k w h ile t h e 9 3 5 9 6 0 M H z is u se d for dow n lin k .

Ea ch ARFCN su ppor t s 8 u se r s w it h e a ch u se r t rDelay a n sm it t in g / r e ce ivin g on a pa r t icu la r t im e 0 1 2 3 4 5 6 7 slot ( TS) .

Uplink (TDMA frame)

1

890 MHz

The technology

Therefore 1 TD M A fram e = 156.25 x 8 = 1250 bit s and has a durat ion of 576.92 μs x 8 = 4.615 m s 29

GSM Del ays Upl i nk TDMA Frames BTS side

The start of the uplink TDMA is delayed of three time-slots

TDMA Frame (4.615 ms)

0

1

2

3

4

5

R

R

R

R

R

T

T

T

T

T

Downlink TDMA BTS

T

T

T Down link

MSs side MS1

MS2

R

Up link T

R

T

Fixed transmit delay of three time-slots

6 R

7 R

R

Ti mi ng Advance 1 - Propagati on Del ay

M2

BTS Frame reference

d1>>d2

d2

TS0

TS1

TS2

TS3

TS4

M1

TS5

TS6

TS7

Propagation Delay τp Bits Overlapping MSs transmit

Ti mi ng Advance 2 - Wi thout Ti mi ng Advance: Col l i si on TX BTS RX BTS

CAN

GSM

CAN

RX MS2 TX MS2

+3TS

RX MS6 TX MS6

yes

W HEN the

WHAT ms-isdn

yes

W HAT

D

GSM

D

the

ms-isdn

RX MS4 TX MS4 RX MS5 TX MS5

HOW

TA

RX MS1 TX MS1

RX MS3 TX MS3

W HAT

HOW

Propagation Delay

W HEN

WHAT

RX MS7 TX MS7 RX MS8 TX MS8

32

Ti mi ng Advance 3 - Wi th Ti mi ng Advance: No Col l i si on CAN

TX BTS RX BTS

CAN

RX MS1 TX MS1

GSM

D

RX MS6 TX MS6 RX MS7 TX MS7

WHEN the

WHAT ms-isdn

yes

D

the

GSM ms-isdn HOW

RX MS4 TX MS4 RX MS5 TX MS5

HOW yes

+3TS - TA WHAT

RX MS2 TX MS2 RX MS3 TX MS3

WHAT

Propagation Delay

WHEN

WHAT

Timing Advance = 2 * Propagation Delay

RX MS8 TX MS8

33

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 34

TOPICS • • • • • • • •

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

35

MS

GSM - Network Structure Um HLR

VLR

BTS BSC Abis

MSC A

B

H

C

MS

AuC

GMSC

BTS E Abis A

MSC

F EIR

E PSTN

BSC Um BTS

X.25 VLR X.25 OMC Server 36

GSM Network SS External PSTN & PDN N/W

VLR

Switching System

AUC HLR

EIR OMC

MSC MS Mobile Station BTS Base transceiver System BSC Base Station Controller MSC Mobile Switching Center BSS BSC HLR Home Location Register VLR Visitor Location Register BTS EIR Equipment Identity Register AUC Authentication Center MS OMC Operation And Maintenance Center

Base Station System 37

GSM Archi tecture VMSC

GSM Air interface

B S C Abis interface

TRAU

BTS BTS

BTS

BTS

A interface

B S C

SMSC

HLR

AUC

MSC

PSTN VLR

EIR

OMCS

BTS BTS

Mobile Station

Network and switching subsystem OMCR

Base Station System

A interface SS7 / speech X.25 SS7 38

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)

39

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 40

SIM-Card and GSM Mobi l e Equi pment Global GSM Mobility Card

=

The Smart Card to use

GSM Contains: - IMSI

SIM-Card

+

The SIM-Card Functi ons Credit Card Size

µ SIM-Card

Global GSM Mobility Card 15 mm

The Smart Card to use

25 mm

Permanent data: - Unique mobile subscriber identity through IMSI number and PIMSI for Packet Mode - Authentication parameter Ki, - Authentication algorithm A3, - Generating encryption key Kc algorithm A8, - PIN code.

GSM Microchip with stored user information

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

Subscri ber Identi fi cati on IMSI

Nature

International Mobile Subscriber Identity

Mobile Station Integrated Services Digital Network Nb

Conformity with E212

Similar to ISDN, Conformity with E164/E213

Identify a PLMN worldwide

MCC

MNC

Meaning

Mobile Country Code

Mobile Network Code

Nb. digits

3

2

Format

MS - ISDN

Identify the subscriber of a PLMN

MSIN H1 H2

x x x ......... x x x

Mobile Subscriber Ident. Nb H1 H2 = Identity of HLR within the home PLMN

max 10

National Significant Mobile Number

CC

NDC

SN M1 M2

xx xx xx xx

Country Mobile Subscriber National Code (where Destination (national definition) subscription Code * M1 M2 = nbr of logical HLR has been made)

1 to 3

2 to 4

total max 15

*This code does not identify a geographical area but an operator

Descri pti on Stored i n SIM Card MCC = 208 (France) 234 (G-B) 262 (Germany) 404,405(India)

MNC = 71(APBSNL) 72(TNBSNL) 20 (Bytel)

Mobile Country Code

Mobile Network Code

3 digits

2 digits

Global GSM Mobility Card The Smart Card to use

Mobile Subscriber Identification Number (MSIN) H1 H2 X X X X X X 10 digits max

NMSI LAI Mobile Country Code

Mobile Network Code

3 digits

2 digits

GSM

IMSI = 15 digits max

Temporary Mobile Subscriber Identity 4 octets

Location Area Code LAC

RAI

Routing Area Code RAC

Descri pti on Stored i n the Network MS-ISDN (15 digits max) Country Code 3 digits max

National Destination Code 2 or 3 digits

Subscriber Number (SN) M1 M2 X X X X X X X X X X X X X 10 digits max

Must be dialed to make a call to mobile subscriber

MSRN

Country Code

Country Code

National Destination Code

Roaming Number (RN)

National Destination Code

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

HO-number

Is a PSTN-like number used to reach a roaming MS

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

NDC = 9448(BSNL-karnataka) 9845,9880(Airtel) 9886(Hutch) 45

= 660, 661, 618 (Bytel)

Descri ptor Embodi ed i n the Mobi l e Equi pment IMEI enables the operator to check the Mobile Equipment Identity at call setup and make sure that no stolen or unauthorized MS is used in the GSM network

PE VED Y T O PR P A

TAC Type Approval Code

FAC

Final Assembly Code

SNR

SP

Serial NumbeR

(SPare)

Internati onal Mobi l e Equi pment Identi ty (IMEI)

PE VED Y T O PR P A

TAC Type Approval Code

FAC

SNR

SP

Serial number

(SPare)

Final Assembly Code

IMEI: #06# 351475 60 926514 4

*

MS Cl assmark Power classes Classmark Revision level RF power Encryption algorithm Frequency Short message LoCation Services MS Positioning Method 8-PSK modulation Multi-slot class Multi-band * **

Typical value for car mounted Typical value for handheld

For GMSK modulation GSM GSM GSM Class 400/850/900 1800 1900 1 1 W** 1 W** 8 W* 2 0.25 W 0.25 W 5W 3 2W 4W 2 W** 4 0.8 W 5 For 8-PSK modulation GSM GSM GSM Class 400/850/900 1800 1900 2W E1 1W 1W 0.5 W E2 0.4 W 0.4 W 0.2 W E3 0.16 W 0.16 W

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 49

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 50

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 51

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

52

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 53

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.

54

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

55

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 GSMPLMN – 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 56 one GSM PLMN.

Interfaces and Protocols Digital Networks ISUP

Abis

A

LAPD

Um

LAPDm

E TUP

BSSAP

F

MAP

MAP MAP

C D

B

POTS

G

57

GSM Entities and Signaling Architecture

58

GSM Protocols • • • • • • • • • • • • •

CM MM RR LAPDm LAPD BTSM BSSAP DTAP MAP MTP SCCP TCAP ISUP

- Connection Management - Mobility Management - Radio resource - LAPD for mobile - Link Access Procedure for D channel - BTS Management Part - BSS Application Part (BSC - MSC) - Direct Transfer Application Part (MS - MSC) - Mobile Application Part - Message Transfer part of SS7 - Signalling Connection Control Part of SS7 - Transaction Capabilities Application Part - ISDN User Part 59

Functional Plane of GSM

MS

BTS

BSC

MSC/VLR

HLR

MSC/ VLR

HLR

GMSC

CC

MM

RR

Trans MS

BTS

BSC

GMSC 60

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTIFIERS USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 61

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 62

Channel s : di fferenti ati ng between Physi cal and Logi cal channel s Physical 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.

63

Channel concept Physical channel: One timeslot of a TDMA-frame on one carrier is referred to as a physical channel. There are 8 physical channels per carrier in GSM,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.Depending on the kind of information transmitted we refer to different logical channels.These logical

channels are mapped on physical channel.

64

Logi cal Channel s on Ai r i nterface LOGICAL CHANNELS

COMMON CHANNELS

COMMON CONTROL CHANNELS

BROADCAST CHANNELS

FCCH

SCH

DEDICATED CHANNELS

BCCH

PCH

DEDICATED CONTROL CHANNELS

SDCCH

RACH

AGCH

SACCH

TCH/F

TRAFFIC CHANNELS

FACCH

TCH/H

TCH/EFR

65

Logical channels Logical channels

Control channels

BCH

CCCH

Traffic channels

DCCH

Half rate

Full rate

FCCHSCH BCCH CBCH PCH AGCH RACH SDCCH SACCH FACCH 66

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). 67 – Repeats once in every 10 frames.

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)

68

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. 69

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.

70

Dedicated Control ChannelsDCCH • •

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.

71

Dedicated Control ChannelsDCCH •

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 72

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.

73

GSM Channel s GSM Channels Traffic Channels (TCHs)

Control Channels

Broadcast Channels (BCHs) Full rate

Half rate

Common Control Channels (CCCHs)

Dedicated Control Channels (DCCHs) (down uplink)

Downlink

Downlink

Uplink Fast

TCH /F

TCH /H FCCH SCH BCCH PCH

Traffic Multiframing

AGCH

CBCH

Signaling Multiframing

RACH SDCCH

FACCH

Slow

SACCH

Traffic Multiframing 74

The Logi cal Channel s on Radi o Interface TS

0123456 7

BTS

MS FCCH

TCH

Frequency correction Synchronization Broadcast control

Traffic (speech-data) SCH

Access request

Answer to Access request

Associated Signaling

BCCH RACH

Subscriber paging

FACCH

PCH

SACCH SDCCH

Radio Measurement + SMS Dedicated Signaling

CBCH Broadcast info

AGCH FCCH CBCH

Broadcast info Dedicated Signaling

SDCCH SACCH

Sys InFo 5, 6 + SMS

SCH

M.S. Pre-synchronization

BCCH RACH Access request PCH

Traffic (speech data) TCH Associated Signaling FACCH

Subscriber paging AGCH

Answer to Access request 75

Logi cal Channel Descri pti on SACCH MESSAGES TCH MESSAGES (1/ 2)

Measures:

- power level of the communication

• Speech

- quality level of the communication

• Data

- level on the beacon frequency of

• Handover Access message (uplink)

the neighboring cells • Timing Advance • Power Control

FACCH MESSAGES

• SMS

• Connection establishment from

SDCCH to TCH

SDCCH MESSAGES • Request for a SDCCH assignment • Request for the end of channel

assignment • Order of commutation 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

• SMS 76

Logi cal Channel Descri pti on FCCH MESSAGES AGCH MESSAGES (2/ 2) -

• no message is sent (all bits 0)

SCH MESSAGES • Frame Number

• For dedicated channel assignment:

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

• Base Station Identity Code (BSIC)

CBCH MESSAGES BCCH MESSAGES

• Specific information

(weather, road information • System Information type 1, 2, 2bis,

2ter, 3, 4, 7, 8 (idle mode)

RACH MESSAGES • Service request:

PCH MESSAGES • messages containing a mobile

identity for a call, a short message or an authentication

- emergency call - answer to an incoming call - outgoing call - short message - call re-establishment - inscription 77

GPRS Channel s DL PBCCH PPCH PAGCH

PDTCH PACCH PTCCH

BSC PCUSN

GPRS CORE

PNCH

NETWORK PDTCH PRACH

PACCH PTCCH UL

PDCH = Packet Data CHannel

Packet Common Control CHannels Packet Traffic CHannels PBCCH 78

Traffi c and Control Mul ti frami ng Control channel

Traffic channel Frame 4.615 ms TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS TS 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

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

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

26 traffic frames = 120 ms 0

1

2

3

4

21 22 23 24 25

0

1

2

3

4

46 47 48 49 50

1326 frames 0

1 0

0

2

3

1

1

4

51 x 26 traffic frames = 6.12 s

2

2

3

26 x 51 control frames = 6.12 s

3

4

5

46 22

47 23

48 24

49

50 25

2042 2043 2044 2045 2046 2047

1 Hyperframe = 2,715,648 frames= 3h 28 min. 53 s 760 ms 79

80

81

Logi cal Channel Mappi ng 1 - Traffi c Channel Combi nati on T

Full Rate - Downlink & Uplink 26 frames = 120 ms

T T T T T T T T T T T T A T T T T T T T T T T T T

time

Half Rate - Downlink & Uplink 26 frames = 120 ms

T0 T1 T0 T1 T0 T1 T0 T1 T0 T1 T0 T1 A0 T1 T0 T1 T0 T1 T0 T1 T0 T1 T0 T1 T0 A1

T : TCH

Ti : TCH

sub-channel no. i

A : SACCH

Ai : SACCH

sub-channel no. i

time

: IDLE 82

Logi cal

Channel

Mappi ng

2 - Dedi cated Si gnal i ng Channel Combi nati on A

A

A

A

Downlink 51 frames = 235 ms

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

A3

D0

D1

D2

D3

D4

D5

D6

D7

A4

A5

A6

A7 time

Uplink 51 frames = 235 ms

A5

A6

A7

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

A3

D0

D1

D2

D3

D4

D5

D6

D7

A4 time

A : SACCH

D : SDCCH

: IDLE 83

Logi cal

Mappi ng

Channel

3 - Common Channel Combi nati on Downlink

Multiframe m-1

Multiframe m Multiframe m+1

51 frames = 235.38 ms

C

FS

B

C

FS

C

C

FS

C

C

FS

C

C

FS

C

C

FS

B time

Frames repeat continuously

PCH/AGCH

BTS

Physical Channel ARFCN (n)

TS (s)

SCH

MS

BCCH

FCCH

Uplink 51 frames = 235.38 ms R R R RR R R RR R R RR R R RR R R RR R R RR R R RRR R R R R RR R R RR R R RR RR RR R R R

F : FCCH

S : SCH

B : BCCH

: PCH / C AGCH

time

R : RACH

: IDLE 84

Logi cal

Channel

Mappi ng

4 - Common Channel Combi nati on

Downlink

51 frames = 235 ms

FS

B

C

FS

C

C

FS

D0

D1

FS

D2

D3

FS

A0

A1

FS

B

C

FS

C

C

FS

D0

D1

FS

D2

D3

FS

A2

A3 time

Uplink 51 frames = 235 ms

D3

RR

A2

A3

RRRRRRRRRRRRRRRRRRRRRRR

D0

D1

RR

D2

D3

RR

A0

A1

RRRRRRRRRRRRRRRRRRRRRRR

D0

D1

RR

D2 time

: AGCH

F : FCCH S : SCH B : BCCH C /PCH

R : RACH

A : SACCH

D : SDCCH

: IDLE 85

86

Why 26 and 51 per Mul ti frame? Frames

0 1

FS

10

B

C

20

FS

C

C

30

FS

C

C

TTTTTTTTTTTTATTTTTTTTTTTT 01

12

40

FS

C

C

FS

50 0 1

C

C

FS

TTTTTTTTTTTTATTTTTTTTTTTT

25 0 1

12

25

Downlink message Uplink message Mobile activity

Rx (n)

Rx

Tx Rx Rx (n)

Tx

Rx (n)

Rx

Tx

Neighboring BTS (downlink) Measurement Windows 87

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 88

From Speech to Radi o Transmi ssi on Speech

Step 1

Digitizing and source coding

Source decoding

Step 2

Channel coding

Channel decoding

Interleaving

De-interleaving

Step 3 Burst formatting

Step 4

Ciphering

Step 5

Modulation

Step 6

Transmission

Burst deformatting

Deciphering

Demodulation equalization

Diversity

89

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)

90

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

91

Why Di gi ti zi ng and Codi ng the Speech?

SPEECH TRANSMISSION BETWEEN MOBILE AND NETWORK

MS

BSS

SPEECH MUST BE DIGITIZED AND CODED Better Quality

Lower Rate

64 kbit/s

Speech Qual i ty – Source Codi ng

Quality Excellent Good Fair Poor Bad

Codec Type

Mean Opinion Score (MOS)

Rate (kb/s)

PCM A law GSM EFR CDMA 13 D-AMPS GSM FR CDMA 8

4.25 4.2 4.2 4 3.8 3.4

64 12.2 13 8 13 8

MOS 5 4 3 2 1

Listening Effort Required Complete relaxation possible, no effort. Attention necessary, no appreciable effort. Moderate effort. Considerable effort. No meaning understood with feasible effort.

93

Speech Coding BP

SPEECH ENCODER

A/D

BAND PASS 300 Hz 3.4 kHZ

Every 125μ s value is sampled from analog signal and quantised by 13 bit word Data rate = 13/125*10 -6 = 104 kbps

CHANNEL CODING

Every 20ms 160 samples taken Data rate = 160 * 13/20ms = 104 kbps

To modulator

1A

1B

2

50

132

78

3 crc bits

Four 0 bits for codec

50 3

132

4

Conv coding rate = 1/2 delay = 4

Linear Predictive Coding & Regular Pulse Excitation Analysis 1. Generates 160 filter coeff 2. 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

LP

D/A

Long term prediction analysis 1. Previous sequences stored in memory 2. Find out the correlation between the present seq. And previous sequences 3. Select the highest correlation sequence 4. Find a value representing the difference between the two sequences.

378 coded bits 456 bits in 20 ms = 22.8 kbps 57 x 8 = 456

1A = Filter Coeff block ampl, LTP params 1B = RPE pointers & pulses 2 = RPE pulse & filter params

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

SPEECH DECODER

78

CHANNEL DECODING

94

Channel Processi ng i n GSM Overvi ew for Ful l Rate 20 ms

Speech blocks

A

20 ms

20 ms

B

C

Codec dependent

Codec dependent

Codec dependent

Source coding Channel coding

A

B

456 bits

A A A A 5 6 7 8

Normal burst

B B B B B B B B 1 2 3 4 5 6 7 8

Interleaving

8 Bursts

A5 B1

C

456 bits

A6 B2

A7 B3

A8 B4

B5 C1

B6 C2

456 bits

8 Sub blocks of 57 bits

B7 C3

C C C C 1 2 3 4

B8 C4

3

57 bits

1

26 bits

1

57 bits

3

Tail

Information

CRL

Training

CRL

Information

Tail 95

96

Channel Processi ng i n GSM Overvi ew for Hal f Rate Speech blocks

20 ms

A

20 ms

20 ms

B

C

Codec dependent

Codec dependent

Codec dependent

Source coding Channel coding

A

B

228 bits

A A A A 1 2 3 4

B B B B 1 2 3 4

Interleaving

A3 B1

4 Bursts

Normal burst

0

1

2

3

4

C

228 bits

5

6

7

0

A4 B2

1

2

B3 C1

3

4

228 bits

4 Sub blocks of 57 bits

C C C C 1 2 3 4

B4 C2

5

6

7

0

1

2

3

4

5

6

7 97

Interl eavi ng: TCH Ful l Rate 0 1 2 3 4 5 6 7 8 ...

...

452 453 454 455

456 coded bits

4

5

0 8 •• •

1 9 •• •

2 10 •• •

3 11 •• •

4 12 •• •

5 13 •• •

6 14 •• •

7 15 •• •

448

449

450

451

452

453

454

455

6

7

0

1

2

3

4

5

6

7

0

1

57 Rows

Divide 456 bits in 8 sub-blocks

2

reordering & partitioning out

3 diagonal interleaving

bit interleaving

burst b0 b1

b56

b0 b1

b56

98

Burst Formatti ng Normal Burst 1 frame: 4.615 ms 0

1

DATA

3

57

2

3

S

Training sequence

1

26

4

S

1

Burst 148 bits

5

6

7

Guard Band

DATA

57

3

8.25

Guard

156.25 bits duration (0.577 ms)

99

Burst Formats Frequency Correction Burst (FCCH) Tail

Data

3 bits

Tail

142 fixed bits (0)

3 bits

Guard Period 8.25 bits

156.25 bits duration (0.577 ms)

Synchronization Burst (SCH) Tail

Data

3 bits 39 encrypted bits

Extended Training Sequence

Data

64 synchronization bits

39 bits

Tail

Guard Period

3 bits 8.25 bits

156.25 bits duration (0.577 ms)

100

Burst Formats Normal Burst Tail

Data

3 bits 57 encrypted bits

Training Sequence 1

26 bits

Data 1

Tail

57 encrypted bits

Guard Period

3 bits 8.25 bits

156.25 bits (0.577 ms)

Dummy Burst Tail Dummy Sequence 3 bits 58 mixed bits

Training Sequence 26 midamble bits

Dummy Sequence Tail 58 mixed bits

Guard Period

3 bits 8.25 bits

156.25 bits (0.577 ms)

Tail 8 bits

Training Sequence

Access Burst Data

Tail

41 synch bits 36 encrypted bits 3 bits

Guard Period 68.25 bits

156.25 bits (0.577 ms) 101

Ci pheri ng Burst to be transmitted

Plain data: Ciphering sequence: XOR: Ciphered data (transmitted): Ciphered sequence: XOR: Recovered data:

Data

S

S

Data

0 1 1 1 0 0 1 0..... 0 0 0 1 1 0 1 0..... 0 1 1 0 1 0 0 0..... 0 0 0 1 1 0 1 0..... 0 1 1 1 0 0 1 0.....

Received burst

Data

S

Training S sequence

Data

102

Interleaving Encoded speech blocks - Diagonal 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

57

57

57

57

57

57

57

57

57

57

57

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

57 57

57

57

57

57

57

57

57

57

57

57

57

57

57

57

57

57

Even bits Odd bits

Bn Bn+1 Bn+2 Bn+3

Encoded control channel blocks - Rectangular 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

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

Tb 3

Coded Data 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

Even bits Odd bits

Bn Bn+1 Bn+2 Bn+3

F Training Sequence F 1 26 1

Coded Data 57

Tb 3

Gp 8.25

103

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

104

Normal Burst 156.25 bits 0.577 ms

T 3

Coded Data 57

Tail Bit(T) Coded Data Stealing Flag Training Seq.

S 1

T. Seq. 26

S 1

Coded Data 57

T 3

GP 8.25

:Used as Guard Time :It is the Data part associated with the burst :This indicates whether the burst is carrying Signaling data (FACCH) or user info (TCH). :This is a fixed bit sequence known both to the BTS & the MS.This takes care of the signal deterioration.

105

156.25 bits 0.577 ms T 3

Training Sequence 41

Coded Data 36

T 3

GP 68.25

Random Access Burst 156.25 bits 0.577 ms T 3

Fixed Bit Sequence 142

T 3

GP 8.25

Freq. Correc. Burst 156.25 bits 0.577 ms T 3

Coded Data 39

Training Sequence 64

Coded Data 39

T 3

GP 8.25

Synchronization Burst 106

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 Downlink 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

BTS > MS

Uplink

5

6

7

MS > BTS 107

Offset

Timing Advance MS1 0 near

1

2

3

4

5

6

7

MS2 0 far

1

2

3

4

5

6

7

MS1 0 near MS2 0 far

At BTS

1

1

2

2

3

3

4

4

5

5

6

6

7

7

At BTS 0

1 0

2 1

3 2

4 3

5 4

6 5

7 6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

108

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)

109

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

110

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 111

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. 112

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

113

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.

114

MS

BTS

MS Location Update (registration) BSC (G)MSC VLR HLR

Action Channel Request (RACH) Channel Assignment (AGCH) TMSI + old LAI

Location Update Request (SDCCH) 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) 115

Security - Authentication MS Ki

RAND

A3 SRES MS

BTS

AuC

RAND SRES SRES

Authentication center provides RAND to Mobile AuC generates SRES using Ki of subscriber and RAND Mobile generates SRES using Ki and RAND Mobile transmits SRES to BTS BTS compares received SRES with one generated by AuC

Auth Result 116

Security - Ciphering MS Ki

RAND

A8

Kc

Um interface

MS

Network Kc

Data

A5

Kc Ciphered Data

A5

Data

Data sent on air interface ciphered for security A5 and A8 algorithms used to cipher data Ciphering Key is never transmitted on air 117

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 118

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

119

GSM Actors NSS BSS

Public Switched Telephone Network

MSC BSC

BTS

VLR

HLR

AUC Mobile subscriber

Fixed subscriber

PLMN Sel ecti on Yes

Is there an up to date found PLMNs list?

Yes

No Creation of a found PLMN list manual mode The user selects a PLMN from the displayed PLMNs

No (manual)

automatic mode The MS selects the first PLMN from the preferred PLMNs list (if it is not in the forbidden PLMNs list) Cell Selection succeed? Yes End of PLMN selection

No (automatic)

Selection of the next preferred possible PLMN

PLMN Sel ecti on •

Consti tuti on of the "Found PLMN l i st" 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

Memorize the beacon frequencies in the precedent selection

=> Create the Found PLMN list

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

(30 in GSM 900 and 40 in GSM 1800)

Ini ti al Cel l Sel ecti on List of the frequencies of the selected PLMN Selection of another PLMN

Eligible cell? No Yes C1 Computation for eligible cells

Suitable cell: Eligible cell

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

Suitable cell? No Yes

Look for the cell with the best C1 in the suitable cells list PLMN set in the forbidden PLMN list

IMSI Attach End of Cell Selection Rejected? No

Yes

Cel l Sel ecti on Purpose: get synchronization with the GSM network prior establishing any communication. 1 1 BTS-5

1

1

BTS-4

H FCC

1 BTS-3

5

SCH

CH BC

This cell BTS-2

2 3 4 BTS-1

Immedi ate Assi gnment BTS

MS 1

MSC

BSC

CHANNEL REQUEST CHANNEL REQUIRED

RACH

2

CHANNEL ACTIVATION 3 4

IMMEDIATE ASSIGNMENT

AGCH

6

OR 6

CM SERVICE REQUEST

SDCCH or TCH LOCATION UPDAT. REQU.

SDCCH or TCH

5

CHANNEL ACTIVATION ACK. IMMEDIATE ASSIGNMENT COMMAND

5

Immediate Assignment

Regi strati on: the Very Fi rst Locati on Update 1 2

BSS 2

IMSI 4 TMSI Release

4 TMSI

BSC 5

MSC 5 6

BTS

2

6 4

TMSI 5

LAI

VLR

HLR IMSI VLR id

3

IMSI TMSI LAI

Intra – VLR Locati on Update 1 2

BSS

TMSI + old LAI new TMSI

2 BSC 3 BTS 4

MSC 3 4 2 New TMSI

TMSI

3 New LAI

VLR IMSI TMSI LAI

IMSI not Required

Inter – VLR Locati on Update BSS

1 2

2

TMSI + old LAI BSC newTMSI

5

MSC

5 7

BTS

7

2 TMSI New TMSI 5

New LAI

New VLR

Old VLR IMSI, TMSI Old LAI

3

RAND, SRES, 4 Kc

IMSI,TMSI LAI RAND, SRES, Kc

6

IMSI not Required

HLR 6 new VLR id

subscriber data

128

IMSI Attach 1

CHANNEL REQUEST IMMEDIATE ASSIGNMENT

BSS 2

3 LOCATION UPDATING

REQUEST (IMSI Attach) Authentication 4 Procedure

LOCATION UPDATING 5 ACCEPT (LAC, TMSI)

BSC BTS

3 4

MSC

5 4

VLR 6

129

IMSI Detach 1

CHANNEL REQUEST IMMEDIATE ASSIGNMENT

3

BSS 2 BSC 3

IMSI DETach INDication CHANNEL RELEASE

IMSI DETach INDication

MSC

BTS 4

VLR

130

Outgoi ng Cal l Great Britain

France

Germany

Telephone network

BSS BSC BTS

Terminating MSC

VLR

Gateway MSC

HLR

FT 131

Mobi l e Ori gi nati ng Cal l BSS

MS CHANNEL REQUEST

Dialing 1

VLR

IMMEDIATE ASSIGNMENT

2

CM SERVICE REQUEST

2

2 3 3

Sending Number

PSTN

MSC

Authentication procedure Ciphering procedure

SETUP (basic) or EMERGENCY

4

CALL PROCEEDING 7

CM SERVICE REQUEST

4

SETUP 5 6

CALL PROCEEDING

IAM

7

Ringing

Assignment procedure

ACM

ALERTING 9

Ringing

CONNECT

Path Established 11

Ring

7

ANM 11

CONNECT ACKnowledge

8 10

ACM = Address Complete Message ANM = ANswer Message IAM = Initial Address Message 132

Mobi l e Termi nati ng Cal l 1 - Pagi ng Pri nci pl e LA1 6

BSC1

4

BTS11

5 BTS12

6

5

MSC/ VLR

1

3

GMSC

PSTN

BSC2

BTS21

2 BTS22

HLR LA2

BSC3

BTS23

BTS31

133

Mobi l e Termi nati ng Cal l 2 - Detai l ed Procedure Visitor PLMN

Home PLMN

International SS7

VLR

Provide Roaming Number (IMSI)

5

HLR 4

Roaming Number (MSRN)

6

9 PAGING REQUEST (TMSI)

11

BSS

Send info to I/C (MSRN)

PAGE (TMSI + LA)

Routing Information (MSRN)

1 MSISDN

3

8 PAGING REQUEST 10 (TMSI + LA)

Send Routing Information (MSISDN)

IAM (MSRN)

7

VMSC

GMSC

IAM 2 (MSISDN)

ISDN

PN

IAM MSISDN MSRN

: Initial Address Message : Mobile Station Integrated Services Digital network Number : Mobile Station Roaming Number

IMSI GMSC VMSC TMSI

: : : :

International Mobile Subscriber Identity Gateway MSC Visitor MSC Temporary Mobile Subscriber Identity 134

Mobi l e Termi nati ng Cal l 3 - End to End Procedure VMSC

BSS

MS

PAGING REQUEST (TMSI or IMSI, LA)

PAGING REQUEST 4

IAM (MSRN)

3

PSTN

GMSC

2

IAM 1 (MSISDN) Dialing

CHANNEL REQUEST (LAC, Cell ID)

5

IMMEDIATE ASSIGNMENT 6 (SDCCH or TCH) CM SERVICE REQUEST (Paging Response)

7

8 9

7

PAGING RESPONSE (TMSI or IMSI, LA)

Authentication procedure Ciphering procedure

Ringing 10 12

Setup, Assignment, Alerting

11

CONNECT 12

Address Complete Message ANswer Message Path Established

135

Cal l Rel ease 1 - Mobi l e Ini ti ated

DISCONNECT

2

2

RELEASE 4

PSTN

Call in progress

1

DISCONNECT RELEASE

3

3

RELEASE COMPLETE

CHANNEL RELEASE 6 7

MSC

BSS

MS

5

Release

RELEASE INDICATION RF Channel Release procedure 8 9

Release tone

136

Cal l Rel ease 2 - PSTN Ini ti ated 1 3

3 BSC

4 5

1

1

BSS

BTS

4 5

MSC

REL 6

2

PSTN

RLC

1 2

Purpose: informs the mobile then releases radio and network resources. On hook

137

Mobile Originated Call • • • • • • •

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

138

Mobile Terminated Call • • • • • • •

Paging Authentication Ciphering Equipment Validation Call Setup Handovers Call Release

139

Mobile Terminated Call MS Paging Assignment CMD (=TCH) on SDCCH

BTSTMSI Paged on PCH BSC

*RESP MS tunes Allocate SDCCH Page on SDCCH REQ MS Ch. * Assgn CMP over AGCH ( TMSI + LAI) over RACH BTS * Phone rings

HLR VLR Query for VLR info

Connect traffic Ch.to trunk GMSC frees SDCCH Query VLR Page Page RES Assgn CMP for LAC and Assign. REQ Paging TMSI the area (+TMSI) Route toNetwork MSC Alerting MSC BSC

AuC

Reply (MSRN) EIR

PSTN

BTS Land to Mobile call (MSISDN)

Authentication and Ciphering procedure done as seen in Location Updation

140

TOPICS • • • • • • • •

GSM CONCEPTS GSM SYSTEM ARCHITECTURE IDENTITIES USED IN GSM GSM CHANNELS GSM RADIO LINK MOBILITY MANAGEMENT CALL MANAGEMENT RADIO RESOURCE MANAGEMENT 141

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

142

Radio Resource Management • • • •

Power Control Hand over Control Discontinuous Transmission Frequency Hopping

143

Power Control

BTS commands MS at different distances to use different power levels so that the power arriving at the BTS’s Rx is approximately the same for each TS - Reduce interference - Longer battery life 144

Handover Means to continue a call even a mobile crosses the border of one cell to another Procedure which made the mobile station really roam Handover causes RxLev (Signal strength , uplink or downlink) RxQual (BER on data) O & M intervention Timing Advance Traffic or Load balancing 145

Handover Types •

Internal Handover (Intra-BSS) – Wi thi n same base stati on - i ntra cel l – Between di fferent base stati ons - i nter cel l

•

External Handover (Inter-BSS) – Wi thi n same MSC -i ntra MSC – Between di fferent MSCs - i nter-MSC

146

Handover Types GMSC

MSC BSC

BSC

C-3 BSC MSC

C-4

C-1

C-2

BSC 147

Intra BSC handover

HO performed HO required Activate TCH(facch) with HoRef#

BSC

Acknowledges and alloctes TCH (facch) if 1. Check for HO passed 2. Channel avail in new BTS

BTS 2

Periodic Measurement Reports (SACCH)

Periodic Measurement Reports

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

HO cmd with HoRef#

Receives new BTS data(FACCH) Release TCH

Cell 2 Periodic Measurement Reports (SACCH)

BTS 1

Cell 1 148

Frequency pl an and i mportance of BCCH Sectored antennas

B5 B6

B4

BPL frequency plan : Broadcast frequencies :

B7

15 Broadcast channels = 48- 62 15 Hopping channels

B3 B1

B8

= 32- 46

B2 B12

MS ( monitoring the broadcast radio B1 in ‘idle mode’ )

B9 B10 B11 F0

F

F1

S

F2

F3

B

B

F4

B

F5

B

F10

…..

F

F11

S

F50

…..

…..

I

• F,S,B exist in t im e slot 0 of each fram e 149

What information does Broadcast Control channel (BCCH) contain?

z

Serves as a Beacon for the Cell

z

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

z

Location Area Identity (LAI)

z

List of neighboring cells which should be monitored by MS

z

List of frequencies used in the cell

z

Cell identity

Back

150

Locati on Updates Loca t ion Upda t e s ca n be cla ssifie d in t o t w o: Pe r iodic Loca t ion Upda t e s: This occurs as per t he t im er set by t he net work operat or. I f t he MS does not perform t his updat e t he MSC m arks t he MS as ‘Det ached’ on t he VLR.

Loca t ion Upda t e on a h a n dove r : This occurs if during a handover t he MS is m oved int o a new Locat ion Area Code ( LAC) . 151

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.

Back

152

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

153

Frequency Hoppi ng • •

Frequency Hoppi ng permi ts the dynami c swi tchi ng of radi o l i nks from one carri er frequency to another. Base Band Hoppi ng – At the BTS each the ti mesl ot i s shi fted to another transcei ver, whi ch i s transmi tti ng at the hop frequency. User wi l l be connected to di fferent Transcei vers dependi ng on hop sequence.

•

Synthesi s Hoppi ng – At the BTS transcei ver changes the frequenci es used. The user wi l l be connected to onl y one transcei ver.

•

Decreases the probabi l i ty of i nterference

•

Suppresses the effect of Rayl ei gh fadi ng

154

Add-on to GSM network : rate for GSM Evolution Enhanced Data PCU; Packet• EDGE Segmentation/re-assembly scheduling is an enhancement ofand GPRS and CSD technologies. • Radio channel access control and management Universal Mobile Telecommunication Standards • Based on the current GSM technology - same TDMA frame structure, • Transmission error detection and retransmission. • Innovative Service Architecture : VHE Concept - providing the us same bandwidth (200 kHz). • Power control the same feelmodulation of its personalized of • look Usesand 8-PSK instead services of GMSK.independent Surf the Internet while on the move SGSN: GPRS mobility network and terminal. • Requires goodSwitched propagation High Speed Circuit Dataconditions. • Encryption • Global Convergence : Fixed/Mobile, Telecom/Datacom, public/private • Allows upto 48 kbps (EGPRS) and upto 28.8 kbps (ECSD) on :every User Data Rate:14.5kbps W@P Gateway • Charging • Mobile Multimedia driven market. channel Useradio multiple timeslots (max=8), • Adaptation of the information to the mobile 160 α-numeric characters GGSN : Data: Interface to the- 2GHz PDN, Internet •SMS Wideband bearers band ( 5 MHz per carrier), -max. 2Mbps • EDGE helps GSM-Only operators to compete with UMTS. hence max: 9.6kbps rate = 115.2kbps. • Compression of theUMTS data User Data Rate UMTS Needs a duplexor in MS for • Buffering of the information One time slot over the air interface Max user data rate : 21.4 kbps simultaneous Tx and Rx Dynamic rate adaptation to suit the radio conditions at EDGE EDGE that time ( 9.05 kbps, 13.4 kbps, 15.6 kbps 21.4 kbps)

Wireless Data

Data Application

GPRS GPRS

HSCSD HSCSD SIM SIM Toolkit Toolkit

GSM GSM DATA DATA

WAP WAP

Circuit Switched technology Packet Switched technology Technology for Applications

W @ P

F o n e

Internet

Mobile Network 98

99

Time

W@P Service

W@P Gateway

2000

2001 155

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

156

Coverage or Traffi c Li mi tati ons TRAFFICLIMITED AREA (10000 subscribers per km2)

COVERAGELIMITED AREA (-75 dBm at cell edge)

COVERAGELIMITED AREA (-70 dBm at cell edge) 157

158

Erl ang Concept Erlang is the unit of statistical resource use

Average number of busy channels during the period of observation (usually, the peak hour). Erlang B At 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 C When more than 1 user request at the same time, instead of rejecting the extra calls, there is a queuing system.

159

Di fferent Types of Cel l s EXTENDED-CELL: macro cell with system coverage extension (≤ 120 km) for coasts...

CONCENTRIC-CELL: macro cell with system coverage limitation inside another macro MACRO-CELL: antenna radiating ‘above’ roofs ---> Wide Coverage (≤ 35 km)

• High sensitivity to interference • Requires "secured" Frequency reuse pattern

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

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

• High isolation from interferences • A few Frequencies intensively reused 160

Cel l Patterns

161

Cel l Sectori zati on

TRI

OMNI

BI

Omni di recti onal Si te Antennas

Bi and Tri sectori al Si te Antennas

Li nk Budgeti ng 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.

- What is the maximum EIRP? - What are the losses in transmission and reception? - Is diversity used?

EIRP:Equivalent Isotropic Radiated Power

- Beyond which distance the communication will cut off? - Is indoor coverage guaranteed? - Is frequency hopping used? - What is the minimum equivalent sensitivity? - What is the maximum equivalent output power? - What are the body losses?

Li nk Budget Parameters •

Overvi ew Standard conf. DLNA conf. Antenna Gain Rx Sensitivity

Radio Link

Common cable Losses Rx Sensitivity

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

Specific Tx Cable Losses Antenna Gain

Combiner losses

Rx Sensitivity Tx PA Output Power

Rx Diversity Gain

Tx PA Output Power

MS

Base Station Duplexer Combiner Power Amplifier DLNA:Diversity Low Noise Amplifier

Other factors for MS Body Losses Common cable losses

Li nk Budget Parameters •

BTS TX Power Ampl i fi er

2.5W PA

GSM 900 S2000L

DCS 1800 S2000L

PCS 1900 S2000L

25W PA

35W PA

20W PA

S2000E S4000 Indoor S4000 Indoor S2000H S4000 Outdoor

S4000 Indoor

30W PA S8000 Indoor S8000 Outdoor

S2000E S2000H S4000 Outdoor

S4000 Indoor S8000 Indoor S8000 Outdoor

S2000E S2000H S4000 Indoor S4000 Outdoor

S8000 Outdoor

Li nk Budget Parameters •

Combi ners

H2D

D D

4.5 4.5dB dBLoss Loss

4.9 4.9dB dBLoss Loss C

Hy/2

TX

TX

2-Way 2-WayHybrid HybridCombiner Combinerwith withDuplexer Duplexer allows Synthesized Frequency Hopping

C

C

C

TX TX TX TX

4-Way 4-WayCavity CavityCombiner Combinerwith with Duplexer Duplexer allows Baseband Frequency Hopping

Li nk Budget Parameters •

Cabl e Losses

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).

Li nk Budget Parameters •

BTS Antenna Gai n 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

Li nk Budget Parameters •

Mobi l e Stati on Parameters 900 MHz

1800/1900 MHz

TX PA Output Power

33 dBm (2W)

30 dBm (1W)

RX Sensitivity

-102 dBm

-100 dBm

Antenna Gain

-2 dBi for Handheld 2 dBi for Car Kit

Common Cable Loss

0 dB for Handheld 2 dB for Car Kit

Body Loss

3 dB for Handheld 0 dB for Car Kit

Li nk Budget Presentati on Parameters Antenna Gain (65 °) 18 dBi

Frequency Base Height Mobile Height Environment

Jumper Loss 0.5 dB Feeder Loss 3 dB

Penetration Factor 15 dB

Sensitivity -110 dBm Coupling system Tx loss 4.5 dB

RXm

1800 MHz 40.0 m 1.5 m Urban

Body Loss 3 dB

Outdoor Minimum Field 95%: -80 dBm Coverage Range 95%: 810 m

Cable Loss 0 dB

Antenna Gain -2 dB

RX

TX

Output Power 30 dBm

RXd

Sensitivity Max TX Output Power 44.8 dBm

-100 dBm

Options Rx Diversity Gain: 5 dB

Base Station

Mobile

Overlapping Margin: 0 dB 173

Li nk Budget Cal cul ati on Exerci se 1: S8000 INDOOR: OPERATING FREQUENCY 1800 MHz

BTS

MS

TX OUTPUT POWER

30.00 W (44.8 dBm)

1.00 W (30.0 dBm)

BODY LOSSES

3.0 dB

COMBINER LOSSES

5.0 dB

None

OVERLAPPING MARGIN

0.0 dB

-110.0 dBm

-102.0 dBm

INDOOR PENETRATION FACTOR

18.0 dB

RX SENSITIVITY RX SENSITIVITY + DIVERSITY

-115.0 dBm

None

COMMON CABLE LOSSES

3.0 dB

0.0 dB

18.0 dBm

-2.0 dBm

ANTENNA GAIN

174

Fadi ng Example of Field Strength Variation for GSM 1800 -10

Zoom on Short Term Fading

-20 Measurement Free Space

Field Strength (dBm)

-30

≅ λ/2

-40

±2m -50 -60

Long Term Fading

-70 -80 -90 0 -100

500

1000

1500

2000

2500

3000

Distance (m)

3500

4000

4500

5000

Cl utters

177

Mobile Station (MS) • •

Hand portable unit Contains Mobile Equipment(ME) and Subscriber Identity Module (SIM)

178