Microsoft PowerPoint - GSM1

Overview of GSM Architecture

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GSM/DCS1800 System

• Some Histories & Some Background

• GSM/DCS1800 System Architecture

• High-Level View of Some Scenarios

• GSM Time Slot Structure

• GSM Logical Channels

• GSM Frame Structure

• Low-Level View of Some Scenarios

• GSM System Diagram& Protocol Stack

• Different Between GSM and DCS 1800

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Milestones of the GSM

1982 1984 1985 1987 1988/89~1991/92 1990

1991 1992 1993 1995 1997

• CEPT decides to establish a Groupe SpecialeMobile (GSM) to develop a set of commonstandards for a future pan-European cellularmobile network

• Establishment of 3 work parties to define &describe the services offered in a GSM (radiointerface, signaling protocol, interfaces,…...)

• Discussion & adoption of a list ofrecommendations to be generated by the group >100 recommendations in series of 12 volumes

• Initial Memorandum of Understanding (MoU)signed by telecommunication network operatororganizations

• GSM becomes a technical committee withinETSI & splits up into GSM group 1-4, latercalled Special Mobile Group (SMG) 1-4

• The GSM specifications for the 900MHz are also applied at 1800 MHzband (DCS1800), a PCN applicationsinitiated in the UK

• July:: Planned GSM commercial launch of GSMservice in Europe (MoU plan) delayed to 1992because of non-availability of type-approvedterminals

• Official commercial launch of GSM service inEurope

• The GSM-MoU has 62 members (signatories) in39 countries worldwide; in addtion 32 potentialmember (observers/applicants) in 19 othercountries

• GSM networks operational or underdevelopment in 60 countries worldwide,with over 5.4 million subscribers

•Over 64 million subscribers

GSMGlobal System for Mobile

Communication

GSM/DCS1800 System (1)

Page-4

GSM Services

Service Category Service Comments

Tele-services y Telephony (Speech)y Emergency calls (speech)y Short Message services: point-to-point

& point-to-multi-point (cell broadcast)y Tele-fax

y Full rate (13Kbps)

y Alphanumeric information: userto user & network to all users

y Group 3

Bearer Services y Asynchronous datay Synchronous datay Asynchronous PAD (packet switched,

packet assembler/disassembler) accessy Alternate speech & data

y 300-9600 bpsy 300-9600 bpsy 300-9600 bps

y 300-9600 bps

SupplementaryServices

y Call forwardingy Call barring

Phase 1Services


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GSM Services

Service Category Service Comments

Tele-services y Telephony (Speech)y Short Message services:

y Half rate (6.5 Kbps)y General Improvements

Bearer Services y Synchronous dedicated packet dataaccess

y 2400-9600 bps

SupplementaryServices

y Calling/connected line identitypresentation

y Calling/connected line identityrestriction

y Call waitingy Call holdy Multiparty communication closed user

groupy Advice of charge Online charge information

Phase 2Services


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GSM/DCS1800 System










)

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GSM System Architecture

OMC

PSTN

ISDN

DataNetwork

BTS

BTS

BTS

BSC

BTS

BTS

BTS

BSC

HLR VLR AUC

MSC

Base Station Subsystem Network Switching Subsystem Public Network

Operation &Maintenance Subsystem

MS

MS


Page-8

GSM System Architecture

AUC�Authentication Center HLR�Home Location RegisterBTS�Base Transceiver Station MSC�Mobile Switching CenterBSC�Base Station Controller OMC�Operation and Maintenance CenterEIR�Equipment Identity Register VLR�Visited Location RegisterGMSC�Gateway Mobile Switching Center

GMSC

MSC BSC

OMCVLR

HLR

AUC

PSTN AEF

C

BD

Abis (through ISDN protocol)

MSUmBTS

EIR

BSC

BTS


• Functional Entities of GSM

Page-9

Mobile Station

• Mobile Station Types– Vehicle-mounted stations– portable stations– handheld stations

• Mobile Station Power Classes– Vehicular & portable units can be either class I or class II– Handheld units can be class III, IV, & V

Class Max. RF Power (W)

I 20

II 8

III 5

IV 2

V 0.8


I 20

II 8

III 5

IV 2

V 0.8


Page-10

Identities of Mobile Station

• Mobile station has three identities– International Mobile Subscriber Identity (IMSI)

– International Mobile Equipment Identity (IMEI)

– Temporary Mobile Subscriber Identity (TMSI)


Page-11


• International Mobile Subscriber Identity– IMSI is assigned to an MS at subscription time

– It uniquely identifies a given MS

– It contains 15 digits• Mobile Country Code (MCC)

– 3 digits (home country)

• Mobile Network Code (MNC)– 2 digits (home GSM PLMN)

• Mobile Subscriber Identification(MSIN)

• National Mobile Subscriber Identity(NMSI)

– 262 02 454 275 1010

Mobile SubscriberIdentification Number (MSIC)

MCC = Germany NMC = private operator D3 private


Page-12


• International Mobile Equipment Identity (*#06#)– IMEI uniquely identifies the MS equipment

– It is assigned by the equipment manufacturer

– It contains 15 digits• Type Approval Code (ATC)

– 6 digits

• Final Assembly Code (FAC)– 2 digits

• Serial Number (SNR)– 6 digits

• Spare (SP)– 1 digit


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• Temporary Mobile Subscriber Identity– TMSI is assigned to MS by the Visitor Location Register (VLR)

– TMSI uniquely identifies an MS within the area controlled by a givenVLR

– A maximum of 32 bits can be used for TMSI


Page-14


• Subscriber Identity Module Card (SIM card)– IMSI

– Authentication Key

– Subscriber information

– Access control class

– Cipher key

– Additional GSM services

– Location Area Identity

– Forbidden PLMN


Page-15

Base Station Subsystem

• Base Station Subsystem (BSS) contains 2 Parts– Base Station Controller (BSC)

– Base Transceiver System (BTS)• It contains the Transcoder Rate Adopter Unit (TRAU)

– GSM-specific speed encoding & decoding is carried out, as well as the rateadaptation function for data

• Power class are also classified in a similar way to MS with 8 classes in 3 dBsteps from 2.5 W to 320 W


Page-16

Network and Switching Subsystem

• Network and Switching Subsystem contains– Switching functions of the GSM

• MSC & GMSC

– Database required for the subscriber

– Mobility management


Page-17

Operational & MaintenanceSubsystem

• Operational and Maintenance Subsystem– Responsibility

• The OMS is responsible for handling system security based on validation ofidentities of various telecommunication entities.

– Performed by• Authentication Center (AUC): The AUC is accessed by HLR to determine whether an

MS will be granted services

• Equipment Identity Register (EIR): The EIR provides MS information used by theMSC. The EIR maintain a list of legitimate, fraudulent or faulty MSs.

• In charge of remote operation and maintenance of PLMN.

• Operational and Maintenance Center (OMC)– The functional entity through which the service provider monitors and controls

the system.


Page-18

GSM QoS Requirements

• GSM Service Quality Requirements

QoS Required TimeTime from switching to service ready 4 sec in the home system and 10 sec in the visiting system

Connect time to called network 4 sec

Release time to called network 2 sec

Time to alert mobile of inbound call 4 sec in first attempt and 15 sec in final attempt

Maximum gap due to handoff 150 ms if intercell and 100 ms if itracell

Maximum one-way speech delay 90ms

Intelligibility of speech 90%

QoS Required TimeTime from switching to service ready 4 sec in the home system and 10 sec in the visiting system

Connect time to called network 4 sec

Release time to called network 2 sec

Time to alert mobile of inbound call 4 sec in first attempt and 15 sec in final attempt

Maximum gap due to handoff 150 ms if intercell and 100 ms if itracell

Maximum one-way speech delay 90ms

Intelligibility of speech 90%


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GSM/DCS1800 System










)

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High-Level View of Some Scenarios

Acknowledgement of new area & TMSI

MS BTS BSC MSC VLR HLR

Channel RequestChannel activation commandChannel activation acknowledgeChannel AssignmentLocation Update RequestAuthentication RequestAuthentication Response

Comparison of the Authenticationparameters

Assignment of the new area & TMSI

Entry of the new area & identityinto VLR & HLR

Channel Release

• GSM Registration Scenarios


Page-21

GSM Call Flow Scenarios

• Call Setup with a Mobile to Land Call– Part I

MS BSS MSC VLR

Um A B

12

3

4

5

6

7

8

SETUP_REQ Access Subscriber Data

SUB_DATA_RESPCall Proceeding

Assign Truck &Radio ChannelAssign Radio

Channel

Radio AssignmentComplete

Truck & Radio Assignment complete


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• Call Setup with a Mobile to Land Call– Part II

MS MSC PSTN

1

2

3

4

5

6

NET_SETUP

Alerting

Connect (Answer)

Connect

ConnectAcknowledgement

NET_ALERT


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• Call Release With Mobile to Land Call– Mobile Initiated

MS BSS MSC PSTN

Um A

12

3

4

5

6

7

CALL_DISCNET_REL

CALL_REL

REL_COMP

CLR_COMM

CHH_REL

CLR_COMP


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• Land to Mobile Call– Part I– Assumption

• MS is registered with the system & has been assigned a TMSI• MS is in its home system

PSTN MSC HLR VLRC

12

34

5

INC_CALL

GET_ROUT

ROUT_INF

INCO_CALL

PERM_PAGE


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• Land to Mobile Call (Paging)– Part II

MS BSS MSC VLR

Um A

1

2

3

4

5

6

7

PERM_PAGE

PAGE_MESS

CH_REQ

DSCH_ASS

PAGE_RESP

PAGE_RESP

PAGE_RESP

B


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• Handoff– MS scans transmission from surrounding BSs in the spare timeslots

• It then reports the measured results back to the fixed network via BS, wherethe handoff decision is made

– Classifications• Internal Handoff

– Inter-BSS Handoff

• External– Intra-MSC Handoff

– Inter-MSC Handoff


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• Handoff– Intra-MSC Handoff


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GSM/DCS1800 System










)

Page-29

GSM Time Slot Structure

Up-link (MS to BS)• 890 MHz ~ 915 MHz (25 MHz Bandwidth)

Down-link (BS to MS)• 935 MHz ~ 960 MHz (25 MHz Bandwidth)

Carriers or Channels• Each up-link or down-link has 124 Carriers with a bandwidth of 200 KHz, excluding 2×100

KHz edges of the band• The use of carrier 1 and 124 are optional for operators.

1 2 3 124

100 kHz 200 kHz 100 kHz

124,,2,1 )1(2.02.935

)1(2.02.890

�=−×+=−×+=

NMHzNF

MHzNF

d

u

• Frequency Bands and Bandwidth


GSM 900

Page-30

Frequency Bands and Bandwidth

Up-link (MS to BS)• 1710 MHz ~ 1785 MHz (75 MHz Bandwidth)

Down-link (BS to MS)• 1805 MHz ~ 1880 MHz (75 MHz Bandwidth)

DCS-1800

Carriers or Channels• Each up-link or down-link has 374 Carriers with a bandwidth of 200 KHz, excluding

885512 )1(2.01805

)1(2.01710

≤≤−×+=−×+=

NMHzNF

MHzNF

d

u


Page-31

• FDMA/TDMA Structure• The total bandwidth is divided into 124×200 kHz bands (FDMA)

• Each 200 kHz band can support maximum 8 users (TDMA)

• The GSM can support up to 992 (124×8) simultaneous users with the full-rate speech coder.

Channel #1 Channel #2 Channel #3 Channel #4 Channel #5 Channel #6 Channel #7 Channel #8



TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7

Freq. #1

Freq. #2

Freq. #124



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Time-Division Duplex (TDD)•No need for a dedicated duplex stage (duplexer); theonly requirements are to have a fast switchingsynthesizer, RF filter paths & fast antenna switchesavailable

• Increased battery life or reduced battery weight

0 1 2 3 4 5 6 7

5 6 7 0 1 2 3 4

BS Transmits

MS Transmits


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Pulsed Transmission•The tendency for a pulsed radio to disturb neighboringfrequency channels is called AM splash.

10µ s 8µ s 10µ s 10µ s 8µ s 10µ s542.8µ s (147 bits)

-70 dB

-30 dB

-6 dB-1 dB4 dB


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• Time Slot Structure or Burst types in GSM– Normal Bursts– Random Access Burst– Frequency Correction Bursts– Synchronization Bursts


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NormalBurst

Tail Bits (TB)• Used as a guard time.& this time covers the periods of uncertainty during the ramping up & down ofthe power bursts form the MS in accordance with the power-versus-time template

TB(3 bits)

Coded Data(57 bits)

TrainingSequence(26 bits)

Coded Data(57 bits)

TB(3 bits)

Guard Time(8.25 bits)

StealingFlag

(1 bits)

StealingFlag

(1 bits)

148 bits = 546.12 µ s

Stealing Flag• Used as an indication to the decoder of whether the incoming burst iscarrying signaling data or user data

Training Sequence• Used to compensate for the effects of multi-path fading.There are 8 different sequences defined in GSM.


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Random AccessBurst

TB(8 bits)

Synchronization Sequence(41 bits)

Coded Data(36 bits)

TB(3 bits)


88 bits = 324.72 µ s


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Frequency-Correction

Burst

TB(8 bits)

Fixed bit Sequence(142 bits)

TB(3 bits)


148 bits = 546.12 µ s


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SynchronizationBurst

148 bits = 546.12 µ s

TB(3 bits)

Coded Data(39 bits)

SynchronizationSequence(264bits)

Coded Data(39 bits)

TB(3 bits)



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GSM/DCS1800 System










)

Page-40

GSM Logical Channels

• ClassificationsLogic Channel

Traffic Channel(TCH)

Control Channel(CCH)

Cell BroadcastChannel (CBCH)

TCH/Full(TCH/F)

TCH/Half(TCH/H)

Broadcast Channel(BCH)

Common ControlChannel (CCCH)

Dedicated ControlChannel (DCCH)

Freq. Correction Channel (FCCH)

Synchronization Channel (SCH)

Broadcast ControlChannel (BCCH)

Paging Channel (PCH)

Access GrantChannel (AGCH)

Random AccessChannel (RACH)

Associated ControlChannel (ACCH)

Stand-Alone DedicatedControl Channel (SDCCH)

Slow Associated Control Channel

(SACCH)

Fast Associated Control Channel

(FACCH)

SACCH/TF SACCH/TH SACCH/C4 SACCH/C8

FACCH/F FACCH/H

SDCCH/4

SDCCH/8


Page-41


• Traffic Channel– Are used to transmit user information (speech or data)

– 2 categories• TCH/Full (TCH/F)

– Allows the transmission of 13 Kbps of speech

• TCH/Half (TCH/H)– Allows the speech coded at a half rate

Logic Channel


TCH/Full(TCH/F)

TCH/Half(TCH/H)




Page-42


• Control Channel (CCH)– Are used to transmit control and signaling information

• Broadcast Channel (BCH)

• Common Control Channel (CCH)

• Dedicated Control Channel (DCCH)

Logic Channel








Page-43


• Control Channel (CCH)– Broadcast Channel (BCH)

• Are point-to-multipoint, downlink-only channels

• Classification– Broadcast Control Channel (BCCH)

– Frequency Correction Channel (FCCH)

– Synchronization Channel (SCH)

Logic Channel



Freq. Correction Channel (FCCH)

Synchronization Channel (SCH)

Broadcast ControlChannel (BCCH)




Page-44


• Control Channel (CCH)– Common Control Channel (CCH)

• Are point-to-multipoint, downlink-only channels that are used for paging &access except for RACH.

• Classifications– Paging Channel (PCH)

– Access Grant Channel (AGCH)

– Random Access Channel (RACH)

Logic Channel




Paging Channel (PCH)

Access GrantChannel (AGCH)

Random AccessChannel (RACH)



Page-45


• Control Channel (CCH)– Dedicated Control Channel (DCCH)

• Are bidirectional, point-to-point channels

• Classifications– Stand-Alone Dedicated Control Channel (SDCH)

– Associated Control Channel (ACCH)• Slow Associated Control Channel (SACCH)

• Fast Associated Control Channel (FACCH)

Logic Channel





Associated ControlChannel (ACCH)

Stand-Alone DedicatedControl Channel (SDCCH)


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GSM/DCS1800 System










)

Page-47

GSM Frame Structure

ChannelCombinations

(I)

• I : TCH/FS + FACCH/FS + SACCH/FS• II : TCH/HS(0,1) + FACCH/HS(0,1) + SACCH/HS(0,1)• III: TCH/HS(0) + FACCH/HS(0) + SACCH/HS(0) + TCH/HS(1) +

FACCH/HS(1) + SACCH/HS(1)• IV: FCCH + SCH + CCCH + BCCH• V : FCCH + SCH + CCCH + BCCH + SDCCH/4 + SACCH/4• VI : CCCH + BCCH• VII: SDCCH/8 + SACCH/8

Each channel combination requires one single physical channel


Page-48

GSM Frame Structure

ChannelCombinations (II)

• I : TCH/FS + FACCH/FS + SACCH/FS

Traffic Channel Frame Structure (26-multi-frame)

T 0 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9T10

T11

S12

T13

T14

T15

T16

T17

T18

T19

T20

T21

T22

T23

T24

I25

T=TCH, S=SACCH, I=Idle

26 Frames = 120 ms


Page-49

GSM Frame Structure

ChannelCombinations (III)

Traffic Channel Frame Structure (26-multi-frame)

• II : TCH/HS(0,1) + FACCH/HS(0,1) + SACCH/HS(0,1)• III: TCH/HS(0) + FACCH/HS(0) + SACCH/HS(0) +

TCH/HS(1) + FACCH/HS(1) + SACCH/HS(1)

T 0t1

T 2t3

T 4t5

T 6t7

T 8t9

T10

t11

S12

T13

t14

T15

t16

T17

t18

T19

t20

T21

t22

T23

t24

T=TCH1 , S=SACCH1 , t=TCH2, s=SACCH2

26 Frames = 120 ms

s25


Page-50

GSM Frame Structure

ChannelCombinations (IV)

• IV : FCCH + SCH + CCCH + BCCH

Signaling Channel Frame Structure (51-multi-frame)

Down-Link :: F=FCCH, S=SCH, B=BCCH, C=CCCH (PCH,AGCH), I=Idle

51 Frames = 235.38 ms

F 0 S 1 T 2BCCH2 ~ 5

CCCH6 ~ 9

F10

S11

CCCH12~19

F20

S21

CCCH22~29

S31

CCCH32~39

F40

S41

CCCH42~49

I50

F30

R 0 R 1R10

R11

R20

R21

R31

R40

R41

R50

R30

Up-Link :: R=RACH


Page-51

GSM Frame Structure

ChannelCombinations (V)

• V : FCCH + SCJ + CCCH + BCCH + SDCCH/4 + SACCH/4



Page-52

GSM Frame Structure

ChannelCombinations (VI)

VI : CCCH + BCCH• Used as a BS has to manages a huge number of transceiver which means the number of

CCCHs provided by combination IV is not enough to handle the network• Assign additional control channels in combination IV. While combination IV always

occupies time slot 0, combination VI is assigned to time slot 2, 4, or 6.• The combination VI multi-frame structure is similar to combination IV.



Page-53

GSM Frame Structure

ChannelCombinations (VII)

• VII : SDCCH/8 + SACCH/8



Page-54

GSM Frame Structure

• Frame Hierarchical Structure– Hyper-frame,super-frame,multi-frame,frame,time slot– A time slot carries 156.25 bits

3 57 57 26 1 1 3 8.25

0 1 2 3 4 5 6 7

0 1 2 …… 23 24 25

0 1 2 …… 47 48 49

0 1 2 …… 2045 2046 2047

156.25 bits Tail DataStealing

Bit Training DataStealing

Bit Tail GuardGSM Time-Slot(Normal Burst)

GSM Frame (4.615 ms)

1 Multi-frame=26 frame(120 ms)

GSM Super-frame(26×51=1326 frame

=6.12 sec)

GSM hyper-frame(3.48 hours)

0 ……1 2 47 48 49 501 Multi-frame=51 frame(3060/13 ms)


Page-55

GSM Frame Structure

• T1, T2 & T3 Counters– T1 counter counts the super-frames

• Whenever a super-frame is completed, T1 is incremented by 1 & 0 ≤ T1 ≤2047

– T2 counter counts the speech frames, which only occur in 26 multi-framestructure & 0 ≤ T2 ≤ 25

– .T3 counter counts the signaling frames, which are 51-multi-framestructure & 0 ≤ T3 ≤ 50


Page-56

GSM Frame Structure

Example of How aMS Behaves

26multi-frame

51multi-frame

T T T T T

B S B S B S B S B S

0

0

1

1

2

2

3

3

5049484746

2524232221

0 1 2 3 2524232221 0 1 2 3 5049484746

B T S

TDMA Frame


Page-57

GSM Frame Structure

SynchronizationWith the Network

When a MS is turned on, it has to orient itself within the network1. It synchronizes itself in frequency2. It synchronizes itself in time3. It reads the system & cell data from base channel or more specifically from BCCH

To find the frequency where the FCCH, SCH & BCCH are beingtransmitted

The MS uses the SCH for this purpose. Since it has found theFCCH, so it already knows that SCH will be follow in the nextTDMA frame


Page-58

GSM/DCS1800 System










)

Page-59

GSMLocation Updating Scenarios

MS BS

Channel Request

Channel Assignment

Authentication Request from the network

Authentication Response from the MS

Request for location updating. This is alreadytransmitted on the assigned channel

Request to transmit in the ciphered mode

Acknowledgement of the ciphered mode

Confirmation of the location updating including the optional assignment TMSI

Channel Release from the network

Logical Channel

RACH

AGCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

SDCCH

Acknowledgement of the new location & the temporary identity


Page-60

GSMCall Establishment Scenarios

MS BS

Channel RequestChannel Assignment

Authentication Request from the networkAuthentication Response from the MS

Answer to the paging from the network

Request to transmit in the ciphered modeAcknowledgement of the ciphered mode

Set up message for the incoming call

Assignment of a traffic channel

Logical Channel

Confirmation

Mobile Terminated Call

PCHRACH

AGCH

SDCCHSDCCH

SDCCHSDCCH

SDCCHSDCCH

SDCCHSDCCH

FACCHFACCH

FACCHFACCH

TCH

Paging of the MS

Acknowledgement of the traffic channel

Alerting (now the caller gets the ringing sound)

Connect message when the MS is off-hookAcceptance of the connect message

Exchange of user data (speech)


Page-61


• Logic Control Channel Structure– Classify by call setup

CCH

CAC

(Common Access Channel)

USC

(User Specific Channel)(After call set-up)

BCH

CCCH

SDCCH

SACCH

FACCH

BCCH

FCCH

SCH (Broadcast Channel)(Before Call Set-up)

(Common Control Channel)(During Call Set-up)

PCH

RACH

AGCH


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GSM/DCS1800 System









• Different Between GSM and DCS 1800)

Page-63

GSM System Diagram

• GSM System Block Diagram– Information Processing

– RF Baseband Processing

Speech Digitizing &source coding

Modulation

Interleaving

Encryption

Burst formatting

Channel coding

Source deconding& D/A

Demodulation

De-interleaving

Decryption

Burst deformatting

Channel decoding

Speech

MS MSC


Page-64

GSM System Diagram

• Source (Speech) Coding– Mobile Station (Analog Signal)

• Low-pass filter, then A/D converter, then RPE-LTP speech encoder

– MSC (Base Station) (Digital Signal)• 8-bit A-law to 13-bit Uniform converter, then RPE-LTP speech encoder

8bit A-law to 13bitUniform Converter

RPE-LTP Encoder

Low-Pass Filter A/D Converter RPE-LTP Encoder

Mobile Station

MSC

Analog Signal

Digital Signal

13×8000=104 kbps

13 ×8000=104 kbps

13 kbps

13 kbps

ToChannel Encoder

ToChannel Encoder


Page-65

GSM System Diagram

• Source (Speech) Coding– Regular Pulse Excited Long-Term Prediction (RPE-LTP) Encoder

• Input has bit rate of 104 kbps

• Has net bit rate of 13 kbps

• Output from RPE-LTP 260 bits every 20 ms

bits per 5 ms Bits per 20 ms

Linear Prediction Coding (LPC) filter 36Long Term Prediction (LTP) filter 9 36Excitation Signal 47 188Total 260Class I 182

(class Ia=50, class Ib=132)Class II 78

bits per 5 ms Bits per 20 ms

Linear Prediction Coding (LPC) filter 36Long Term Prediction (LTP) filter 9 36Excitation Signal 47 188Total 260Class I 182

(class Ia=50, class Ib=132)Class II 78


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GSM System Diagram

RPE-LTP Speech Encoder

Cyclic Redundancy Encoder

1/2 Convolutional Encoder

260 bits

20 msClass I: 182 bits

Class II: 78 bits

50 bits

132 bits

53 bits

185 bits4 tail bits all equal to zero

189 bits

378 bits

456 bits

20 ms

Speech& Channel

Coding


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GSM System Diagram

• Structure of Interleaver– interleaving speech frames onto TDMA frame


Page-68

GSM System Diagram

Data& ChannelCoding (I)

TCH/F9.6• 9.6 Kbps refers to the user’s transmission rate, the actual rate is brought up to 12 Kbps through channel

coding in the terminal equipment; that is, 12 Kbps is the rate delivered to the MS.

User Information

1/2 Convolutional Encoder

240 bits

20 msAdd 4 “0” bits

488 coded bits

456 bits

20 ms

Puncturing of 32 coded bits


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GSM System Diagram

Data& ChannelCoding (II)

Structure of Interleaver• The blocks are spread over 22 bursts. Even though the interleaving covers 22 bursts, it is

referred to as a 19-bursts interleaving plan.• 456 bits = 16 parts of 24 bits each (16× 24= 384) + 2 parts of 18 bits each (2×18=36) + 2 parts of 12 bits each (2× 12=24) + 2 parts of 6 bits each (2× 6=12)

• A burst (time slots) contains information from either 5 or 6 consecutive data blocks;that is,c 4 parts of 24 bits each and 1 part of 18 bits (96 + 18 = 114) or d 4 parts of24 bits each and 1 part of 12 bits each and 1 part of6 bits each (96+12+6=114)

• 1st & 22nd burst contains 6 bits each (12 bits); 2nd & 21st burst contain 12 bits each(24 bits); 3rd & 20th carry 18 bits each (36 bits) & we have 6 bursts. We needanother 16-burst. We then put 24 bits in each of the 4th~19the bursts (384 bits).


Page-70

GSM System Diagram

Signaling& ChannelCoding (I)

Channel Coding of Signaling Channels• Signaling information contains a maximum of 184 bits. It does NOT make a difference whether the type of

signaling information to be transmitted is mapped onto a BCCH, PCH, SDCCH or SACCH. The formatalways stays the same.

• Special format are reserved for the SCH & RACH• FCCH requires no coding at all

Signaling Information

Block Encoder (Fire Code)

184 bits

Fire coded adds 40 parity bits to the 184 bit = 224 fire-coded bits, then adds 4 “0” bits

456 bits

1/2 Convoluational Encoder


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GSM System Diagram

Signaling& ChannelCoding (II)

Bit Number of the Coded Bits Position within the frame structure0 8……448 Even bits of burst N

1 9……449 Even bit of burst N+1



4 12……452 Odd bits of burst N+4




Bit Number of the Coded Bits Position within the frame structure0 8……448 Even bits of burst N








Structure of Interleaver


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GSM System Diagram

Modulation (I)

GMSK• is a constant-envelop variety of modulation & it lacks of AM in the carrier with aconsequent limiting of the occupied bandwidth.

• The constant amplitude of the GMSK signal makes it suitable for use with high-efficiencyamplifiers.


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GSM Protocol Stack

General Viewof GSM protocol

Layer 1

LAPDm

RR

MM

CM

Layer 1 Layer 1 Layer 1

LAPDm LAPD LAPD

RR BTSM

CM

MM

BSSMAP/DTAP

SCCP

MTP

BSSMAPDTAP

SCCP

MTP

RR

BTSM

Um Abis A

MS BTS BSC MSCSignaling Architecture

Layer3


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GSM Protocol Stack

GSM protocol(I)

Layer 2(Data Link Layer)

Responsibilities of LAPD/LAPDm• Organization of Layer 3 information into frames• Peer-to-peer transmission of signaling data in defined frame formats• Recognition of frame formats• Establishment, maintenance & termination of one or more data links on signaling channels• (Un)Acknowledgement of transmission & reception of numbered information frames (I-frames)

• Unacknowledge transmission & reception of unnumbered information frames (UI-frames)


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GSM Protocol Stack

GSM protocol(II)

Layer 2 (Data Link Layer)

Frames Format• 4 types of formats: A, B, Abis, Bbis• The bis designation is sometimes written as a prime mark (Abis = A’)

Address Field(variable length)

Control Field(8 bits)

Length Indication(variable length)

Fill Field(variable length)

Format A

Address Field(variable length)

Control Field(8 bits)


Fill Field(variable length)Format B

Information Field(variable length)


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GSM Protocol Stack

GSM protocol(III)

Layer 2 (Data Link Layer)

Frames Format• 4 types of formats: A, B, Abis, Bbis• The bis designation is sometimes written as a prime mark (Abis = A’)

Length Indication (variable length) Fill Field (variable length)Format Abis


Fill Field(variable length)

Format BbisInformation Field(variable length)


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GSM Protocol Stack

GSM protocol(IV)

Layer 3 (Network Layer)

Network Layer• Also referred to as the “signaling layer”• Use a protocol that contains all the functions & details necessary to establish, maintain & thenterminate mobile connections for all the services offered within a GSM.. The network layer alsoprovides control functions to support additional services such as supplementary services & shortmessage services

3 sub-layers• Radio Resource Management (RR)• Mobility Management (MM)• Connection Management (CM)


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GSM Protocol Stack

GSM protocol(V)


Radio Resource Management sub-layer (RR sub-layer) is responsible for• The management of the frequency spectrum• The GSM’s reactions to the changing radio environment• Everything related to maintaining a clear channel between the system and the MS• Handoff from one cell to another

Procedures for the RR sub-layer used to cover these tasks• Channel assignment• Channel release• Channel change & handoff procedure• Change of channel frequencies, hopping sequences (hoppingalgorithms) and frequency tables

• Measurement reports from the MS• Power control and timing advance• Cipher mode setting


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GSM Protocol Stack

GSM protocol(VI)


Mobility Management sub-layer (MM sub-layer) is responsible for• cope with all the effects of handling a mobile user that are not directly related to the radiofunction such as

• Support of user mobility, registration, and management of mobility data• Checking the user and equipment identity• Checking if the user is allowed to use the services and what kind of extra services areallowed

• Support of user confidentiality (registering the user under a TMSI)• Provision of user security• Provision of an MM connection to the CM sublayer

Procedures for the MM sub-layer used to cover these tasks• Location Update procedure• Periodic updating• authentication procedure• IMSI attach & detach procedure.• TMSI reallocation procedure• Identification procedure


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GSM Protocol Stack

GSM protocol(VII)


Connection Management sub-layer (CM sub-layer) is responsible for• It manages all the functions necessary for circuit-switched call control & there are otherentities within the CM sub-layer to cope with providing supplementary services & SMS

Procedures for the CM sub-layer used to cover these tasks• Call establishment procedures for mobile-originated calls• Call establishment procedure for mobile-terminated call• Changes of transmission mode during an ongoing call (incallmodification)

• Call reestablishment after interruption of an MM connection• Dual-tone Multi-frequency (DTMF) control procedure for DTMFtransmission.


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GSM Protocol Stack

GSM protocol(VIII)

Layer 3 (Network Layer) Message Structure

TI flag(1 bit)

TI(3 bits)

ProtocolDiscriminator

(4 bits)

0(1 bit)

Message Type(7 bits)

Information Elements“Mandatory”

(variable bytes)

Information Elements“Optional”

(variable bytes)

TI:: Transaction Identifier

Double Check the frame format ???


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GSM Protocol Stack

GSM protocol(IX)


TI flag(1 bit)

TI(3 bits)


(4 bits)

0(1 bit)



(variable bytes)


(variable bytes)

It is used to distinguish between (possible) multiple parallel CMconnections and between the various transactions taking place overthese simultaneous CM connections


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GSM Protocol Stack

GSM protocol(X)


TI flag(1 bit)

TI(3 bits)


(4 bits)

0(1 bit)



(variable bytes)


(variable bytes)

P ro toco l P ro toco l D isc rim in ato rR ad io R esou rce M gm t 0 110

M ob ili ty M gm t 0 101C a ll C on tro l 0 011

S h ort M essage S erv ice 1 001S u pp lem en tary S erv ice 1 011

Test P roced u re 1111A ll o th er va lu e are reserv ed

P ro toco l P ro toco l D isc rim in ato rR ad io R esou rce M gm t 0 110

M ob ili ty M gm t 0 101C a ll C on tro l 0 011

S h ort M essage S erv ice 1 001S u pp lem en tary S erv ice 1 011

Test P roced u re 1111A ll o th er va lu e are reserv ed


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GSM Protocol Stack

GSM protocol(XI)


TI flag(1 bit)

TI(3 bits)


(4 bits)

0(1 bit)



(variable bytes)


(variable bytes)

• It indicates the function of the Layer 3 message•Uses only low 6 bits for addressing 64 differentmessage in a protocol, another bit is used a sendsequence variable & may be used for MM and CMmessages


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GSM Protocol Stack

GSM protocol(XII)


TI flag(1 bit)

TI(3 bits)


(4 bits)

0(1 bit)



(variable bytes)


(variable bytes)

There are 4 possible combination of Information Element•Mandatory fixed length•Mandatory variable length•Optional fixed length•Optional variable length


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GSM Protocol Stack

GSM protocol(XIII)

Layer 3 (Network Layer)Example of a Call Establishment Sequence

M S Transmits Network TransmitsChannel Request Ö

Õ Immediate AssignmentConnection M anagement

Service RequestÖ

Õ Authentication RequestAuthentication Response Ö

Õ Ciphering M ode CommandCiphering M ode Complete Ö

Setup Ö

Õ Call proceedingÕ Assignment command

Assignment Complete Ö

Õ AlertingÕ Connect

Connect Acknow ledge Ö


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Digital Cellular System (DCS)-1800

• General Description– As a European ETSI standard for PCN

– Based on GSM technology but configured around a hand-portable• Based on GSM technology to overcomes the development problems

• Lower power mobile station & smaller cell size– cell radius ≤ 1 km in a dense urban environment

– cell radius ≤ 5 km in the rural environment


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• Technical Description– The allocated bandwidth

• 1710~1880 MHz providing 75 MHz duplex bands with a 20 MHz spacing

• The BTS links to the BSC may use 38 GHz radio to avoid laying costlyunderground cable links

– Mobile and Base Station Power Class



I 1

II 0.25


I 1

II 0.25

C la ss M a x . R F P o w e r (W )

I 2 0 ~ (≤ 4 0 )I I 1 0 ~ (≤ 2 0 )I I I 5 ~ (≤ 1 0 )IV 2 .5 ~ (≤ 5 )

C la ss M a x . R F P o w e r (W )

I 2 0 ~ (≤ 4 0 )I I 1 0 ~ (≤ 2 0 )I I I 5 ~ (≤ 1 0 )IV 2 .5 ~ (≤ 5 )

Mobile Station Base Station


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• DCS1800 vs. GSM– DCS-1800 provides a maximum of 375 radio channels compared to 124

for GSM-900

– DCS-1800 is designed to support hand-portable terminal with a transmitpower not exceeding 1 W



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GSM/DCS 1800 in Taiwan

@F�@g� í3Kh Ý�*� Çï

»K AMPS 090, 091

»K GSM 900 0932, 0933

Äe�Õ

»K DCS 1800 0937

ój æ��ò »K DCS 1800 0935

òñ�Õ »K DCS 1800 0936

Õ�ò >K DCS 1800 09380 ~ 09383

6!�Õ ÄK DCS 1800 09384 ~ 09386

6!�Õ ûK DCS 1800 09387 ~ 90389

òñ�Õ >K GSM 900 09310 ~ 09313

6Õ�ò ÄK GSM 900 09314 ~ 09316

h\�Õ ûK GSM 900 09317 ~ 09319

@F�@g� í3Kh Ý�*� Çï

»K AMPS 090, 091

»K GSM 900 0932, 0933

Äe�Õ

»K DCS 1800 0937

ój æ��ò »K DCS 1800 0935

òñ�Õ »K DCS 1800 0936

Õ�ò >K DCS 1800 09380 ~ 09383

6!�Õ ÄK DCS 1800 09384 ~ 09386

6!�Õ ûK DCS 1800 09387 ~ 90389

òñ�Õ >K GSM 900 09310 ~ 09313

6Õ�ò ÄK GSM 900 09314 ~ 09316

h\�Õ ûK GSM 900 09317 ~ 09319


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