Curs 1 -GSM_Network

7/21/2019 Curs 1 -GSM_Network

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Introduction to the GSM Network

GSM: Global System for Mobile communication

o Pan-European standard for communication with mobiles, already adopted by more

than 400 operators in 173 countries and now the world-wide reference for mobile

radio networks. Since 1995 (phase 2), this standard harmonizes the 900 MHz GSMsystem and the 1800 or 1900 MHz Digital Cellular Systems (DCS).

GSM 900:

o 2 x 25 MHz frequency bands around 900 MHz. (extended : 2 x 35 MHz)

GSM 1800:

o 2 x 75 MHz frequency bands around 1800 MHz.

GSM 1900: (North and South American variant of the GSM 1800):

o 2 x 75 MHz frequency bands around 1900 MHz.

History

Mobile network "Prehistory":

o 1946: St Louis (Missouri)

o 1970 - 80: NATEL (Switzerland)

1st Generation: Analogue cellular networks

o 1979: Chicago:AMPS

o 1981: Sweden: NMT

o 1985: UK: TACS

2nd Generation: Digital networks

o 1992: Europe: GSM

o

1995: US: IS95 (CDMA) 3rd Generation: Universal(?) Standards

o 2001: Japan IMT-2000: UMTS

public

residential

office PABX

PABX

Small Cells Medium Cells Large Cells

GSM

PSTN PSTN PSTN


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From 2G to 3G

2G services 3G services

GPRS

Up to 160Kbps

Internet services

R97/98/99 (GSM)

E-GPRS

Up to 384Kbps

Internet services

R99 (GSM)

UMTS

Up to 2Mbps

Multimedia

VoiP

R5 (3GPP)

GSM

GERAN

Multimedia

VoiP

R4/R5

(3GPP)

UMTS

Up to 2Mbps

Internet

services

R99 (3GPP)

General Concepts: PLMN and Mobile Stations

PLMN

PLMN = Public Land Mobile Network

PSTN = Public Switched Telephone Network

ISDN = Integrated Services Digital Network

PDN = Packet Data Network

ISDN

PSTN

......

PDN

......

......

......

......

......

......

......

General Concepts: Cellular Coverage

Omni-directional

Unidirectional

Sectored

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Example of a 12-Cell Three-sector Pattern

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

3 10

14 7 8

692

5

11

12

14 7 8

692

5

11

12

14 7 8

692

5

11

12

14 7 8

692

5

11

DD

Radio Resources are limited :

To increase Spectrum Efficiency, specifictechniques are introduced :

o Power Control

o Handover

o Frequency Hopping

o Discontinuous Transmission (DTX)

downlink

uplink

......

............

......

......?

GSM architectureOperators

Users

External

Networks

MSMS

BSSBSS NSSNSS

OSSOSS

GSM

Types of Mobile Stations

SIM card

(includingTAF)

TA

R

S

MT1

MT0

MT2

TE2

TE2

TE1

Um"plug-in" SIM

ISDN

ISDN concepts GSM concepts

MT = Mobile Termination

TE = Terminal Equipment

TE1 = ISDN

TE2 = V or X typeTA(F) = Terminal Adaptor (Funct ion)

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4/21

GSM architecture: Base Station System

PSTN/ISDNPSTN/ISDN

BTS

NSS

BSC

BTS

CBC

Other

BSCs

GSM architecture: Network and Switching System

VLRVLR

PSTN/

ISDN

PSTN/

ISDN

MSCMSC

BSS

AuCAuC

HLRHLRHLR

SMS-C

EIR

GCR

GSM architecture: GPRS

Packet SwitchingMSC/VLR

GSM+GPRS

BSS with

PCU

PSTN/ISDNPSTN/ISDN

GPRSBackbone

SGSN

Internet

GGSN

GPRSBackbone

SGSN

Internet

GGSN

GPRSBackbone

GPRSBackbone

SGSN

InternetInternet

GGSN

Circuit Switching

BSS

HLR

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GSM interfaces and protocols

HLRHLR GCRAuC

E

B C

D

F

GH

I

Ab is

BCDEFGHI

PSTN

ISDN

BTS - BSC

MSC-VLR(SM-G)MSC-HLR

HLR-VLR(SM-G)MSC-MSC (SS7 basic ) + MAP

MSC-EIRVLR-VLR

HLR-AuCMSC-GCR

MSC-PSTN (SS7 basic) + TUP or ISUP

MSC-ISDN

LAPD(ISDN type)

(BSSAP = BSSMAP + DTAP)

A BSC - MSC (SS7 b asic ) + BSSAP

BTSBTS

LAPDm(GSM specific)

Um (Radio) MS - BTS

BS

C

BS

C

MSCMSC

BTS

PSTN /

ISDN

MS

VLRVLR VLR

VLR

EIREIR

GPRS interfaces and protocols

Gc GGSN-HLR IP/SS7

LAPDm(GSM specific)

Gs

Gb

Um (Radio)

Gi GGSN-Data Network IP

MS

BSS - SGSN

Gr SS7SGSN-HLR

Gf SS7SGSN-EIRSGSN-MSC/VLR

GnSGSN-GGSN IP

IPSGSN-SGSN

MS - BTS

Gs

GfGr

Gn

Gn

Gc SS7

BSSGP

BSS

with

PCU

BSS

with

PCU

HLRHLR EIREIR

Data

Network

SGSN

GGSN

SGSNMSC

Position of Transcoding Unit (TRAU)

Abi s in ter face A in terf ace

2Mb link, each channel = 16 Kbps

2Mb link, each channel = 64 Kbps

MSC Site

MSC/VLRBSC

MSC/VLR

MSC/VLR

TRAUBTS

TRAUBTS

BTS TRAU BSC

BSC

BSC SiteBTS Site

BTS Site

BTS Site

BSC Site

BSC Site

MSC Site

MSC Site

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RADIO INTERFACE:essential part of GSM specifications because of:

Inter-PLMN COMPATIBILITY ==> Complete Specification (to the nearest bit)

Very elaborate SPECTRUM EFFICIENCY optimization techniques:

Reduction of INTERFERENCE to Manage a large number of Mobiles per km

TRAFFIC: information interchanged from USER-TO-USER, after setting up the call,requiring dedicated radio resource allocation. In GSM, traffic can be an interchange of

speech or data

SIGNALLING: information interchanges (in some cases, without the user's knowledge)

between the mobile equipment and network machines

o Out of Call : required for managing mobiles, eg. : location update

o During a Call : required for various reasons, eg.: handover, access to a supplementary

service, call release

MS statusPacket switcing mode (GPRS)

Switch

-off

Switch

-offSwit

ch-on

Switch

-on

"Connected"

"Power Off"

"Idle""Idle"

Endo

f

transac

tionEndo

f

transac

tionNe

tworkA

ccess

Netwo

rkAcce

ss

Circuit Switching Mode (GSM)

MS not

reachable

MS

reachable

"Idle"Attachm

entto

network

Attachmentto

network

Detachm

ent

Detachm

ent

Out of TimeOut of Time

Packet Tx or RxPacket Tx or Rx

Detachm

ento

rOut

ofTim

e

Detachm

ento

rOut

ofTim

e

"Ready""Ready""Stand-by""Stand-by"

MS notreachable

MS

reachable

Radio Resources

Dedicated

Signalling

Channels

Common

Access

Channels

Common

Broadcast

Channels

Mobilepre-synchronization

" Idle" Status "Connected" Status

Network Access Out of callsignalling phase

TRAFFIC phase

Access

procedure

(Optional)

Channels

to be used

Dedicated

Traffic

Channels

Main

Tasks

&

Types of

Inter-change

Frequency

search

Timing

Synchro

SystemParameter

Analysis

(Paging)

Access

Request

Dedicated

ChannelAssignment

Same dedicated

channel used for :

- Authentication

- Signalling:

. Location Updating. Short Messages

. (Traffic Channel

Assignment)

Traffic

Signalling

Frequency

Monitoring

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Physical Channels : the TDMA Frame

1 BTS (eg. 3 carriers)

TDMA frame = 4.615 ms

1 "CHANNEL" (in 1 direction)

Same "CHANNEL" (if bidirectional)

time axis

Time slot (or burst window)

1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 701 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70

1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70

22

17

7

22

17

7

Time shift betweentransmit and receive : 3 TS

Frequencyaxis

UPLINKBand

MS -> BTS

DOWNLINK

Band(BTS ->MS)

Physical Channels : the Normal Burst

TDMA frame = 4.615 ms

CHANNEL

time axis

guard timeguard time

Training sequenceTraining sequence

577 s

Time Slot (TS) or Burst Period (BP)

1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 701 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70

22

17

7

Burs

t

Burs

t

Data (114 bits)Data (114 bits)

26 bits

"Stealing Flags"

S = 0

S = 1

57 bits 57 bits+

+

Traffic (or Signalling out of call)

Signalling during call57 bits 57 bits

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Training Sequences :

8 different bit patterns, chosen so that:

o They are easily recognizable (very accurate auto-correlation function)

o They are easily distinguishable from one another (little correlation between each

pattern)

Stealing Flags :

Logical Channels: Principle of Mapping with Physical Channels

1 2 3 5 6 7TS

Frequency Correction

Timing synchronization

System information

Frequency Correction

Timing synchronization

System information

Subscriber paging

Response to access request

Subscriber paging


Out of call signalling -> MSi

Power Control -> MSi

Out of call signalling -> MSi

Power Control -> MSi

Traffic samples -> MSj

In call signalling -> MSj

Traffic samples -> MSj

In call signalling -> MSj

BTS MS

example : " Beacon" frequency, downlink:

FCCH

SCH

BCCH

PCH

AGCH

SDCCH

SACCH

TCH

FACCH

FCCH

SCH

BCCH

PCH

AGCH

SDCCH

SACCH

TCH

FACCH

0 4

FCCH

BCCH

PCH

AGCH

SDCCH

SACCH

TCH

FACCH

SCH

FCCH

BCCH

PCH

AGCH

SDCCH

SACCH

TCH

FACCH

SCH11

22

33

44

Traffic sample decoding

In call signalling receipt

Traffic sample decoding

In call signalling receipt

Power Control

Out of call signalling receipt

Power Control

Out of call signalling receipt

Mobile presynchronization

Subscriber paging


Mobile presynchronization

Subscriber paging


Logical Channels - Time Division Multiplexing (GSM)

0 1 2 3 4 5 6 7TS 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7TS

1 2 3 4 5 6 7 8 9 10 201 2 3 4 5 6 7 8 9 10 20 30 40 50 0 1

1 2 3 4 5 6 7 8 9 10 20 232425

Multiframe : 51 frames (= 235 ms approx.)

"TRAFFIC" t ype Multiframe :

"SIGNALLING" type Multiframe :

1 TDMA frame = 120/26 # 4.615 ms

1 2 3 4 5 6 7 8 9 10 20 232425 0

Multiframe : 26 frames = 120 ms

0

Logical Channels - Time Division Multiplexing (GPRS)

1 2 3 4 5 6 7 8 9 10 201 2 3 4 5 6 7 8 9 10 20 30 40 50 51 1

Multiframe : 52 frames (= 240 ms.)

52 Frame - Multiframe on pdch:

0 1 2 3 4 5 6 7TS 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7TS

1 TDMA frame = 120/26 # 4.615 ms

Block 0 Block 1 Block 2Block 0 Block 1 Block 2 Block 3 Block 4 Block 5Block 3 Block 4 Block 5 Block 6 Block 7 Block 8Block 6 Block 7 Block 8 Block 9 Block 10 Block 11

0

8


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1 2 3 4 5 6 7 8 9 10 201 2 3 4 5 6 7 8 9 10 20 30 40 50 51 0

Multiframe : 52 frames (= 240 ms.)

Block 0 Block 1 Block 2Block 0 Block 1 Block 2 Block 3 Block 4 Block 5Block 3 Block 4 Block 5 Block 6 Block 7 Block 8Block 6 Block 7 Block 8 Block 9 Block 10 Block 11

Data Flow to User BData Flow to User A Data Flow to User C

TFI 28 TFI 2 TFI 19

TFI =28

Data

TFI =28

Data

BSN =21

TFI =28

Data

TFI =28

Data

TFI =28

Data

TFI =28

Data

BSN =22BSN =23

TFI =28

Data

BSN =24

TFI =28

Data

TFI = 2

Data

BSN =25BSN =12

TFI =28

Data

BSN =24

TFI =28

Data

TFI = 2

Data

BSN =25BSN =12

TFI = 2

Data

BSN =13

TFI = 2

Data

TFI = 2

Data

BSN =14BSN =15

TFI = 2

Data

BSN =13

TFI = 2

Data

TFI = 2

Data

BSN =14BSN =15

TFI = 19

Data

BSN =75

TFI = 19

Data

TFI = 19

Data

BSN =76BSN =77

0

Radio Interface - Channel Mapping

F S B B B B c c c c

31

-

51 1

Multiframe : 51 frames (= 235 ms approx.)

F S F S F SF SF Sc c c c

21

c c c cc c c c c c c cc c c c c c c cc c c c c c c cc c c c c c c cc c c c c c c cc c c cc c c cc c c c

1 2 3 4 5 6 7 8 9 10 201 2 3 4 5 6 7 8 9 10 20 41

F = FCCH S = SCH B = BCCH

LOGICAL

CHANNEL

FCCH

Frequency

Correction

1 every 10 frames

(46 ms)

OCCURRENCE

and/or USABLE BIT

RATE

as FCCH (46 ms), 8 TSafter

SCH

Synchro

BCCH

BroadcastControl

1 TS every 4 consec. framesevery 51 frames,

giving 456 usable bitsevery 235 ms

- General information (system) concerning the station:- Identity of operator, access authorized or not,

- Organization of logical channels in the cell (paging...),- Frequencies used, Frequency hopping...,

- Time-Outs applicable...

- Locking the mobile local oscillator on the exact frequency

- Roughly estimating the position of the receive window

- Exact synchronization of receive window

- Decoding the Frame Number (from 0 to 2,715,647)

ROLES and USES of INFORMATION CARRIED

LOGICAL

CHANNEL

RACH

Random

Access

Only uplink

OCCURRENCE

and/or USABLE BIT

RATE

These 2 sub-channels

share the "CCCH"

channel based

on variable rules

according to cell and

operator

AGCH

Access

Grant

PCH

Paging

- used by the network to signal a call to a mobile:

Short format identity, unambiguous in the cell

- used by the mobile to request access to the network

("Channel Request" message with mobile short format identity)

- used by the network to acknowledge the access request and

assign a dedicated channel to the mobile (" immediate

assignment" message with identity echo)


-

R = RACH

DOWNLINK

f s b b b b C C C CC C C C

31 51 1211 2 3 4 5 6 7 8 9 10 201 2 3 4 5 6 7 8 9 10 20 41

f s f s f s f sC C C CC C C C C C C CC C C C C C C CC C C C C C C CC C C C C C C CC C C C C C C CC C C C C C C CC C C C C C C CC C C C -

(Multiframes : 51 frames)

f = FCCH s = SCH b = BCCH

f s

C C C C = CCCH (PCH or AGCH)

UPLINK

R R R RR R R R R RR R R RR RR RR R R RR R R R R RR R R R R RR R R RR RR RR R R RR R R R R RR R R R R RR R R RR RR RR R R RR R R R R RR R R R R RR R R RR RR RR R R RR R R R R RR R R R R RR R R RR RR RR R R RR RR RR R R RR RR RR R R RR R R R

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- Out of call signalling, such as location update, authentication,

transition to encrypted mode, assignment of a traffic

channel...

SACCH

Slow

Associated

Control

SDCCH

Standalone

Dedicated

Control

LOGICAL

CHANNEL

8 TSs every 2x51 frames,

giving 456 bits / 235 ms

---> 1.94 kbit/s

OCCURRENCE

and/or USABLE BIT

RATE

4 TSs every 2x51 frames,

giving 456 bits / 470 ms

---> 950 bit/s

- Non-urgent procedures (background), occurrence ~0.5

sec:measurement reports, power monitoring, timing advance,

+ Short Message Service (SMS)


DOWNLINK

(Multiframes : 51 frames)

D = SDCCH A = SACCH

UPLINK

-

-- -

- - -

-- -

- -D0 D1 D2 D3 D4 D5 D6 D7D0 D1 D2 D3 D4 D5 D6 D7

D0 D1 D2 D3 D4 D5 D6 D7D0 D1 D2 D3 D4 D5 D6 D7

A0

A4

A0

A4

A1 A2 A3

A5 A6 A7

A1 A2 A3

A5 A6 A7

D0 D1 D2 D3 D4 D5 D6 D7D0 D1 D2 D3 D4 D5 D6 D7

D0 D1 D2 D3 D4 D5 D6 D7D0 D1 D2 D3 D4 D5 D6 D7 A0

A4

A0

A4

A1 A2 A3

A5 A6 A7

A1 A2 A3

A5 A6 A7

-

-- -

- - -

-- -

- -

SACCH

Slow

Associated

Control

TCH/F

TCH/HTrafficFull & Half Rate

- Non-urgent procedures (background), occurrence ~ 0.5 sec:

(as SACCH associated with a SDCCH)

- Signalling after TCH set-up: end of call processing, "high

speed" signalling

- Traffic at max rate 13 kbit/s

(Speech encoded at 13 kbit/s or Data at up to 9600 bit/s)

- Traffic at max rate 5.6 kbit/s

(Speech encoded at 5.6 kbit/s or Data at up to 4800 bit/s)4 TS every 480 ms --->

~ 1 kbit/sTCH cycle stealing :--->

max 11.4 or 22.8 kbit /s

24 TSs every 120 ms

---> 22.8 kbit /s12 TSs every 120 ms

---> 11.4 kbit /s

LOGICAL

CHANNELOCCURRENCE

and/or USABLE BIT

RATE


1 2 3 4 50T T T T TT

1 2 3 4 50T T T T TT

1 2 3 4 50 1 2 3 4 50T T T T TT T T T T TT

1 2 3 4 50 1 2 3 4 50T T T T TT T T T T TT

Multiframe : 26 frames (= 120 ms)

A -1 2 3 4 5 6 7 8 9 10 110 1 2 3 4 5 6 7 8 9 10 110 13 14 15 16 17 18 19 20 21 22 2312131415161718192021222312

A -T T T T T T T T T T TT T T T T T T T T T T TT T T T T T T T T T T TT T T T T T T T T T T TT T T T T T T T T T T TT T T T T T T T T T T TTT T T T T T T T T T TT T T T T T T T T T T TT

T i = Sample i, TCH/F channel A = Associated SACCH

117 8 9 10 116T T T T TT T T T T TT

7 8 9 106T T T T TT T T T T TT

1A1

A

1A1

A2

A2

A2

A2

A

= Sample i, channel TCH/H n2

= SACCH associated with TCH 2

Ti = Sample i, channel TCH/H n1

A1 = SACCH associated with TCH 1 A2

Ti

2 "HALF-RATE" + 2 SACCHs :

T T T T TT T T T T TTT T T T TT T T T T TT T T T T TT T T T T TT

T T T T TT T T T T TT

1 "FULL-RATE" + 1 SACCH :

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

TS

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

"Beacon" frequency

Otherfrequencies

FCCH + SCH + BCCH + PCH + AGCH

uplink direction

downlink direction

RACHTS 0 :

TS 1 : 8 SDCCH/8 + 8 SACCH/8 in each direction

other TSs: TCH (+ SACCH / FACCH) in each direction

BTS

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11/21

Examples : Number of Frequencies Number of TCH Channels ERLANGS (formula B, blocking 2%)

3 22 15

4 30 22

5 38 29

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7TS

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

Beacon

frequencyOther

frequency

(FCCH + SCH + BCCH) + (PCH + AGCH + RACH) + (4 SDCCH/4 + 4 SACCH/4)

TS 0 of beacon

frequency:

other TSs: TCH + SACCH (+ FACCH))BTS

Structure of the Multiframe in " Time Slot" 0 (Config. n 1: combined BCCH) :

DOWNLINK (Multiframes of 51 frames)

F = FCCH S = SCH B = BCCH C = CCCH (PCH or AGCH) R = RACH Dn/An = SDCCH / SACCH/4

UPLINK

F S B C F S F S F S -F SC C D0 D1 D2 D3 A0 A1

F S B C F S F S F S -F SC C D0 D1 D2 D3 A2 A3

R R R RR R R R R R R RR R R R R R RR R R R R RR RD3 A2 A3 D0 D1 D2R R R RR R R R R RR R R RR RR RR R R RR R R R R RR R R R R RR R R RR RR RR R R RR R R RR R RR RR R R RR R R RR RR RR RD3 A2 A3 D0 D1 D2

R R R RR R R R R RR R R RR RR RR R R RR R R R R RR R R R R RR R R RR RR RR R R RR R R RR R RR RR R R RR R R RR RR RR RD3 A0 A1 D0 D1 D2

Radio Interface - Timing Advance

BTS

MS

Presynchronized

BTSTx

Rx

Tx

RxMS1

TS i

TS i

T.A.measured by BTS

Access Burstforward propagation time

BTS TxRx

Tx

RxMS1

TS i

TS i

(after TA)- TA

forward propagation time

return propagation time

Radio Interface - Subscriber Paging

The Network knows the LOCATION AREA (LA) in which the mobile is travelling.

An LA can cover more than one cell.

The PCH channel is used to signal a Call to a mobile. The same "Paging" message istransmitted to all cells in the area (shaded areas above).

Only a mobile in "IDLE" state (pre-synchronized) can respond to paging.

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12/21

BSC

Radio Interface - Access to the Network

An access request is always initiated by the MS. (when an MS is called, the "paging"

procedure is used).

The RACH channel is used to transmit the "CHANNEL REQUEST" message.

The channel is called "random" since the mobile chooses the call TS randomly. This means

that there is a risk of collision.

Collisions are resolved by retransmission after pseudo-random delays.

MS1

MS5

MS2 MS3 MS4 MS4

MS5

MS1

MS5

MS2 MS3 MS4 MS4

MS5

Radio Interface - Logical Channel Summary

Abbreviation Name Type Role/Info carried Burst format

Frequency Correction CHannel MP --> MS Frequency for synthesizer alignment Frequency

Synchronization CHannel MP --> MS Timing sync - Frame N Sync

Broadcast Common CHannel MP --> MS Broadcast system information Normal

Random Access CHannel PP MS Subscriber paging (paging) Normal

Access Grant CHannel PP --> MS SDCCH channel assignment (Imm.Ass) Normal

Cell Broadcast Control CHannel MP --> MS Broadcast short messages (SMS/CB) Normal

Notification CHannel MP --> MS Accessibility notification (VGCS/VBS) Normal

Dedicated

signalling

(out of call)

Standalone Dedicated Ctrl CH. PP Out of call signalling Normal

Slow Associated Control CH. PP Measurements - P Contr. - Timing adv. Normal

Traffic / Full Rate CHannel PP 13 kbit/s traffic Normal

Traffic / Half Rate CHannel PP 5.6 kbit/s traffic (phase 2) Normal

Slow Associated Control CH. PP Measurements - P Contr. - Timing adv. Normal

Fast Associated Control CH. PP In call signalling (cycle stealing) Normal

Family

FCCH

SCH

BCCH

Broadcast

CCCH

Dedicated

Traffic +

signalling

(during call)

RACH

PCH

AGCH

CBCH

NCH

SDCCH

SACC

HTCH/FTCH/H

SACCH

FACCH

Radio Interface - Discontinuous Transmission

Principles (Mandatory in the mobile and on the BTS uplink path) :

DTX (Discontinuous Transmission) : reduced rate transmission (~ 500 bit/s) during silences

VAD (Voice Activity Detection): Measurement of signal strength for detecting moments of

"silence (neither speech nor tone) - adaptive-threshold FILTER

Comfort Noise Generation: In receive mode, reconstitution of background noise based onthe characteristics received in Silence Descriptor (SID) frames, to avoid giving the receiving

user the impression that the line has been cut off

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13/21

S*S*

S S' S 'S ' S' S 'S 'S 'S"

480 ms

BTS

TRAU --> BTS

MS BTS

SPEECH

SILENCE

SID FRAME

TRAU

MS

......

Radio Interface - Radio Channel generation

ChannelEncoding

Speech

Digitizationand

Encoding

InterleavingBurst

FormattingEncryption Modulation Transmission

ReceptionDemodulationDecryptionBurst

Deformatting

De-interleaving

ChannelDecoding

Speech

Decoding

POWER CONTROL

260 bits / 20 ms :13 kbit/s 22.8 kbit/s

(per channel)

270.8 kbit /sFR Speech f rames :

(modulated)

Radio Interface - GMSK Modulation

GMSK = Gaussian Minimum Shift Keying:

convolution of an MSK ramp (/2 - width: 1

bit), by a Gaussian function: 0-1 or 1-0 bit

transitions => smooth" transitions of /2

Properties:

o Gradual transitions avoid the need to filter

signal harmonics which are very weak

o Spectrum efficiency ~ 1 bit/Hertz (270.8

kbaud/200 kHz)

o

Modulation spectrum: To preventcatastophic interference, it is essential to

avoid using adjacent frequencies in adjacent

cells.

/2

t

0-Tb

(t)

Tb

MSK

Tb/2-Tb/2

GMSKGMSK

dB

0

-10

-20

-30

-70

0 100 200 300 400-100-200 kHz

200

KHz

200

KHz

Radio Interface - Raleigh fading" f "

"GAP" in frequency " f " reception

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14/21

Radio Interface - Frequency Hopping

N-frequency hopping groups can be defined for each TS (N>=4)

The overall system capacity remains unchanged (eg. : 32 mobiles on 4 frequencies)

0 1 2 3 4 5 6 70 1 2 3 4 5 6 7TS

"Beacon" frequency

Other

frequencies

FCCH/ SCH/ BCCH/ CCCH

SDCCHNo Hopping

TS0 : Hopping over 4 frequencies TS3 : Hopping over 5 frequencies

Radio Interface - Power Control

Power Control (PC) is used to minimize interferences

PC algorithm in BSC (processing and decision)

PC Mandatory for MS: steps of 2dB every 60 msec , option for BTS: 15 steps of 2 dB

8 W

~ 3 mW

2 15

28 dB

5

13

39

PC

steps

19 17 31 31 29 dBm

time

= 60 ms(commands)

Possible values of Output Power

(GSM 900 MS)

2 W33 33

P max MS 2W

19

Output

Power(dBm)

PC Level

Example of PC Commands

(GSM 900 MS)Output

Power(dBm)

19

Radio Interface - Space Diversity

......

Rx

Chain 1

Rx

Chain 2

RESULT

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Space Diversity is used against fading in the uplink direction

The same signal with different multi-paths is received in the Base Station where it is

processed within 2 independent chains : a Discriminator then identifies the best signal

GSM number and identities: Subscriber identifications

IMEI / IMEISV

( International Mobile Equipment Identity )

TAC FAC SNR SP

Type Approval CodeFinal Assembly Code

Serial NumbeR

(SPare)

( International Mobile Equipment Identi ty and Software Version number) (Phase 2+)

TAC FAC SNR SVN

Software Version Number

IMEI

:

IMEISV:

......

GSM number and identities: Mobile Equipment identification

IMSI MS - ISDN

( International Mobile Subscriber Identity )

International Identity E212 compliantNature

( Mobile Station - Integrated Service Digital Network n )

Directory Number ISDN type, E.164/E.213 compliant

MCC MNC MSINH1 H2 x x x ........ x x x

MobileCountry

Code

MobileNationalCode

Mobile Subscriber Identity Numberincluding H1 H2 identifying the HLR

Format

Meaning

N of digits

Examples

Characteristics

3 2 max 10

234

208 01

10

Stored in SIM module and AuC

CC NDC SNM1 M2 x x x x x x x x

CountryCode

National

Code*Destination

Subscriber Number( national identity )

including M1 M2 identifying the HLR

1 to 3 2 to 4

44 802 Cellnet GSM44 385 Vodafone GSM44 956 Mercury DCS44 973 Hutchinson DCS

33

33

607/8

609

61 MC DU to 69 MC DU LYON

01 MC DU to 09 MC DU MASSENA

11 xxxx to 3x xxxx LA FOURCHE

All ocated to an IMSI (by MMC) in the HLR

69 xx xx xxxx LYON

94 xx xx xx xx MASSENA

?

France

U.K.

Orange

Cegetel

total up to 15

* instead of identifying a geographic area, the NDC identifies an OPERATOR:

( national identity )NMSI

GSM number and identities: Geographic identification

MCC MNC LAC CI

LAI

CGI

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BSS / NSS Protocols and Software Modules: general

S.C.1S.C.1 S.C.1S.C.1

SCCP

MTP 3

MTP 2

S.C.1

SCCP

MTP 3

MTP 2

S.C.1

TCAP

MAP

TCAP

MAP

SCCP

MTP 3

MTP 2

S.C.1

DTAPDTAP

SCCP

MTP 3

MTP 2

S.C.1

DTAPDTAP

LAPDLAPDLAPDmLAPDm LAPDLAPD

SS (SMS)SS (SMS)SS (SMS)

BSSMAPBSSMAP

MMMM

CCCC

BSSMAPBSSMAPRRRR

RR

RR'RR' BTSMBTSMBTSMBTSM

LAPDmLAPDm

(SMS)

SSCC

MM

(Relays)

MS BTS BSC MSC / VLR NSS(eg. : HLR)

Um A bis A (D)

1

2

3

(Relays)

BSS / NSS Protocols and Software Modules: Radio Interface

- Call handling and routing

- DTMF facilities- Access to Supplementary Services

- Short Message Service

- Paging management- Ciphering mode management

- Frequency redefinition

- Dedicated channel assignment

- Handover management

- Measurements and power control

Protocol

Discriminator

RR Radio ResourceManagement

Meaning

MM Mobility Management- Location Updating

- Ciphering mode management

- Frequency redefinition

- Dedicated channel assignment

Function

Call Control

Supplementary Services

Short Message Service

CC

SS

SMS

Entities

MS - BSC(and BTS)

MS -

MSC / VLR

MS - MSC

(+ HLR)

(+ SMS-C)

Entities

MS - BSC(and BTS)

MS -

MSC / VLR

MS - MSC

(+ HLR)

(+ SMS-C)

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17/21

BSS / NSS Protocols and Software Modules: GPRS protocols

GTPGTPGMM

BSSGP

LLC

MS BSS SGSN GSN

Um Gn

Layer Model for Signalling plan (GPRS)

relay

L1 bis

Frame

Relay

L1 bis

Frame

Relay

L1

L2

L1

L2

L1

L2

L1

L2

L1 RF

MAC

L1 RF

MAC

L1 bis

Frame

Relay

L1 bis

Frame

Relay

L1 RF

MAC

L1 RF

MAC

RLC

LLC

Gb

IP

UDP

SM

BSSG

PRLCIP

GSMS

UDP

GMM

SMG

SMS

GMM

SMG

SMS

GTPGTP

GSN

GTPSNDCP SNDCP

BSSGP

LLC

MS BSS SGSN GGSN

Um Gn

Layer Model for Transmission plan (GPRS)

relay

L1 bis

Frame

Relay

L1 bis

Frame

Relay

L1

L2

L1

L2

L1

L2

L1

L2

Physical

Layer

MAC

Physical

Layer

MAC

L1 bis

Frame

Relay

L1 bis

Frame

Relay

Physical

Layer

MAC

Physical

Layer

MAC

RLC

LLC

Gb

GTP

IP

UDP &

TCP

IP / X25

Appl i

BSSG

PRLCIP

UDP &

TCP

IP / X25

Header Data

Header DataHeader Data

LLC

PHYSICAL

CRC CRC CRCCRC CRC CRCRLC MAC

IP/X25

SNDCP

Division of the SDU in 2 blocks

Compression of each part

Label added for each block

LLC EncapsulationCRCCRC

RLC Encapsulation

LLC frame splitted

into blocks

HeaderHeaderHeader

= < 1520 BytesHeader = < 1520 BytesHeader

Channel Coding CS1 to CS4

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

Block 1 Block 2 Block 3 Block 8

CRCHeader

Channel Coding CS1 to CS4Channel Coding CS1 to CS4

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

Block 1 Block 2 Block 3 Block 8Block 1 Block 2 Block 3 Block 8

CRCHeader CRCHeader

HeaderHeader

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18/21

Level 3 GSM procedures: Setting up the radio connection

SDCCH N

MM CM_SERVICE REQUEST

SDCCH N

RACH

MSCHANNEL REQUEST

IMMEDIATE ASSIGN.

BTS BSC MSC

Um A bis A

CHANNEL REQUIRED

ASSIGNMENT of anSDCCH Channel

CHANNEL ACTIV.

ACTIVATION ofChannel indicated

CHANNEL ACTIV. ACK

AGCH

CONNECTION to theSDCCH Channel

SDCCHSDCCHSABM ESTABLISH INDIC.

SCCP CONNECT REQUEST

SCCP CONNECT CONFIRM

T3101

T9105

IMM. ASSIGN. CMD

RR

RR


RR

BTSM

BTSM

BTSM

SDCCHSDCCH UA



......

Level 3 GSM procedures: Security Functions

Authentication

o

Checks that the Mobile Station is the required station and not an intruder

Ciphering

o All Information (Signalling, Speech and Data) is sent in ciphered mode, to avoid

monitoring and intruders (who could analyze signalling data)

Temporary Identification (TMSI)

o used instead of IMSI for safety reason: tracing of MS not so easy on air interface

o Allocated at least when MS is registered in a new VLR (but may be allocated at each

transaction)

SIM card

A3A3

AuCRadio Channel

A8A8

Ki Ki

Random number selection

A3A3

A8A8

A3 A3

A8A8

A5A5A5A5

= ?

Identification key (128 bits)

RAND (128 bits )

RAND

Signed ref. (32 bits) SRES SRES

Cipher command

OK

Kc : Cipher key

for the call (64 bits)

Kc

Speech - Data - Signall ing Speech - Data - SignallingCiphered data

Ciphering/Deciphering Ciphering/Deciphering

BTS

A5A5

...

...

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19/21

Level 3 GSM procedures: Mobile Originating Call

TCH allocation

CHANNEL ACTIV.

DATA REQUEST

MS BTS BSC MSC/VLR

A bis A

CALL PROCEEDING

DATA INDICATION

SCCP DATA

SCCP DATASET - UP

ASSIGNMENT CMD

PHYS. CTX REQ. SCCP DATACIC selection

AUTHENTICATION

CIPHERING

CHANNEL REQUEST

IMMEDIATE ASSIGN.

RACH

AGCH

SDCCH N

SDCCH

Ciphered

SABM

UAESTABLISH INDIC. SCCP CONNECT REQUEST

SCCP CONNECT CONFIRM

SDCCH

PHYS. CTX CONF.

TCH

CHANNEL ACTIV. ACK

DATA REQUEST

Assignment Cmd

TCH

T3107RELEASE REQ *Local End

Um

RR

RR

CM Serv. Req.MM CM Serv. Req.MMCM Serv. Req.MM CM Serv. Req.MM

CM Serv. Req.MM CM Serv. Req.MM

CC

CC

Set - UpCC

Call Proceeding.CC Call Proceeding.CC

Set - UpCC

Assignment RequestBSSMAPBTSM

BTSM

BTSMBTSM

RRRR

* if no answer from MS

IAMISUP

...... PSTN or ISDN

Off-hooking

Called P. ringing

ConnectConnect

Alert ing

Assign. compl.Assign. compl.

DATA REQUEST

MS BTS BSC MSC/VLR

Um A bis A

ALERTING

DATA INDICATION

SCCP DATA

SCCP DATAASSIGNMENT COMPL.

RF CHANNEL REL.

SCCP DATA

FACCHSABM

UAESTABLISH INDIC.

RF CHANNEL REL. ACK

DATA REQUESTCONNECTSCCP DATA

ACM

ANM

DATA IND.CONNECT ACK ConnectAck

CONVERSATION PHASE

Alert ing

Connect

Ack

...... PSTN or ISDN

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20/21

Level 3 GSM procedures: Mobile Terminating Call

MOBILE

CHANNEL REQUESTIMMEDIATE ASSIGNMENT

PAGING RESULT

AUTHENTICATION REQUEST

AUTHENTICATION RESPONSE

CIPHERING MODE CMDCIPHERING MODE COMPLETE

SET UP

CALL CONFIRMED

ASSIGNMENT CMDASSIGNMENT COM

ALERTING

CONNECT

CONNECT ACK

SET-UP of anRR CONNECTION (MT)

SERVICE INDICATION

AUTHENTICATION

TRANSITION to CIPHERING mode

START OF CALL

TRAFFIC CHANNEL

CALL CONFIRMATION

CALL ACCEPTED

ASSIGNMENT

PSTN or ISDN

PAGING REQUEST

...

...

GSM

Network

GSM

Network

Level 3 GSM procedures: International Call

GMSC

PSTN

VMSC VLR

HLR

Visited PLMN

interrogation

Home PLMN

COUNTRY 1COUNTRY 2

COUNTRY 3

Incoming

Incoming

Outgoing

Outgoing

International SCCPGateways......

Level 3 GSM procedures: Location Updating

General

o This procedure is always initiated by the Mobile Station and involves providing the

VLR (and HLR if required) with its current position,

o The visited VLR stores the Location Area (LA),

o The LA n (LAI) received is updated dynamically in SIM non-volatile memory.

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21/21

Normal Location Update

o When the mobile is switched on without having stored the LAI (eg.: initial use of

SIM),

o When the mobile is switched on in a different LA from the LA stored in the SIM,

o When the pre-synchronized mobile moves from one LA to another (same or different

VLR).

Periodic Location Updateo

When the SIM internal counter overflows

(This counter is automatically incremented by the mobile when it is switched on)

Level 3 GSM procedures: Handover

3 Phases :

o Identification of requirement, Selection of a new cell, Execution

Mobile Station:

o Continuous Quality and Received Power Control

o

Continuous adjacent cell Power monitoringo Transmission of measurement reports to the BTS (every 0.5s)

Network:

o The BTS measures the Quality and the received Power from the mobile

o The BSC runs the Power Control and Handover central algorithm

o The BSC controls the handover operation

Handover Types:

o Intra-BSC / Inter - BSC, Intra - MSC / Inter - MSC (first and subsequent)

o Internal (within the same BTS) if there is uplink or downlink interference

o Synchronized / non-synchronized

BSC

BSC

BSC

BSC

BTS 1

BTS 2MSC /

VLR

MSC /

VLR

MSC /VLR

PSTN

(Intra BSC)

Curs 1 -GSM_Network

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Transcript of Curs 1 -GSM_Network