1_introduction to GSM

7/31/2019 1_introduction to GSM

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System Model

AUC

HLR EIR

SS

BSS

MSC

BTS

MS

NMCandOMC

SwitchingSystem

Signalingtransmission

Call connectionsand

signalingtransmission

BaseStationSystem

Othernetworks

BSC

GMSC

VLR


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Network elements in GSM

MS

PLMN

PSTN

ISDN

AUC

EIRHLR

VLR

MSC

BSC

BTS

GMSC


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SA2

MSC

VLR

MSCMSC

VLR

BSC

BSC BSC

BSC

LA1LA2

GMSC

MSC

BTS

SA1

HLR

AUC

EIR

SA - Service Area

LA - Location Area

BTS - Base Transceiver Station

BSC - Base Station Controller

MSC - Mobile Switching Center

VLR - Visitor Location Register

GMSC - Gateway MSCEIR - Equipment Identity Register

AUC - Authentication Center

HLR - Home Location Register

Mobile identity

SIM card


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Base Station System

Base Station System

BSC

BTS


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BSS in Ericssons GSM Systems

MSC TRC BSC

BSSSS

RBS

BSC/

TRC RBS


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Transmission Rates in BSS

MSC/VLR

TRC

BSC

RBS

BSC/TRC

RBS

RBS

RBSRBS

RBS RBS

RBS

BSC

RBS

RBSRBS

RBS

MSC/VLR

BSC

RBSRBS

64 kbits/sper call

16 Kb/sfull-rate

33.8 Kb/s per full-rate call

16 Kb/s

full-rate

16 Kb/s

full-rate

16 Kb/sfull-rate

64 kbits/sper call


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Switching System

SS

MSC/

VLR

EIR

ILR

GMSC

DTI

AUC

HLR

SMS-GMSC

SMS-IWMSC


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VLR-HLR Interaction

HLR

UpdateDelete

MSC/VLR MSC/VLR


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Mobile Station

MEMobileEquipment

SIM SubscriberIdentityModule


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GSM interfaces

MS BTS BSC MSC HLR

VLR

MSC

EIR

VLR

Um Abis A

B

C

E

F

D

G

AUC

H


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A Cell

Cell


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Macro, Mini, Micro and Indoor Cells

Antenna positions

Macro

Mini

MicroPico


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MSC Service Area

cell 6

cell 1 cell 5

cell 4 cell 2 cell 3

MSC

LA1LA3

LA5

LA4

VLR


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Relation Between Areas in GSM

GSM Service Area

PLMN Service Area

(one per operator)

MSC Service Area

Location Area

Cell


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"Hardware" view of a Sample Network

HLR

EIR

AUC

GMSC

ILR

MSC/VLR 1PSTN

MSC Service Area 2MSC Service Area 1

LEGENDMSC Boundary

BSC BoundaryPCM LinksBase Station

MSC/VLR 2

BSC 1B

BSC 1C

BSC 2B

BSC 1A

BSC 2A

BSC 2C


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"Software" view of a Sample Network

LA 1-B

LA 1-A

LA 2-D

LA 2-A Cell 2-A-25

LA 2-B

HLR

EIR

AUC

GMSC

ILR

MSC/VLR 1PSTN

MSC Service Area 2MSC Service Area 1

LEGENDMSC Boundary

BSC BoundaryPCM Links

Base Station

MSC/VLR 2

LA 2-C


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Authentication Procedure

MSC/VLR

1. RAND

3. SRES

MS2. MS calculates SRES using RAND + Ki

(SIM-card) throug A3 and Kc using RAND+Ki

through A8.

4. Compare SRES received fromMS with SRES in triplet. If theyare equal access is granted.

MSC/VLR Mobile service Switching CenterMS Mobile StationRAND Random numberSRES Signed Response


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Authentication in GSM

VLR

MSC

HLRAUC

Subscriber number (IMSI)

Code key (Ki)

Random number (RAND)Signal response (SRES)

RAND / SRES

RAND

SRES

Figure D.6.4


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Equipment Identification

MSC/VLR

MS

EIR

3. Check IMEI

4. Access/barring info

1. IMEI request

2. IMEI

IMEI International Mobile station Equipment IdentityEIR Equipment Identity RegisterMSC/VLR Mobile services Switching Center


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OSS CNA


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OSS Provides Central Supervision of all Network

OMC OMC

HLR

AUC/EIR

TRC

MSC

BSC

BTS

Operationand

Support System

NMC


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Gateway products for

billing informationand service

SOG and BGW

GSM Modes


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GSM Modes


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Operation Overview

Attached (On)

Detached (Off)

Idle

Busy

Roaming

Paging

Handover

Mr. Bond!!


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Roaming

MSC/VLR

MSC/VLR

LA1

LA2

The RBS Listening for Channel Requests and


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The RBS Listening for Channel Requests and

Measuring the Uplink on an Established

Connection

Signal strength!Quality!Timing!

Accessburst!

MS

MS

MS MS

RBS


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Monitoring BCCH Carriers


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GSM Frequency Bands

0.8GHz 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

GSM 900 GSM 1800 GSM 1900


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Frequency bands for the different GSM-based

networks. (Values within brackets refer to E-GSM)

Network type

GSM 900 (880)890-915/(925)935-960 MHz GSM 900

GSM 1800 1710 - 1785/1805 -1880 MHz GSM 1800

GSM 1900 1850 - 1910/1930 -1990 MHz GSM 1900

EricssonsImplementations

Frequency bandUL/DL

Uplink and Downlink on a Radio Channel


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p

Uplink

Downlink


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System Parameters

f

up link down link

Carrier spacing

Duplex spacing

Bandwidth spacing


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Duplex Distance

890 960915 935MHz

Uplink Downlink

DuplexDistance(45MHz)

Bandwidth(2x25MHz)


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Duplex distances for different frequency bands

StandardGSM900GSM1800 S1900

Duplexdist.45MHz 95MHz 80Hz


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Carrier Separation

Carrier Separation(200KHz)

895.4 895.6MHz


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Neighboring Cells Cannot Have the Same

Frequency (Simplified)

B

G

A

C

G

AD

F

F

E


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TDMA

0

Frequency 1

1 2 3 4 5 6 7


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Basic TDMA frame, timeslot, and burst structures

0 1 2 3 4 5 6 7

4.615ms

3 57 1 26 1 57 3

Burst

148Bits

156.25Bits0.577ms

DataTrainingData


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Analog Signal


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Digital Signal


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A/D Conversion

Analog

A/D Conversion

Digital


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Analog Signal Sampling

t

Analogue signal

t

Sampling

Ts

t

Sampled signal


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Regeneration of Digital Signal

Transmitted Received Regenerated


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Quantization

q7

q6

q5

q4

q3

q2

q1

q0

Ts 2Ts 3Ts 4Ts 5Ts 6Ts 7Ts 8Tstime

}

Sampled

value

Quantized

value

D=Quantizederror


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Path loss Shadowing Rayleigh fading Signal strength Time dispersion Time Alignment

Parameters that are important for GSM


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Problems Solution

FadingDistance Eventually leading to handover

Shadowing Make a better coverage of the cell or smaller cells

Rayleigh Antenna diversity- two antennas on the BS, 5-6 m apart

Repeated change of frequencies after each frame

Sh d i


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Shadowing

R Si l St th


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Rx Signal Strength

Fadingmargin

SS(dB)

Distance(meters)

Global meanvalue

Fadingdip(Rayleigh)

Receiver sensitivity

R Si l St th V Di t


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Rx Signal Strength Versus Distance

log(distance)

Signallevel(

dB)

Pathloss( )

Rayleighfading(-)

Lognormalfading( )

R l i h F di


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Rayleigh Fading

Reuse distance and carrier-to-interference ratio


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S (dB)

S(A,f1)

S(B,f1)

Reuse distance for f1 Distance from A

>18 dB in analog systems

>7 dB in digital systemsC

I

FigureD.5.4

I C

A B


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Co-channel interference

f1

f1

B

A

Figure D.5.3

Acceptable

Speech quality


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The Time Alignment Problem


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The Time Alignment Problem

A. Close to BTSBTS

TDMA-frameB. Far away

from BTSA.

B.

TS0 TS1 TS2


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Intermodulation in a 900 MHz cellular system

8 9 0 9 0 0 9 1 0 9 2 0 9 3 0 9 4 0 9 5 0 9 6 0 M

R X b a n d

D u p l e x d i s t a n c e ( D )

T X b a n d

A l l o c a t e d R X b a n d ( B )

( 1 0 M H z i nt h i s e x a m p l e )

A l l o c a t e d T X b a n d ( B )

( 1 0 M H z i n t h i s e x a m p l e )I M 7 I M 5 I M 3

Intermodulation (IM) in cellular systems


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System

GSM900

DCS1800

PCS1900

NMT450

Duplex

distance,

D, (MHz)

45

95

80

10

IM3

22.5

47.5

40.0

5.0

IM5

15.0

31.7

26.7

3.3

IM7

11.3

23.8

20.0

2.5

IM9

9.0

19.0

16.0

2.0

Maximum band, B, (MHz) to avoid IM order:

Worst-case relations

IM3 in Rx band if D/B < 2IM5 in Rx band if D/B < 3

IM7 in Rx band if D/B < 4

IM9 in Rx band if D/B < 5

Definitions:IM3, IM5, etc.=Intermodulation products of 3rd, 5th, etc.,

D = Duplex distance (MHz)B = Allocated band (MHz)

Worst case = IM from the lowest and

the highest frequencies in the allocated band

Intermodulation (IM) in cellular systems

Co-Channel Interference


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Co Channel InterferenceCarrier Interference

Distance

f1 f

1

dB

C I

Adjacent Channel Interference


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Adjacent Channel Interference

AC

Carrier Adjacent

Distance

f1 f2

dB f2

= f1

+ 200 kHz

-9 dB3 dB

Locating the BTS close to the reflecting object to


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Locating the BTS close to the reflecting object to

combat ISI

D2

D0

D1

Pointing the antenna away from the reflecting object


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Pointing the antenna away from the reflecting object

to combat ISI

Mountain Sitewithantennapointingaway

Channel Coding


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Channel Coding

Blockcoder

50 Very important bits

132 Important bits

78 Not so important bits

1:2Convolutional

Coder

456

4 Tail bits

53 bits 378 bits

Space Diversity


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p y

Tx Rx (B)Rx (A)

AntennaDiversity

Diversity

SystemOutput

ReceiverSensivity

Level

ReceivedSignalLevel

A, B combined

Receiver A

Receiver B

No Diversity

Tx Rx

Interleaving


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g

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4

message blocks

interleaving

interleavedmessage blocks

Received Interleaved Message Blocks


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g

1 X 3 4 1 X 3 4 1 X 3 4 1 X 3 4

Frequency Hopping


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q y pp g

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

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

Downlink C1

Uplink C1

N N + 1

TDM A frame no.

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

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

Downlink C2

Uplink C2

N N + 1

TDM A frame no.

Timing Advance


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0 1 2 3 4 5 6 7

T i m e

0 1 2 3 4 5 6 7

S y n c h r o n i z a t i o n t i m e

S t a r tS e n d i n g

Segmentation and Speech Coding


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01100011000111110011100

Speech Code

20 ms

Speech Signal

Interleaving of 20 ms of Encoded Speech


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19

1 72 5IIIIIII

IIIII

4 4 9

21 0IIIIIIIII

IIIII

4 5 0

31 1IIIIIIIII

IIIII

4 5 1

41 2IIIIIIIII

IIIII

4 5 2

51 3IIIIIIIII

IIIII

4 5 3

61 4IIIIIIIII

IIIII

4 5 4

71 5IIIIIIIII

IIIII

4 5 5

81 6IIIIIIIII

IIIII

4 5 6

8 b l o c k s

5 7 b i t s

Speech Frame


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20 ms speech

456 bits = 8x57

A

20 ms speech

456 bits = 8x57

B

20 ms speech

456 bits = 8x57

C

20 ms speech

456 bits = 8x57

D

Second Level of Interleaving

A/8


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A/8

A/8

A/8

A/8

B/8 A/8

B/8 A/8

B/8 A/8

B/8 A/8

C/8 B/8

C/8 B/8

C/8 B/8

C/8 B/8

D/8 C/8

D/8 C/8

D/8 C/8

GSM Transmission Process


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33.8 kbit/s

22.8 kbit/s

13 kbit/s

8 kHz13 bits

Transmitting part

Receiving part

Speaker

ReceiverDemodulator

Adaptive

Equalization

De-ciphering

De-interleaving

Channel decoding

Speech decoding

D/A-conversion

TransmitterModulator

Burst formatting

CipheringInterleaving

Channel coding

Speech coding

Segmentation

A/D-conversionMicrophone

13 kbit/s

Transmitting part

Receiving part

TransmitterModulator

Burst formatting

CipheringInterleaving

Channel coding

D/D-conversion

8 kHz8 bits64 kbit/s PCM

ReceiverDemodulator

Adaptive

Equalization

De-ciphering

De-interleaving

Channel Decoding

GSM Network

Mobile equipment

GPRS Logical Architecture


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Traffic and signaling

Signaling

TE Terminal EquipmentMT Mobile Terminal

MS Mobile Station

BSS Base Station SystemBTS Base Transceiver Station

BSC Base Station ControllerGMSC Gateway Mobile Services Switching

Center

MSC Mobile services Switching Center

VLR Visitor Location RegisterHLR Home Location Register

AUC Authentication CenterEIR Equipment Identity Register

SGSN Serving GPRS Support Node

GGSN Gateway GPRS Support Node

Um Air InterfaceA, Abis Interfaces (GSM)

Gx Interfaces (GPRS)

External

IP Network

(CorporateLAN)

Gi

TE MT

MS

BSC

GMSC

MSC/VLR

SGSN

EIR

HLR

AUC

GGSNIP-Backbone

Network

External

IP Network

(Internet)

External

X.25 Network

GsGf

Gr

BTS

Gb

UmISDN/

PSTN

Gn

A

Other

PLMN

Gp

BSS Abis

1_introduction to GSM

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