1_Introduction to GSM(GSM_GPRS Sys Overview)

8/3/2019 1_Introduction to GSM(GSM_GPRS Sys Overview)

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System Model:

AUC

HLR EIR

SS

BSS

MSC

BTS

MS

NMC and OMC

Switching System

Signaling transmissionCall connections and

signaling transmission

Base Station System

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 AreaLA - Location AreaBTS - Base Transceiver StationBSC - Base Station Controller

MSC - Mobile Switching CenterVLR - Visitor Location RegisterGMSC - Gateway MSCEIR - Equipment Identity RegisterAUC - 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/s

per call

16 Kb/s

full-rate33.8 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-GMSCSMS-IWMSC


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VLR-HLR Interaction:

HLR

UpdateDe

lete

MSC/VLR MSC/VLR


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Mobile Station:

ME

MobileEquipment

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

LEGEND

MSC BoundaryBSC 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-ACell 2-A-25

LA 2-B

HLR

EIR

AUC

GMSC

ILR

MSC/VLR 1PSTN

MSC Service Area 2

MSC Service Area 1

LEGEND

MSC BoundaryBSC BoundaryPCM LinksBase 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+Kithrough A8.

4. Compare SRES received from

MS with SRES in triplet. If theyare equal access is granted.

MSC/VLR Mobile service Switching CenterMS Mobile Station

RAND 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

EIR3. 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

Operation and

Support System

NMC


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SOG and BGW:

Gateway productsfor billing informationand service

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

LA 1

LA 2

Th RBS Li t i f Ch l R t d


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The RBS Listening for Channel Requests andMeasuring the Uplink on an Established Connection:

Signal strength!

Quality!Timing!

Access

burst!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


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Uplink and Downlink on a Radio Channel:

Uplink

Downlink


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System Parameters:

up link down link

f

Carrier spacing Bandwidth spacing

Duplex spacing


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Duplex Distance:

890 960915 935MHz

Uplink Downlink

Duplex Distance (45 MHz)

Bandwidth (2 x 25 MHz)


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Duplex distances for different frequency bands:

Standard GSM 900 GSM 1800 GSM 1900

Duplex dist. 45 MHz 95 MHz 80 MHz


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Carrier Separation:

Carrier Separation (200 KHz)

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

4.615 ms

3 57 1 26 1 57 3

Burst

148 Bits

156.25 Bits0.577 ms

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

}

Sampledvalue

Quantizedvalue

D = Quantized error


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Parameters that are important for GSM:

Path loss

Shadowing

Rayleigh fading

Signal strength

Time dispersion

Time Alignment


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Problems Solution Fading:

Distance 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 mean value

Fading dip (Rayleigh)

Receiver sensitivity

R Sig l St gth V Di t


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Rx Signal Strength Versus Distance:

log (distance)

Signallevel(

dB)

Path loss ( )

Rayleigh fading (-)

Log normalfading ( )

Rayleigh Fading:


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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 systems

C

I

I C

A B

Figure D.5.4


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Co-channel interference:

f1

f1

B

A

Acceptable

Speech quality

Figure D.5.3

Time Dispersion:


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Time Dispersion:

1

1

1.

0

0

2.

1

1

3.

1

0

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

Intermodulation in a 900 MHz cellular system:


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Intermodulation in a 900 MHz cellular system:

890 900 910 920 930 940 950 960 MHz

RX band

Duplex distance (D)

TX band

Allocated RX band (B)(10 MHz inthis example)

Allocated TX band (B)(10 MHz in this example)

IM7 IM5 IM3

Intermodulation (IM) in cellular systems:


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( ) y

System

GSM900

DCS1800

PCS1900

NMT450

Duplexdistance,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:

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

Worst-case relationsIM3 in Rx band if D/B < 2IM5 in Rx band if D/B < 3IM

7

in Rx band if D/B < 4IM9 in Rx band if D/B < 5

Co-Channel Interference:


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CarrierInterference

Distance

f1 f

1dB

C I

Adjacent Channel Interference:


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AC

CarrierAdjacent

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 Site with antenna

pointing away

Channel Coding:


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g

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

TxRx (B)Rx (A)

AntennaDiversity

DiversitySystemOutput

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


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Timing Advance:


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0 1 2 3 4 5 6 7

Time

0 1 2 3 4 5 6 7

Synchronization time

StartSending

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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191725I

IIIIII

IIIII

449

210III

IIIIII

IIIII

450

311III

IIIIII

IIIII

451

412III

IIIIII

IIIII

452

513III

IIIIII

IIIII

453

614III

IIIIII

IIIII

454

715III

IIIIII

IIIII

455

816III

IIIIII

IIIII

456

8 blocks

57 bits

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

AdaptiveEqualization

De-ciphering

De-interleaving

Channel decoding

Speech decoding

D/A-conversion

TransmitterModulator

Burst formatting

CipheringInterleaving

Channel coding

Speech coding

Segmentation

A/D-conversion

Microphone

13 kbit/s

Transmitting part

Receiving part

TransmitterModulator

Burst formatting

CipheringInterleaving

Channel coding

D/D-conversion

8 kHz8 bits

64 kbit/s PCM

ReceiverDemodulator

AdaptiveEqualization

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 TerminalMS Mobile Station

BSS Base Station SystemBTS Base Transceiver StationBSC Base Station ControllerGMSC Gateway Mobile Services Switching

CenterMSC Mobile services Switching CenterVLR Visitor Location RegisterHLR Home Location RegisterAUC Authentication Center

EIR Equipment Identity RegisterSGSN Serving GPRS Support NodeGGSN Gateway GPRS Support NodeUm Air InterfaceA, Abis Interfaces (GSM)Gx Interfaces (GPRS)

ExternalIP Network(CorporateLAN)

Gi

TE MT

MS

BSC

GMSC

MSC/VLR

SGSN

EIR

HLR

AUC

GGSNIP-Backbone

Network

ExternalIP Network(Internet)

External

X.25 Network

GsGf

Gr

BTS

Gb

UmISDN/PSTN

Gn

A

OtherPLMN

Gp

BSS Abis

Documents

1_Introduction to GSM(GSM_GPRS Sys Overview)