GSM Overview Modified by Moham

7/29/2019 GSM Overview Modified by Moham

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GSM Overview

Radio Team24 July 2006


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GSM Overview2

Contents

Introduction

Radio Spectrum & Coverage

Basic GSM Network Structure

Radio Signal Generation

Mobile Calls


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GSM Overview3

Spectrum Allocation (GSM 900)

GSM 900 Frequency Allocation

F (MHz)915890

Uplink1 2 3 4 121 122 123 124

F (MHz)

Downlink

960935

1 2 3 4 121 122 123 124

890.2

890.4

890.6

935.2

935.4

935.6

200 KHz

1

1

121

121

Downlink 935 960 MHz

Uplink 890 915 MHz

ARFCN Absolute Radio Frequency Channel Number


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GSM Overview4

GSM 1800 Frequency Allocation

F (MHz)17851710

Uplink1 2 3 4 371 372 373 374

F (MHz)

Downlink

18801805

1 2 3 4 371 372 373 374

1710.2

1710.4

1710.6

1805.2

1805.4

1805.6

200 KHz

Downlink 1805 1880 MHz

Uplink 1710 1785 MHz

Spectrum Allocation (GSM 1800)


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GSM Overview5

GSM 900 Band

960 MHz

VODAFONEMobinil

890 MHz 915 MHz

935 MHz

902.5 MHz

947.5 MHz

25 MHz

12.5 MHz 12.5 MHz


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GSM Overview6

Frequency Reuse

Total no of channels (frequencies) = 124

Every channel can be shared between 8 subscribers max.

Maximum no of simultaneous calls = 8 X 124 = 992!!

Why do we need frequency reuse?

The frequency reuse is performed by dividing the whole availablefrequencies between a group of neighboring cells which is called frequency

reuse pattern or a Cluster, and then repeat this cluster over the whole

network on 2 conditions:

The group of frequencies allocated to a given cell must not be used in the adjacent

cells. Enough distance between the cells in which the same group of frequencies are

reused.


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GSM Overview7

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

FrequencyReuse

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1


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GSM Overview8

GSM CoveragePlanTo provide coverage for a large service are of a mobilenetwork we have 2 Options:

(A) Install one transceiver with

high radio power at the center of

the service area

Drawbacks

The mobile equipments used in this

network should have high output power

in order to be able to transmit signals

across the coverage area.

The usage of the radio resources would

be limited.

(B) Divide the service area into

smaller areas (cells)

Advantages

Each cell as well as the mobile

handsets will have relatively small

power transceivers.

The frequency spectrum might be

reused in two far separated cells,

Unlimited capacity of the system.

Good interference characteristics


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GSM Overview9

Dead Spots

Cell Geometry

Problem of omni directional antennas


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GSM Overview10

R R

To solve the dead spot problem

The number of cells required to cover a given area.

The cell transceiver power.

Tradeoffs

R

Cell GeometricalShape


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GSM Overview11

TransceiverAntenna

Omni-Directional AntennaSectorial Antenna


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GSM Overview12

The cells will take the form of overlapping circles.

Due to the obstacles in the coverage area the actual shape of

cells would be Random.

Sectorial Antenna

Sectorial Antenna


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GSM Overview13

Umbrella Cell

Overlaid &

Underlaid CellsNormal Cell Normal Cell

CellClassification


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GSM Overview14

Questions ?GSM Overview

Technical Session


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GSM Overview15

Basic GSM Network Structure


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GSM Overview16

Basic GSM NetworkStructure

BSC

BTS

PTT

Another

SwitchingNode

HLR

MSC/VLR

Radio Interface

PABXAnother MSC

GW Of another network

MS


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GSM Overview17

The Mobile Station(MS)

The Mobile Equipment is said to be a Mobile Station if the

SIM Card is added to it

+


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GSM Overview18

The Base Transceiver Station (BTS)

Record and passes to the BSC the Signal strength measurements.

Perform the network end of the ciphering/encryption process.

Radio Transmission and reception.


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GSM Overview19

The Base Station Controller (BSC)

Manages the Radio Communication with the mobile station.

Controls the handover of calls in progress Between BTS

Supervises the performance of the each BTS

Allocates channels to the mobile


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GSM Overview20

The Home Location Register (HLR)

Stores for each mobile:

Current location.Allowed/barred

services.

Authentication data.

Supplementary

services.

Data base that stores and manages subscriptions.


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GSM Overview21

The Visitor Location Register (VLR)

In our network, the VLR is integrated with the MSC

It stores a copy of the HLR Profile for all the currently

registered subscribers who are covered by cells belonging

to the MSC coverage area.


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GSM Overview22

The Mobile Services Switching Center(MSC)

Administers its Base Station Controller(s)

BSC(s).

Switches calls to/from mobile subscribers. Records charging and accounting details.

Provides the Visitor Location Register (VLR) functionality.

Provides the gateway to other networks.


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GSM Overview23

GSM Identities

CC : Country CodeNDC: Network Destination Code

SN : Subscriber Number

20 10 1100477

(CC) (NDC) (SN) (CC) (NDC) (SN)

VF UK MSISDN VFE MSISDN

44 385 196099

Mobile Station ISDN Number

(MSISDN)


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GSM Overview24

IMSI Structure

MCC:Mobile Country Code.MNC:Mobile Network Code.

MSIN:Mobile Station Identification Number.

234 15 1021000899

(MCC) (MNC) (MSIN)

VF UK IMSI

602 02 1234567890

(MCC) (MNC) (MSIN)

VFE IMSI

International Mobile Subscriber Identity


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GSM Overview25

International Mobile Equipment Identity(IMEI)

SNRFACTACIMEI

TAC = Type Approval

CodeFAC = Final Assembly

CodeSNR = Serial Number

Identifies the Type

Identifies the manufacturer


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GSM Overview26

GSM Complete Model

SS

BTS

O S S

ISDN

PLMN

PSTN M I N

S C

B G W

H L R

AUC

SMSC-GMSC

SMS-IWMSC

E I R

GWMSC

MSC/VLR

BSC

BSS


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GSM Overview27

Questions ?


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GSM Overview28

Mobile Calls


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GSM Overview29

Mobile Terminating Calls

Mobile Originating Calls

Mobile Calls


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GSM Overview30

Mobile OriginatingCalls

1. The mobile sends a call request along with itsIMSI to its serving MSC/VLR which will mark the

mobile as busy.

2. Authentication is performed by the MSC to

verify the mobile access to the network, and

then ciphering is initiated in order to protect the

mobile call on the radio path.

3. The mobile sends a call setup message to theMSC with information about the call type,

services required and the dialed number.

4. MSC checks the categories of the mobile

subscriber to verify that he is authorized to use

the required services, and then a link is

established between the MSC and BSC.

5. BSC checks the mobile serving BTS for an idle

traffic channel and then orders that BTS to seize

this channel for a call.

6. The BSC informs the MSC when the traffic

channel assignment is complete, and then the

MSC/VLR starts to analyze the dialed number

and sets up a connection to the calledsubscriber.

BSC

PSTN

MSC


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GSM Overview31

PSTN

HLR

GMSC MSC BSC

1

3

2

5

4

7

6

9

8

Mobile TerminatingCalls


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GSM Overview32

Questions ?GSM Overview

Technical Session


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Thank you

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GSM Overview Modified by Moham

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