1.gsm basic and cellular concepts

8/8/2019 1.GSM Basic and Cellular Concepts

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BSNL GSM

BY:

SHYAM SUNDER SAINIJTO (MSC)

CMTS Division, Udaipur


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Any time Anywhere

Mobility & Roaming

High capacity & subs. density Efficient use ofradio spectrum

Low cost

Flexibility

Innovative Services

MOBILE COMMUNICATION

OBJECTIVES


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History First mobile service started in 1946 in St.

Louis, Missouri, USA.

Manually operated service, restricted area ofservice, only few lucky subscribers.

Between 1950-60, it evolved to be

automatic with decreased cost.

Mobile telephony service appeared in its

useful form in 1960s.


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1946- 1960s 1980s 1990s 2000s

Appeared 1G 2G 3G

Analog Digital Digital

Terrestrial Terrestrial Terr. & Sat


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1 G -analog (cellular revolution)

- only mobile voice services

WIRELESS GENERATIONS

2 G - digital (breaking digital barrier)

- mostlyfor voice services & data deliverypossible

3 G - Voice & data ( breaking data barrier)

- Mainlyfor data services where voice services

will also be possible


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GSM Architecture


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B

T

S

MSC VLR

HLR

PSTN

ISDN

Data

Networks

Airinterface

OSS

B

T

S

B

T

S

MSC VLR

BSCBSC

A Interface

A-bis interface


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Abbreviation BSC - Base Station Controller

BTS - Base Transceiver Station

MSC-

Mobile Switching Center HLR - Home Location Register

EIR - Equipment Identity Register

AUC - Authentication Center

VLR - Visitor Location Register

OMC - Operation & Maintenance Center


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CELLULAR MOBILE CONCEPTS


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Propagation lossL in dBs

Transmit power PTand antenna gain GT

VoiceChannels

Orcontrol

channels

Lines to

MSC

Sitenoice

MS

Operating distance d

Planned cell radius R

Cell radio range - radius R max

Radio Cell Parameters


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GSM Network Structure

GSM Service Area: Total area served by the

combination ofall member countries where a mobilecan be served.

PLMN Service Area:It is one N/W area.

MSC Service Area:There can many MSC/VLR in onePLMN area.It is one Mobile Exch. Area.

GMSC: All I/C calls for PLMN N/W will be routedthrough GMSC. In a GSM/PLMN N/W all mobileterminated calls will be routed to a Gateway MSC.Call connections betweenPLMNs , or to fixed N/Wsmust be routed to a GMSC.The GMSC contains the

Inter workingfunctions to make these connections.

LocationArea

Cells


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LOCATIONAREA:There are several LA in a MSC/VLR

combinationA LA is a part ofthe MSC/VLR service area in

which a MS may move freelywithout updating location

information to the MSC/VLR exchange that control the LA.

Within a LA a paging message is broadcast in order to find

the called mobile subs. LA can be identified by system usingthe LAI.

CELL.A cell is an identity served by one BTS. The MS

distinguishes between cells using the BASE STATION

IDENTIFICATION CODE(BSIC) that the cell site broadcastover the air.


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GSMRelation between areas in GSM

Location AreaCell

Area served by a BTS

LocationAreaMSC ServiceAreaPLMN ServiceArea

GSM ServiceArea


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GSM

PLMN Service Area

V

MSC

MSC

MSC

MSC

VLR

VLR

VLR

I II

IVIII

I


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GSM

MSC Service Area

MSC

VLRLA1

LA2

LA3

LA6

LA4

LA5


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GSM

Cells

MSC

VLR

LA1

LA2

LA3

LA6LA4

LA5

C1C2 C3

C6C5

C4

C=CELL


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GSM

LA Coding

MCC

LAI

LACMNC

3 digit 3 digit 2Octets

MCC:Mobile country code, MNC: Mobile N/W Code,

LAC: Location Area code


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Location area consist of one or more than one cell which may

be served by one or more BSC s.

All the cells in a Location area are served by single VLR.

2. Location Area Identity (LAI ) -

Each location area in a GSM PLMN is identified by a Location

Area Identity ( LAI ).

Location Related Identities


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HLRSS 7

BSC

MSC 2

VLR 1

VLR 2

BSC

BSC

BSC

LA 1

LA 2

LA 3

BTS

BTS

BTS

BTS

BTS

BTS

Location Area

MSC 1


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LAI = MCC + MNC + LAC

MCC - Mobile Country Code.

MNC - Mobile Network Code.

LAC - Location Area Code .

Maximum length of LAC is 16 bits.

Thus there can be maximum of 65,536 Location Areas defined

in one GSM PLMN.

MCC MNC LAC

3 digits 2 digits 2 octets max

LAI

( 16 bits )

Location Related Identities


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ACLUSTER OF CELLS

4

5

6

7

2

3

11 2 3 4 5 6 7

GIVEN FREQ.

RESOURCE



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14

2

1

3

5

6

7 2

6

3

4

5

7

DR

CELLULAR PRINCIPLE N=7

12 3 456 7

Frequency Reuse Pattern N=7

Given Freq Resource



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GSM

CAPACITY CONSIDERATIONS

1

1

1

1

2

88 Access Channels

1--Signaling

7- Voice

With 2 % GoS

2.94 E

2.94E/25mE=120 Subs

120 Subs/Sector v 3 = 360 Subscribers


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Public Land Mobile Network INDIAhas adopted GSM standard for PLMN.

Digital Cellular System.

Operates at 900 MHz. International Roamingfacility.

Power class 0.8 to 20W.

Cell Radius upto 35 Kms.

Maximum mobility speed 250 Km/hr.


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Communication-

Mobile

TelephoneExchange

SubscriberLine(2W)

Inter-Exchange

Junction

Mobile SwitchingCentre (MSC)

BSC BTSMS


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GSM

Uplink & Downlink

Uplink means Reverse Path

Downlink means Forward Path

BT

S


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GSM

Specifications - I

Frequency Bands -

Mobile to Cell (UP-LINK) - 890 to 915 MHz

Cell to Mobile (DOWN -LINK) - 935 to 960 MHz

Bandwidth - 25 MHz

Carrier Separation - 200 KHz

Access Method - TDMA/FDMA

Modulation - GMSK


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GSM

Specifications - II

Number ofChannels - 124

Voice Channel Coding - ( 13 Kbps)

FULL RATE - 13Kb/s ; HALF RATE - 6.5 Kb/s

Bit Rate - 270.833 Kbps


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GSM - MULTIPLE ACCESS GSM uses both FDMA & TDMA

Freq

Mhz.890.2

0

890.4

1

890.6

2

890.8

3

891.0

4 5

915

124

FDMAAccess along Frequency axis Each RF carrier 200khz apart Total 124 RF Channels available.

One or more carrier assigned to each base station

In most cases 124 RF Channels are used

...

1.gsm basic and cellular concepts

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