Finalised GSM Overview

7/29/2019 Finalised GSM Overview

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GSM

An Industrial TrainingPresentation

ON

By: Rahul Mishra

08720902809


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What is GSM?

The Global System for Mobile communicationsis a digital cellular communications system. It

was developed in order to create a commonEuropean mobile telephone standard but it hasbeen rapidly accepted worldwide.

Formerly it was Groupe Spciale Mobile (founded1982) now: Global System for Mobile Communication


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Evolution of GSM.

The idea of cell-based mobile radio systemsappeared at Bell Laboratories (in USA) in theearly 1970s. However, mobile cellular systemswere not introduced for commercial use until the1980s.

But in the beginnings of cellular systems, eachcountry developed its own system, which was anundesirable situation for the following reasons:

The equipment was limited to operate onlywithin the boundaries of each country.

The market for each mobile equipment waslimited.


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In order to overcome these problems, the Conference ofEuropean Posts and telecommunications (CEPT) formed, in1982 ,the Group Special Mobile (GSM) in order to develop apan-European mobile cellular radio system . The

standardized system had to meet certain criteria: Spectrum efficiency

International roaming

Low mobile and base stations costs

Good voice quality

Compatibility with other systems such as ISDN (IntegratedServices Digital Network)

Ability to support new services


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GENERATION OF GSM

1st generation:- Analog mobile technologies :- AMPS , TACS & NMT.

2nd generation:- digital mobile technologies :- GSM , CDMA

2.5generation:- Enhancement of GSM:- GPRS

3rd generation:- Technologies coursed by ITU-IMT

The following table lists the key events in the GSM evolution

AMPSAdvanced Mobile Phone System

TACS----Total Access Communication System.

NMT----Nordic Mobile Telephones


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GSM

EDGE

2.5 G

GPRS

2G

2.5 g+

UMTS 3GWCDMA


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GPRS-Wireless Data Services .

EDGEProvides 3 times the data capacity of

GPRS. 3G---Uses WCDMA technologies Over Air

interface (5MHz),provides fastercommunication like voice, fax and internet.video calling, live streaming


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GSM STANDARDSGSM-900 Standard

The GSM-900 standard is a standard for digital voice transmission in the 900 MHz band.This so called primary band" includes two sub bands of 25 MHz

GSM-1800 Standard

In GSM-1800, 1800 MHz band was allocated for digital mobile telephone services whichhas frequency of 75 MHz. This was three times the bandwidth allocated for GSM-900.

GSM-1900 Standard

GSM-1900 is the standard for the 1900MHz band. It includes the same networkcomponent as the GSM-900 or GSM-1800. The band width of this standard is 60 MHz.

GSM Channels/Carriers

The following table will show the channels and carriers of different GSM models

P E GSM R GSM GSM GSM


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P-

GSM(Pri

mary-

GSM)

900

E-GSM

900(Exte

nded-

GSM)

R-GSM

900(Rail

ways-

GSM)

GSM

1800

GSM

1900

Uplink frequency 890-915

MHz

880-915

MHz

886-915

MHz

1710-

1785

MHz

1850-

1910

MHz

Down link

frequency

935-960

MHz

925-960

MHz

931-960

MHz

1805-

1855MHz

1930-

1990MHz

Channel spacing 200 kHz 200 kHz 200 kHz 200

kHz

200 kHz

Carrier

Frequency

124 174 144 374 299

Duplex spacing 45 MHZ 45 MHZ 45 MHZ 95

MHZ

80 MHZ


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Type of access Technology

FDMA (Frequency division Multiple Access):- In FDMA,signals from various users are assigned differentfrequencies. Frequency guard bands are maintainedbetween adjacent signal spectra to minimize crosstalk

between channels. TDMA (TIME DIVISION MULTIPLE ACCESS):- In a TDMA

system, data from each user is conveyed in time intervalscalled Time slots. Several slots make up a frame . Each

slot is made up of a preamble plus information bitsaddressed to various stations .the functions of thepreamble are to provide identification and incidentalinformation and to allow synchronization of the slot at theintended receiver .Intersymbol interference is the mainproblem in the TDMA.


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GSM NUMBERING STRUCTURE:

MSISDN :- The real telephone numberof a mobilestation is the mobile subscriber ISDN number(MSISDN). It is assigned to the subscriber (his or her

SIM, respectively), such that a mobile station set canhave several MSISDNs depending on the SIM. -CC+NDC+SN - 12digits

IMSI - Each registered user is uniquely identified byits international mobile subscriber identity (IMSI). It isstored in the subscriber identity module (SIM) Amobile station can only be operated if a SIM with avalid IMSI is inserted into equipment with a validIMEI. MCC (3)+MNC (2)+MSIN (10) - 15 digits


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TMSI - The VLR, which is responsible for the current location of asubscriber, can assign a temporary mobile subscriber identity(TMSI) which has only local significance in the area handled by theVLR. It is stored on the network side only in the VLR and is notpassed to the HLR. 4 octets

IMEI - The international mobile station equipment identity (IMEI)uniquely identifies a mobile station internationally. It is a kind ofserial number. The IMEI is allocated by the equipmentmanufacturer and registered by the network operator andregistered by the network operator who stores it in the EIR. Bymeans of IMEI one recognizes obsolete, stolen or non-functional

equipment. TAC+FAC+SNR+Spare - 15 digits LAI - The Location Area Identifier (LAI) is also structured

hierarchically and internationally unique as follows:MCC+MNC+LAC


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GSM Multiplex structure

GSM works on a combination of frequency-divisionmultiplexing and time-division multiplexing forproviding multiple access by mobile stations.

GSM utilizes a cellular concept, in which ageographical area is divided into planned radio cells ,with one BTS per cell with which a mobile can make

contact. The radio cells, each having the exclusive useof specific FDM channels. The same frequencies areonly used after sufficiently long distances inneighboring cell clusters. The cell radius can varyaccording to user density from 300 mtrs to 35 Kms.


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Cells


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GSM ARCHITECTURE


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Different interfaces used in

Mobile Um interface The "air" or radio interface standard that is used

for exchanges between a mobile (ME) and a base station (BTS /BSC).

Abis interface This is a BSS internal interface linking the BSCand a BTS

A interface The A interface is used to provide communicationbetween the BSS and the MSC.

B interface The B interface exists between the MSC and the VLR

C interface The C interface is located between the HLR and aGMSC or a SMS-G.


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D interface The D interface is situated between the

VLR and HLR. E interface The E interface provides communication

between two MSCs.

F interface The F interface is used between an MSCand EIR.

G interface The G interface interconnects two VLRs ofdifferent MSCs.

H interface The H interface exists between the MSCthe SMS-G. It transfers short messages

I interface The I interface can be found between theMSC and the ME.


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BASIC PARTS OF GSM

BSS:BTS and BSC

NSS:MSC,HLR,VLR ,EIR,AUC OSS : OMCR, OMCS

( )


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Mobile station(MS)

The mobile station (MS) represents the terminal equipment used by the wirelesssubscriber supported by the GSM Wireless system. Man machine interface. The SIM

may be a removable module, while the equipment identity is not linked to a particularsubscriber.

Functions of a Mobile Station :-

Radio transmission termination. Radio Channel Management.

Speech Encoding/Decoding .Radio Link error Protection.

Flow control of data. Mobility Management.

SIM (Subscriber identity Module) - It is basically a removable smart card in compliancewith the ISO 7816 standard and a plug-in module (25 x 15 mm) .It includes amicroprocessor with all the subscriber-related information . SIM (and consequentlyMS) is protected by a Personal Identification Number (PIN). It has a PIN Unblocking Key(PUK) used to unblock it.

Information stored in a SIM card- Serial number

International Mobile Subscriber Identity (IMSI)

Security authentication and cyphering information

Temporary Network information (LAI, TMSI)


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BSSThe BSS is responsible for communicating with mobile stations in cell areas.

BTS is a network element with transmission and reception devices (transceivers) to andfrom the MS, including

antennas

signal processing specific devices for the Air interface management

It can be considered as a complex radio modem controlled by the BSC

It is involved also in the transmission and reception with the BSC through the A-bisinterface

It has just executive functions (no management

Function

Broadcast/receive to/from the MS either signalling and traffic signals Perform source and channel coding

Modulate/Demodulate signals to be broadcasted/received through the Air interfaceradio channel

Multiplex the information to be transmitted over each carrier.


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BSC One BSC controls one or more BTSs and can performinter-BTS and intra-BTS handover.

BSC Function

Control and supervise the BTSs

Configure each cell with the allocation and the release of trafficand signalling channels

Manage the paging operation

Collect the signals quality measures acquired by the BTSs overthe downlink and uplink channels

Manage all the radio interfaces Manage the handover procedures

Transcode and Sub-multiplex the bit stream


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Function of NSS

Call control identification of the subscriber

establishing a call and release of the connection after the call is over Mobility management

taking care of the location of the subscribers before, during and aftera call

Collecting the charging information about a call number of the caller and of the called subscriber

length and type of the provided services

Transfer the acquired charging information to the Billing centre

Signalling with other networks and BSS through the differentinterfaces

Subscriber data handling

Data storage permanently or temporarily in some databases

OMCR:- It is used to monitor and maintain the alarms of the system.


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Comprises of the

Base Transceiver Station (BTS)

Base Station Controller (BSC)

Base Station Subsystem


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Input alarms include :- Power supply unit- input failure

It is due to loss of AC power

Power supply unit- output failure

Due to loss of output power because of failureof PSU

Smoke alarm

BTS cabinet over temperature (max. 70C )


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Types of GSM handover

Within the GSM system there are four types of handover that can be performedfor GSM only systems:

Intra-BTS handover: This form of GSM handover occurs if it is required to changethe frequency or slot being used by a mobile because of interference, or otherreasons. In this form of GSM handover, the mobile remains attached to the samebase station transceiver, but changes the channel or slot.

Inter-BTS Intra BSC handover: This for of GSM handover or GSM handoff occurswhen the mobile moves out of the coverage area of one BTS but into anothercontrolled by the same BSC. In this instance the BSC is able to perform thehandover and it assigns a new channel and slot to the mobile, before releasing theold BTS from communicating with the mobile.

Inter-BSC handover: When the mobile moves out of the range of cells controlledby one BSC, a more involved form of handover has to be performed, handing over

not only from one BTS to another but one BSC to another. For this the handover iscontrolled by the MSC.

Inter-MSC handover: This form of handover occurs when changing betweennetworks. The two MSCs involved negotiate to control the handover

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Finalised GSM Overview