gsm_seminar_ppt_by santosh singh nit hamirpur

8/3/2019 Gsm_seminar_ppt_by Santosh Singh Nit Hamirpur

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GSM GLOBAL SYSTEM FOR

MOBILE COMMUNICATION

SUBMMITTED BY:-SANTOSH SINGHROLL # 08446


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DISCUSSION TOPICS

History

System Architecture

GSM operation

Frequency Resources

Access Technologies

Handoff

Numbering arrangements


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HISTORY

Early 1980s there were analog technologies:

Advanced Mobile Phone Services(AMPS)in NorthAmerica.

Total Access Communications System(TACS) in the UK. Nordic Mobile Telephone(NMT) in Nordic countries.

Each country developed its own system which caused

problems:

System worked only within the boundaries of each

country.

Mobile equipment manufacturers markets were limitedby the operating system.


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HISTORY(contd.)

Solution was GSM, which is digital technology and was developedby

CEPT(Conference of European Posts and Telecommunications).

The Goals of GSM:

High speech quality

Low-cost mobile sets and base stations

Support for international roaming one system for all of Europe

Support for range of new services and facilities

Compatibility with ISDN and other telephone company services.

Enhance privacy

Security against fraud


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System Architecture


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System Architecture

Mobile Station (MS)

The Mobile Station is made up of two entities:

Mobile Equipment (ME)

Subscriber Identity Module (SIM)

Mobile Equipment: Produced by many different manufacturers

Must obtain approval from the standardization body

Uniquely identified by an IMEI (International Mobile

Equipment Identity)

Mobiles transmit and receive voice at 13 kbps over air

interface


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System ArchitectureMobile Station (MS) contd.

Subscriber Identity Module (SIM)

Smart card containing the International Mobile SubscriberIdentity (IMSI),serial number ,subscriber key(ki)

SIM features and contents are personalized by theservice activator

Protected by a password or PIN

MS also stores some temporary data on SIM duringoperation


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System Architecture

Base Station Subsystem (BSS)

Base Station Subsystem is composed of two parts that

communicate across the standardized Abis interface

Base Transceiver Station (BTS)

Base Station Controller (BSC)


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System ArchitectureBase Station Subsystem (BSS) contd.

Base Transceiver Station (BTS):

Houses the radio transceivers that define a cell

Transmits and receives voice at 13 kbps to the mobiles

Commands mobiles to set Tx power and

handovers

hi


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System Architecture

Base Station Subsystem (BSS) contd.

Base Station Controller (BSC)

Several BTS are connected to one BSC

BSC manages channel allocation , handovers and

release of channels at connected BTSs BSC Connects to each BTS on an Abis interface and to

the MSC on A interface

BSC has the entire database for all cell parameters

associated with the BTSs

S A hi


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System Architecture

Network Subsystem

Mobile Switching Center (MSC):

Exchange where calls are established , maintained andreleased

It contains Database for all subscribers and there

associated features Communicates with BSCs on MS side and with PSTN on

fixed line side

Three main jobs:

1) connects calls from sender to receiver2) collects details of the calls made and received

3) supervises operation of the rest of the networkcomponents

S t A hit t


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System Architecture

Network Subsystem contd.

Home Location Registers (HLR)

MSC has all subscribers database stored in HLR

HLR has all permanent subscribers database

MSC communicates with HLR to get the data forsubscriber on call

HLR will have the series of all subscriber numberswhich may not be activated or issued

S t A hit t


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System Architecture


Visitor Location Registers (VLR) A subscription when activated is registered in VLR

VLR has all the subscriber number which are activated

MSC communicates with HLR for subscribers coming from different

MSCs and if found valid then register them in its VLR

TRAU-transcoder/rate adaption unit

TRAU converts the data rates between 13kbps GSM rate to 64kbpsstandard ISDN(integrated service digital network) rate and viceversa

TRAU can be allocated with the BTS,BSC or MSC or it can be aseparate unit.

S stem Architect re


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System Architecture


Authentication Center (AUC)

Authentication is a process by which a SIM is verified

Secret data and the verification process algorithm are stored atAUC

AUC is the element which carries out the verification of SIM

Associated with HLR

Equipment Identity Register (EIR)

EIR is the Mobile Equipment Database which has a series of IMEIs

MSC ask the mobile to send its IMEI

MSC then check the validity of IMEI with the EIR

All IMEI are stored in EIR with relevant classification : white list ,black list , grey list


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GSM OPERATION

Speech decoding

Channel decoding

De-interleaving

De-ciphering

DemodulationModulation

(GMSK)

Ciphering(Encryption)

Interleaving

Channel Coding

Speech coding

Radio Interface

Speech Speech

13 Kbps

22.8 Kbps

22.8 Kbps

33.6 Kbps

270.83 Kbps


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Frequency Resource

GSM900 :

uplink: 890~915MHz

downlink: 935~960MHzduplex interval: 45MHz

Bandwidth of uplink and downlink: 25MHz

1 channel carrier frequency: 200KHz124 channels(of 200 KHz each)

1 gaurdband of 200KHz


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Access Technologies


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FDMA

In FDMA, we assume that a base station can receive radiosignals in a given band of spectrum, i.e., a range ofcontinuous frequency values.

The band of frequency is broken up into smaller bands, i.e.,

subbands.

Each transmitter (user) transmits to the base station usingradio waves in its own subband.


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FDMA (Contd)

A sub band is also a range of continuous frequencies, e.g.,824 MHz to 824.1 MHz. The width of this subband is 0.1 MHz= 100 KHz.

When a users is assigned a subband, it transmits to the basestation using a sine wave with the center frequency in thatband, e.g., 824.05 MHz.

When the base station is tuned to the frequency of a desireduser, it receives no portion of the signal transmitted by anotherin-cell user (using a different frequency).

This way, the multiple local transmitters within a cell do notinterfere with each other.


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TDMA

In pure TDMA, base station does not split up itsallotted frequency band into smaller frequencysubbands.

Rather it communicates with the users one-at-a-time, i.e., round robin access.


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HANDOFF

When a mobile moves into a different cell while a conversation is in

progress, the MSC automatically transfers the call to a new channelbelonging to the new base station.

Handoff operation

identifying a new base station

re-allocating the voice and control channels with the new basestation.

Handoff Threshold

Minimum usable signal for acceptable voice quality (-90dBm to-100dBm)

handoff margin Handoff margin cannot be too large or too small.

If is too large, unnecessary handoffs burden the MSC

If is too small, there may be insufficient time to complete

handoff before a call is lost.

usableminimum,, rhandoffr PP


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A Handoff

Suppose a user is transmitting and receiving signals from a givenbase station, say B1.

Assume the user moves from the coverage area of one base station

into the coverage area of a second base station, B2.

B1 notices that the signal from this user is degrading.

B2 notices that the signal from this user is improving


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A Handoff

At some point, the users signal is weak enough at B1 andstrong enough at B2 for a handoff to occur.

Specifically, messages are exchanged between the user, B1,and B2 so that communication to/from the user is transferred

from B1 to B2.


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Numbering Arrangement

It will uniquely identify a mobile station. It is a decimal

number of 15 digits. Its structure is:

TAC+FAC+SNR+SP

TAC=model ratification code, 6 digits

FAC=factory assembling code, 2 digits SNR=sequence code, 6 digits

SP=reserved, 1 digit

International mobile equipment identity(IMEI)

N mbering Arrangement


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International Mobile Subscriber Identification number

(IMSI)

It identifies a unique international universal number of a mobilesubscriber, which consists of MCC+MNC+MSIN.(15 digits)1) MCC: country code, 404(3 digits)2MNC: network code, 00 or 01(2 digits)3MSIN: subscriber identification (10 digits)

the IMSI of user will be written into the SIM card by specificdevice and software and be stored into the HLR with otheruser information.


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It is the subscriber number commonly used.

CC+NDC+ SN CC: country code,

NDC: network code,

SN: subscriber number

Mobile Subscriber ISDN NumberMSISDN


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THANK YOU

gsm_seminar_ppt_by santosh singh nit hamirpur

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