gsm system introduction 1
TRANSCRIPT
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GSM System introduction
By
Muhammad Farhan Shafique
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Introduction
Global System for Mobile Communication (GSM)
Anybody 500 million users (may 2001)
Anywhere 168 countries (may 2001)
Any media voice, messaging, data, multimedia
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GSM Architecture
OMC
Home Location Register
AuC
Equipment ID
Network
Management
Center
B
TS
B
TS
B
TS
ME
ME
ME
SubscriberIdentity
Module
SubscriberIdentityModule
SubscriberIdentityModule
Base station
controller
PSTN
Mobile
switchingcenter
Data
communication
network
BTS = Base Transceiver Station
AuC = Authentication Center
OMC = Operation and Maintenance Center
PSTN = Public Switched Telephone Network
ME = Mobile Equipment Visitor LocationRegister
Base Station Subsystem
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Mobile Station (MS)
TEMPORARY DATA PERMANENT DATA
- Temporary Subscriber Identity Permanent Subscriber Identity
- Current Location Key/Algorithm for Authentication.
- Ciphering Data
Provides access to the GSM n/w
Consists of
Mobile equipment (ME)
Subscriber Identity Module (SIM)
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Block diagram of GSM MS
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SIM (Subscriber Identity Module)
Billions of Calls
Millions of Subscribers
Thousand of Different Types of Telephones
Hundreds of Countries
Dozens of Manufacturers.
And only one Card: The SIM
Administrative data
Security data
Subscriber data
Roaming data
PLMN (Public Land Mobile Network
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SIM
The real identity of GSM MS and its subscriberis the data stored in SIM.
ME+SIM=MS
Consists of ROM and EEPROM SIM memory is divided in to different directories
like hard disk.
SIM communicate directly with VLR andindirectly with HLR.
It consists of IMSI,MSISDN,LAI and many otherinformation like ciphering key, location updatestatus,
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IMEI
International Mobile Station Equipment
Identity
a serial number which uniquely identifies the
mobile station internationally.
usually requested from the MS by the network at
registration and comprises:
Type App rova l Code (TAC): 6 decimal digits
F ina l Assemb l y Code (FAC): 6 decimal digits
Ser ia l Num ber (SNR): 6 decimal digits
Spare(SP): 1 decimal digit
IMEI = TAC + FAC + SNR + SP (19 digits)
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IMSI
International Mobile Subscriber Identity
t h eunique identifier stored on the SIM
a MS will only operate if a SIM with a valid IMSI is
inserted into equipment with a valid IMEI as this is
the only way to bill the subscriber
comprises:
Mobile Country Code (MCC): 3 decimal digits
Mobile Network Code (MNC): 2 decimal digits
Mobile Subscriber Identification Number (MSIN): 10decimal digits
IMSI = MCC + MNC + MSIN (15 digits)
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MSISDN
Mobile Subscriber ISDN Number
the real telephone number of the subscriber / MS
stored on the HLR and associated with the IMSI
protects the confidentiality of the IMSI making
fraud more difficult
comprises:
Coun t r y Code (CC): up to 3 decimal places
Nat ion a l Des t i na t ion Cod e (NDC): typically 2 or 3 decimalplaces
Subsc r i be r Num be r (SN): maximum 10 decimal places
MSISDN = CC + NDC + SN
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LAI
Location Area Identity
Each location area of a PLMN has its own identifier
Location Area ID (LAI)
internationally unique comprising: Country Code (CC): 3 decimal digits
Mobile Network Code (MNC): 2 decimal digits
Location Area Code (LAC): maximum of 5 decimal digits
LAI = CC + MNC + LAC
Broadcast regularly on the Broadcast Control Channel (BCCH)
Mobile recognises LAI stored on SIM and change of LA
gives rise to location update request
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Base Station Subsystem (BSS)
With air interface BSS provides MS and
NSS. It consists of following elements.
One or more BTS base (transceiverstation)
One BSC (Base station controller)
One TRAU (transcoding rate and
adaptation unit)
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Base transceiver station
(BTS) provides GSM radio coverage within
a cell. It comprises radio transmitting and
receiving equipment (including antennas)
and associated signal processing. Today
the size of BTS is just as compared to mail
box.
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Implementation
TO NSS
O&M Module Operation and maintenance functionality/clock distribution
Digital signalprocessing (NF
functionality)
HF Transmitter
(HF-TX)
Input filter
Output filter
HF Receiver(HF-RX)
Slowf
reque
ncy
hopping
Transmission
system
TRX
Block Diagram of a BTS with one TRX
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Functionality of BTS 1
Transmitter/receiver module:
This is the most important part of BTS from
signal processing point of view.
It consist of Low frequency parts for DSP and
HF part for GMSK modulation/demodulation.
All other parts of BTS are associated with TRX
and performs auxiliary or administrative
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Functionality of BTS 2
Operation and maintenance module.
It consist of at least one central unit which
administrate all other parts of BTS. That central unit contain system and
operation software.
It also provides Human machine interface
for local control of BTS.
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Functionality of BTS 3
Clock Module Module of clock generation and distribution is also a part
of O&M.
Although the trend is to derive the reference clock from
PCM signal but it is necessary when BTS is tested instandalone environment with out link to BSC.
When analyzing errors clock plays major role especiallywhen handover takes place minor deviation can createbig errors.
The accuracy of signal has to be 0.05 part per million.For example a clock generator that derives clock from10MHz signal has to provide the clock with accuracy of10MHz0.5Hz.
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Functionality of BTS 4
Input and output filters.
Both input and output filters are used to limit the
bandwidth of received and transmitted.
Input filters are generally non adjustable filters
which lets pass all GSM 900, DCS 1800, PCS
1900 in uplink direction.
Output filters are controllable by O&M centerthat limits the bandwidth of 200KHz in down link
direction.
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BTS configuration
Standard configuration
Umbrella cell configuration.
Sectorized BTS configuration.
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Standard configuration
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Umbrella cell configuration
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Sectorized configuration