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Need to be wireless.where wire-line
is limitedHuman Connectivity ?
Remote control of instruments
Defense Forces
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Emergency
Rural
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Always Connected
Anytime, Anywhere, Anything
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Recent and Future Wireless Communications
SystemsRecent Systems
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What is GSM ?
Global System for Mobile (GSM) is a
second generation cellular standard
developed to cater voice services and
data delivery using digital modulation
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GSM: History
Developed by Group Spciale Mobile (founded 1982) which wasaninitiativeof CEPT ( Conferenceof European Postand
Telecommunication )
Aim : toreplacetheincompatibleanalogsystem
PresentlytheresponsibilityofGSMstandardizationresides with special
mobilegroupunderETSI ( Europeantelecommunication StandardsInstitute )
Fullsetofspecificationsphase-I becameavailablein 1990
UnderETSI, GSMisnamedas GlobalSystem forMobile
communication Todaymanyprovidersalloverthe worlduseGSM (morethan 135
countriesin Asia, Africa, Europe, Australia, America)
Morethan 1300 millionsubscribersin worldand 45 millionsubscriberin
India.
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GSM System Architecture
BSC
BSC
MSC
MS
MS
MS BTS
BTS
BTS
GMSC
PSTN
ISDNPDN
EIR
AUC
HLR
VLR
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GSM System Architecture-I
Mobile Station (MS)
Mobile Equipment (ME)
Subscriber Identity Module (SIM)
Base Station Subsystem (BSS)
Base Transceiver Station (BTS)
Base Station Controller (BSC)
Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Home Location Register (HLR)
Visitor Location Register (VLR)
Authentication Center (AUC)
Equipment Identity Register (EIR)
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System Architecture
Mobile Station (MS)
Mobile Equipment
Portable, vehicle mounted, hand held device
Uniquely identified by an IMEI (International MobileEquipment Identity)
Voice and data transmission
Monitoring power and signal quality of surrounding cellsfor optimum handover
Power level : 0.8W 20 W
160 character long SMS.
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System Architecture
Mobile Station (MS) contd.
Subscriber Identity Module (SIM)
Smart card contains the International Mobile Subscriber
Identity (IM
SI
) Allows user to send and receive calls and receive other
subscribed services
Encoded network identification details
- Key Ki,Kc and A3,A5 and A8 algorithms
Protected by a password or PIN
Can be moved from phone to phone contains keyinformation to activate the phone
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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 allowing
operation between components made by different suppliers
1. Base Transceiver Station (BTS)
2. Base Station Controller (BSC)
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System Architecture
Base Station Subsystem (BSS)
Base Transceiver Station (BTS):
Encodes,encrypts,multiplexes,modulates and feeds the
RF signals to the antenna.
Communicates with Mobile station and BSC Consists ofTransceivers (TRX) units
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System Architecture
Base Station Subsystem (BSS)
Base Station Controller (BSC)
Manages Radio resources for BTS Assigns Frequency and time slots for all MSs in its area Handles call set up Transcoding and rate adaptation functionality Handover for each MS Radio Power control
It communicates with MSC and BTS
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System Architecture
Network Switching Subsystem(NSS)
Mobile Switching Center (MSC)
Heart of the network
Manages communication between GSM and other networks Call setup function and basic switching
Call routing
Billing information and collection
Mobility management
- Registration
- Location Updating
- Inter BSS and inter MSC call handoff
MSC does gateway function while its customer roams to othernetwork by using HLR/VLR.
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System Architecture
Network Switching Subsystem
Home Location Registers (HLR)
- permanent database about mobile subscribers in a large servicearea(generally one per GSM network operator)
- database contains IMSI,MSISDN,prepaid/postpaid,roamingrestrictions,supplementary services.
Visitor Location Registers (VLR)
- Temporary database which updates whenever new MS enters its area,
by HLR database- Controls those mobiles roaming in its area
- Reduces number ofqueries to HLR
- Database contains IMSI,TMSI,MSISDN,MSRN,LocationArea,authentication key
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System Architecture
Network Switching Subsystem
Authentication Center (AUC)- Protects against intruders in air interface
- Maintains authentication keys and algorithms and providessecurity triplets ( RAND,SRES,Kc)
- Generally associated with HLR
Equipment Identity Register (EIR)- Database that is used to track handsets using the IMEI
(International Mobile Equipment Identity)
- Made up of three sub-classes: The White List, The BlackList and the Gray List
- Only one EIR per PLMN
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Call Routing
Mobile startup
Call Originating from MS
Call termination to MS
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GSM uses paired radio channels
0 124 0 124
890MHz 915MHz 935MHz 960MHz
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CELLULAR PHONE SWITCHED ON
It first scans the group of forward controlchannels, to determine the one with thestrongest signal and than monitors the control
channel until the signal drops below a efficientlevel.
In this case it again scan for control channelwith strong base station signal
5% are control channels and rest 95% are forvoice and data channels.
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INCOMINGCALL
MSC dispatches the request to all base stations in the cellularsystem.
MIN(subscribers telephone number),is broadcasted as apaging message over all forward control channels.
The mobile receives the paging message and responds byidentifying itself over the reverse control channel.
The base station relays the acknowledgement sent by mobile
and informs MSC of handshake. MSC instructs the Base Station to move the call in unused
voice channel within the cell.
Base Station signals the mobile to change frequency tounused forward and reverse voice channels
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At this point another data message(alert) is
transmitted over the forward voice channel to
instruct the mobile telephone to ring.
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OUTGOING CALL
A call initiation request is sent on the reverse
control channel.
This includes MIN,ESN,and the telephone no.of the called party
Also includes SCM(Station Class
Mark),maximum transmitter power level of
the user.
BTS forward the request to MSC.
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Handoff Strategies
When a mobile moves into a different cell while a
conversation is in
progress, the MSC automatically transfers the call to a
new channel
belonging to the new base station.
Handoff operation
identifying a new base station
re-allocating the voice and control channels with the
new base station.
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MSC validates the request, make connection
to the called party through PSTN.
Instructs the BTS and mobile user to move toan unused forward and reverse voice channel
to begin conversation.
Case for roamers(FCC renewed for
unregistered ,HLR-billing status, VLR)
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Sectoring
Decrease the co-channel
interference and keep the cell
radius R
unchanged
Replacing single omni-
directional antenna by several
directional antennas Radiating within a specified
sector
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An illustration of a cellular system.
The Towers represents the Base Stations which
provides the radio access between mobile users
and the Mobile Switching Center(MSC)
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The Cellular Concept
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Frequency Reuse
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Future OfGSM
2ndGeneration
GSM -9.6 Kbps (data rate)
2.5Generation ( Future ofGSM)
HSCSD (High Speed ckt Switched data)Data rate : 76.8 Kbps (9.6 x 8 kbps)
GPRS (General Packet Radio service)
Data rate: 14.4 - 115.2 Kbps
EDGE (Enhanced data rate for GSM Evolution)
Data rate: 547.2 Kbps (max)
3 Generation
WCDMA(Wide band CDMA)
Data rate : 0.348 2.0 Mbps
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