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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
Network Subsystem contd.
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
Network Subsystem contd.
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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Numbering Arrangement
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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Numbering Arrangement
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
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