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AMEEN AKBAR
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GSM stands for Global System for Mobile
Communication
1st totally digital cellular telephone system
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Teleservices (TS)Telephony, emergency calls, voice
messaging
Bearer services (BS)
SMS and cell broadcast, 9.6kbit/s
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Supplementary Service (SS)
Barring outgoing call, International
calls, roaming calls
Call forwarding under variousconditions
Call hold , Call waiting
Call transfer to a third party
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Base TransceiverStation (BTS)
Base TransceiverStation (BTS)
Base StationController (BSC)
Abis interface
Base Station (BS
)
Base TransceiverStation (BTS)
Base TransceiverStation (BTS)
Base StationController (BSC)
Mobile Stations
(MS)
Um interface
A interface
Base Station (BS)
Abis interface
CCITTSignalling
System No. 7(SS7)
interface
MobileSwitching
Centre(MSC)
GMSC
PSTN
VLRVLR
HLRHLR
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Subscriber: user who pays subscriptioncharges for using mobilecommunication services.
Mobile Station: is a subscriber unitintended for use while on the move at
unspecified locations. It could be ahand-held or a portable terminal.Base Station: a fixed radio station used
for communication with MS. It is locatedat the centre of a cell and consist ofTransmitters and Receivers.Mobile Switching Centre : it coordinates
the routing of calls, do the billing, etc.
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MS consist of : Mobile Equipment (ME)
Subscriber Identification Module (SIM)
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Subscriber Identity Module (SIM) is asmart card which stores informationabout the subscription and feature ofservices.
Stored information including:Authentication Key KiEncryptionIMSI and TMSI
SIM card is protected by a PersonalIdentity Number (PIN) of the user
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International Mobile SubscriberID(IMSI) 15 digit = 3 for country code, 3 formobile networkcode and 9 for mobile ID number.
Temporary Mobile Subscriber
ID(TMSI) per-call basis ID for security reasonto avoid sending IMSI over the air
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BSS consist of two part : Base Transceiver
Station (BTS) Base Station Controller
(BSC) BTS is a radio-end which
determine a cell coverage andprovide link with MS.
BTS include Transmitters andReceivers, antenna and signalprocessing unit as well asinterface.
BTS communicate with MS viaUm (air) interface
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BSC handle radio-channel setup,
frequency hopping,and handoverwithin BSC
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HLR contain databaseof users, including allthe subscriptionrecords
HLR records theupdate location ofevery user formobility management
purposes
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VLR is a temporarydatabase of user
VLR is used to handle aroamer connection.
VLR could be accessedby MSC for every callset up.
Every MSC isconnected to a VLR,but a VLR could be
connected to severalMSC
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Access MechanismAccess Mechanism
FDMA, TDMA, CDMA
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Frequency multiplexFrequency multiplex
Separation of the whole spectrum into smaller frequencybands
A channel gets a certain band of thespectrum for the whole time Advantages:
works also for analog signals Disadvantages:
waste of bandwidthif the traffic isdistributed unevenly
inflexible
guard spaces
k2
k3
k4
k5
k6
k1
f
t
c
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f
t
c
k2
k3
k4
k5
k6
k1
Time multiplexTime multiplex
A channel gets the whole spectrum for a certainamount of time Advantages:
only one carrier in themedium at any time
throughput high evenfor many users
Disadvantages: precise
synchronization
necessary
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Code MultiplexCode Multiplex
Each channel has a unique code All channels use the same spectrum at
the same time Advantages:
Bandwidth efficient No coordination and
synchronization necessary Good protection against
interference and tapping Disadvantages:
Lower user data rates More complex signal regeneration
Implemented using spread spectrumtechnology
k2
k3
k4
k5
k6
k1
f
t
c
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Various Access MethodVarious Access Method
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CellsCells
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Cell structureCell structure
Implements space division multiplex: base stationcovers a certain transmission area (cell) Mobile stations communicate only via the base station Advantages of cell structures:
higher capacity, higher number of users less transmission power needed more robust, decentralized base station deals with interference, transmission
area etc. locally Problems:
fixed network needed for the base stations
handover (changing from one cell to another)necessary
interference with other cells Cell sizes from some 100 m in cities to, e.g., 35 km on
the country side (GSM) - even less for higher frequencies
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Capacity of a CellularCapacity of a Cellular
SystemSystem
Frequency Re-Use DistanceThe K factor or the cluster sizeCellular coverage or Signal to
interference ratioSectoring
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Handover MechanismHandover Mechanism
BS1 BS2
A B
RS
L
Level at B
Level which HO occured
time
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Hexagonal Cell GeometryHexagonal Cell GeometryDefine coordinate axes,
U & V, at 60o anglesFor given frequency
reuse plan, go i steps
in U direction andjsteps in V direction
Number of cells in
reuse pattern is2 2
N i ij j= + +
U
V
(2,1)
(1,3) (u,v)
1 3/
i =2
j = 1
N= 7 reuse pattern
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1
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5
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7
1
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7
2
1
1
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7
1
2
3
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5
67
1
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7
The Cell Structure for K = 7The Cell Structure for K = 7
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11
1
2 2
22
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4 4
45
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7
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8
889
99
9
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1010
10
1111
1111
1212
12 12
Cell Structure for K = 12Cell Structure for K = 12
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Increasing cellularIncreasing cellular
system capacitysystem capacity
Cell sectoring Directional antennas subdivide cell into 3
or 6 sectors
Might also increase cell capacity byfactor of 3 or 6
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Increasing cellularIncreasing cellular
system capacitysystem capacity
Cell splitting Decrease transmission power in base and
mobile
Results in more and smaller cells
Reuse frequencies in non-contiguous cellgroups
Example: cell radius leads 4 foldcapacity increase
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Performance characteristics ofPerformance characteristics of
GSMGSM Communication
mobile, wireless communication; support for voiceand data services
Total mobility
international access, chip-card enables use of accesspoints of different providers
Worldwide connectivity
one number, the network handles localization High capacity
better frequency efficiency, smaller cells, morecustomers per cell
High transmission quality
high audio quality and reliability for wireless,uninterrupted phone calls at higher speeds (e.g., fromcars, trains)
Security functions
access control, authentication via chip-card and PIN
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Disadvantages of GSMDisadvantages of GSM
No full ISDN bandwidth of 64 kbit/s tothe user
Reduced concentration while drivingElectromagnetic radiationAbuse of private data possibleHigh complexity of the system
Several incompatibilities within the GSMstandards
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Thank YouThank You
