Dar es Salaam Institute of Technology (DIT)
ETCT 06204
Digital Cellular Network
Ally, J
jumannea@gmail.com
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GSM Fundamentals
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GSM system overview
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The GSM system is a frequency- and time-division cellular
system, each physical channel is characterized by a carrier
frequency and a time slot number
Cellular systems are designed to operate with groups of
low-power radios spread out over the geographical service
area. Each group of radios serve MSs presently located
near them. The area served by each group of radios is
called a CELL
Uplink and downlink signals for one user are assigned
different frequencies, this kind of technique is called
Frequency Division Duplex (FDD)
Data for different users is conveyed in time intervals called
slots , several slots make up a frame. This kind of technique
is called Time Division Multiple Access (TDMA)
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Cell Technique-Macro Cell and Micro Cell
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A certain radio coverage area formed by a set of
transceivers that connected to a set of antennas is called a
CELL.
Macro Cell
❑ In the beginning , High-Power BTSs are adopted to
provide services. The BTS covers a wider area , but its
frequency utilization is not efficient. So, it can only
provide a few channels for subscribers.
Micro Cell
❑ Later the Low-Power BTS joins the system for getting a
better service area with high capacity . At the same time
it adopts the frequency reuse technique to improve the
efficiency of the frequency utilization and also the whole
capacity of the network.
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Multiple Access Technique
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Multiple Access Technique allows many
subscribers to use the same communication
medium.
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There are four kinds of basic Multiple Access
Technique : FDMA , TDMA, CDMA, and
OFDMA
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GSM system adopt FDD-TDMA
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The Frequency Spectrum
Duplex Separation: 45MHz
Channel Bandwidth: 200KHz
Duplex Separation:
Channel Bandwidth:
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95MHz
200KHz
Frequency Reuse
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The frequency resource of mobile system is very limited.
The different Subscribers can use the same frequency in
different places.
The quality of communication must be ensured.
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Cell Types
Omni-directional Cell
Omni
1
1
120 Degree Cell
120
degree
3
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2
GSM-GPRS Network Component
MSC/VLR
PSTN
ISDN
GMSC
GSM /GPRS BSS
BSC
MS
HLR/AUC
BTS
PCU
SS7
BSC
SMS system
MS
BTS
Internet,
Intranet
GPRS Backbone
SGSN
GGSN
OMC
CG
BG
Other PLMN
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Interface Between Different Entities
MSC/VLR
PSTN
ISDN
GMSC
GSM /GPRS BSS
Abis
MS
BSC
A
HLR/AUC
BTS
C/D/Gs
PCU
BSC
SS7
Gb
MS Um
SMS system
Gr/Gs/Gd/Ge
Gc
BTS
GPRS backbone
SGSN
Gi
GGSN
Ga
OMC
CG
BG
Gp
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Internet,
Intranet
Other PLMN
Mobile Station—MS
MS=ME+SIM
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Subscriber Identity Module – SIM
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Base Station Subsystem – BSS
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MSC
The Base Station
Controller – BSC
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The Base Transceiver
BSS
Station – BTS
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TC/SM
The Trans-coder – TC
BSC
and Sub Multiplexer
(SM)
BTS
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Packet Control Unit-----PCU
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Packet data
switching
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Bridge between
SGSN and BSC
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Provide Pb and
Gb interface
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The Network Switching System
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Mobile-Service Switching Center –
MSC
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Call Processing
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Operations and Maintenance Support
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Interface management
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Inter-network & Inter-working
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Billing
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Home Location Register – HLR
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Subscriber ID (IMSI and MSISDN)
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Current subscriber VLR (current location)
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Supplementary service information
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Subscriber status (registered/deregistered)
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Authentication key and AuC functionality
HLR is database used for the management
of subscribers
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Visitor Location Register – VLR
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Mobile Status (IMSI attached / detached / busy
/ idle etc.)
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Location Area Identity(LAI)
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Temporary Mobile Subscriber Identity(TMSI)
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Allocating the Roaming Number
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Equipment Identity Register – EIR
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White List
Black List
Grey List
IMEI is Checked In White List
If NOT found
EIR focus on the
equipment , not the
subscriber!!
IMEI is Checked in Black/Grey List
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OMC Functional Architecture
Security
Management
Event/Alarm
Management
MMI
OS
DB
Fault
Management
Configuration
Management
Performance
Management
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Service Area
Service Area
PLMN service area
PLMN service area
PLMN service area
MSC service area...
MSC service area...
Location area...
Location area...
cell
cell
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......
LAI
MCC
MNC
LAC
Location Area Identification
The LAI is the international code for a location area.
MCC：Mobile Country Code，It consists of 3 digits .
For example: The MCC of Tanzania is "640"
MNC：Mobile Network Code，It consists of 2 digits .
For example: The MNC of Zantel is "03"
LAC： Location Area Code，It is a two bytes BCD code(hex).
The value 0000 and FFFF is invalid.
For example: 640-03-0011
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CGI
CGI: Cell Global Identification
The CGI is a unique international identification for a cell
The format is LAI+CI
LAI: Location Area Identification
CI: Cell Identity. This code uses two bytes hex code to
identify the cells within an LAI.
For example : 640-03-0011-0001
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BSIC
BSIC（Base Station Identification Color Code)
NCC
BCC
BSIC
NCC: PLMN network color code. It comprises 3 bit. It
allows various neighboring PLMNs to be
distinguished.
BCC: BTS color code. It comprises 3 bit, used to
distinguish different cells assigned the same
frequency!
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MSISDN
MSISDN: Mobile Station International Standard Data Network
CC
NDC
SN
National (significant)
Mobile number
Mobile station international
ISDN number
CC: Country Code. For example: The CC of Tanzania is “255".
NDC: National Destination Code. For example: The NDC of
Vodacom is 755, 754, 764.
SN: Subscriber Number. Format:H0 H1 H2 H3 ABCD
Example: 255-764-030690
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IMSI
Not more than 15 digits
3 digits
2 digits
MCC
MNC
MSIN
NMSI
IMSI
MCC: Mobile Country Code，It consists of 3 digits .
For example: The MCC of Tanzania is “640"。
MNC: Mobile Network Code，It consists of 2 digits .
For example: The MNC of zantel is "03"。
MSIN: Mobile Subscriber Identification Number. H1H2H3 S ABCDEF
For example: 773-675000
NMSI: National Mobile Subscriber Identification，MNC and MSIN
form it together.
For Example of IMSI : 640-03-773-675000
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TMSI (Temporary Mobile Subscriber
Identification)
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The TMSI is assigned only after successful subscriber
authentication.
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The VLR controls the allocation of new TMSI numbers
and notifies them to the HLR.
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TMSI is used to ensure that the identity of the mobile
subscriber on the air interface is kept secret.
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The TMSI consists of 4 bytes( 8 HEX numbers) and
determined by the operator.
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IMEI (International Mobile Station
Equipment Identification)
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Physical Channel and Logical Channel
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Two types of Logical Channel
Traffic Channel (TCH) :
Transmits traffic information,
include data and speech.
Control Channel (CCH) :
Or Signaling Channel, transmits
all kinds of control information.
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Traffic Channel (TCH)
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Control Channel (CCH)
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Broadcast Control Channel – BCCH
CCH
The information carried on the BCCH
is monitored by the MS
BCH
periodically when it is in idle mode
BCCH: Broadcast Control Channel
FCCH: Frequency Correction Channel
BCCH
Synch.
Channels
SCH
FCCH
SCH: Synchronization Channel
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Common Control Channel – CCCH
CCH
The CCCH is responsible for
transferring control information
between all mobiles and the
network.
CCCH
RACH: Random Access Channel
PCH: Paging Channel
AGCH: Access Granted Channel
CBCH: Cell Broadcast Channel
RACH
uplink
CBCH
downlink
PCH/AGCH
downlink
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Dedicated Control Channel – DCCH
DCCH is assigned to a single
wireless connection for
measurement and handover
purpose.
SDCCH: Stand-alone Dedicated
Control Channel
ACCH: Associated Control Channel
SACCH:
Slow
Associated
Control Channel
FACCH: Fast Associated Control
Channel
CCH
DCCH
SDCCH
FACCH
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ACCH
SACCH
Uplink Logical channel
CCH
RACH
CCCH
SDCCH
SACCH
DCCH
FACCH
TCH/F
TCH/H
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TCH
DCH
Downlink Logical channel
FCCH
CCH
BCCH
SCH
BCCH
CCCH
PCH
AGCH
SDCCH
DCH
DCCH
SACCH
FACCH
TCH
TCH/F
TCH/H
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How to use these channels?
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Power Control
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DTX and VAD
Discontinuous Transmission – DTX
Voice Activity Detection – VAD
Battery Saving
Interference reduction
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Timing Advance (TA)
The mobile phone should
send the signal in advance!
TA
Transmission delay t
Transmission delay t
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GSM Development Evolution
3G
2 Mbps
2.5G
384 kbps
115 kbps
2G
57.6 kbps
9.6 kbps
GPRS
HSCSD
GSM
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EDGE
IMT-2000
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