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Transcript of 11520957-GSM-basic
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GSM Foundation Course
• Course Content Basic Telephony & Cellular
Principal of Cellular Communication
GSM Features
GSM Network Components
GSM Terrestrial Interfaces
Basic GSM Processes
GSM Air Interface
Radio Interface Optimization, Supplementary services &
Contemporary Networks
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ESSAR Telecom
• Telecom Service Provisions– GSM – Basic– Internet
• ESSAR– GSM Service Provider in Punjab, Delhi,
Rajasthan, U.P (East) & Haryana– Basic Service Provider in the state of Punjab.
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Service Industry
• Service Provider is not a Equipment
Manufacturer.
• The Service Provider has a license to operate in a
geographical boundary (state/circle/ country).
• It buys equipment from OEM Suppliers (Vendors).
• Installs & commissions the equipment thus
making it’s own Network.
• Provides the desired service to it’s subscribers.
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ESSAR CELLPHONE
Punjab
Haryana
U.P (East)Rajasthan
Delhi
Coverage Area
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ORGANISATION STRUCTURE
PROMOTERS
TECHNICAL PLANNING
IMPLEMENTATION
OPERATIONS
OPERATIONS SYSTEM SUPPORT
BILLING
IT
ACTIVATIONS
MARKETING
CUSTOMER CARESALES
SUPPORT FUNCTIONS
HR, ADMIN, ACCOUNTS
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Basic Telephony
•Off Hook
•Dial Tone
•Dialing Digits
•RBT
•Conversation
•Ring
•Off Hook & Conversation
•Signaling•Traffic
SWITCH / EXCHANGE
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2 Mb E1 (PCM)
Sample Rate 8 kHz8 bits per sample
64 kbps
1
31
16
0
300 - 3400 Hz
E1 b
i t s tream
1st TCH
17th TS
30thTCH
15th TCH
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Wireless Telephony
BSC
BTS BTS
Mobile Subscriber...
MSC
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Wireless Communication
• Alternative means of wireless communication
– Walkie - Talkie– Pagers– Trunked private radios
• Mobile Phone - the magic technology that enables everyone to communicate anywhere with anybody.
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Cellular Communication
• A cellular system links Mobile subscribers to Public
Telephone System or to another Mobile subscribers.
• It removes the fixed wiring used in a traditional
telephone installation.
• Mobile subscriber is able to move around, perhaps
can travel in a vehicle or on foot & still make & receive
call.
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Advantage of Cellular Communication
• Mobility
• Flexibility
• Convergence
• Greater QOS
• Network Expansion
• Revenue/Profit
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WHAT IS CELLULAR TELEPHONY ?
CONSIDERATIONS -
FREQUENCY
SUBSCRIBER DENSITY
COVERAGE
Base Station
Base Station
Base Station
Base StationBase Station
Base Station
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The Cell
• Cellular Radio involves dividing a large service area
into regions called “cells.”
• Each cell has the equipment to switch, transmit and
receive calls.
• Cells - Reduce the need of High powered transmission
• Cells - Conventionally regarded as being hexagonal,
but in reality they are irregularly shaped.
• Cell shape is determined by the nature of the
surrounding area e.g. Hills , tall building etc.
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The CELL
What is a cell ?
A cell is a certain area that can be reached with one transceiver
or A small collection of
transceivers on different channels at a single base site.
The hexagonal-shaped communication cells are artificial & are generated to simplify the planning & design of a cellular network.
BTS
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Coverage & Capacity
• Coverage
– Percentage of the geographical area covered by cellular service where mobile telephony is available
• Capacity -
– Number of calls that can be handled in a certain area within a certain period of time.
– Capacity can also refer to the probability that users will be denied access to a system due to the simple unavailability of radio channels.
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Cells
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Cell Size
• Large Cells
• 35 Km
• Remote Areas
• High Transmission
Power
• Few subscribers
• Small Cells
• Near about 1 KM
• Urban Areas
• Low Transmission
Power
• Many Subscribers
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MICRO CELL
Below Rooftop~ Railway Platforms, Airports,~ Busy Shopping Bazaar etc.
Low Tx Power~ 1 Watt max.
Limited Coverage~ 200m - 500m
Hotspot Solution
Special Algorithms for HO
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PICO CELLS
Pico Cell
Inside offices, Buildings
Very Low Tx Power~ Less than 1 Watt
Limited Coverage~ 50 -100m
Capacity Solution
Special Algorithms for HO
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Analog Mobile Telephony
• End of 1980’s Analog Systems unable to
meet continuing demands
– Severely confined spectrum allocations
– Interference in multipath fading environment
– Incompatibility among various analog systems
– Inability to substantially reduce the cost of
mobile terminals and infrastructure required
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Digital Mobile Telephony
• Spectrum space - most limited and precious
resource
• Solution - further multiplex traffic (time
domain)
• Can be realized with Digital Techniques only.
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Different Standards Worldwide
• Till 1982 Cellular Systems were exclusively
Analog Radio Technology.
• Advanced Mobile Phone Service (AMPS)
– U.S. standard on the 800 MHz Band
• Total Access Communication System (TACS)
– U.K. standard on 900 MHz band
• Nordic Mobile Telephone System (NMT)
– Scandinavian standard on the 450 & 900 MHz
band
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GSM History and Organization
• 1979 Europe wide frequency band reserved for Cellular
• 1982 “Groupe Speciale Mobile” created within CEPT
• 1986 GSM had full time in Paris
• 1988 ETSI takes over GSM Committee
• 1990 The phase 1 GSM Recommendations frozen
• 1991 GSM Committee renamed “Special Mobile Group” and GSM renamed as “ Global System for Mobile Communication”
• 1992 GSM is launched for commercial operations
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GSM - IN CELLULAR TELEPHONY
• Each Cell in the Cellular Network consists of one or more RF carriers.
• An RF carrier is a pair of radio frequencies– One used in upward direction by MS - Uplink– Other used in downward direction by BTS -
Downlink– The transmit and receive frequencies are
separated by a gap of 45 MHz in GSM of 75 MHz in DCS.
• There are 124 carries in GSM Band. With each carrier carrying 7 timeslots, only 124 x 7 = 868 calls can be made!
• Frequency Reuse is the solution
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Uplink-Downlink
Downlink = 935 to 960 MHz
Uplink = 890 to 915 MHz
BTS Tx MS Rx
BTS Rx MS Tx
dl
ul
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Frequency & ARFCNu
l= 8
90 t
o 9
15 M
Hz
dl=
935
to
960
MH
z
Ful(n) = 890.0 + (0.2) *n MHz
Fdl(n) = Ful + 45 MHz
where n =ARFCN ; 1 n 124
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TDMA F
RAME n
+10 7
3
0
5
01
2
0 7
3
0
5
01
2
4.61
5 m
S
TDMA F
RAME n
T D M
A
TDMA & FDMA
F D M A200KHz
Uplink - MS Tx890MHz to 915MHz
Downlink - BTS Tx935MHz to 960MHz
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GSM Burst & TDMA Frame
0 1 2 3 4 5 6 7 2 4 5 6 730 1
FRAME 1 FRAME 2
Training sequenceInformation Information
GUARD PERIOD GUARD PERIOD
TAIL BITS TAIL BITS
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Frequency Reuse Pattern
Three types of frequency reuse patterns
• 7 Cell reuse pattern
• 4 cell reuse pattern
• 3 cell reuse pattern
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Cell Dia = R
FREQUENCY RE - USE
– Frequency Re-use
7/21 cell cluster
1
2
3
45
6
7
Two re-use distances
D D/R = (3N)1/2
where N is Cluster size
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Principal Of Sectorization
• Omni Directional Cells• 120 degree Sectors • 60 Degree sectors
– Each Sector in a Site has its own allocation of Radio Carriers.
• Advantage
– By frequent reuse of frequency more capacity can be achieved.
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a1a2
a3a3
a4a6
a5
Cell Sectorisation
OMNI CELL
1 ANTENNA
b1
b2
b3
120O CELLS
3 ANTENNAS
60O CELLS
6 ANTENNAS
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3 Site Reuse Pattern
c2
c1
c3
a1
a2
a3
b1
b2
b3
c1c2
c3Cell Re-use
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Cellular 1Planning Steps
– Cellular Topology • Cell splitting & Cell Repeat Patterns
3 cluster site 3/9 cell cluster 4 cluster site 4/12 cell cluster
Sites in the middle
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GSM Antennas
• Directional Antennas
• Vertically Polarized.
• Collinear Dipole Array with
8 to 12 elements.
• Beam Width 45o, 60o, 90o.
• High Gain Antennas with
gain of 16 to 18 dbi.
• Mechanically/Electrically
Downtiltable.
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Features of GSM
• Compatibility
• Noise Robust
• Increased Capacity & Flexibility
• Use of Standard Open Interfaces
• Improved Security & Confidentiality
• Cleaner Handovers
• Subscriber Identification
• ISDN Compatibility
• Enhanced Range of Services
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Compatibility
• With rapid Developments there was a need for a common Standard for Mobile Communication.
• With GSM, one could drive from Germany to Spain without a Call Drop.
• Due to versatility of GSM, it was adopted by many countries, even outside Europe.
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Noise Robust
• To combat the problems due to Noise-
Digital Interface is used.
• Digital Interface
– Protect these errors using Error Detection & Correction Techniques.
– Immune to higher levels of noise and interference
– Improvements in Quality as well as Efficiency- Robust Air Interface.
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Increased Capacity and Flexibility
• Analogue Air Interface
– Every connection requires a
separate RF carrier and thus
RF hardware.
– System Expansion
• Time Consuming
• Costly & Labor Intensive.
• Intricate RF Planning.
• Digital Interface
– 8 simultaneous conversations
on one RF carrier.
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Standardized Open Interfaces
• Low Price
– Uses standard interfaces like C7, X.25 etc.
Versatility to choose equipment from different
manufacturer thereby reducing the pricing
monopoly.
• Flexibility
– Great flexibility in situating Network
components because of Standard Interfaces.
– Efficient use of terrestrial links.
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Better Security & Confidentiality
• High Security risk for
Analogue System operators.
• GSM
– No Eavesdropping
– High speech and data
confidentiality.
– Digitized, Encoded and
Encrypted (A8 algorithm)
– Subscriber Authentication
(A3 algorithm)
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Cleaner Handovers
• The mobile measures up to 32 adjacent cells for
– Signal Strength (RxLevel)
– Signal Quality (RxQual)
– updated every 480 mS and sends to BTS
• Sophisticated Handover based on
– RxLevel
– Interference
– RxQual
– Timing Advance
– Power Budget
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Base Station 2
Base Station 3
Base Station 1
Handovers
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ISDN Compatibility
• ISDN (Integrated Services Digital Network)
– Advanced Telecom Network designed to carry
voice and user data over the standard
telephones lines.
• 2B+D Signalling and information on ISDN line.
• The GSM Network is designed to operate within
the ISDN System.
• GSM provides features compatible with ISDN.
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GSM NETWORK ELEMENTS
PSTNEC
MSC
HLR
AUC
VLR
EIRIWF
TRAU BSC
BTS
Network Switching System
BSS
SIM
ME
MS
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GSM Network Components
• Mobile Station consists of two parts-
– Mobile Equipment (ME)
– Subscriber Identity Module (SIM)
• ME
– Hardware e.g. Telephone, Fax Machine,
Computer.
• SIM
– Smart Card which plugs into the ME. NETCOMP
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Mobile Equipment (ME)
• ME are of three types-
– Vehicle Mounted
– Portable Mobile Unit
– Handportable Unit
• ME’s have distinct features-Classmarks sent in
initial message to Network.
NETCOMP
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ME (Classmark Information)
• Revision Level
– Phase of the GSM specs ME comply with.
• RF Power Capability
– Max power ME is able to Transmit.
• Ciphering Algorithm Used
– Presently A5
– Phase 2 specifies Algorithms A5/0 to A5/7.
• Frequency Capability
• SMS CapabilityNETCOMP
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Typical Settings
Mobile Equipment
Class Power O/p
1 20 W
2 8 W
3 5 W
4 2 W
5 0.8 W
NETCOMP
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SIM
Subscriber Interface Identity Module
The SIM stores
– Subscriber Parameters
– Personal Data for identifying
Subscriber to the Network.
– IMSI,, MSISDN, PIN, PUK, Ki,
A3, A8 (for Kc generation)
– Space reserved for TMSI & LAI
--------------
--------------
Small SIM
Full Size SIM Card
--------------
--------------
NETCOMP
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SIM - Internal Structure
CPU
EEPROM
RAM
ROM
I/O8
User Data 16 kB
Basic Operating System16 to 24 kB
Working Area for CPU256 to 512 bytes
NETCOMP
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SIM(IMSI)
• IMSI(International Mobile Subscriber Identity)
– Transmitted over Air Interface on initialization
– Permanently stored on SIM card
– 15 digit Decimal
MCC (3) MNC (2) MSIC (10)
NETCOMP
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• LAI (Location Area Identity)
– MCC 3 digit number (BCD), two Octets ( A & B)
– MNC 2 digit number (BCD), one Octet
– LAC 3 digit number (Binary) , two Octets
0-65535
– CI 5 digit number (Binary) , two Octets
0-65535
SIM (LAI)
LACMCC MNC CI
NETCOMP
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SIM
• MSISDN – 10 digit number to which a subscriber is being
called.• PIN (Personal Identification Number)
– Four digit PIN– An internal security to Protect the SIM from
illegal use.– Card blocks itself after three wrong entries
• PUK (Personal Unblocking Key)– 8 digit code to unblock the SIM Card
• Ki (Authentication Key), A3 & A8 AlgorithmsNETCOMP
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SIM (TMSI)
• Temporary Mobile Subscriber Identity
– Periodically changed by the System Management on instances like location update etc.
• Reason for use of TMSI
– To prevent a possible intruder from identifying GSM users, TMSI is used
• Management
– Assignment, Administration & Updating is performed by VLR.
NETCOMP
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Transcoder
• Converts 64 Kbps PCM circuits from MSC to 16
Kbps BSS circuits.
• Each 30 channel 2 Mbps PCM link can carry 120
GSM - specified voice channels.
NETCOMP
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Transcoder
MSC BSS
XCDR120 GSM TCH
1 2 3 4
Transcoder Information from FOUR calls (4x16 KBPS put into ONE 64 KBPS timeslot
30 Channel PCM
1234
NETCOMP
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Base Station System (BSS)
• BSS (Base Station System)– BSC (Base Site Controller)– BTS (Base Transceiver Station)– XCDR (Transcoder)
Network Switching System (NSS)
XCDR
BSC
BTSNETCOMP
BTS
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Base Station System (BSS)
• BSC– Controls upto 40 BTS– Conveys information to/from BTS– Connects terrestrial circuits & Air Interface
Channels– Controls handovers between BTSs under itself
• BTS– Contains RF Hardware– Limited control functionality– 1 - 6 carriers in a BTS Cabinet– 7 - 48 simultaneous calls per BTS
NETCOMP
BTS
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A BTS Cabinet
OUTER VIEWINNER VIEWNETCOMP
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BSS Configuration
• Collocated BTS
• Remote BTS
• Daisy Chain BTS
• Star Configuration
• Loop Configuration
NETCOMP
BTS
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Daisy Chain Configuration
BSC
BTS
BTS
BTS NETCOMP
All B
TS
on
1 E1
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Star Configuration
BSC
BTS
BTS BTS
BTS
NETCOMP
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Loop Configuration
BSC
BTS
BTS BTS
BTS
Loop Configuration
NETCOMP
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Network Switching System(NSS)
• NSS (Network Switching System)
– MSC (Mobile Switching Centre)
– HLR (Home Location Register)
– VLR (Visitor Location Register)
– EIR (Equipment Identity Register)
– AUC (Authentication Centre)
– IWF (Interworking Function)
– EC (Echo Canceller) NETCOMP
MSC
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MOBILE SWITCHING CENTRE
NETCOMP
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GSM Network Component
• MSC
– Call Switching
– Operation & Management Support
– Internetwork Interworking
– Collects call billing data
• Gateway MSC
– MSC which provides interface between PSTN & BSS’s in the GSM Network.
NETCOMP
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Home Location Register (HLR)
• Reference database for the Subscriber profiles-
– Subscriber ID (IMSI & MSISDN)
– Current VLR Address
– Supplementary Services subscribed
– Supplementary Service Information
– Subscriber Status (Registered/deregistered)
– Authentication Key and AUC functionality
– TMSI
– MSRN NETCOMP
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Visitor Location Register (VLR)
• Temporary Data, which exists as long as the subscriber is active in a particular Coverage area.
• Contains the following-
– Mobile Status (Busy/ Free/ No Answer/etc.)
– Location Area Identity (LAI)
– TMSI
– MSRN (Mobile Station Roaming Number)
NETCOMP
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Equipment Identity Register (EIR)
• Contains Database for validating IMEI
– White List (valid ME)
– Black List (Stolen ME)
– Grey List (Faulty ME)
NETCOMP
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• Provides function to enable the GSM System to interface with Public/Private Data Networks.
• The basic feature of the IWF are – Rate Conversion
– Protocol adaptation
• IWF incorporates Modem Bank.
e.g. GSM DTE PSTN DTE
IWF Analogue Modem
Inter Working Function
NETCOMP
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Echo Canceller
• Echo is apparent only in Mobile - Land conversation & is generated at the 2 wire to 4 wire interface.
• To avoid it, Echo Canceller (EC) is used.
– Echo is irritating to MS Subscriber
– Total Round Trip delay of 180 ms in the GSM system
– EC is placed on the PSTN side of the Switch
– Cancellation up to 68 ms with ECNETCOMP
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Operation & Maintenance Centre
• Event & Alarm Management
• Fault Management
• Performance Management
• Configuration Management
• Security Management
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o The OMC has access to the (G)MSC, BSC.
o Handles error messages being reported from the Network
o Controls the traffic load of the BSC, and the BTS.
Operation & Maintenance Centre
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o NETWORK MANAGEMENT CENTRE (NMC)– Offers Hierarchical Regionalised Network
Management of a complete GSM system.
• Functionality of the NMC
• Monitors Nodes on the Network
• Monitors Network Element Statistics
• Monitors OMC regions & provides
information to OMC staff
• Enables Long Term Planning for
entire Network
NETWORK MANAGEMENT CENTRE
MMI RAM>
MMI RAM>
MMI RAM>
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NMC
OMC OMC
OMC
REGION 2 REGION 3
REGION 1
NETWORK
NETWORK MANAGEMENT CENTRE
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GSM Terrestrial Interfaces
Broadly classified into two types of interfaces-
• Standard Interfaces
– 2 Mbps Trunks (E1)
– Signalling System No. 7 SS7 ( CCS7)
– X.25 (Packet Switched Mode)
• GSM Interfaces
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GSM Interfaces
• Um MS - BTS
• Abis BTS - BSC
• A BSC - MSC
• B MSC - VLR
• C MSC - HLR
• D VLR - HLR
• E MSC - MSC
• F MSC - EIR
• G VLR - VLR
• H HLR - AUC
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Basic Processes
• AUTHENTICATION
• CIPHERING
• REGISTRATION
• CALL ESTABLISHMENT
• HANDOVER / HANDOFF
• ROAMING
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AUTHENTICATION ALGORITHM
NSS
MS
HLR
AUC
AUTH.ALGORITHMS
A3
SIM
MS
AUTH.ALGORITHMS
A3
Ki
RAND
RAND
COMPARE
SRES
SRES
Ki
AIR INTERFACE
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Ciphering
• Data protection is required on air interface.
• A5 algorithm is used.• A specific key called Ciphering Key (Kc), is
generated from RAND and A8 algorithm. • A8 is on the SIM.
A8
RANDKi
Kc
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Ciphering
A5Data
Kc
Ciphered
Data A5
Kc
Data
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ROAMING
MSC
ME
ME
PSTN
MSC
VLR
HLR
INDIA
UK
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o The mobile roams to another country (UK) and requests a
Location Update when switched ‘ON’.
o The VLR (UK) informs the home HLR (India) of the mobile’s
new location (UK).
o The HLR updates its location information and sends the
subscriber information to the VLR (UK).
o The HLR requests the subscriber information be removed
from the VLR (India).
o The VLR (India) acknowledges, and removes the subscriber
information from its database.
o After the mobile’s registration is completed in UK’s MSC/VLR,
the mobile is able to use network services (MOC, MTC etc.)
ROAMING
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Transmission Media
• Access Network
– Microwave 15 /23 GHz
• Backbone Network
– Microwave 7 GHz
– Optical Fibers
– Leased Line( From Dot or any other
service provider on any media)
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Access Microwave ( 15 GHz)
• 14.250 to 14.500 MHz and
14.400 to 15.350 MHz
• 4 QAM & 16 QAM Modulation
• Split Mount Version with Hot
Standby Facility
• Bandwidth ranging from 1.25
MHz to 28 MHz depending
upon Data Rate and
Modulation type
• 4 E1 Radio with 3 spot
frequencies in our case
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Backbone Microwave (7 GHz)
• 7.125 to 7.850 MHz and 7.725
to 8.500 MHz
• 4 QAM & 16 QAM Modulation
• Split Mount Version with hot
standby facility
• Bandwidth ranging from 1.25
MHz to 28 MHz depending
upon Data Rate and
Modulation type
• 16 E1 Radio with 1 spot
frequencies in our case
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Optical Fiber
• Low Losses 0.5 dB/km & High Data Rates
• Types of Fiber– Step Index– Graded Index
# Graded Index are better.
Modes of Light in fiber
– Mono Mode
– Multi Mode
# Mono Mode has less losses than Multi Mode.
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Optical Fiber
Different Possible Combinations Mono Mode Step Index 10 / 125 m
Mono Mode Graded index
Multi Mode Step Index 100 / 300 m
Multi Mode Graded Index 75 / 130 m Mono Mode Graded Index would have been
the best but fabrication not possible
140 Mbps OLTE , Mono Mode Step Index in our case
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Channels On Air Interface
• Physical Channel • Logical Channel
• Physical Channel
– Physical channel is the medium over which the information is carried.
• Logical Channel
– Logical channels consists of the information carried over the Physical Channel.
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TDMA F
RAME n
+10 7
3
0
5
01
2
0 7
3
0
5
01
2
4.61
5 m
S
TDMA F
RAME n
T D M
A
TDMA & FDMA
F D M A200KHz
Uplink - MS Tx890MHz to 915MHz
Downlink - BTS Tx935MHz to 960MHz
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LOGICAL CHANNELS
0 1 2 3 4 5 6 7
3
57 encrypted
57 encrypted
26 training
1S
1S
3T
8.25GP
3T
577S
577S x 8 = 4.615mS
TDMA Frame
Normal Burst
26 Frame Multi-frame
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BURST
• Time is divided into discrete periods
called “Timeslots”
• The Time Slots are arranged in a sequence
, conventionally numbered 0 to 7.
• Each repetition of this sequence is called
a TDMA Frame.
• The information content carried in one
time slot is called a “burst”.
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BURST
• Information– Main Area where the Speech, Data or Control info
is held • Guard Period
– To enable the burst to hit the time slot (0.031ms)• Stealing Flags
– 2 bits are set when TCH is to stolen by a FACCH• Training Sequence
– For estimation of transfer characteristics of physical media
• Tail Bits– Used to indicate beginning and end of the burst.
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Five Types of Burst
• Normal BurstTraffic & Control Channels Bi-directional
• Frequency Correction Burst
FCCH Downlink
• Synchronization Burst
SCH Downlink
• Dummy Burst
BCCH Carrier Downlink
• Access Burst
RACH Uplink
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GSM Logical Channels
• TCH
– SACCH
– FACCH
• Control Channels
– BCCH
– CCCH
– ACCH
– DCCH
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LOGICAL CHANNELS
TDMA Frame
26 Frame Multi-frame
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
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Frames & Multiframes
• Several Logical channels share one time slot.
• Individual channels are sequenced, & each
channel gets the time it requires.
• Sequence is carried out using Multiframes.
– Traffic Channel occupy a 26-frame multiframe
(120 ms)
– Control Channel occupy a 51-frame multiframe
(235 ms).
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Traffic Channels - TCH
TCH
TCH
TCH / FS 9.6
DATA
TCH / HS
4.8
2.4
FACCHSAACH
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BCCH Channel
CCH
BCCH
BCCHSynchronizing Channels
FCHSCH
Broadcast Control Channel - Downlink only
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Channels On Air Interface
• BCCH
– Transmitted at all times & conveys information about Cell Timing and Configuration
• BCCH, FCCH, SCH
• CCCH
– Used by BSS & MS when trying to initiate a connection over the air
• RACH, PCH, AGCH, CBCH
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Channels On Air Interface
• DCCH
– Used to convey signaling information during call setup
• SDCCH
• ACCH
– Used to transmit signaling information when a call is in progress
• FACCH & SACCH
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Channels On Air Interface
• ACCH
– SAACH
• Conveys Power Control & Timing
Information in the downlink direction.
• RSSI and Quality reports in the uplink
direction.
– FACCH
• To carry out user authentication and handovers. It steals the TCH burst and inserts its own information.
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Channels On Air Interface
• Acronyms
– BCCH Broadcast Control Channel
– CCCH Common Control Channel
– DCCH Dedicated Control Channel
– ACCH Associated Control Channel
– SDCCH Standalone Dedicated Control Channel
– RACH Random Access Channel
– PCH Paging Channel
– AGCH Access Grant Channel
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Channels On Air Interface
• BCCH– Location Area Identity
– List of neighbouring cells, to be monitored
– List of frequencies used in the cell
– Cell Identity
– Power Control Indicator
– DTX permitted
– Access Control (e.g emergency calls, call
barring)
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Channels On Air Interface
– Always transmitted at constant power at all
times
– Dummy burst are sent to ensure continuity
when no traffic information is sent.
• FCCH– Mobile corrects the frequency of its internal
time base by reading this logical channel.
– Easily detected by the mobile.
– After FCCH, mobile is able to detect SCH
which contains timing information.
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Channels On Air Interface
• SCH– Carries the information for mobile to
synchronize to the TDMA frame structure &
know the timing of the individual timeslots.
– Frame Number & BSIC (Base Station Identity
Code)
• CCCH– RACH
• Transmitted by the Mobile when it wishes to
gain access to the system
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Channels On Air Interface
– PCH
• Transmitted by the BTS when it wishes to
contact a specific mobile.
– AGCH
• Transmitted by the BTS to assign dedicated
resources to an MS such as SDCCH
– CBCH
• To transmit messages to all mobiles within
a cell. CBCH will steal some time of an
SDCCH to do this.
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Channel Combinations
• Full rate Traffic Channel Combination
– TCH8/FACCH + SACCH
• Broadcast Channel Combination
– BCCH + CCCH
• Dedicated Channel Combination
– SDCCH8 + SACCH8
• Combined Channel Combination
– BCCH + CCCH + SDCCH4 + SACCH4
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Channel Combinations (Timeslots)
– Traffic Channel Combination• TCH8/FACCH +SACCH
• Can be on any Time slot
– Broadcast Channel Combination• BCCH +CCCH
• Can be on Timeslot 0, 2, 4, 6
– Dedicated Channel Combination• SDCCH8 + SACCH8• Any Time slot
– Combined Channel Combination• BCCH + CCCH +SDCCH4 + SACCH4• Can only be on 0 Timeslot
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TCH Multiframe
0 5 10
SACCH
15 20
IDLE
Downlink & Uplink SACCH
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BCCH/CCCH Multiframe
• BCCH/CCCH
– In Downlink direction the timeslot (physical
channel) is shared by a different logical
channels.
– In the Uplink direction all timeslots are
allocated to RACH.
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BCCH/CCCH Multiframe
10 20 30 40 50
Downlink to MS
Uplink from MS
0 10 20 30 40 50
FS FS FS FS S IFCCCH8 TS
CCCH4 TS
BCCH CCCH8 TS
CCCH8 TS
CCCH8 TS
RR RRRRRR RR RR RR RR RR RRRR RR RR RRRRR RRR RR R R RR RR RRRR R RRRR
0
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Combined Multiframe
– BCCH and SDCCH share a common timeslot
• Less No. of subscribers support (as only 4
SDCCH)
• 102 frame structure
• Superframes And Hyperframes
• 1326 TDMA frames (26*51) make a superframe
• 2048 superframes make one hyperframe, after
which ciphering and frequency hopping
algorithm are restarted.
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Combined Multiframe
0 10 20 30 40 50
F
F
S
S
BCCH F
F
S
S FS FS
S
S A2
A0 A1
A3
I
I
F
FCCCH8 TS
F S FSCCCH8 TS
CCCH
4 TS
CCCH
4 TS
BCCH D2
D2 D3
D3
D0 D1
D0 D1
0 10 20 30 40
D3 R
R
R
R A2 A3D3
A0 A1 R
R
R
R D2
D2R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
D0 D1
D1D0
50
Downlink to MS
Uplink from MS
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SDCCH Multiframe
0 10 20 30 40 50
I
I
Downlink to MS
Uplink from MS
I
I
I
I
D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3
D0 D1 D2 D3 D4 D5 D6 D7 A4 A5 A6 A7
0 10 20 30 40 50
I
I
I
I
I
I
D0 D1 D2 D3 D4 D5 D6 D7A1 A2 A3 A0
D0 D1 D2 D3 D4 D5 D6 D7A5 A6 A7 A4
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Block - 1 : 1, 5, 9 ….. Samples
Block - 2 : 2, 6, 10, …… Samples
& so on for Block - 3 & Block - 4.
Voice Coding
LPC
RPE
Divid
ed in
to 4 B
locks
of 40 S
amp
les each
LTP
Class Ia Class Ib Class II
50 bits 132 bits 78 bits
20 mS Sample Rate 8 kHz
13 bits per Sample160 Samples
2080 bits
104 kbps
Reduction in DataSpeech Encoder selects Blockwith Most Energy
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Channel Coding
• Error Protection And Detection– To protect the logical channel from
transmission errors by the radio path, different coding schemes are used.
• Coding & Interleaving Schemes dependent upon logical channel to be encoded.
• 3 Coding Protection schemes– Speech Channel Encoding– Control Channel Encoding– Data Channel Encoding
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Speech Channel Coding
• Speech Information of 20 ms block is divided
over 8 GSM burst.
• 260 bits are grouped in three classes depending
upon the intelligible part of speech
• After encoding 456 bits block is interleaved
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Speech Channel Coding
ParityCheck
456 bits
Class 1b 132 bits
Class 1a 50 bits
Class 2 78 bits
50 1323 4
Convolutional Code
378 78
Tail Bits
378 78
Convolutional Coding
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Control Channel Encoding
• Control Channel Encoding– Block of 184 bits received by BTS– Bits are protected by Cyclic Codes of Class
Fire Codes– Adds 40 Parity Bits– 4 Tail Bits are added– Convolution Coding is done
• O/p from 184 Signalling bits is 456 bits.
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Control Channel Coding
184
Coding
184 40 Parity Bits
Convolutional Coding
456
456 bits
4TB
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Data Channel Coding
240
184
Convolutional Coding
488
4
Punctuate
456
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Interleaving
• Responsible for Robustness of the GSM air interface
• 10 -20 % burst destroyed or corrupted on the air interface.
• Spreads the content of one information block across several TDMA timeslots.
• Two types of Interleaving -
– Diagonal Interleaving
– Rectangular Interleaving
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DIAGONAL INTERLEAVINGSPEECH
Speech Blocks
456 bits
EIGHT blocks of 57 bits,Sent on 8 ALTERNATE timeslots
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
456 bits
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RECTANGULAR INTERLEAVINGCONTROL CHANNEL
Data Blocks
456 bits
114Bits Odd
114Bits Odd
114Bits Even
114Bits Even
FOUR blocks of 114 bits,Sent on 4 timeslots
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
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Interleaving
• Interleaving Depths– Speech - 8 blocks– Control - 4 blocks– Data - 22 blocks
• Speech & Data blocks are diagonally interleaved• Control block is rectagularly interleaved
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Interleaving
TRAU Frame Type
Data
Control
Speech
Number of GSM Burst Spread Over
22
4
8
TRAU = Transcoder Rate Adaption Unit
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MOBILE TO LAND
MSC
BSC
BTS
PSTN
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Multiple Point of Interconnect
BSS TRAFFIC
POI TRAFFIC
BSS TRAFIC POI TRAFIC
7 GHz BACKBONE
CITY A
CITY B
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Call Scenarios
• Mobile to Mobile
– Intra-city
– Inter-city
• Mobile to Land
– Intra-city
– Inter-city
• Land to Mobile
– Intra-city
– Inter-city
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Mobile To Land Sequence
1
3
CHANNEL REQUEST
DCCH ASSIGN
SIGNALLING LINKESTABLISHED
REQUEST FOR SERVICE
SET CIPHER MODE
SET-UP
EQUIPMENT ID REQUEST
AUTHENTICATION
MS BSS MSC VLR HLR PSTN EIR
RACH
AGCH
SDCCH
SDCCH
Call Info7
4
6
5
2CR
CC
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8 COMPLELTE CALL
CALL PROCEEDING
9 ASSIGNMENT COMMAND
INITIAL & FINAL ADDRESS (IFAM)
ASSIGNMENT COMPLETE (ACM)
10
ANSWER(ANS)
11
CONNECT ACKNOWLEDGE
SDCCH
SDCCH
ASSIGNMENT COMPLELTE
MS HEARS RINGTONEFROM LAND PHONE
ALTERING
RING TONESTOPS
CONNECT
(channel)
(TCH)
FACCH
FACCH
FACCH
TCH
(circuit)
FAACH
BILLING STARTS
Hello!
MS BSS MSC VLR HLR PSTN EIR
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Land to Mobile Sequence
Initial & Final Address Msg. (IFAM)
Send Routing Information
Routing Information Ack
INITIAL & FINAL ADDRESS (IFAM)
Send Info for I/c Call Setup
Channel Request
Signalling Link Established
MSISDN
Paging Request
PAGE
DCCH Assign
PCH
AGCH
SDCCH
IMSI
MS BSS MSC VLR HLR GMSC PSTN
MSISDN
MSRN
MSRN
MSRN
TMSI
LAI &TMSI
TMSIRACH
Page ResponseSDCCH
TMSITMSI &
status
Status
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Land to Mobile Sequence
Complete Call
SETUP
CALL Confirmation
ADDRESS COMPLETE
Assignment Command
Ring Tone at MS
Alert
Assignment Complete
Connect
TMSI
MS BSS MSC VLR HLR GMSC PSTN
SDCCH
SDCCH
TCH
FACCH
Connect ACK
<SDCCH>
Channel Circuit
FACCH
Subscriber Picks Up
FACCH
ANSWER TCH
BILLING STARTS
FACCH
Ringing Stops at Land Phone
RingTone at Land Phone
Hello
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Mobile Initiated Call Clearing
1 DISCONNECT
PSTN RELEASE
MOBILE RELEASE
2 PSTN RELEASECOMPLETE
MS BSS MSC VLR HLR PSTNFACCH
FACCH
MOBILE RELEASE COMPLETE
3 CLEAR COMMAND
CHANNEL RELEASE
5 RLSD
4
UA
CLEAR COMPLETE
DISC
RELEASE COMPLETE
FACCH
FACCH
MS -MSC SignallingReleased
FACCH
FACCH
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Inter-BSS Handover Sequence
1
3
Periodic MeasurementReports
Handover Required
Handover Request
Handover Req Ack
Information Interchange
Handover Complete
Clear Command
Handover Command
MS BSS BSS MSC HLR PSTN
SAACH
7
4
6
5
2 TMSI Cct. Code
HO ref No.
HO Ref No.
FACCH
FACCH
Periodic Measurements Reports
SAACH
8
9
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Radio Interface Optimization
• Transmission Timing
• Power Control
• VAD and DTX
• Multipath Fading
• Equalization
• Diversity
• Frequency Hopping
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THREE TIMESLOT OFFSET
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
Mobile Rx
Mobile Tx3 TS Offset
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TIMING ADVANCE
6 70 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5
BURST arrivesLATE
BURST arrivesIN TIME
BURST sent early
T = 3.69S to 233S
Cell Radius = 35km
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Power Control
Cell Radius = 35km
•In steps of 2dB
•Enhances Battery Life
•Reduces Interference13 dBm (min)
33 dBm (max)
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Dis-Continuos Transmission
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
VAD - Voice Activity Detection
•MS identifies presence/ absence of speech
•Generates Comfort noise
DTX - Dis-Continuous Transmission
•MS does not TX during silence period
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MULTI-PATH PROPAGATION
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DIVERSITY
Approx. 10 Wavelengths3.3 meters
Diversity Receiver
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FREQUENCY HOPPING
F0
F2
F3
F4
FN
F1
T I M E
FR
EQ
UE
NC
Y
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5
FREQUENCY HOPPINGMobile Activity
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Mobile Rx
MONITORING Other Cell
6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5
Mobile Tx
Rx1
Rx2
Tx1
Tx2
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Speech Services
• Telephony (13 kbps full rate)
• Emergency Call (with/without SIM card in the Mobile Station)
• Short Message Services (SMS)
• Point to Point (128 Byte Max.)
• Cell Broadcast(75 bytes Max.)
• Dual Personal and Business Numbers.
– Allows calls to be made and billed, either to business or personal numbers.
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Data Services (Bearer Services)
• Data rates supported as of today are
– 2.4 Kbps
– 4.8 Kbps
– 9.6 Kbps
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Supplementary Service - Call Waiting
Call in Progress
PSTN Phone
Another Mobile Calls. Kept Waiting ……...
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Supplementary Services - Call Hold
1. Call in Progress
2. Put on Hold
3. Calls another Mobile
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Supplementary Services - Call Forwarding
Incoming Call
Voice MailSystem
PSTNPhone
AnotherMobile
Divert if
•All Calls
•Busy
•Not Reachable
•No Answer
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Supplementary Services
• Calling Line Identification– Present– Absent
• Connect Line Identification
– Present
– Absent
• Closed User Group - CUG
– Only incoming
– Only outgoing
• Operator Controlled Barring
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Voice Mail System
ANSWERING MACHINE
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Voice Mail System
MSC
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Short Message Service
SMSC
MSC
BTS
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Short Message Service
SMSC
MSC
BTS
Point to Multipoint
Point to Point
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PRE - PAID SYSTEM
• SIM BASED– Data on SIM– Decrements with use– Over the air charging !!??
• NETWORK BASED
– Data secure on with the network– Over the air re-charging– Features
• Inquiry• Warnings …..
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SEPARATE GSM & WLL INFRASTRUCTER
DUAL BAND / MODEHANDEST
MSC GSM BSC
GSM BTS
PSTN FIXED LINE SWITCH CDMA BSC
CDMA BTS
CDMA BTS
GSM BTS
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SEPARATE GSM & WLL INFRASTRUCTER
GSM + CDMA
GSM GSM
CDMA
Call Drop.Toggle to GSM
Still on GSM.Toggle to WLL
GSM
On WLL
DUAL BAND / MODEHANDEST
GSMCoverage
CDMACoverage
Every individual is a WLL subscriber under any and only one CDMA BTS and is a regular subscriber for the rest of the GSM network in the whole of Punjab.The subscriber also has the advantage of roaming within & outside the country.
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COMMON GSM & CDMA INFRASTRUCTER
DUAL BAND / MODEHANDEST
MSC
GSM BSCGSM BTS
PSTN
CDMA BSC CDMA BTS
A - INTERFACE
A - INTERFACE
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IRRIDIUM
• BTS in the Sky– LEO ~1400km– Inter Satellite Links - 22.55GHz to 23.55GHz– L-Band (1616MHz to 1626.5 MHz)– Band Width - 10.5MHz– Use TDM/FDMA scheme– World-Wide Coverage
• 60+ Now Operational• Small Hand held terminals• Dual Mobiles under development
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