Training-Gsm-Basic by santosjj

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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.

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
Coverage Area

ORGANISATION STRUCTURE
PROMOTERS
TECHNICAL
PLANNING

Punjab Haryana Rajasthan

Delhi

IMPLEMENTATION OPERATIONS

SALES

MARKETING
CUSTOMER CARE

OPERATIONS SYSTEM SUPPORT SUPPORT FUNCTIONS
BILLING IT ACTIVATIONS

U.P (East)

HR, ADMIN, ACCOUNTS

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Basic Telephony

2 Mb E1 (PCM)
0 1st TCH 1

•Signaling •Traffic
SWITCH / EXCHANGE

15th TCH 16

17th TS
•Off Hook •Dial Tone •Dialing Digits •RBT •Conversation
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300 - 3400 Hz

Sample Rate 8 kHz 8 bits per sample

64 kbps

•Ring •Off Hook & Conversation
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31 30thTCH

Wireless Telephony

Wireless Communication

MSC

• Alternative means of wireless communication – Walkie - Talkie – Pagers – Trunked private radios

BSC BTS BTS

• Mobile Phone - the magic technology that enables
Mobile Subscriber...
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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

WHAT IS CELLULAR TELEPHONY ?
CONSIDERATIONS FREQUENCY SUBSCRIBER DENSITY
Base Station Base Station Base Station

COVERAGE
Base Station Base 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.
What is a cell ?

The 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.
BTS

The hexagonal-shaped communication cells are artificial & are generated to simplify the planning & design of a cellular network.

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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

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
Inside offices, Buildings Very Low Tx Power ~ Less than 1 Watt Limited Coverage ~ 50 -100m Capacity Solution Special Algorithms for HO Pico Cell
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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.

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 • 1982 • 1986 • 1988 • 1990 • 1991 Europe wide frequency band reserved for Cellular “Groupe Speciale Mobile” created within CEPT GSM had full time in Paris ETSI takes over GSM Committee The phase 1 GSM Recommendations frozen GSM Committee renamed “Special Mobile Group” and GSM renamed as “ Global System for Mobile Communication” 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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• 1992

Uplink-Downlink

Frequency & ARFCN Ful(n) = 890.0 + (0.2) *n MHz

Downlink = 935 to 960 MHz

Fdl(n) = Ful + 45 MHz
where n =ARFCN ; 1 ≤ n ≤ 124

BTS Tx

dl

MS Rx

Uplink = 890 to 915 MHz

BTS Rx

ul
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MS Tx
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TDMA & FDMA
0 5 3 0 5 3 0
200KHz
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GSM Burst & TDMA Frame
FRAME 1 0 1 2 3 4 5 6 7 0 1 FRAME 2 2 3 4 5 6 7

7

1 0

0 7

2

GUARD PERIOD

GUARD PERIOD
Training sequence

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0

2 FDMA

Uplink - MS Tx 890MHz to 915MHz Downlink - BTS Tx 935MHz to 960MHz

Information TAIL BITS

Information 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

FREQUENCY RE - USE

– Frequency Re-use
Two re-use distances

2 7 1 6 5 4 3

D Cell Dia = R

D/R = (3N)1/2
where N is Cluster size

7/21 cell cluster

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Principal Of Sectorization
• Omni Directional Cells • 120 degree Sectors • 60 Degree sectors

Cell Sectorisation

b2 b1

– Each Sector in a Site has its own allocation of Radio Carriers.
OMNI CELL

b3 a2 a1 a6 a5
60O CELLS
6 ANTENNAS

a3 a4

120O CELLS
3 ANTENNAS

• Advantage – By frequent reuse of frequency more capacity can be achieved.

1 ANTENNA

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3 Site Reuse Pattern

Cellular 1Planning Steps

c2 c1 c3 a2 a1 a3 Cell Re-use c2 c1 c3
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– Cellular Topology • Cell splitting & Cell Repeat Patterns b2 b1 b3

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 NoiseDigital 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 EfficiencyRobust 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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Handovers

Base Station 2

Base Station 3 Base Station 1

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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
EC PSTN MSC IWF VLR HLR AUC EIR Network Switching System

ME SIM MS
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TRAU BTS

BSC

BSS

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GSM Network Components
• Mobile Station consists of two parts– Mobile Equipment (ME) – Subscriber Identity Module (SIM) • ME

Mobile Equipment (ME)
• ME are of three types– Vehicle Mounted – Portable Mobile Unit – Handportable Unit
• ME’s have distinct features-Classmarks sent in

– Hardware e.g. Telephone, Fax Machine,
Computer. • SIM

initial message to Network.
NETCOMP NETCOMP

– Smart Card which plugs into the ME.
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ME (Classmark Information)
• Revision Level
– Phase of the GSM specs ME comply with.

Mobile Equipment Class
1 2 3 4 5

Power O/p
20 W 8W 5W 2W 0.8 W Typical Settings
NETCOMP

• 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 Capability
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NETCOMP

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SIM
Subscriber Interface Identity Module
---------------------------

SIM - Internal Structure
Basic Operating System 16 to 24 kB

EEPROM
User Data 16 kB

ROM

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
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Full Size SIM Card

I/O 8 CPU
NETCOMP

Small SIM
---------------------------

RAM

Working Area for CPU 256 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)

SIM (LAI)
• LAI (Location Area Identity)

MCC
– MCC – MNC – LAC

MNC

LAC

CI

3 digit number (BCD), two Octets ( A & B) 2 digit number (BCD), one Octet 3 digit number (Binary) , two Octets

0-65535
– CI 5 digit number (Binary) , two Octets

0-65535
NETCOMP 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 Algorithms
NETCOMP

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. MSC
30 Channel PCM

Transcoder
NETCOMP

BSS

1234 1 2 3 4 XCDR
120 GSM TCH

NETCOMP

Transcoder Information from FOUR calls (4x16 KBPS put into ONE 64 KBPS timeslot

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Base Station System (BSS)

• BSS (Base Station System) – BSC (Base Site Controller) – BTS (Base Transceiver Station) – XCDR (Transcoder) XCDR

Network Switching System (NSS)

BSC
BTS

NETCOMP

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

A BTS Cabinet

BTS

NETCOMP

INNER VIEW
65 66

NETCOMP

OUTER VIEW

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BSS Configuration
• Collocated BTS • Remote BTS • Daisy Chain BTS • Star Configuration • Loop Configuration
BTS

Daisy Chain Configuration

BSC
All BTS on 1 E1

BTS BTS
NETCOMP

BTS
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NETCOMP

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Star Configuration

Loop Configuration

BTS

BTS

BTS

BSC

BTS

BTS

BSC

BTS
Loop Configuration

BTS
NETCOMP

BTS
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)
MSC

MOBILE SWITCHING CENTRE

– EC (Echo Canceller)
NETCOMP NETCOMP

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GSM Network Component
• MSC – Call Switching – Operation & Management Support – Internetwork Interworking – Collects call billing data

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)

• Gateway MSC – MSC which provides interface between PSTN & BSS’s in the GSM Network.
NETCOMP

– 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)

Equipment Identity Register (EIR)
• Contains Database for validating IMEI
– White List (valid ME) – Black List (Stolen ME) – Grey List (Faulty ME)

NETCOMP

NETCOMP

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Inter Working Function
• 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.

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 EC
NETCOMP NETCOMP

e.g. GSM DTE
IWF
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PSTN DTE
Analogue Modem

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Operation & Maintenance Centre
• Event & Alarm Management • Fault Management • Performance Management • Configuration Management • Security Management

Operation & Maintenance Centre
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.

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NETWORK MANAGEMENT CENTRE
o NETWORK MANAGEMENT CENTRE
(NMC) – Offers Hierarchical Regionalised Network Management of a complete GSM system.

NETWORK MANAGEMENT CENTRE NMC
OMC OMC OMC

• 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
MMI RAM> MMI RAM> MMI RAM>

REGION 2

REGION 3 REGION 1

NETWORK

GSM Terrestrial Interfaces
Broadly classified into two types of interfaces• Um • Abis • A – 2 Mbps Trunks (E1) – Signalling System No. 7 SS7 ( CCS7) – X.25 (Packet Switched Mode) • B • C • D • E • F • G • H
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GSM Interfaces
MS - BTS

• Standard Interfaces

BTS - BSC BSC - MSC MSC - VLR MSC - HLR VLR - HLR MSC - MSC MSC - EIR VLR - VLR HLR - AUC
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• GSM Interfaces

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Basic Processes
• AUTHENTICATION • CIPHERING • REGISTRATION • CALL ESTABLISHMENT • HANDOVER / HANDOFF • ROAMING

AUTHENTICATION ALGORITHM

HLR

Ki

NSS
AUC
RAND

AUTH. ALGORITHMS A3

SRES

COMPARE

AIR INTERFACE
RAND SRES

MS

SIM MS

Ki

AUTH. ALGORITHMS A3
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Ciphering
• Data protection is required on air interface.

Ciphering

• A5 algorithm is used. • A specific key called Ciphering Key (Kc), is
generated from RAND and A8 algorithm. • A8 is on the SIM.

Ki

RAND

Kc
Data

Kc Ciphered Data

A8
Kc
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A5

A5

Data

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ROAMING

ROAMING
o The mobile roams to another country (UK) and requests a

PSTN
MSC HLR INDIA ME MSC VLR

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

UK ME

MSC/VLR, the mobile is able to use network services (MOC, MTC etc.)

Transmission Media • Access Network
– Microwave 15 /23 GHz

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

• Backbone Network
– Microwave 7 GHz – Optical Fibers – Leased Line( From Dot or any other service provider on any media)

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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 µm Mono Mode Graded index Multi Mode Step Index 100 / 300 µm

•

Multi Mode Graded Index 75 / 130 µm
•

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

TDMA & FDMA
0 5 3 0 5 1 0 7

• Physical Channel
– Physical channel is the medium over which the information is carried.

0 7

2

• Logical Channel
– Logical channels consists of the information carried over the Physical Channel. 0
200KHz
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3 1

0

2 FDMA
100

Uplink - MS Tx
890MHz to 915MHz

Downlink - BTS Tx
935MHz to 960MHz

LOGICAL CHANNELS
3
3 T 57 encrypted 1 26 1 S training S 577µS µ 57 encrypted 3 T 8.25 GP

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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Normal Burst

0 1 2 3 4 5 6 7
577µS x 8 = 4.615mS µ

TDMA Frame

26 Frame Multi-frame

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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 Burst
Traffic & Control Channels Bi-directional

• Frequency Correction Burst
FCCH Downlink

• Synchronization Burst
SCH Downlink

• Dummy Burst
BCCH Carrier Downlink

• Access Burst
RACH
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Uplink

GSM Logical Channels • TCH
– SACCH – FACCH
TDMA Frame

LOGICAL CHANNELS

01234567012345670123456701234567

• Control Channels
– BCCH – CCCH – ACCH – DCCH
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26 Frame Multi-frame

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Frames & Multiframes
• Several Logical channels share one time slot.

Traffic Channels - TCH
TCH

• 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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TCH

DATA

TCH / FS

TCH / HS

9.6 4.8

2.4

SAACH

FACCH
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BCCH Channel • BCCH
CCH Broadcast Control Channel - Downlink only
Synchronizing Channels

Channels On Air Interface

– Transmitted at all times & conveys information about Cell Timing and Configuration • BCCH, FCCH, SCH

BCCH

• CCCH
– Used by BSS & MS when trying to initiate a connection over the air • RACH, PCH, AGCH, CBCH

BCCH

SCH
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FCH
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Channels On Air Interface • DCCH
– Used to convey signaling information during call setup • SDCCH

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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• ACCH
– Used to transmit signaling information when a call is in progress • FACCH & SACCH

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Channels On Air Interface
• Acronyms
– BCCH – CCCH – DCCH – ACCH – SDCCH – RACH – PCH – AGCH Broadcast Control Channel Common Control Channel Dedicated Control Channel Associated Control Channel Standalone Dedicated Control Channel Random Access Channel Paging Channel 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.

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)

• 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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• 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.

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

TCH Multiframe

– Broadcast Channel Combination
• BCCH +CCCH • Can be on Timeslot 0, 2, 4, 6 0 5 10 SACCH 15 20

I D L E

– 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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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.

BCCH/CCCH Multiframe
Downlink to MS

F S BCCH CCCH FS 4 TS

CCCH 8 TS

FS

CCCH 8 TS

FS

CCCH 8 TS

FS

CCCH 8 TS

I

0

10

20

30

40

50

Uplink from MS
RR RR RR RRRR RR R R RR RR RR RR RR RR RR RR RR RR RR R RR RR RRRR RR RR RR

0
121

10

20
122

30

40

50

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.
123 D3 RR A2

Combined Multiframe
Downlink to MS
F S BCCH CCCH F S 4 TS F S BCCH CCCH F S 4 TS CCCH 8 TS CCCH 8 TS F S D0 D1 FS D2 D3 FS A0 A1 I

F S D0

D1

F S D2

D3

FS

A2

A3

I

0

10

20

30

40

50

Uplink from MS
D3 RR A0 A1 RR RR RR RR RR RR RR RR RR RR RR R D0 D1 RR D2

A3

RR RR RR RR RR RR RR RR RR RR RR R D0

D1

RR D2

0

10

20
124

30

40

50

SDCCH Multiframe
Downlink to MS

Voice Coding
104 kbps

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

A3

I I I

20 mS

Sample Rate 8 kHz 13 bits per Sample 160 Samples 2080 bits

D0

D1

D2

D3

D4

D5

D6

D7

A4

A5

A6

A7 I I I

LPC RPE
Divided into 4 Blocks of 40 Samples each

0

10

20

30

40

50

Class Ia 50 bits

Class Ib 132 bits

Class II 78 bits

Uplink from MS
A1 A2 A3 I I I D0 D1 D2 D3 D4 D5 D6 D7 A0

A5

A6

A7

I I I

D0

D1

D2

D3

D4

D5

D6

D7

A4

Reduction in Data Speech Encoder selects Block Block - 1 : 1, 5, 9 ….. Samples with Most Energy
Block - 2 : 2, 6, 10, …… Samples

0

10

20

125

30

40

50

LTP

126

& so on for Block - 3 & Block - 4.

21

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

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

127

128

Speech Channel Coding

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.

Parity Check 50

Class 1a 50 bits

Class 1b 132 bits

Class 2 78 bits Tail Bits

3

132

4

Convolutional Coding Convolutional Code 378 378 456 bits
129 130

78 78

Control Channel Coding

Data Channel Coding

184 Coding 184 Convolutional Coding 456 456 bits
131

240

40

4

184 Convolutional Coding 488 Punctuate 456
132

4

Parity Bits TB

22

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
Speech Blocks

DIAGONAL INTERLEAVING

SPEECH

EIGHT blocks of 57 bits, Sent on 8 ALTERNATE timeslots

456 bits

456 bits

0 1 234 5 6 7 0 1 234 5 6 7 0 1 234 5 6 7 0 1 234 5 6 7
133 134

RECTANGULAR INTERLEAVING

CONTROL CHANNEL
Data Blocks

Interleaving
• Interleaving Depths – Speech - 8 blocks – Control - 4 blocks – Data - 22 blocks • Speech & Data blocks are diagonally interleaved • Control block is rectagularly interleaved

FOUR blocks of 114 bits, Sent on 4 timeslots
114 Bits Odd

456 bits

114 Bits Even

114 Bits Odd

114 Bits Even

0 1 234 5 6 7 0 1 234 5 6 7 0 1 234 5 6 7 0 1 234 5 6 7
135 136

Interleaving

TRAU Frame Type

Number of GSM Burst Spread Over 8 4 22

Speech Control Data

TRAU = Transcoder Rate Adaption Unit
137

138

23

MOBILE TO LAND

PSTN

BTS

BSC

MSC

139

140

Multiple Point of Interconnect
– Intra-city
CITY A

Call Scenarios
• Mobile to Mobile – Inter-city • Mobile to Land – Intra-city – Inter-city • Land to Mobile

CITY B

– Intra-city – Inter-city

BSS TRAFIC

POI TRAFIC

141

142

Mobile To Land Sequence
MS 1 2 3 4 5 6 7
CHANNEL REQUEST DCCH ASSIGN SIGNALLING LINK ESTABLISHED REQUEST FOR SERVICE AUTHENTICATION SET CIPHER MODE SET-UP EQUIPMENT ID REQUEST

8

COMPLELTE CALL CALL PROCEEDING

MS SDCCH SDCCH

BSS

MSC

VLR

HLR PSTN

EIR

9

ASSIGNMENT COMMAND

(circuit)

BSS

MSC

VLR

HLR

PSTN EIR
ASSIGNMENT COMPLELTE INITIAL & FINAL ADDRESS (IFAM) ASSIGNMENT COMPLETE (ACM)

(channel) FAACH (TCH)

RACH AGCH

SDCCH

CR

10 ALTERING MS HEARS RINGTONE FROM LAND PHONE ANSWER(ANS) 11 CONNECT RING TONE STOPS

FACCH

CC

Hello!
FACCH FACCH

SDCCH
Call Info
143

BILLING STARTS

CONNECT ACKNOWLEDGE

TCH
144

24

Land to Mobile Sequence
Initial & Final Address Msg. (IFAM) Send Routing Information

Land to Mobile Sequence
HLR GMSC PSTN MSISDN
Complete Call

MS

BSS

MSC

VLR

MS

BSS

MSC TMSI

VLR

HLR GMSC PSTN

SETUP

IMSI
Routing Information Ack INITIAL & FINAL ADDRESS (IFAM) Send Info for I/c Call Setup PAGE Paging Request Channel Request DCCH Assign Signalling Link Established Page Response

MSISDN
CALL Confirmation ADDRESS COMPLETE Assignment Command Assignment Complete Alert

SDCCH SDCCH <SDCCH> Channel FACCH FACCH TCH FACCH Ringing Stops at Land Phone Circuit RingTone at Land Phone

MSRN MSRN MSRN PCH TMSI RACH AGCH SDCCH SDCCH TMSI 145 TMSI & status Status TMSI LAI & TMSI

Ring Tone at MS Subscriber Picks Up
ANSWER

Connect

BILLING STARTS
FACCH TCH
146 Hello

Connect ACK

Mobile Initiated Call Clearing
MS
1 DISCONNECT PSTN RELEASE MOBILE RELEASE 2 PSTN RELEASE COMPLETE MOBILE RELEASE COMPLETE MS -MSC Signalling Released 3 CLEAR COMMAND CHANNEL RELEASE 4 DISC UA CLEAR COMPLETE 5 RLSD RELEASE COMPLETE FACCH FACCH FACCH FACCH FACCH

Inter-BSS Handover Sequence
PSTN
MS 1 2 3 4 5 6 7 8 9
Periodic Measurement Reports Handover Required Handover Request Handover Req Ack Handover Command Information Interchange Handover Complete Clear Command Periodic Measurements Reports

BSS
FACCH

MSC

VLR

HLR

BSS

BSS

MSC

HLR

PSTN

SAACH

TMSI Cct. Code HO ref No. FACCH HO Ref No. FACCH

SAACH
148

147

Radio Interface Optimization
• Transmission Timing • Power Control • VAD and DTX • Multipath Fading • Equalization • Diversity • Frequency Hopping

149

150

25

THREE TIMESLOT OFFSET

TIMING ADVANCE

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

0

1

2

3

4

5

6

7

Mobile Rx

3 TS Offset

BURST sent early

BURST arrives LATE

0

1

2

3

4

5

6

7

Mobile Tx
δT = 3.69µS to 233µS µ µ Cell Radius = 35km BURST arrives IN TIME

151

152

Power Control
•In steps of 2dB

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

•Enhances Battery Life •Reduces Interference
13 dBm (min)

VAD - Voice Activity Detection
•MS identifies presence/ absence of speech •Generates Comfort noise

33 dBm (max)

DTX - Dis-Continuous Transmission
•MS does not TX during silence period
Cell Radius = 35km 153 154

MULTI-PATH PROPAGATION

DIVERSITY

Diversity Receiver

Approx. 10 Wavelengths 3.3 meters
155 156

26

FREQUENCY HOPPING

FREQUENCY HOPPING Mobile Activity
Rx1 Rx2 Tx1 Tx2

FN F4
FREQUENCY

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

Mobile Rx 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

F3
6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5

F2
6 7 0 1 2 3 4 5 6 7 0 1

Mobile Tx 2 3 4 5

F1 F0
157

MONITORING Other Cell

TIME

158

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.

159

160

Data Services (Bearer Services)
•

Supplementary Service - Call Waiting
Call in Progress

Data rates supported as of today are – 2.4 Kbps – 4.8 Kbps – 9.6 Kbps
PSTN Phone

161

162

27

Supplementary Services - Call Hold
1. Call in Progress 2. Put on Hold

Supplementary Services Call Forwarding
Voice Mail System

Divert if
•All Calls PSTN Phone Another Mobile •Busy •Not Reachable •No Answer

3. Calls another Mobile Incomi ng Call

163

164

Supplementary Services
• Calling Line Identification – Present – Absent • Connect Line Identification – Present – Absent • Closed User Group - CUG – Only incoming – Only outgoing • Operator Controlled Barring

Voice Mail System

ANSWERING MACHINE
165 166

Voice Mail System

Short Message Service

SMSC

MSC
MSC

BTS
167 168

28

Short Message Service

PRE - PAID SYSTEM
• SIM BASED – Data on SIM – Decrements with use – Over the air charging !!??

SMSC

Point to Point

• NETWORK BASED – Data secure on with the network – Over the air re-charging – Features • Inquiry • Warnings …..

Point to Multipoint

MSC

BTS
169 170

SEPARATE GSM & WLL INFRASTRUCTER

CDMA BTS

PSTN

FIXED LINE SWITCH

CDMA BSC CDMA BTS

GSM BTS

DUAL BAND / MODE HANDEST

MSC

GSM BSC GSM BTS

171

172

SEPARATE GSM & WLL INFRASTRUCTER

COMMON GSM & CDMA INFRASTRUCTER
A - INTERFACE

CDMA Coverage

GSM

Call Drop. Toggle to GSM

GSM Coverage

CDMA BSC

CDMA BTS

CDMA

GSM + CDMA
On WLL PSTN MSC

Still on GSM. Toggle to WLL

DUAL BAND / MODE HANDEST
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.

A - INTERFACE

DUAL BAND / MODE HANDEST
GSM BTS GSM BSC

GSM

GSM

173

174

29

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

175

176

30


								
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