gsm training_gurgaon full theory

8/3/2019 Gsm Training_gurgaon Full Theory

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GSM INTRODUCTION

ADA CELLWORKS PVT LTD


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INTRODUCTIONINTRODUCTION

The global system for mobile communications(GSM) is a set of recommendations andspecifications for a digital cellular telephone

network (known as a Public Land Mobile Network,or PLMN). These recommendations ensure thecompatibility of equipment from different GSMmanufacturers, and interconnectivity betweendifferent administrations, including operations

across international boundaries.


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THE GSM NETWORKTHE GSM NETWORK

The GSM network is comprised of the followingcomponents: Network Elements

The GSM network incorporates a number of networkelements to support mobile equipment. They are listed anddescribed in the GSM network elements section of thischapter.

GSM subsystems

In addition, the network includes subsystems that arenot formally recognized as network elements but arenecessary for network operation. These are described in the

GSM subsystems (non-network elements) section of thischapter.

Standardized Interfaces

GSM specifies standards for interfaces between networkelements, which ensure the connectivity of GSM equipmentfrom different manufacturers. These are listed in the

Standardized interfaces section of this chapter.


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THE GSM NETWORKTHE GSM NETWORK --CONTINUEDCONTINUED

Network Protocols For most of the network communications on these

interfaces, internationally recognized communications

protocols have been used These are identified in the Network protocols section of

this chapter.

GSM Frequencies

The frequency allocations for GSM 900, Extended GSMand Digital Communications Systems are identified in theGSM frequencies section of this chapter.


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DIGITAL NETWORKSDIGITAL NETWORKS

GSM networks are digital and can cater forhigh system capacities. They are consistentwith the world wide digitization of the

telephone network, and are an extension ofthe Integrated Services Digital Network(ISDN), using a digital radio interface betweenthe cellular network and the mobile subscriber

equipment.


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INCREASED CAPACITYINCREASED CAPACITY

The GSM system provides a greater subscribercapacity than analogue systems. GSM allows 25 kHz. Peruser, that is, eight conversations per 200kHz. Channel pair(a pair comprising one transmit channel and one receive

channel). Digital channel coding and the modulation usedmakes the signal resistant to interference from the cellswhere the same frequencies are re-used (co-channelinterference); a Carrier to Interference Ratio (C/I) level of 9dB is achieved, as opposed to the 18 dB typical with

analogue cellular. This allows increased geographic reuseby permitting a reduction in the number of cells in thereuse pattern. Since this number is directly controlled bythe amount of interference, the radio transmission designcan deliver acceptable performance.


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CGI : CELL GLOBALCGI : CELL GLOBALIDENTITYIDENTITY

MCC MNC LAC CI

LAI

CGI

MCC = Mobile Country Code

MNC = Mobile Network Code

LAC = Location Area CodeCI = Cell Identity


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MSISDNMSISDN

CC NDC SN

98 XXX 12345

CC = Country Code

NDC = National Destination Code

SN = Subscriber Number


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MSISDNMSISDN

The Mobile Subscriber ISDN(MSISDN) number is the telephone

number of the MS. This is thenumber a calling party dials to reachthe subscriber. It is used by the landnetwork to route calls towards the

MSC.


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IMSIIMSI

IMSI (International MobileSubscriber Identity) NetworkIdentity Unique To A Sim.

MCC MNC MSIN

404 XX 12345..10

SIM = Subscriber Identity Module

MCC = Mobile Country Code

MNC = Mobile Network Code

MSIN = Mobile Subscriber Identity Number


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IMEIIMEI

IMEI : Serial number unique to eachmobile

TAC FAC SNR SP

6 2 6 1

IMEI = International Mobile Equipment Identity

TAC = Type Approval CodeFAC = Final Assembly Code

SNR = Serial Number

SP = Spare


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SUBSCRIBER IDENTIFICATIONSUBSCRIBER IDENTIFICATION

International Mobile Subscriber Identity (IMSI)

Just the IMEI identifies the mobile equipment, other

numbers are used to identify the mobile subscriber.Different subscriber identities are used in different phasesof call setup. The International Mobile Subscriber Identity(IMSI) is the primary identity of the subscriber within themobile network and is permanently assigned to that

subscriber. Temporary Mobile Subscriber Identity (TMSI)

The GSM system can also assign a Temporary MobileSubscriber Identity (TMSI). After the subscribers IMSI hasbeen initialized on the system, the TMSI can be used for

sending backward and forward across the network toidentify the subscriber. The system automatically changesthe TMSI at regular intervals, thus protecting thesubscriber from being identified by someone attempting tomonitor the radio channels. The TMSI is a local numberand is always transmitted with the Local numbers and is

always transmitted with the Location Area Identification


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SUBSCRIBER IDENTIFICATIONSUBSCRIBER IDENTIFICATIONMODULE (SIM)MODULE (SIM)

By making a distinction between the subscriberidentity and the mobile equipment identity, a GSMPLMN can route calls and perform billing based on theidentity of the subscriber rather than the mobileequipment being used. This can be done using a

removable Subscriber Information Module (SIM). Asmart card is one possible implementation of a SIMmodule.

IMSI. This is transmitted at initialization of themobile equipment.

TMSI This is updated periodically by the PLMN MSISDN This is made up of a country code, a

national code and a subscriber number.

Location Area Identity (LAI) This identified thecurrent location of the subscriber.

Subscriber Authentication Key (KI) This is usedto authenticate the SIM.


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EQUIPMENT IDENTITY NUMBEREQUIPMENT IDENTITY NUMBER

International Mobile station EquipmentIdentity (IMEI)

Each MS is identified by an International Mobilestation Equipment Identity (IMEI) number which is

permanently stored in the mobile equipment. Onrequest, the MS sends this number over the signallingchannel to the MSC. The IMEI can be used to identifyMS,s that are reported stolen or operating incorrectly.

Equipment Identity Register ( EIR ) A listing of the allowed IMEI is maintained by the

PLMNs in the Equipment Identity Register (EIR) tovalidate the mobile equipment.


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Frequency BandsFrequency Bands

Uplink 890 915 MHz 25 MHz

Downlink 935 960 MHz 25 MHz

100 KHz 200 KHz 100 KHz

1 43 1242 .

A 200 KHz carrier spacing has been chosen. Excluding 2x100 KHz edges of

the band, this gives 124 possible carriers for the uplink and downlink. The

use of carrier 1 and 124 are optional for operators.


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GSM Network ArchitectureGSM Network Architecture

BTS

BTS

BTS

BTS

BTS

BSC

BSC

TRAU

MSC

HLRAUC

VLR

EIR

PSTN

SMSC


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MSMS Mobile StationMobile Station

Mobile station provides user access toGSM network for voice and data

All GSM mobiles comply to GSM standards Subscriber data is read from a SIM card

that plugs into ME

SIM ME

MS


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MS (cont..)MS (cont..)

Each MS has a unique number calledas IMEI number, which is stored inEIR for authentication purposes

Mobile camps on to the GSM networkthrough the BTS serving the cell

Mobile also scans neighboring cells

and reports signal strengths Mobile transmits and receives voice

at 13 kb/s over the air interface


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Mobile Station Output PowerMobile Station Output Power

CLASS 1 20 watts Vehicle andPortable

CLASS 2 8 watts Portable andVehicle

CLASS 3 5 watts Hand-Held

CLASS 4 2 watts Hand-Held (GSM)CLASS 5 0.8 watts Hand-Held(DCS 1800)

Output power determines:


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Mobile Station IdentitiesMobile Station IdentitiesMSISDN : Mobile Station ISDN Number

It is the human identity used to call a Mobile

Station

CC SNNDC MSISDN98 250 00134

CC Country Code

NDC National Destination Code

SN Serial Number


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IMSI (International MobileIMSI (International MobileSubscriber Identity)Subscriber Identity)

MCC Mobile Country Code

MNC Mobile Network Code

MSIN Mobile Subscriber Identity

Number

MCC MSINMNC IMSI

3 2 or 3

Not more than 15

NMSI


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IMEI (International MobileIMEI (International MobileEquipment Identity)Equipment Identity)

TAC SPFAC IMEISNR

6 162 15 TAC Type Approval Code

FAC Factory Assembly Code

SNR Serial Number

SP Spare digit (usually used tospecify software version)


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SIM ( Subscriber IdentitySIM ( Subscriber IdentityModule)Module)

Removable module inserted when

the subscriber wants to use the ME Two sizes: credit card size and stamp

size

SIM features and contents arepersonalized by the Service Activator

ROM 6kb to 16 kb

RAM 128 bytes to 256 bytes

Space to insert SIM photo


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Contents of SIMContents of SIM

Serial Number

IMSI, Subscriber Key Ki, CipheringKey Kc

Algorithms for authentication andciphering

Network Code PIN, PUK

Charging Information

Abbreviated Dialling


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SIM SecuritySIM Security

Two level protection

When mobile is turned on, it will askfor user to enter PIN (Personal IdNumber)

3 tries for PIN, after that PIN locked

To unblock PIN, there is PUK (Pin

Unblock Key) 10 attempts of PUK allowed

After that SIM is blocked


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BTS (Base Transceiver Station)BTS (Base Transceiver Station) BTS has a set of Transceivers (TRXs) to

communicate with mobiles in its area

One BTS covers one or more than one cell

The capacity of a cell depends on number of

transceivers in the cell BTS is connected to the BSC through Abis

Interface which is 2Mbps

BTS transmits and receives voice at 13kbps

over air interface to the mobiles. BTS commands mobiles to set Tx. Power,

timing advance and Handovers


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BTSBTS


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BSCBSC Base Station ControllerBase Station Controller Several BTSs are connected to the BSC

BSC Manages channel allocation,handovers and release of channels atconnected BTSs

BSC connects to the BTS via the Abisinterface and to the MSC on A interface

BSC has the entire database of cellparameters associated with the BTSs.

No mobile data is stored in the BSC Less connections for MSC as intelligence is

made common to all BTSs by the BSC

Several BTSs are connected to the BSC

BSC Manages channel allocation,handovers and release of channels atconnected BTSs

BSC connects to the BTS via the Abisinterface and to the MSC on A interface

BSC has the entire database of cellparameters associated with the BTSs.

No mobile data is stored in the BSC Less connections for MSC as intelligence is

made common to all BTSs by the BSC


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BSCBSC


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TRAUTRAU Transcoder RateTranscoder RateAdaptation UnitAdaptation Unit

BTS

BSC PSTN

13 kbps 16 kbps 16 kbps 64 kbps

MSC and TRAU


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TRAU (cont..)TRAU (cont..) The MSC is based on ISDN

switching. The Fixed Network isalso ISDN based.

ISDN has speech rate of 64 kbps.Mobile communicates at 13 kbps.

TRAU converts the data rates

between 13kbps GSM rate to64kbps Standard ISDN rate

TRAU can be collocated with the

BTS, BSC or MSC or it can be a


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Location of TranscoderLocation of Transcoder

Collocated with MSC, BSC, BTS

Separate Unit

MSC Transcoder BSC


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MSCMSC Mobile Switching CentreMobile Switching Centre

BSC

BSC

BSC

BTSs PSTN

HLR

VLR


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MSC (cont..)MSC (cont..) Exchange where calls are established,

maintained and released

Database for all subscribers and theirassociated features.

Communicates with the BSCs on the A interfaceand with PSTN on fixed line.

MSC is weighted on the number of subscribersit can support. E.g. an MSC of 1 lac subscribers

means one MSC is enough till subscriber baseincreases upto 1 lac, beyond which anotherMSC is required.


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Multiple MSCsMultiple MSCs When there is more capacity, there are

more than one MSCs. All MSCs have to communicate with oneanother and to the outside world.

Very complicated to connect each MSC to

each other and each MSC to PSTN So there is a concept of GMSC (GatewayMSC)

BSC

BSC

MSC

MSC

GMSC PSTN


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HLRHLR Home Location RegisterHome Location Register

MSC has all subscriber databasestored in HLR

HLR has all permanent subscriberdatabase

HLR has a database which describesthe subscribers profile i.e. basicfeatures and supplementary services

MSC communicates with the HLR toget data for subscribers on call


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RegisterRegister

A subscription when activated is

registered in VLR VLR has all the subscriber numbers

which are active.

VLR has a temporary database of allactive subscribers (on/off, locationinformation)

MSCVL

R

HLR


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VLR (cont..)VLR (cont..)

MSC MSCVLR

HLR

VLR

MSC communicates with HLR forsubscribers coming from differentMSCs. If the subscriber is foundvalid, then it registers the subscriber

in the VLR


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AUCAUC Authentication CentreAuthentication Centre Authentication is a process by which

a SIM is verified Secret data and the verification

process algorithm are stored in AUC

AUC is the element which carries outthe verification of the SIM

AUC is associated with the HLR

MS MSC HLR AUC


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EIR (Equipment Identity Register)EIR (Equipment Identity Register) EIR is the Mobile Equipment

Database which has a series ofIMEIs

MSC asks the Mobile to send itsIMEI

MSC then checks the validity of

IMEI with the EIR All IMEIs are stored in EIR with

relevant classificationsEIR

MSC


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Classification of IMEIsClassification of IMEIsWhite list: This contains the IMEI of

type approved mobiles

Black List: List of IMEIs which should be

barred because either they are stolen or

are not functioning properly

Grey list: List of IMEIs which are to be

evaluated before they are put in black list


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Billing Centre (BC)Billing Centre (BC)

BC Generates the billing statementfor each subscriber

BC may be directly connected to the

MSC or through a mediation device MSC sends CDRs (Call Detail

Records) to the BC

According to the template of pulserates and units set, BC creates a billaccording to the destination calledand the call duration


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Billing Centre (BC) (cont..)Billing Centre (BC) (cont..)

CDRs

Templates for unit costs


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OMCOMC Operations andOperations andMaintenance CentreMaintenance Centre

Also called the NOC (Network

Operations centre) It is the central monitoring and

remote maintenance centre for all

network elements OMC has links to BSCs and MSCs


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OMCOMC Operations andOperations andMaintenance CentreMaintenance Centre

Also called the NOC (Network

Operations centre) It is the central monitoring and

remote maintenance centre for all

network elements OMC has links to BSCs and MSCs


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OMCOMC

OMC System

BSC

BSC

BSC

BTSs

BTSs

BTSs

OMC Terminals


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GSM ChannelsGSM Channels


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GSM ChannelsGSM Channels

Physical ChannelOne time slot on one carrier is called

physical channel. Logical Channel

Information carried by physicalchannels is called logical Channels.

Logical channels are mapped onphysical channels.


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Logical ChannelsLogical Channels

Traffic channels: Used for speech anddata

Full Rate(TCH/F)

Half Rate(TCH/H) Control channels: Used for signaling

.i.e. setting up a radio connection, call orcontrolling an MS during conversation

BCH(Broadcast channels)CCCH(common control channels)

DCCH(dedicated control channels)


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Traffic Channels(TCH)Traffic Channels(TCH)

TCH/F

(fullRate)

TCH/H

(halfRate)

Traffic Channels(TCH)


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Control Channels(CCH)Control Channels(CCH)

CCH(Control Channel)

BCH CCCH DCCH

BCCH RACH CBCH SDCCH ACCHSynch.

Chanels

SACCHFACCHPCH/

AGCHFCCHSCH


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BCH(Broadcast ChannelsBCH(Broadcast Channels))

BCCH(Broadcast Control Channels)

Downlink Only.

Broadcast information of the servingcell (System Information).

Transmitted on timeslot zero of BCCHcarrier.

Reads only by idle mobile at least onceevery 30 secs.


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BCH(Broadcast Channels)BCH(Broadcast Channels)contdcontd

SCH(Synchronisation Channels)

Downlink Only

Carries information for framesynchronisation.

Contains frame number and BSIC(BaseStation Identity Code).


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BCH(Broadcast Channels)BCH(Broadcast Channels)contdcontd

FCCH(Frequency CorrectionChannels)

Downlink Only.

Enable MS to synchronies to thefrequency.


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CCCH(Common ControlCCCH(Common ControlChannel)Channel)

RACH(Random Access Channel)

Uplink only.

Used by the MS when making its firstaccess to the Network.

The reason for access could be initiationof a call or a page response.


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CCCH(Common ControlCCCH(Common ControlChannel) contdChannel) contd

AGCH(Assess Grant Channel)

Downlink only.

Used for acknowledgement of theaccess attempt sent on RACH.

Used by the network to assign asignaling cannel upon successful

decoding of access bursts.

( l( l


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CCCH(Common ControlCCCH(Common ControlChannel) contdChannel) contd

PCH(Paging Channel)

Downlink only.

The network will page the MS ,if there isa incoming call or a short Message.

It contains the MS identity number, theIMSI or TMSI.

CC ( di d C lCC ( di d C l


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DCCH(Dedicated ControlDCCH(Dedicated ControlChannel)Channel)

SDCCH (Stand-alone DedicatedControl Channel)

Uplink and Downlink.

Used for call setup, authentication,ciphering location update and SMS.

DCCH(D di d C lDCCH(D di d C l


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DCCH(Dedicated ControlDCCH(Dedicated ControlChannel) contdChannel) contd

SACCH(Slow Associated ControlChannel)Downlink and Uplink.

Used to transfer signal while MS haveongoing conversation on traffic or whileSDCCH is being used.

On the forward link, the SACCH is used

to send slow but regularly changingcontrol information to each mobile onthat ARFCN, such as power controlinstructions and specific timing advance

instructions


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SACCH(Slow Associated ControlChannel) contd

The reverse SACCH carries information about

the received signal strength and quality of the

TCH, as well as BCH measurement results

from neighboring cells.

DCCH(D di t d C t lDCCH(D di t d C t l


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DCCH(Dedicated ControlDCCH(Dedicated ControlChannel) contdChannel) contd

FACCH(Fast Associated ControlChannel)

Downlink and uplink.

Associate with TCH only.

It is used to send fast message likehand over message.

Work by stealing traffic bursts.

M i Ph i lM i Ph i l


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Mapping on PhysicalMapping on PhysicalChannelsChannels

The Logical channels are mapped onthe physical channels.

The TDMA frames are groupedtogether into multi-frame.

26 TDMA multi-frame for Traffic.

51 TDMA multi-frame for control signal.


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Channel CombinationChannel Combination

Combined

All the controlling signals are in the timeslot 0 of the Multi-frame.

Non Combined

Dedicated controlling signals are in timeslot 1 of the Multi-frame.


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CombinedCombined

Cell with single carrier.

Timeslot 0 :BCCH+CCCH+SDCCH.

Timeslot 1-7 :TCH/FACCH+SACCH.


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Non CombinedNon Combined

Cell with Two carrier

Timeslot 0 (of carrier 1) BCCH+CCCH.

Timeslot 1 (of carrier1) SDCCH+SACCH.

Timeslot 2-7 & 0-7(of both carriers)TCH/FACCH+SACCH.


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SYSTEM INFORMATION


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SYSTEM INFORMATION 1SYSTEM INFORMATION 1

When frequency hopping is used in cell MS needsto know which frequency band to use and whatfrequency within the band it should use inhopping algorithm.

Cell channel description

Cell Allocation Number(CANO)-Informsthe band number of the frequency channels used.

00-Band 0(current GSM band)

Cell Allocation ARFCN(CA ARFCN):-ARFCNs used for hopping.It is coded in a bitmapof 124 bits.


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SYTEM INFORMATION 1SYTEM INFORMATION 1

124 123 122 121

024 023 022 021 020 019 018 017

016 015 014 013 012 011 010 009

008 007 006 005 004 003 002 001


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RACHControl ParametersAccess Control Class(ACC) :-Bitmap

with 16 bits. All MS spread out on class 0 9 .Priority groups use class 11-15. A bit set to 1

barred access for that class. Bit 10 is used totell the MS if emergency call is allowed or not.

0 All MS can make emergency call.1 - MS with class 11-15 only can

make emergencycalls.

Cell barred for access(CB):-0- Yes

1- No


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RACHControl ParametersRe-establishment allowed(RE):-

0- Yes

1- NoMax_retransmissions(MAXRET):-Number

of times the MS attempts to access the Network[1,2,4 or 7].

Tx-integer(TX):- Number of slots to spreadaccess retransmissions when a MSattempts to access the system.

Emergency call allowed:-Yes/No.


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SYSTEM INFORMATION 2SYSTEM INFORMATION 2 System Information Type 2 message

consists of the Double BA list whichdefines the BCCH frequencies used in theneighboring cells.

The Double BA list provides the MS withdifferent frequencies on which to measure,depending on whether the MS is in idle oractive mode.

In active mode, the MS should measureon a reduced number of frequencies inorder to improve the accuracy ofmeasurements.


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SYSTEM INFORMATION 2SYSTEM INFORMATION 2 In Idle mode,the MS should measure on

larger number of frequencies, so that thetime required for the MS to access thenetwork after power on is reduced.

The MS is also informed which PLMNs itmay use.

As well as System Information Type 2,it isalso possible to have System InformationType 2 Bis and System information Type 2Ater, depending on the size of the BA List.

System Information Type 2 Bis/Ter areoptional.


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Neighbor Cell Description:-BA Indicator(BA IND):- Allows to

differentiate measurement results related todifferent list of BCCH frequencies sent to

MS.BCCH Allocation number(BANO):-

Band 0 is used.

PLMN Permitted(NCCPERM):-This the

PLMN color codes permitted and tells the MSwhich network color codes(NCC) on the BCCHcarriers it is allowed to monitor when it is in thiscell.

.


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RACHControl ParametersAccess Control Class(ACC) :-Bitmap

with 16 bits. All MS spread out on class 0 9. Priority groups use class 11-15. A bit set

to 1 barred access for that class. Bit 10is used to tell the MS if emergency call isallowed or not.

0 All MS can make emergency call.1 - MS with class 11-15 only can

make emergencycalls.

Cell barred for access(CB):-0- Yes

1- No


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Re-establishment allowed(RE):-

0- Yes

1- No

Max_retransmissions(MAXRET):-Numberof times the MS attempts to access the Network[1,2,4 or 7].

Tx-integer(TX):- Number of slots to spreadaccess retransmissions when a MS

attempts to access the system.Emergency call allowed:-

Yes/No.


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BCCH ARFCN Number(BAIND):- ARFCNsused for in a Bitmap of 124 bits

124 123 122 121

024 023 022 021 020 019 018 017

016 015 014 013 012 011 010 009

008 007 006 005 004 003 002 001


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The System Information Type 3 containsinformation on the identity of the current LA andcell identity, because a change means that theMS must update the network.

System Information 3 also as Control ChannelDescription parameters used to calculate thePaging group.

When the MS is in idle mode it decides which

cells to lock to. Information needed by the MS forcell selection is also broadcast in the Type 3information.


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8 7 6 5 4 3 2 1

1 1 1 1

LAC

LOCATIONAREAIDENTITTY(LAI)

MCCDIG 1MCCDIG 2

MCCDIG 1MNCDIG 1MNCDIG 2

CI

CI

CELL IDENTITY

LAC


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Control Channel Description

Attach / Detach(ATT):-0 = Allowed

1 = Not Allowed

bs_agblk:-Number of block reserved forAGCH [0-7] Ba_pmfrms:-Number of 51frame multi-frames between transmission ofpaging messages to MS of the same group

T3212:- Periodic location update timer .[1-255 deci hours].


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cch_conf Physical channels combined No. of CCH

0 1 timeslot(0) No 9

1 1 timeslot(0) Yes 3

2 2 timeslot(0,2) No 18

4 3 timeslot(0,2,4) No 27

6 4 timeslot(0,2,4,6) No 36


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Cell optionsDTX:-Whether Discontinuous

Transmission used or not.PWRC:-Power control on the downlink.

0 = Not used.1 = Used.

Radio linktimeout(RLINKT):-Radio link time-out

is the time before an MS disconnectsdue to failure in decoding SACCHmessage. Sets the timer T100 in the MS.


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Cell Selection ParametersRxlev_access_min:- Minimum

received signal level at the MS for which it ispermitted to access the system.

0-63 = -100dBm to 47 dBm.

Mx_txpwr_cch:- Maximum power the MSwill use when accessing the system.

Cell_reselect_hysteresis:- Used for cell

reselection. RACHControl Parameters.


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Location Area Identification.

Cell Selection ParametersRxlev_access_min:- Minimum

received signal level at the MS for which it ispermitted to access the system.

0-63 = -100dBm to 47 dBm.

Mx_txpwr_cch:- Maximum power the MSwill use when accessing the system.

Cell_reselect_hysteresis:- Used for cellreselection.


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RACHControl Parameters

max_retransmissions(MAXRET)tx_integer(TX)Cell barred for access(CB).

Re-establishment allowed(RE)Emergency Call Allowed

Access Control Class (ACC)


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CBCH Description(Optional) :

CHN:- This is the channel number for CBCH.

It is controlled internally in BSC.

TSC:- Training Sequence Code. BaseStation Color Code(BCC) part of BSIC is used.

CBCHNO:- Absolute RF channel number ofCBCH.

MAC:- Mobile Allocation in the cell, describesthe frequencies to be used in the hoppingsequence if frequency hopping is used.


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SYSTEM INFORMATION 4SYSTEM INFORMATION 4Hopping Channel(H):-Informs if CBCH

Channel is hopping or single.

ARFCN:- If H=0;MAIO:- If H=1, informs the MS where to

start hopping.Values [0-63].HSN:- If H=1,

informs the MS in what order thehopping should take place. Values[0 63].

HSN=0 Cyclic Hopping.MA:-Indicates which RF Channels are usedfor hopping. ARFCN numbers

coded in bitmap.


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Sent on the SACCH on the downlink to the MS indedicated mode.

On SAACH, the MS also receives informationabout the BCCH carrier in each neighboring cell.

This may differ from those sent in Systeminformation type 2.

It is also possible to have system InformationType 5 Bis and System Information Type 5Ter,

depending on the size of the BA list.


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Neighbor Cell Description:-

BA-IND:-Used by the Network todiscriminate measurements results related to

different lists of BCCH carriers sent by theMS(Type 2 or 5). Values 0 or1(different from type 2).

BCCH

Allocation number:-00-Band 0(current GSMband).


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BCCH ARFCN:-Neighboring cells ARFCNs.Sent as a bitmap.

0-Not used1-Used.

124 123 122 121

024 023 022 021 020 019 018 017

016 015 014 013 012 011 010 009

008 007 006 005 004 003 002 001


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Ms in dedicated mode needs to know if the LAhas changed.If so, it must perform locationupdating when the call is released.

MS may change between cells with different

Radio link timeout and DTX.

Cell Identity.

Location Area Identification.

PLMN permitted.


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Cell options:

DTX

PWRC

Radio Link timeout.


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SYSTEM INFORMATION 7/8SYSTEM INFORMATION 7/8

System Information Types 7 and 8 containCell Reselect parameters. Their function is

to supplement System Information Type4.


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GSM InterfacesGSM Interfaces (Um) Air interface - MS to BTS

A bis interface - BTS to BSC

A Interface - BSC to MSC B Interface - MSC to VLR

C interface - MSC to HLR

AUC


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MSC

BSC

VLRHLR

AUC

EIR

GMSC

MS

A Interface

A bis Interface

Air Interface

B InterfaceC Interface

F Interface

D InterfaceH Interface

To other

Networks


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GSM InterfacesGSM Interfaces

The interfaces between MSC and MS iscalled A, Abis and Um interfaces.

On these interfaces only three layers are

defined.They are not corresponding to theOSI (Open System Interconnection)model.


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A InterfaceA Interface

A interface between the BSC and the MSC

The A interface provides two distincttypes of information, signalling and traffic,

between the MSC and the BSC. The speech is transcoded in the TRC and

the SS7 (Signalling system) signalling istransparently connected through the TRC

or on a separate link to the BSC.


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Abis InterfaceAbis Interface

The A-bis interface responsible for transmittingtraffic and signalling information between theBSC and the BTS.

The transmission protocol used for sending

signalling information on the A-bis interface isLink Access Protocol on the D Channel (LAPD)


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(Um) Air Interface(Um) Air Interface

This is the interface between the mobile stationand the Base station.

The Air interface uses the Time Division

Multiple Access (TDMA) technique to transmitand receive traffic and signalling informationbetween the BTS and MS.

The TDMA technique is used to divide eachcarrier into eight time slots.These time slots are

then assigned to specific users,allowing up toeight conversations to be handledSimultaneously by the same carrier.


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7 56

34 12 0

1 2 43 5 76

Down Link

Up Link 0

Time Slot

This interface is the radio interface between themobile station and the network and uses layer

Three messages. On Layer three messages we have the division

of message types into CM (communication

Management), MM (Mobility Management), and

RR (Radio Resource Management).

Connection ManagementConnection Management


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Connection ManagementConnection Management(CM)(CM)

There are three entities within CM:

Call Control(CC) Which handles theprocedures concerning call control. e.g.setup,Change of bearer service.

Supplementary Service (SS) Which handlessuch as call bearing, call waiting , callforwarding etc.

Short Message Service (SMS) Enables theMS to handle short message transfer to and

from the network.


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Mobility Management (MM)Mobility Management (MM)

Mobility management handles functions forauthentication, location updating,

identification and others concerning themobility of the mobile station.


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Radio ResourceRadio Resource

Management (RR)Management (RR) It contains the functions concerning the radio

link. Here we find the capability toestablish,maintain and release the radioconnection between the network and the mobilestation, which includes the handover procedure.


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B InterfaceB Interface

The B interface between the MSC and the VLRuses the MAP/TCAP protocol.

Most MSCs are associated with a VLR, making theB interface "internal".

Whenever the MSC needs access to dataregarding a MS located in its area, it interrogatesthe VLR using the MAP/B protocol over the Binterface.


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C InterfaceC Interface

The C interface is between the HLR and a MSC.

Each call originating outside of GSM (i.e., a MSterminating call from the PSTN) has to go

through a Gateway to obtain the routinginformation required to complete the call, and theMAP/TCAP protocol over the C interface is usedfor this purpose.

Also, the MSC may optionally forward billing

information to the HLR after call clearing.


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D InterfaceD Interface

The D interface is between the VLR and HLR.

It uses the MAP/TCAP protocol to exchange thedata related to the location of the MS and to themanagement of the subscriber.


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E InterfaceE Interface

The E interface interconnects two MSCs.

The E interface exchanges data related tohandover between the anchor and relay MSCsusing the -MAP/TCAP+ISUP/TUP protocol.


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F InterfaceF Interface

The F interface connects the MSC to the EIR.

It uses the MAP/TCAP protocol to verify thestatus of the IMEI that the MSC has retrievedfrom the MS.


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G InterfaceG Interface

The G interface interconnects two VLRs ofdifferent MSCs.

It uses the MAP/G protocol to transfer subscriberinformation, during e.g. a location update

procedure.


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Encoding andEncoding andInterleavingInterleaving

of Informationof Information

SignalSignalinin

GSMGSM


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Topics for discussionTopics for discussion

Speech Encoding

Data Encoding

Interleaving for Voice,Control andData signals


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Speech Encoding cktSpeech Encoding ckt

Voice

Encoding

Channel

codinginterleaving

RF Modulation

Raw

Voice

signal


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Voice Encoding cktVoice Encoding ckt

Vocoder I/p20 msecspeech

blocks

13Kbps Vocoder Vocoder O/p260bits


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Channel codingChannel coding

Channel Coding is done to protectthe logical channels fromtransmission errors introduced by the

radio path. The coding schemes depend on the

type of the logical channels, hence

the coding can differ from speech,control and data .


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Channel Coding for speechChannel Coding for speech

Class class 1b class 2

1a

50 3 132 4 tailBits parity bits

Convolutionalcoder

coder, k=5

456 bits=378 bitsfromConvolutioncoder+ 78 class 2 bits

260bits


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Channel coding for SpeechChannel coding for Speech

The 260 bits of speech info from thevocoder is broken down into three parts.

Class 1a- 50 bits , these represent the

filter coefficients of the speech and are themost important for proper detection of thespeech at the receiver and hence aregiven maximum protection. 3 additional

parity bits are derived from the class 1abits for cyclic redundancy check (CRC).

Channel coding for SpeechChannel coding for Speech


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contdcontd

Class 1b - 132 bits are not paritychecked but are fed into theconvolutional coder along with 4 tail

bits which are used to set theregisters in the receiver to a knownstate for decoding purpose.

Class 2- 78 bits, these are not soimportant and are not protected butare combined with the output of theconvolution coder.


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Control Channel CodingControl Channel Coding

184 bits

Controldata

184 40 4 tail

Firecoded paritybits

ConvolutionalCoder

456bitsoutput


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Control Channel CodingControl Channel Coding

The control information is received inblocks of 184 bits.

These bits are first protected with a cycliccode called as Fire code, which is useful incorrection and detection of burst errors.

40 Parity bits are added, along with 4 tailbits.

These 228 bits are given to the CC whoseoutput is again 456 bits at a bitrate of22.8Kbps.

The control channels include the RACH,PCH, AGCH etc.

h l dh l d


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Data Channel CodingData Channel Coding

240 bits 4 tail

Data bits

ConvolutionalCoder

Output= 488 bits

AfterPuncturingOutput=456bits

Ch l C dCh l C d


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Data Channel CodingData Channel Coding

The data bits are received in blocks of 240bits. These are directly convolution codedafter adding 4 tail bits.

The output of the CC is now 488 bits,which actually increases the bitrate to24.4 Kbps.

To keep the bitrate constant on the airinterface we need to puncture the output

of the CC. Hence, we have a final bitrateof 22.8 Kbps again .

Ch l C di dCh l C di d


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Channel Coding contdChannel Coding contd

The above explanation was givenkeeping in view a full rate Traffic,Control, or Data channel.

For Half rate or Lesser rates thesame principle of channel codingholds good, with slight differences in

the encoding process.

I l iI l i


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InterleavingInterleaving

Having encoded the logical channelinformation, the next step is to buildits bit stream into bursts that can be

transmitted within the TDMA framestructure. This is the stage where theinterleaving process is carried out.

Interleaving spreads the content of

one information block across severalTDMA timeslots or bursts.

I t l i tdI t l i td


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Interleaving contdInterleaving contd

The following interleaving depths are used:

Speech 8 blocks

Control 4 blocks Data 22 blocks

The interleaving process for a speechblock is shown wherein which a 456 bit

speech block is divided into 8 blocks of 57bits each and each of these odd and even57 bit blocks are interleaved diagonally onto alternate bursts on the TDMA frame.


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Speech InterleavingSpeech Interleaving8* 57 bitseach= 456 bits

OfSpeechblockN

57

Even

OfN-1

57

Even

OfN

Speechblock

N-1

57

odd

OfN-1

57

odd

OfN

Thespeechisspreadover8 suchnormalburstsEachnormalburstconsistsoftwoblocksof57 bitspeech

fromdifferent 20msecblocks(sayN, N-1)alongwith

26bittrainingsequenceT and 2 flagF plus6startstopbits .

T+FT+FT+F

456bitspeechdata

C t l D t I t l iC t l D t I t l i


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Control Data InterleavingControl Data Interleaving

114 114 114 114

456bitscontroldata

Thecontroldataisspreadover4 blocksusingrectangular

interleavinginstead

of

diagonal

interleaving

as

in

speechthereceiverwillhavetowaitforatleast

2 multiframesbeforebeingabletodecodethecontrol

message

TDMA

Burstblocks

D t I t l iD t I t l i


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Data InterleavingData Interleaving

114 114 114 114

Burst 1 Burst 22Burst 2 Burst 3 Burst 4 Burst 19

First6

bitsFirst6

bits

Last6

bits

Last6

bits

456bitdatablock

D t I t l i tdD t I t l i td


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Data Interleaving contdData Interleaving contd

Here the data block of 456 bits is dividedinto 4 blocks of 114 bits each.

The first 6 bits from each of the 114 bitblocks is inserted in to each frame, the

second 6 bits from each of the 114 bitsinto the next frame and so on spreadingeach 114 block over 19 TDMA bursts whilethe entire 456 bits is spread over 22

TDMA bursts. Thus the data interleaving is said to have

a depth of 22 bursts.

D t I t l i tdD t I t l i td


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Data Interleaving contdData Interleaving contd

The reason why data is spread over suchalong period of time is that if data burst iscorrupted or lost, only a small part of it islost which can be reproduced at the

receiver. This wide interleaving depth does produce

a time delay during transmission but thatis acceptable since it does not affect the

data signal quality at the receiver, unlikespeech where delay could result in badquality of signal to the subscriber.

*Note The interleaving used in data is

diagonal interleaving.

I t l i Ad tI t l i Ad t


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Before Deinterleaving3 successiveburstscorrupted

After Deinterleaving

Thecorruptedburstsarespreadover alengthequaltothe

interleavingdepthsothattheeffectoftheerrorsisminimized.

Interleaving AdvantageInterleaving Advantage

Ai I t f Bit tAi I t f Bit t


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Air Interface BitrateAir Interface Bitrate

The information which is now coded andinterleaved at 22.8 Kbps now has to betransmitted over the Air interface to theBTS.

The information burst is not sent directly ,but is sent in ciphered form within a burstenvelope. This ciphering is done using

ciphering keys and algorithms known bothby the mobile and the BSS.

Ai Inte face Bit ate contdAi Inte face Bit ate contd


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Air Interface Bitrate contdAir Interface Bitrate contd

The Kc is the ciphering key and A5algorithm are applied to theinformation(speech or data) which

increases the bitrate to a final rate of33.8 Kbps from/to each mobile.

If we assume all 8 timeslots of the

cell to be occupied then the bitrate ofthe Air interface comes to 33.8 * 8=270.4 Kbps/channel.



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A5 Algorithm

KcInformation

Block22.8 Kbps

SentonAirinterface

Cipheredinformationburst

33.8 Kbps



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1 2 3 4 5 6 7 8

Mobile

Txsat33.8 Kbps

Cellrxs 8*33.8

KBps= 270.4 Kbps

PerTDMAframe

Cellcoveragearea

TDMAFn TDMAFn+1

Deinterleaving at theDeinterleaving at theReceiverReceiver


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ReceiverReceiver

At the receiver the reverse process ofDeinterleaving and decoding have to takeplace respectively, so as to recover theinformation from the signal.

After Deinterleaving the signal will bedecoded which is the reverse process ofthe Convolutional coding, using Viterbidecoders.

The decoder can recover lost or corrupteddata up to 4 successive bits, because thememory depth of the CC is 4(for k=5).

ChannelizationChannelization


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Frequency band has severalapplication segments

Certain blocks of the Band are

reserved for certain applications byregulating authorities

Technologies have decided their

frequency bands E.g. AMPS/DAMPS: 824-894 MHz

Channelization methodsChannelization methods


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Channelization methodsChannelization methods

Channelization can be done primarilyby three methods:

FDMA (Frequency Division MultipleAccess)

TDMA (Time Division Multiple Access)

CDMA (Code Division Multiple Access)

FDMAFDMATime

Power


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Frequency

Time

E.g. AMPS band is divided into 30KHz channels (1666 Freq. channels)

Television Channels (Star, Zee,Sony,..)

TDMATDMAi

Power


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E.g. AMPS has 3 timeslots on each30 KHz channel

Frequency

Time

CDMACDMA


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Frequency channel is divided intocode channels

E.g. in IS-95 CDMA, 1.228 MHz

channel is divided into 64 CodeChannels

Each user has a particular code

Codes are orthogonal to each other,do not interfere with each other

Duplex Access MethodsDuplex Access MethodsAmplitude


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F1 F2 Frequency

p

Time

Tx Rx

Frequency Division Duplex (FDD) Transmit on one frequency and

receive on another frequency

Time Division DuplexTime Division DuplexAmplitude


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pp

Time division duplex

Tx and Rx is on the same frequencybut on different times

F1 Frequency

Time

Tx

Rx

GSM AirInterfaceGSM AirInterface


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Separate Bands for Uplink and

DownlinkDownlink: 935-960Mhz (EGSM: 925-

960MHz)

Uplink: 890-915 MHz (EGSM: 880-915MHz) TDMA and TDMA Multiplex

124 Frequency Channels (ARFCN) forGSM900

1 to 124 fro current band

975 to 1023 for E-GSM

200kHz Channels

8 Mobiles share ARFCN by TDMA

GSM Air interface (1800)GSM Air interface (1800)


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GSM Air interface (1800)GSM Air interface (1800)

1800: Downlink: 1805-1880 MHz

1800: Uplink: 1710-1785 MHx

374 ARFCNs

Separation of 95 MHz

ARFCNs are numbered from 512 to885 inclusive


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Speech CoderSpeech Coder


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RPE/LTP coder(Regular Pulseexcitation/Long termPrediction)

Converts 64 kbpsspeech to 13 kbps

At the end we get13kbps speech i.e.

260 bits in 20 ms

20 ms blocks

Speech Coder

Bits Ordered

50 very

important

bits

132

important

bits

78 other

bits

Error CorrectionError Correction


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Type 1a 50 3(CRC)Type 1b 132 Type II 78

Reordering

25 66366 25 4 Type II 78Type 1a

Type 1b Type 1b

Type 1a

Tail

Half rate convolutional code

378 Type II 78

456 bits from 20 ms of speech

Diagonal InterleavingDiagonal Interleaving


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456 bits from 20ms of speech 456 bits from 20ms of speech

57 57575757575757 57 57575757575757

57 57 57 5757 57575757 5757 5757 5757 57

Traffic channel (TCH) bursts carry two 57bit blocks (114)

Each 120 ms of speech = 456*6 = 2736bits2736/114 = 24 bursts i.3. 24 framesMultiframe has 26 frames in 120ms.

There are 2 spare frames .. 1 SACCH, 1 Idle

Convolutional Coding andConvolutional Coding andInterleavingInterleaving


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Bits to be Tx ed: HELLO

Convolutionally encoded:HHEELLLLOO

Interleaved: EE HH LL LL OO

Bits Rx ed: EE HH LL LL OO

De-Interleaved: HHEELLLLOO

Viterbi Decoded: HELLO

Speech Coding ProcessSpeech Coding Process


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20 ms

Speech Coder

260 bits 13 kbps

0 1a 132 1b 78 II

Channel Coder

456 bits 22.8 kbps

Transceiver (BTS)

Transcoder Handler

260 bits

456 bits

16 kbps

TRAU frame260 + 60 = 320 bits

Abis

13 kbps

TRAU frameTRAU frame


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TRAU frameTRAU frame

260 bits info + 60 TRAU bits = 320bits/20ms = TRAU frame

60 bits contain frame Information

data which indicates speech, data,O&M, full rate/half rate

60 bits = 35 synchronization + 21

control + 4 timing

Midamble or Training BitsMidamble or Training BitsTail Bits

Control Bit Control BitTail Bits


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3 357 261 571 8.25

Data Midamble Data Guard

Period

8 midamble patterns (Colour codes) of 26 bits(BSIC)

RACH and SCH have longer 41 and 64 bitMidambles

Equalizer estimates channel impulse responsefrom midamble

Mathematically construct inverse filter

Uses inverse to decode bits

Downlink and UplinkDownlink and Uplink


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Downlink and UplinkDownlink and Uplink

Uplink lags downlink by 3 timeslots

Uplink and downlink use same

timeslot number Uplink and downlink use same

channel number (ARFCN)

Uplink and downlink use differentbands (45 MHz apart for GSM 900)

Measurements made by MSMeasurements made by MSand BTSand BTS


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and BTSand BTS

RxQual

0 < 0.2% 1 0.2 0.4 %

3 0.4 0.8 % 4 0.8 0.16 %

5 1.6 3.2 % 6 3.2 6.4 %

7 6.4 12.8 %

Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)

Uplink RXLEV (-48 to -110 dbm)Uplink RXQUAL (0-7)

Mobile Power ControlMobile Power Control


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Mobile Power ControlMobile Power Control

Path Loss

Power Command

Mobile is commanded to change itsTransmit Power

Change in Power is proportionate tothe Path Loss

Change in Power is done in steps of

2 dbs

Timing AdvanceTiming Advance


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TDMA approach requires signals toarrive at BTS at the correct time

A mobile at 30 km will be late by

100micro seconds Timing advance is in the range of 0-

62

One unit is 550m So maximum cell size is 63*0.55 =

~35 kms

Concepts of Channels in GSMConcepts of Channels in GSM


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Concepts of Channels in GSMConcepts of Channels in GSM

A company vehicle is used for severalpurposes in a day

Similarly in GSM, the timeslots are used for

different purposes at different times

Frames and MultiframesFrames and Multiframes

Control Channel Traffic Channel


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0 654321 7

3 Data 1Midamble1 Data 3 8.25 bits

156.25 bits 576.92 micro sec

4.615 ms

Time

Slot

Frame

0 50 0 25

Control Channel

Multiframe

Traffic Channel

Multiframe

GSM OperationsGSM Operations


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GSM OperationsGSM Operations

Location Update

MobileOriginated Call

MobileTerminated Call

Handover

SecurityProcedures

Cell Barring

DTX

Cell Broadcast

Short Message

Service

Emergency calls

Supplementary

Services

Roaming

Mobile Turn OnMobile Turn On


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Mobile Turn OnMobile Turn On

Mobile Searches for BroadcastChannels (BCH)

Synchronizes Frequency and Timing

Decodes BCH sub-channels (BCCH)

Checks if Network Allowed by SIM

Location Update

Authentication

Location AreaLocation Area


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Location AreaLocation Area

Location Area 1

Location

Area 2

BTS

BTS

BTS

BTS

BTS

BTSBTS

BTS

BSC

BSC

BSC MSC

Location Area IdentityLocation Area Identity


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Location Area IdentityLocation Area Identity

Location area is the area covered by one ormore BTSs where a mobile can move freelywithout updating the system

One Location area can be covered by oneor more BSCs, but ony one MSC.

MCC LACMNC

Importance of Location AreaImportance of Location Area


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Importance of Location AreaImportance of Location Area

Reduce Paging load

Resource Planning

Smaller Location Areas Locationupdate increases

Larger Location Areas Paging loadincreases

What is Location Update?What is Location Update?


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What is Location Update?What is Location Update?

MSC should know the location of theMobile for paging

Mobile is continuously changing

location area Mobile when changes Location Area

informs the MSC about its new LA

Process of informing MSC about newLocation area is Location Update

Types of Location UpdatesTypes of Location Updates


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ypes o oca o Up a esypes o oca o Up a es

1. Normal LocationUpdate

2. IMSI Attach

3. Periodic LocationUpdate

Hi,

I am in Location area

xxx

IMSI AttachIMSI Attach


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Mobile turns off and sends an IMSIDetach to MSC

Mobile turns on again and comparesLAI

If same, sends an IMSI attach toMSC

Is the received

LAI same as

before

Normal Location UpdateNormal Location Update


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pp

Mobile Turns on Power

Reads the new LAI

If different, does a Location Update

Is the received

LAI same as

before


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What happens at LocationWhat happens at LocationUpdate?Update?


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pp

Mobile changes location area

Reads the new Location Area from

BCCH

Sends a RACH (request for channel)

Gets a SDCCH after AGCH

Sends its IMSI and new and oldLAI in aLocation Update request to MSC onSDCCH

What happens at locationWhat happens at locationupdate cont..update cont..


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pp

.. . .

MSC starts Authentication

If successful, Updates the newLocation area for the Mobile in theVLR

Sends a confirmation to the Mobile Mobile leaves SDCCH, and comes to

idle mode

Mobile Originated CallMobile Originated Call


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gg

Channel RequestImmediate Assign

Service Request

Call Proceeding

Set Up

CipheringAuthentication

Alerting

Assignment

Connection

Mobile Terminated CallMobile Terminated CallPaging


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Channel RequestImmediate Assign

Set Up

Ciphering

Authentication

Paging Response

Assignment

Call Confirmed

Alerting

Connection

Security FeaturesSecurity Features


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yy

Authentication

Process to verify Authenticity ofSIM

Mobile is asked to perform anoperation using identity unique toSIM Ciphering

Process of coding speech forsecrecy

The speech bits are EXORed withbit stream unique to MS

Security Features (TMSISecurity Features (TMSIReallocation)Reallocation)


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))

GSMInfrastructure

Mobile

Location Update

TMSI Allocation

Call Setup

TMSI Reallocation

TMSI- Temporary Mobile Subscriber Identity

Security FeaturesSecurity Features(Identity Check)(Identity Check)


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( y )( y )

EIR

Sends IMEI

Identity Check

White listed /Grey Listed/ Black

Listed mobiles

HandoverHandover


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Cell 1 Cell 2

Handover is a GSM feature by which the

control/communication of a Mobile is transferredfrom one cell to another if certain criterias are

met. It is a network initiated process.

Criteria forHandoverCriteria forHandover


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Receive Quality (RXQUAL) on uplinkand downlink

Receive Signal Strength (RXLEV) on

uplink and downlink Distance (Timing Advance)

Interference Level

Power Budget

Handover DecisionHandover Decision


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BSC process the measurements reported byMobile and the BTS

BTS

BTS

BTS

BTS

BTS

BTS

Mobile has measurements of six neighbors

Handover Decision (cont..)Handover Decision (cont..)


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BSS performs averaging function onthese measurements every SACCH

frame (480ms)

Handover Decision algorithm is

activated after a set number ofSACCH frame periods by comparisonagainst thresholds

Types of HandoversTypes of Handovers


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INTRA-CELL HANDOVERS

INTER-CELL HANDOVERS

INTRA-BSC HANDOVERS

INTER-BSC HANDOVERS

INTER-MSC HANDOVERS

INTRAINTRA--CELLHANDOVERCELLHANDOVER


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C0

C1

Handover between timeslots of same frequency

Handover between different frequencies of the same cell

(to reduce interference)

MSC is not aware about this

InterInter--cell Handovercell Handover


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Handover between cells of the same BTS

BTS

Cell 1 Cell 2

InterInter--cell Handover (cont..)cell Handover (cont..)


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MSC is told about HO

BTS -> BSC -> MSC

Why MSC is informed?In case of change of LA, MSC may need

LAC for paging. As MS is busy, a linkalready exists. So, MSC can send a tone

in case of call waiting, and does notneed to page again.

This is needed also for billing and calltracing

INTRAINTRA--BSC HandoverBSC Handover


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MSC BSC

BTS

BTS

This HO takes place if the cell to which handover

is to be done belongs to the same BSC

Inter BSC HandoverInter BSC Handover


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MSC

BSC BTS

BTSBSC

The MSC is completely involved in this Handover

Inter MSC HandoverInter MSC Handover


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BSC

BSC

MSC

MSC

BTS

BTS

GMSC/

PSTN/

Backbone

In this case the handover takes place through the

interconnecting element which can be GMSC or

PSTN or private Backbone between the MSCs

Cell BarringCell Barring


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BTS

Cell Barring is a GSM feature by which certainmobiles could be barred access to certain cells

Cell barring is activated/deactivated at BTS level

Cell barring is done for mobile categories andpriorities

Cell BarringCell Barring


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Every mobile has an access class

The access class is stored in the SIM

Classes 0-9 are termed normal calsses

Classes 11-15 are emergency classes

Every cell has a set parameter which

defines which access classes arebarred for the particular cell. Thisparameter is broadcasted on theBCCH


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o ce c v yo ce c v yDetector)Detector)


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Senses for speech in 20ms blocks

Removes stationary noise

VAD is an energy detector

Compares Energy of filtered speechthreshold

It determines which 20ms blocks

contain speech and it only forwardsthose frames

Evaluation of BackgroundEvaluation of BackgroundNoiseNoise


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Background noise is always presentwith speech

DTX cuts off this noise with speech

Gives an uncomfortable feeling tothe listener

VAD takes care of this by inserting

comfort noise at the receiving endwhen speech discontinues.

Emergency CallsEmergency Calls


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GSM specs define 112 as anemergency number

112 is accessible with or without

SIM Without SIM it is sent on the bestchannel

Mobile on sensing 112 sets theestablishment cause toemergency call in the RACH

Routing of this call be done to a

Cell (Re)selectionCell (Re)selection


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Cell reselection is done using C1 pathloss criterion.

The purpose is to ensure that the MS

is camped on to the cell with thebest transmission quality.

The MS will camp on to the cell with

the highest C1 value if C1 > 0.

TheThe followingfollowing parametersparameters areare usedused totocalculatecalculate thethe CC11 criterioncriterion


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The received signal at the MS side. Rxlev_access_min - broadcast on

the BCCH - The minimum receivedlevel at the MS required for access tothe network.

Ms_txpwr_max_cch - themaximum power that an MS may use

when initially accessing the network. The maximum power of the MS

C1 = AC1 = A -- Max(B,0)Max(B,0)


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A = Received level Average -Rxlev_access_min.

B = MS_txpwr_max_cch - maximumoutput power of the MS

Cell Reselect HysteresisCell Reselect Hysteresis


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Cell reselection on the border of two locationareas result in a location update. When an MSmoves on the border of two location areas lots oflocation updates take place. To avoid theselocation updates, the reselect hysteresis isintroduced.

A location update is performed only if:

The C1 value of the new location area is higherthan the C1 value in the current location area

and

The received signal strengths have at least adifference of the reselect hysteresis.


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Cellular conceptCellular concept

Why to use the cellularWhy to use the cellularconcept ?concept ?


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Solves the problem ofSpectralcongestion and user capacity bymeans offrequency reuse.

Offers high capacity in a limitedspectrum allocation.

Offers system level approach, usinglow power transmitters instead of a

single, high power transmitter (largecell) to cover larger area.

A portion of the total channels


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po t o o t e tota c a e s

available is allocated to each basestation.

Neighboring base stations are

assigned different groupschannels, in order to minimizeinterference.

Cell shapeCell shape


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1-Omni-directional cell-site (Omni-directional antenna).

2-Rhombus-shaped sectors(Directive antenna).

3-Hexagonal shaped sectors(Directive antenna).

Cell sizeCell sizeLarge cell : (up to 70km in diameter)


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Large cell : (up to 70km in diameter)It exists where :1-Radio waves are unobstructed.2-Transmission power can cover the area.3-low subscriber density.

Small cell : (up to 2km in diameter)It exists where :

1-Radio waves are obstructed.

2-Low transmission power to decreaseinterference.

3-High subscriber density.

Types of cellsTypes of cells1-Macro-cells 2-Micro-


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1 Macro cells 2 Microcells.

3-Pico-cells. 4-Umbrella-cells.

What is a cluster ?What is a cluster ?


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A cluster is agroup of cells.

No channels are

reused within acluster.

It is the unit of

design.

Cluster sizeCluster size


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Definition : It is The number ofcells per cluster

N = i^2 + ij + j^2Where :

i = 0, 1, 2.& j = 0,1,2. etc.

N = 1 , 3 , 4 ,7, 9 , 12 ,

Types of clustersTypes of clusters


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1-N=7 omni frequency plan (2-directional).

2-N=7 trapezoidal frequency plan

(1-directional).3-N=9 omni frequency plan.

4-Tricellular plans

a) N=3 tricellular plan (3/9).b) N=4 tricellular plan (4/12).

C anne assignmentC anne assignmentstrategiesstrategies


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Considerations :1) Max. capacity.2) Min interference.3) Perfect handover.

Types of assignment strategies :1) Fixed :

Each cell has permanent predetermined set ofvoice channels.

New calls served by unused channels of this cell.

Borrowing strategy if all channels are occupied.High probabiltity that call is Blocked if channels

are occupied.( disadv.)

2) Dynamic :

Channels are not allocated to different


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cells permanently.

Each new call BTS requests newchannel from MSC.

MSC allocate a channel, by using analgorithm that takes into account:

1- Frequency is not already in use.2- Min. reuse distance to avoid co-

channel interference.

Adv. of dynamic assignment


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strategy :

1) Increase channel utilization

( Increase trunking efficiency ).

2) Decrease probability of a blockedcall.


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Frequency reuseFrequency reuseConceptConcept


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Reuse clusterReuse cluster


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CoCo--channel Reuse ratiochannel Reuse ratio(Q)(Q) ::


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R : cell radius.

D : reuse distance.

Q = D/R. =sqrt(3N).

Where :

N : cluster size


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Handover

Handover

Definition : procedure that allowsMS to change the cell or time-slot


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to keep as good link as possibleduring all the call.

Types of handoverTypes of handover


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IntraCell : bet. 2 channels of samecell.

InterCell : bet. 2 channels of 2

different cell & same BTS.

InterBTS (intra BSC) : 2 cells ofdifferent BTS Same BSC.

InterBSC : bet. 2 cells of differentBSCs & same MSC.

Measurements beforeMeasurements beforehandoverhandover


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1- Measurements from MSto BSC :a) Strength of BTS signal.

b) Quality of BTS signal.

c) Signal strength of 6 neighbor BTSs.

2-Measurements from BTSto BSC :

a) Strength of MS signal.b) Quality of MS signal.

c) Distance between serving BTS &MS.

Different causes ofDifferent causes ofhandoverhandover

Different causes of

Handover


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Bettercell HOEmergency HO

Level QualityPBGT

TrafficcausesInterferenceDistance

Basic handover algorithmsBasic handover algorithms


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a)Min. acceptable performancealgorithm:

MS power is increased whenquality deceases till handover isthe only way.

b) Power budget algorithm:

Prefer direct handover whenquality deceases withoutincreasing MS power first .

Handover priorityHandover priority


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1) UL quality cause (orinterference).

2) DL quality cause (orinterference).

3) UL level cause.

4) DL level cause.

5) Distance cause.

6) Better cell cause.


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InterferenceInterference

Sources of interferenceSources of interferenceinclude:include:


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1) Another mobile in the same

cell.2) A call in progress in theneighboring

cell.3) Other BTSs operating in thesame frequency band.

Interference effectsInterference effects ::


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In voice channel causes crosstalk

In control channels it leads missed

and blocked calls due to errors in thedigital signaling.

Main types ofMain types ofinterference :interference :


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1) Co-channel interference.

2) Adjacent channelinterference.

1) Co1) Co--channel interferencechannel interference


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Source : Near cell using samefrequency.

It is a function ofreusedistance(D/R).

General rule :

io = No. ofco-channel interfering cells.

S = Signal power from a desired BS.Ii= interference power caused by the

ith interfering co-channel cell BS.

Another form :

C/I = 10 log {(1/n)(D/R)*m}


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Where :

m = propagation constant(deps on nature of environment)

n = number of co-channelinterferers.

Can be minimized by :Choosing minimum reuse distance

= (2.5.3)(2R).

2) Adjacent channel2) Adjacent channelinterferenceinterference


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Source : A cell using a frequencyadjacent to the one in another celldue to imperfect recievers filter.

General rule : ACI= -10Log[(d1/d2)*m] Adj ch isolation.


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Can be minimized by :

1-careful filtering2-careful channel assignments

3-Directional antenna.

Where :d1: distance between MS &

proper BTs d2: dist. Bet MS & adjBTS causing interference.

Adj ch isolation = Filterisolation = - 26db.


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Traffic engineeringTraffic engineering

theorytheory

Why do we need toWhy do we need toknow traffic?know traffic?


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The amount of traffic during peak

hours allows us to dimension our

wireless system for a certain GOS.

GOS : probability of having a callblocked during busy hour (blockrate).

Traffic intensity (E)Traffic intensity (E)


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Erlang : A unit of traffic intensity

measure.

1 Erlang = 1 circuit in use for 1 hour.

T ( in Erlangs) = [No. of calls perhour*average call holdingtime(sec.)] / [3600]

Typical traffic profileTypical traffic profile


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Traffic tablesTraffic tables


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Blocked calls are notheld

Erlang BTable

Blocked calls are held inthe queue indefinitely

Erlang CTable

Blocked calls are held inthe queue for a time =the mean holding time

PoissonTable

ErlangErlang B tableB table

( ) [ ( )* ( ) ]


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P(N;T) = [ (T^N)*exp(-T) ]/ N!

GOS2%

GOS1%

N

0.2230.1532

1.0930.8694

5.0844.4610

13.18212.020

30.99729.040

TrunkingTrunking


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Sharing channel among severalusers.

Trunking efficiency (nT) :Measures the number ofsubscribers that each channel in

every cell can accommodate.

nT = (traffic in Erlangs / no. of


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System capacitySystem capacity

S : total duplex channels available for use= k*N


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Where:N : cluster size.k : No. of channels / cell.

C : total No. of duplex channels insystem;

C = M*k*N.

Where :M : No. of times the cluster is

Improving systemImproving systemcapacitycapacity


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Cell splitting.

Sectoring.

Cell splittingCell splitting


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SectoringSectoring

W di ti l t i t d


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We use directional antennas insteadof being omnidirectional

What does sectoringWhat does sectoringmean?mean?


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We can now assign frequency setsto sectors and decrease the re-usedistance to fulfill :1) More freq reuse.

2) Higher system capacity.

3) Improve S/I ratio ( better signal quality ).

How S/I ratio is improved?-e.g. In 120 degree sectoring theres only

2 interferers instead of 6 incase ofomnidirectional N=7 cluster.


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Directional frequency reuseDirectional frequency reuse


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Here we use7/21 pattern for

frequencyallocation.


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Comparison betweenComparison between

various types ofvarious types ofclustersclusters

N = 7 omni frequencyN = 7 omni frequencyplan :plan :


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n = 6 , m = 4.

D / R = 4.583.

1) Co-channelinterference ratio :

C / I = 18.6 dB.

2) Adjacent channelinterference :

ACI = -26 dB @ d1=d2.

N = 7 trapezoidalN = 7 trapezoidalfrequency planfrequency plan


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n = 2 , m = 4.

D / R = 6.245.

1) Co-channelinterference ratio :

C / I = 28.8.

2) Adjacent channelinterference : disappearsbecause the channels areassigned alternatively tothe cells.

Trunking efficiency :

312 one direction voice channels


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312 one direction voice channelsN = 7

312 / 7 = 44.57 ~ 44 ch./cell.

From Erlang-B table @ GOS = 2%

T = 35 E.

nT = 35 / 44 = 79.55 %.

N = 9 omni frequency planN = 9 omni frequency plan

n = 4 m = 4


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n = 4 , m = 4.

D / R = sqrt ( 3 * 9 )= 5.2.

1) Co-channelinterference :

C / I = 22.6 dB.

2) Adjacent channelinterference :

ACI = -38 dB @ d2= 2 (d1).

Trunking efficiency :

312 one direction voice channels

N = 9


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N = 9 312 / 9 = 34.67 ~ 34 ch./cell.

From Erlang-B table @ GOS = 2%

T = 25.529 E. nT = 25.529 / 34 = 75.085 %.

Conclusion : nT 7 > nT 9

But C/I 7 > C/I 9

ACI 7 > ACI 9

4 / 12 cell pattern4 / 12 cell patternn = 1 , m = 4.

D / R t (3* 4)


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D / R = sqrt (3* 4)= 3.732.

C / I = 22.87 dB.

Trunkingefficiency :

No. of channels/cell

= 312 / 12 = 26ch./cell.

From Erlang-B table@ GOS = 2 %.

T = 18.4 E/cell.

3 / 9 cell pattern3 / 9 cell patternn = 1 , m = 4.

D / R = sqrt (3* 3) = 3


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D / R = sqrt (3* 3) = 3.

C / I = 19.1 dB.

Trunking efficiency : No. of channels/cell

=312 / 9 = 34 ch./cell.

From Erlang-B table @

GOS = 2 %. T = 25.5 E/cell.

nT = 25.5 / 24 = 75 %.

120 degree cell sectoring120 degree cell sectoringn = 2 , m = 4.

D / R = sqrt(3 * 7) =


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D / R = sqrt(3 * 7) =4.583.

Co-channel interference :

C / I = 23.436 + 6dB(due

to isolation) = 29.436 dB.

Trunking efficiency:

No. of channels/cell = 312

/ 21 = 14.857. From Erlang-B @ GOS=2%

T= 8.2003.

nT = 8.2003 / 14.857

=56.216%.

References :

Motorola CP02

NOKIA SYSTRA


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NOKIA SYSTRA


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