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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SYSTEM INFORMATION 1SYSTEM INFORMATION 1
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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SYSTEM INFORMATION 1SYSTEM INFORMATION 1
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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SYSTEM INFORMATION 2SYSTEM INFORMATION 2
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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SYSTEM INFORMATION 2SYSTEM INFORMATION 2
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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SYSTEM INFORMATION 2SYSTEM INFORMATION 2
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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SYSTEM INFORMATION 2SYSTEM INFORMATION 2
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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SYSTEM INFORMATION 3SYSTEM INFORMATION 3
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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SYSTEM INFORMATION 3SYSTEM INFORMATION 3
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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SYSTEM INFORMATION 3SYSTEM INFORMATION 3
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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SYSTEM INFORMATION 3SYSTEM INFORMATION 3
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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SYSTEM INFORMATION 3SYSTEM INFORMATION 3
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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SYSTEM INFORMATION 3SYSTEM INFORMATION 3
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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SYSTEM INFORMATION 4SYSTEM INFORMATION 4
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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SYSTEM INFORMATION 4SYSTEM INFORMATION 4
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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SYSTEM INFORMATION 4SYSTEM INFORMATION 4
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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SYSTEM INFORMATION 5SYSTEM INFORMATION 5
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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SYSTEM INFORMATION 5SYSTEM INFORMATION 5
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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SYSTEM INFORMATION 5SYSTEM INFORMATION 5
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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SYSTEM INFORMATION 6SYSTEM INFORMATION 6
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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SYSTEM INFORMATION 6SYSTEM INFORMATION 6
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.
Air Interface Bitrate contdAir Interface Bitrate contd
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Air Interface Bitrate contdAir Interface Bitrate contd
A5 Algorithm
KcInformation
Block22.8 Kbps
SentonAirinterface
Cipheredinformationburst
33.8 Kbps
Air Interface Bitrate contdAir Interface Bitrate contd
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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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