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DISCUSSION TOPICS
• 2 G System Architecture
• 2.5 G
• 3G
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GSM – GLOBAL SYSTEM FOR MOBILE COMMUNICATION
Nizar ZARKA 2005
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Global System for Mobile
( Group Special Mobile )
G S MG S M
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HISTORY GSM• Early 80’s Several first generation analog cellular
systems in Europe but incompatible - limited roaming
• 1987-1989 ETSI standards for pan-European Global System for Mobile Communications (GSM, originally Group Special Mobile) at 900 MHz– 1992 GSM is launched– 1990-1993 Standards for Digital Cellular System at
1800 MHz (DCS 1800, recently renamed GSM 1800; US version is PCS 1900)
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Building Blocks
• AMPS – Advanced Mobile Phone System
• TACS – Total Access Communication System
• NMT – Nordic Mobile Telephone System
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Building Blockscontd.
AMPS – Advanced Mobile Phone System
• analog technology
• used in North and South America and approximately 35 other countries
• operates in the 800 MHz band using FDMA technology
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Building Blockscontd.
TACS – Total Access Communication System
• variant of AMPS
• deployed in a number of countries
• primarily in the UK
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HISTORYcontd.
• GSM criteria – – Good subjective speech quality– Low terminal and service cost– Support for international roaming – one system for all of
Europe– Ability to support handheld terminals– Support for range of new services and facilities– Enhanced Features– ISDN compatibility– Enhance privacy– Security against fraud
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GSM: History
• 1982 CEPT (Conference of European Posts and Telegraphs) establishes Groupe Speciale Mobile
• Motivation develop European mobile network• Support European roaming and interoperability in
landline• Increase system capacity• Provide advanced features• Emphasis on STANDARDIZATION, supplier
independence• Low cost infrastructure and terminals
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GSM: History
• 1989 European Telecommunications Standardization Institute (ETSI) takes over standardization• changes name: Global System for Mobile Communication• 1990 First Official Commercial launch in Europe• 1992 first paying customers were signed up for service• By 1993 there were 36 GSM networks in 22 countries• Early 1994 there were 1.3 million subscribers worldwide• 1995 GSM Specifications ported to 1900 MHz band• By 1996 there were more than 25 million subscribers
worldwide• GSM is the most popular 2G technology
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GSM Market
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GSM System Architecture
PSTN
Data Terminal
HLR/VLR
MSCBSC
OMC(Operation & Maintenance
Center)
OperationTerminal
BTS
HandsetA
X.25
A-bis SS7
Network sub-system PSTNRadiosub-system
Mobilestation
UM
SIMcard
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GSM System Architecture
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Functional Architecture
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GSM System Architecture
VLR = Visitor Location Register AUC = Authentication Center
BTS = Base Transceiver Station HLR = Home Location Register
ADC = Admission Data Center EIR = Equipment Identity Register
OMC = Operation Maintenance Center
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Radio Station Subsystem (RSS)
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System ArchitectureMobile Station (MS)
The Mobile Station is made up of two entities:
1. Mobile Equipment (ME)
2. Subscriber Identity Module (SIM)
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BTS Base Transceiver Station. The BTS comprises the radio transmission and reception devices, and also manages the signal processing related to the air interface.
BSC Base Station Controller. The BSC manages the radio interface, mainly through the allocation, release and handover of radio channels.
MSC Mobile Switching Centre. The MSC is basically an ISDN-switch, coordinating and setting up calls to and from MSs.
GSM General Architecture
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VLR Visitor Location Register. The VLR contains all the subscriber data, both permanent and temporary, which are necessary to control a MS in the MSCs coverage area
HLRHome Location Register. The HLR database is used to store permanent and semi-permanent subscriber data; as such, the HLR will always know in which location area the MS is (assuming the MS is in a coverage area), and this data is used to locate an MS in the event of a MS terminating call set-up.
GSM General Architecture
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The AuC database contains the subscriber authentication keys and the algorithm required to calculate the authentication parameters to be transferred to the HLR.
AuC: Authentication Centre
GSM General Architecture
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System ArchitectureMobile Station (MS) contd.
Mobile Equipment
• Produced by many different manufacturers• Must obtain approval from the
standardization body• Uniquely identified by an IMEI
(International Mobile Equipment Identity)
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International Mobile Equipment Identity ( IMEI )International Mobile Equipment Identity ( IMEI )
TAC = Type Approval CodeFAC = Final Assembly CodeSNR = Serial NumberSP = Spare
IMEI = TAC + FAC + SNR SP+
6 digits 2 digits 6 digits 1digit
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System ArchitectureMobile Station (MS) contd.
Subscriber Identity Module (SIM)
• Smart card containing the International Mobile Subscriber Identity (IMSI)
• Allows user to send and receive calls and receive other subscribed services
• Encoded network identification details• Protected by a password or PIN• Can be moved from phone to phone –
contains key information to activate the phone
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International Mobile Subscriber Identity ( IMSI )International Mobile Subscriber Identity ( IMSI )
IMSI = MCC + MNC + MSIN
NMSI
3 digits 2 digits
Not more than 15 digits
MCC = Mobile Country CodeMNC = Mobile Network CodeMSIN = Mobile Station Identification NumberNMSI = National Mobile Subscriber Identity
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GSM Security:The SIM card (Subscriber Identity Module)
• Must be tamper-resistant• Protected by a PIN code (checked locally by the SIM)• Is removable from the terminal• Contains all data specific to the end user which have to reside in the Mobile Station:
– IMSI: International Mobile Subscriber Identity (permanent user’s identity)– PIN– TMSI (Temporary Mobile Subscriber Identity)– Ki : User’s secret key – Kc : Ciphering key – List of the last call attempts– List of preferred operators– Supplementary service data (abbreviated dialing,– last short messages received,...)
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System ArchitectureBase Station Subsystem (BSS)
Base Station Subsystem is composed of two parts that communicate across the standardized Abis interface allowing operation between components made by different suppliers
1. Base Transceiver Station (BTS)
2. Base Station Controller (BSC)
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System ArchitectureBase Station Subsystem (BSS) contd.
Base Transceiver Station (BTS)
• Houses the radio transceivers that define a cell• Handles radio-link protocols with the Mobile Station• Speech and data transmissions from the MS are recoded• Requirements for BTS:
ruggednessreliabilityportabilityminimum costs
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System ArchitectureBase Station Subsystem (BSS) contd.
Base Station Controller (BSC)
• Manages Resources for BTS• Handles call set up• Location update• Handover for each MS
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Base Transceiver Station and Base Station Controller
• Tasks of a RSS are distributed over BSC and BTSBTS comprises radio specific functionsBSC is the switching center for radio channels
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System ArchitectureNetwork Subsystem
Mobile Switching Center (MSC)
• Switch speech and data connections between:Base Station ControllersMobile Switching CentersGSM-networksOther external networks
• Heart of the network• Three main jobs:
1) connects calls from sender to receiver2) collects details of the calls made and received3) supervises operation of the rest of the network components
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System ArchitectureNetwork Subsystem contd.
• Home Location Registers (HLR)- contains administrative information of each
subscriber(IMSI,Services,,)- current location of the mobile
• Visitor Location Registers (VLR)- contains selected administrative information from the HLR- authenticates the user- tracks which customers have the phone on and ready to receive
a call- periodically updates the database on which phones are turned
on and ready to receive calls
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System ArchitectureNetwork Subsystem contd.
• Authentication Center (AUC) - mainly used for security- data storage location and functional part of the network- Ki is the primary element
• Equipment Identity Register (EIR)- Database that is used to track handsets using the IMEI
(International Mobile Equipment Identity)- Made up of three sub-classes: The White List, The Black List
and the Gray List- Optional database
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Authentication and Encoding
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Cryptographic algorithms of GSM
R Ki
A3 A8
R S Kc Triplet
Random number User’s secret key
A5 Ciphering algorithm Authentication
Kc: ciphering keyS : signed resultA3: subscriber authentication (operator-dependent algorithm)A5: ciphering/deciphering (standardized algorithm)A8: cipher generation (operator-dependent algorithm)
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Ciphering in GSM
A5
CIPHERINGSEQUENCE
PLAINTEXTSEQUENCE
Kc FRAME NUMBER
Sender(Mobile Station or Network)
Receiver(Network or Mobile Station)
CIPHERTEXTSEQUENCE
A5
CIPHERINGSEQUENCE
Kc FRAME NUMBER
PLAINTEXTSEQUENCE
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Authentication Procedure in GSM
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Ciphering Procedure in GSM
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Authentication principle of GSMMobile Station Visited network Home network
IMSI/TMSI
IMSI (or TMSI)A8 A3
Ki R
Kc S
IMSI
Triplets (Kc, R, S)
TripletsAuthenticate (R)
A8 A3
Ki R
Kc S’ Auth-ack(S’)S=S’?
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A3/A8
K1/Kc Rand(From MSC)
SRES
A3/A8
K1/Kc
SRES
MS MSC
Compare
Authentication & Encryption
Authentication/Encryption
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GSM 900GSM 900
890 900 910 920 930 940930 950 960 Freq
45 MHz
Uplink ( Mobile to Base )
Downlink ( Base to Mobile )
25MHz/200KHz=124 channels 124 channels
25 MHz
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GSM Frequency RangeGSM Frequency Range
• 890 - 915 MHz Uplink / MS Transmit
• 935 - 960 MHz Downlink / MS Receive
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880 900 910 920 930 940930 950 960 Freq
45 MHz
Uplink ( Mobile to Base )
Downlink ( Base to Mobile )
174 channels 174 channels
890
35 MHz10 MHz
EGSM 900EGSM 900
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GSM1800GSM1800
1710 1735 1760 1785 1800 1825 1850 1875 Freq
95 MHz
Uplink ( Mobile to Base )
Downlink ( Base to Mobile )
374 channels 374 channels
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Channel Numbering
• In 900 MHz band: 890-915 MHz Uplink band, 935-960 MHz Downlink
Radio carrier is a 200kHz channel=> 125 pairs of radio channels
Called Absolute Radio Frequency Channel Number (ARFCN)
ARFCN numbers given by f(n) = 890 +.2n MHz for Uplink band n = 0,…124
Corresponding downlink is f(n) + 45 MHzChannels and ARFCN slightly different in other frequency
bands
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Channel Numbering
• In EGMS 900 : 880-915 MHz Uplink band, 925-960 MHz Downlink
=> 174 pairs of radio channels ARFCN numbers: 974-1023
f(n) = 890 +.2(n –1024) MHz for Uplink n =975,…1023
Corresponding downlink is f(n) + 45 MHz
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Channel Numbering
• In GMS 1800 : 1710-1785 MHz Uplink band, 1805-1880 MHz Downlink
=> 374 pairs of radio channels ARFCN numbers: 512-885
f(n) = 1710 +.2(n –511) MHz for Uplink n =512,…885
Corresponding downlink is f(n) + 95 MHz For GSM 1900: Same but shifted 100MHz
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Cell Planning• Reusing frequencies
in different geographic areas:– 7 cell repeat pattern
is typical, but other patterns are also common
A3 A1A2
G3 G1G2 C3 C1
C2
B3 B1B2
F3 F1F2
D3 D1D2
E3 E1E2
G3 G1G2
F3 F1F2
C3 C1C2
A3 A1A2
B3 B1B2
E3 E1E2
D3 D1D2
7-cell reusepattern
Frequencyreuse
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Cell Patterns
1
323
27
16
45
K=3K=7
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Cell Patterns
4
15
63
7 27
16
45
K=7
Distance=2.5-3 Times Cell DiameterMaximum cell diameter 35Km
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Cell Types
Micro Cell
Cell
A
B
C
Selective Cell
Umbrella Cell
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TDMA Frame Structure TDMA Frame Structure
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GSM - TDMA/FDMA
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Time Division Multiple Access (TDMA)Time Division Multiple Access (TDMA)
5 6 7 0 1 2 3 4 5 6 7 0 1 3 42
0.577ms
4.6ms
MS Only transmits at its own timeslot Speed 9.6Kb/s
ON ON
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Power
GSM 900 GSM 1800MS 2W(33dBm) 0.8W(29dBm)BTS 40W(47dBm) 20W(43dBm)
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Power Time TemplatePower Time Template
542.8 us / 147 Bits
10 8 1010 8 10Time
Power
-70
0
dB
Upper Limit
Lower Limit
Actual
us
Normal Burst
Bit rate= 270Kb/s
5dBm30dBm
Power= 0. 1mW1W
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GSM Physical Channels
::
Frequency 124
Frequency 2
Frequency 1 Ch 1
Timeslot 1
Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
::
2 3 4 5 6 7 8
TDMA frame = 4.615 ms
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Uplink & DownlinkUplink & Downlink
Downlink / MS Receive
5 6 7 0 1 2 3 4 5 6 7 0 1 3 42
0 6 7 0 1 2 3 4 5 6 71 3 42
Uplink / MS Transmit
5
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GSM: FDD Channels
Uplink and Downlink channels have a 3 slot offset – so that
MS doesn’t have to transmit and receive simultaneously
MS can also take measurements during this offset time and delay
between next frame
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Frequency HoppingFrequency Hopping
MOD
Coupler
Switch
Synth
Register
ControlUplink
BS 1 BS 2MonitoringRX LevRX Qual
Downlink 1
65
124
1
65
124
Home BS
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Registration in the Network
• Channel Request• Channel Activation• Channel Activation Ack• Channel Assignment• Location Update Req• Authentication request• Authent Response• Comparison• Assign Area&TMSI• Ack of new Area &TMSI• Entry into VLR-HR• Channel Release
Action MS BTS BSC GMS VLR HLR
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Mobile Originated Call Establishment
• Channel Request• Channel Assignment
• Call Est. Request• Authentication Req.• Auth. Response• Ciphering Command• Ciphering complete• Setup message,indicating the number• Call proceeding,Net routes call to numb.• Assignment of the traffic channel• Assignment complete
•MS BTS Action
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Mobile Originated Call Establishment
• Alerting,the called number-ringing• Connect, the called party accepted the call• Connect Ack., both can talk• Exchange of speech data
•MS BTS Action
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GSM operation from speech Input to Output
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GSM Speech Coding
4 KHz
300Hz-3.4KHz
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• Regular pulse excited - long term prediction (RPE-LRP)
• speech encoder (RELP speech coder)
LPC: linear prediction coding filter : Vocal Model
LTP: long term prediction – pitch + input: Excitation
RPE: Residual Prediction Error: Additional tuning
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Speech Generation
LPC: linear prediction coding filter : Vocal Model
LTP: long term prediction – pitch + input: Excitation
RPE: Residual Prediction Error: Additional tuning
FilterLPC
Excitation:LTP Periodic+RPE: tuning
Speech
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Error protection for speech signals in GSM
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Convolution code
+ +
+++
input
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Interleaving Format
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Enhanced Full Rate Voice Channel Coding
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Structure of normal BurstTail: 3 bits *2 guard time (bits to 0). It covers the period of uncertainty during the ramping up & down of the power burst from mobile
Coded Data: 57 bits*2
Stealing flag: indication to receiver if burst carries signaling or data
Training sequence: Receivers synchronization with burst (multipath fading)
Guard Period: time
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Multipath
Mobile
BTS
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Modulation
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Example of MSK
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S(t) = d(t) cos (t/2T) cos 2ft + d(t) sin (t/2T) sin 2ft.
GMSKGMSK ModulationModulation
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GMSK ModulationGMSK Modulation
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GSM Radio Interface Um Bursts
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ZürcherHochschuleGSM Radio Interface UmTypes of BurstStructure of Normal Burst• 2 x 3 Tail Bits (TB)• 2 x 1 Stealing Flag (Switch between Traffic / Control Payload)• 2 x 57 Payload Bits• 26 Bits Training Sequence :Fixed bit sequence used for channel
estimation allowing optimum channel equalization Five Different Types of Burst• Normal Burst - Traffic and Control Payload• Frequency Correction Burst - All Zeroes Sequence:sine wave(mobile
synchronize with the system), send it by the network to Ms during fixed interval. It allows to synch the MS clock with System clock
• Synchronization Burst - Special Fixed Sequence: Allows Ms to synchronize with the base station.
• Random Access Burst - Extended Guard Period of 68.25 Bits (252 s):MS transmit it at random times & only when MS has to access to the network
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Burst Types
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GSM Logical Channel Structure
CCH
TCH/F(13Kb/s)
TCH/H
BCH CCCH DCCH
FCCH SCH BCCH PCH AGCH RACH
TCH
ACCH SDCCH
FACCHSACCH
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Logical Channels
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GSM Logical Channels
• 2 groups of logical channels, TCH, CCH and CBCH
• TCH is used to carry voice or data traffic• CCH is used for control functions
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GSM Logical Channels, cont..
• TCH:Traffic channels = full rate (TCH/F) at 13 kb/s
or half rate (TCH/H) at 6.5 kb/s
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GSM Logical Channels, cont..
• CCH consists of 3 groups of logical control channels, BCH, CCCH and DCCH
• BCH (broadcast channel): point-to-multipoint downlink only. Contains three sub-channels, BCCH, FCCH and SCH– BCCH (broadcast control channel): send cell
identities, organization info about common control channels, cell service available, etc
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GSM Logical Channels
– FCCH (frequency correction channel): send a frequency correction data burst containing all zeros to effect a constant frequency shift of RF carrier
– SCH (synchronization channel): send TDMA frame number and base station identity code to synchronize MSs
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GSM Logical Channels, cont…
• CCCH (common control channel): Consists of three sub-channels, PCH, AGCH and RACH. This channels is used for paging and access – PCH (paging channel): to page MSs– AGCH (access grant channel): to assign
MSs to stand-alone dedicated control channels for initial assignment
– RACH (random access channel): for MS to send requests for dedicated connections
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GSM Logical Channels, cont…
• DCCH (dedicated control channel): bi-directional point-to-point -- main signaling channels. Consist of two sub-channels, SDCCH and ACCH– SDCCH (stand-alone dedicated control
channel): for service request, subscriber authentication, equipment validation, assignment to a traffic channel
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GSM Logical Channels, cont…
– SACCH consist of two sub-channels, SACCH and FACCH• SACCH (slow associated control channel):
for out-of-band signaling associated with a traffic channel, eg, signal strength measurements
• FACCH (fast associated control channel): for signaling on a traffic channel, eg, for handoff messages
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MS Camp on Flow ChartMS Camp on Flow Chart
MS Turn On
MS searches channelsand orders by signalstrength
MSStrongest
BCCH
FCCH on BCCH and adjusts timebase
SCH on BCCH and fine tunes timebase & timing
Decode BCCH & store info
Is BCCHin PLMN ?
MSNext Strongest
BCCH
YES
NO
YES
NO
NO
Location =Previous Location?
YES
YES
MS camped on - listens for page, can request service
Using SACCH - adjust power, TA & report RX Qualetc
MS goes to the assigned SDCCH ( Freq., timeslot, ... )for authentication + location Update
MS sendsRACH
BS assigns SDCCH to MS using the CCCH
MS = Mobile StationBCCH = Broadcast Control ChannelFCCH = Frequency Correction ChannelSCH = Synchronization ChannelPLMN = Public Land Mobile Network
SDCCH = Stand Alone dedicated Control ChannelSACCH = Slow Associated Control ChannelCCCH = Common Control ChannelRACH = Random Access Channel
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GSM Signaling / Traffic ChannelsGSM Signaling / Traffic Channels
SIGNALING TRAFFICBASE STATION
SIGNALING TRAFFIC
BCCH CCCH DCCH TCH
FCCH SCH PCH RACH AGCH SDCCH SACCH FACCH
MOBILE STATION
Network Ident.LAIBA listSystem parameters
MS searchesfor the strongestBCCH and locksonto it
MS adjusts its frequency
MS in idle mode listens to the CCCH
MS Sync. tothe network
MS receivespaging requests
MS sendsAccess requests
messages
BS sends Access GrantedMessage
Main SignallingChannel duringa period of TCH
MS measure-ment results
Fast SignallingChannel
Signalling afterAccess to network Granted
Speech / Data
BCCH = Broadcast Control Channel CCCH = Common Control Channel DCCH = Dedicated Control Channel TCH = Trafic Channel
FCCH = Frequency Correction ChannelSCH = Synchronization Channel
PCH = Paging ChannelRACH = Random Access ChannelAGCH = Access Grant Channel
SDCCH = Stand Alone Dedicated Control ChannelSACCH = Slow Associated Control ChannelFACCH = Fast Associated Control Channel
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Originated CallOriginated Call
BS pages MS usingthe CCCH MS sends RACH
BS ORIGINATED CALL
MS ORIGINATED CALL
MS responds withRACH
BS assigns MS to SDCCH
or TCH
MS transmits and receives speech on TCH
TCH
Using the FACCH onTCH authentication &location update
Using the SDCCH, authentication,call setup, and TCH assignment
Using the SACCH, BS commands MS to adjust power + timing, MS
reports power + Rx quality of BCCH + adjacent BCCH
MS transmits + receives speechon TCH
Using the SACCH on TCH, MSreports power + Rx quality , BScommands MS to adjust power ,TA
During inactive timeslots, MS measures adjacent cells, BCCH
Call disconnected by MS or BS
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Call Operation Types
Registration
Upon powering up, the MS scans common control channels and locks onto channel with strongest signal- Searches for FCCH on RF carrier, finds SCH to synch up
After synchronization the MS decodes BCCH – decides whether to update location register or not.
Once registered or locked on to BCCH
Mobile Originating (MO) Call
Mobile types in number presses Send
Mobile Terminating (MT) Call
Mobile registered and phone On – received incoming call
GSM Call Management
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GSM Registration
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GSM Registration
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MTC/MOC general behavior
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GSM MOC Calling from MS
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GSM MTC Calling to MS
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GSM MTC Calling to MS (cont)
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Call Setup (MS terminating)
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Dedicated Control ChannelsDedicated Control Channels are bidirectional point-to-pointchannels, that allow authentication, signaling, handover and the exchange of measurement values:
• Stand Alone Dedicated Control Channel (SDCCH) used for call setup (authentication, signaling, assignment of actual TCH), localization updates
• Slow Associated Control Channel (SACCH):is always coupled with a SDCCH or TCH and is used for the exchange of measurement values and control parameters Downlink : Control of MS Power Level and MS Timing Advance Uplink : Measurement reports (MS reception levels) used by the BTS for its handover-decisions
• Fast Associated Control Channel (FACCH): is activated in case of increased signaling demand e.g. during handover.
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Broadcast Channels
BCH: Broadcast Channels are used for synchronization purposes and broadcasting of cell-specific information in the downlink from BTS to MS
• Broadcast Control Channel (BCCH): broadcasts general information on
the BTS as well as cell specific information like cell identification, Services…
• Synchronization Channel (SCH): carries information for frame synchronization of the MS (e.g.TDMA frame number FN) and for identification of the BTS (e.g Base Station Identity Code BSIC)
• Frequency Correction Channel (FCCH): carries information for frequency correction of the MS
•
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Mapping of Logical onto Physical Channels
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Common Control Channels• CCH:Common Control Channels are point-to-multipoint
channels used mainly for access control:
• Paging Channel (PCH) - downlink onlyused by the BTS for paging and localizing the MS
• Random Access Channel (RACH) - uplink onlyused by any MS to request allocation of a signaling
channel
• Access Grant Channel (AGCH) - downlink onlyused to allocate a SDCCH or directly a TCH
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GSM Radio Interface UmMapping of Traffic Channels (TCH)
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Traffic Channels (TCH)