SlideShare a Scribd company logo
1 of 158
Download to read offline
ObjectivesObjectives
Understand Concept of Cellular
Understand the functional blocks in a GSM Network
Understand the Air Interface with Channels
Understand Mobile Call Setup Operations
Basics
Agenda
Need for Cellular
Introduction to Cellular
Channelization Concept
GSM Evolution and Markets
GSM Network Arhcitecure
GSM Air Interface Parameters
GSM Speech Coding
Physical and Logical Channels
Frames and MultiFrames
GSM Basic Operations
Telephony
Communication is today's basic need
Telephone has become part of life
Fixed Line Telephones
What are the drawbacks ?
Fixed Line Telephones
No Mobility
Delay in New Connections
Security Hazards
Prone to Failures ( Line Disconnection, etc
)
Very less value added services
Mobile Communications
Drawbacks of Fixed Phones have triggered
wireless communications
"Call People , Not Places ""Call People , Not Places "
MCG Spokane Division RTEd Sem, 1000-1268 9/93
Company ConfidentialH
First Wireless Signal
3
Postcard: Chicago Daily News
Wireless Access Methods
Authoring Division Name File Name
Security Notice (if required)
H
Wireless Communication Model
Source
Display
Transmitter
Receiver
Media of transmission is Radio Frequency
Authoring Division Name File Name
Security Notice (if required)
H
Types of Wireless Communications
Simplex
The direction of transmission is in one direction only
BEEP
Ex : Broadcast Services ( AM/FM Radios, Television )
Paging Services
Authoring Division Name File Name
Security Notice (if required)
H
Types of Wireless Communications
Half - Duplex
The direction of transmission is alternate in both directions
Tx
Rx
Tx
Rx
"A
"
"B
"
A transmits -- B receives, then
B transmits -- A receives
Ex : PTT Handsets, Trunked Radios
Authoring Division Name File Name
Security Notice (if required)
H
Types of Wireless Communication
Duplex
The direction of transmission is simultaneous in both directions
Ex : Cordless Telephones, Mobile Phones, Microwave Radios
Is there separate frequency of transmission at both ends ?
Authoring Division Name File Name
Security Notice (if required)
H
The Electromagnetic Spectrum
MICROWAVE
S
AMBROADCASTRADIO
SHORT-WAVE
RADIO
MOBILE
RADIO
VHF
TV
FMBROADCAST
RADIO
MOBILE
RADIOVHF
TV
FIBEROPTICS
COMMUNICATION
VISIBLE
LIGHT
1MH
z
10MH
z
100MH
z
1GHz 10GH
z
100
GHz
10
12
1
0
14
1
0
15
M
F
H
F
VH
F
UH
F
SHF EH
F
1µ
m
1000
m
100
m
10
m
1
m
10c
m
1cm 1m
m
Wireless Communication !!! At what frequency ?
Authoring Division Name File Name
Security Notice (if required)
H
Selection of Band for Wireless
Communication
MF : 300 KHz - 3 MHz ( Domestic Radios )
HF : 3 MHz - 30 MHz
VHF : 30 MHz - 300 MHz ( FM, Paging, PTT )
UHF : 300 MHz - 3 GHz ( Mobile Radios, Cordless Phones )
SHF : 3 GHz - 30 GHz ( Microwave Band )
Properties of Radio Frequencies
Low Frequency - Less Loss ,,, High Frequency - More Loss
To overcome loss , more power required,
More Power - Health hazards
Low Frequency - High Beamwidth - Wider and Deeper Coverage
Selection of Band will depend on Application
Frequency Band is subdivided into Application Band
Application Band is further divided into Technology Channels
Authoring Division Name File Name
Security Notice (if required)
H
Channelization
Frequency Band has several application segments
Certain blocks of the Band are reserved for certain applications by regulating
authorities and as well by standard Technologies
Technologies have decided on fixed bandwidth Channels within these bands
Example : Mobile Communications
AMPS / DAMPS : 824 MHz -- 894 MHz ( 50 MHz + 20 MHz separation)
GSM : 890 MHz -- 960 MHz -- ( 50 MHz + 20 MHz separation)
These 50 Mhz are bands are further divided into Channels
Channelization can be done by three methods
--- FDMA
--- TDMA
--- CDMA
Authoring Division Name File Name
Security Notice (if required)
H
Channelization Methods
FDM
A Power
Frequency
Time
FDMA
Ex: AMPS / DAMPS band is divided into 30 Khz Channels ( 1666 Freq Chs)
GSM band is divided into 200 Khz Channels ( 250 Freq Chs ).
Television Channels ( Star, Zee, Sony, MTV, BBC, CNN etc. )
Authoring Division Name File Name
Security Notice (if required)
H
Channelization Methods
Frequency
Power Time
FDMA/TDMA
TDM
A
Each FDMA Channel is divided into Timeslots
Each Timeslot is of fixed period
This method increases the number of Channels in a system
Ex: DAMPS has 3 timeslots on each 30 Khz Channel ( 4998 Channels)
GSM has 8 timeslots on each 200 Khz Channel ( 2000 Channels )
Authoring Division Name File Name
Security Notice (if required)
H
Channelization Methods
CDMA
FrequencyCDMA
Power
Time
Frequency Channel is divided into Code Channels
1.25 MHz of FDMA Channel is divided into 64 Code Channels
Authoring Division Name File Name
Security Notice (if required)
H
Mobile Telephony -- Channelization
Mobile Telephony needs Duplex Communication
How many Channels will be required for one call ?
What type of Channels ?
-- FDMA, TDMA, FDMA/TDMA , FDMA/CDMA or something
else
Authoring Division Name File Name
Security Notice (if required)
H
Duplex Access Methods
Frequency Division Duplex
(FDD)
Frequency
Amplitude
Time
F1 F2
Tx Rx
Time Division Duplex
(TDD)
Frequency
Amplitude
Time
F1
Tx
Tx
Rx
Rx
Introduction to Cellular
Communications
Need for Cellular
Cellular network has cells of different
sizes. Bigger cells are used where
subcriber density is low. Smaller cells are
used where subscriber density is high.
Cellular structure
High way
Cell Configuration
Omnidirectional Cell
BTS
Sectorial Cell
BTS
Frequency
Reuse
GSM uses concept of cells
One cell covers small part of network
Network has many cells
Frequency used in one cell can be used
in another cells
This is known as Frequency Re-use
F=1
F=2
F=3
F=4,8
F=5,9
F=6,10
F=7
F=1
F=2
F=3
F=4,8
F=5,9
F=6,10
F=7F=1
F=2
F=3
F=4,8
F=5,9
F=6,10
F=7
F= 1,2,3,4,5,6,7,8,9,10
Clusters
Co-Channel ( Re-use ) Cells
Distance between two cells
using same frequencies
1,13,29
D
D=R x SQRT( 3 x N )
N= Cluster size ( 7 in this case )
R=Radius of one cell
D=Dist between two cells using same channels
1,13,29
1,13,29
1,13,29
D R
Cell
Splitting
Macro Cell
Macro Cell
Micro
Cells
Micro
Cells
Pico Cell
Macro Cell
AuthoringDivisionName FileName
SecurityNotice(if required)H
Mixed Cell Structure
Macrocell
base station
Indoor
Picocell
Indoor
Picocell
Microcell
base stations
Microcell network
Macrocell network
Gsm basics
Authoring Division Name File Name
Security Notice (if required)
H
GSM TECHNOLOGY -
Standards & Implementation.
GSM900
DCS1800
Authoring Division Name File Name
Security Notice (if required)
H
GLOBAL System for Mobiles
GSM900
239 licenses in 109 countries now
44 million subscribers now
One New subscriber Every Second !
> 200 million subscribers by Year 2000
Authoring Division Name File Name
Security Notice (if required)
H
Personal Communications
Networks
USA: PCS1900
for new PCS
UK: DCS1800
Mercury One-2-One
Microtel-Orange
Germany:
DCS1800
E Net
France: DCS1800
For new PCN Australia: DCS1800
for new PCN
Thailand:
DCS1800
AIS
DCS1800
PCS1900
Hong Kong:
DCS1800
for 6 New PCNs
Authoring Division Name File Name
Security Notice (if required)
H
Evolution of GSM
GSM Requirements
Good subjective speech quality
Encryption of user information
Must operate in the entire 890 - 960 Mhz frequency band
Spectral efficiency
Support for international roaming
Minimize modifications to the existing fixed public networks
Low handsets and service cost
ISDN compatibility
Support for range of new services and facilities
Authoring Division Name File Name
Security Notice (if required)
H
The Global Standard
• Full Urban coverage in Western
Europe
• WW Roaming available
• Subscribers can utilize multiple
networks
• First dualband networks
appearing in Europe and Asia
• Full Urban coverage in Western
Europe
• WW Roaming available
• Subscribers can utilize multiple
networks
• First dualband networks
appearing in Europe and Asia
• Full Urban coverage in Western
Europe
• WW Roaming available
• Subscribers can utilize multiple
networks
• First dualband networks
appearing in Europe and Asia
Authoring Division Name File Name
Security Notice (if required)
H
Other GSM standards
GSM 900 and DCS 1800 use the same standards
DCS 1800 specs are defined as a delta standard to GSM specs
Same GSM switches can be used for DCS 1800
Some software upgrading may be required ( if RR are manged by switch )
Dual Mode handsets will be required to support both
PCS 1900
DCS 1800
ETSI has assisted ANSI T1 and
TIA TR-46 committees to formulate
specs for PCS 1900.
Authoring Division Name File Name
Security Notice (if required)
H
Evolution of GSM
1982 : Group Special Mobile formed within CEPT
1986 : A permenent Nucleus formed
1987 : Radio transmission Techniques are chosen.Field trials
completed
1987 : GSM becomes ETSI technical committee
1987 : 13 Operators sign a memorandum of uderstanding
1989 : Prototype ( validation ) systems are on the air
1990 : GSM Phase I specifications are finalised
1991 : UK,France,Germany andItaly introduce GSM services
1992 : Motorola cuts over the first commercial system built for
COMVIQ on Sept 1
1994 : GSM Phase 2 specifications released
1996 : GSM Phase 2+ specs are now defined
GSM Phase I specification document has 5230 pages !!!
• Full Urban coverage in Weste
Europe
• WWRoaming available
• Subscribers can utilize multip
networks
• First dualband networks
appearing in Europe and Asia
The History
Authoring Division Name File Name
Security Notice (if required)
H
Growth
• Full Urban coverage in Western
Europe
• WW Roaming available
• Subscribers can utilize multiple
networks
• First dualband networks
appearing in Europe and Asia
• Full Urban coverage in Western
Europe
• WW Roaming available
• Subscribers can utilize multiple
networks
• First dualband networks
appearing in Europe and Asia
• Full Urban coverage in Western
Europe
• WW Roaming available
• Subscribers can utilize multiple
networks
• First dualband networks
appearing in Europe and Asia
Authoring Division Name File Name
Security Notice (if required)
H
Technology Evolution
• Full Urban coverage in Western
Europe
• WW Roaming available
• Subscribers can utilize multiple
networks
• First dualband networks
appearing in Europe and Asia
• Ful l Ur ban cover age i n Wester n
Eur ope
• WW Roami ng avai l abl e
• Subscr i ber s can uti l i ze mul t i pl e
net w or k s
• Fi r st dual band netw or k s
appear i ng i n Eur ope and Asi a
Authoring Division Name File Name
Security Notice (if required)
H
GSM 2G+
• HSCSD - High Speed Circuit Switched Data
– Multiple TDMA timeslots allocated for data transmission
– Bandwidth on demand, up to 64kBit/s
– Compatible with existing GSM network infrastructure
• HSCSD - High Speed Circuit Switched Data
– Multiple TDMA timeslots allocated for data transmission
– Bandwidth on demand, up to 64kBit/s
– Compatible with existing GSM network infrastructure
• HSCSD - High Speed Circuit Switched Data
– Multiple TDMA timeslots allocated for data transmission
– Bandwidth on demand, up to 64kBit/s
– Compatible with existing GSM network infrastructure
Authoring Division Name File Name
Security Notice (if required)
H
IMT-2000 / 3G+
(International Mobile Telecommunications -2000)
• HSCSD-HighSpeedCircuitSwitchedData
–MultipleTDMAtimeslotsallocatedfordatatransmission
–Bandwidthondemand,upto64kBit/s
–CompatiblewithexistingGSMnetworkinfrastructure
• HSCSD-HighSpeedCircuitSwitchedData
– MultipleTDMAtimeslotsallocatedfordatatransmission
– Bandwidthondemand,upto64kBit/s
– CompatiblewithexistingGSMnetworkinfrastructure
Authoring Division Name File Name
Security Notice (if required)
H
GSM Standards structure
01 Series : General
02 Series : Service aspects
03 Series : Network aspects
04 Series : MS-BS interface and
protocols ( air interface layer 2 & 3)
05 Series : Physical layer on the Radio
path ( air interface layer 1)
06 Series : Speech coding specs.
Authoring Division Name File Name
Security Notice (if required)
H
GSM STANDARDS - Continued
07 Series : Terminal adaptation for
mobile stations
08 Series : BSS - MSC interfaces ( A &
Abis)
09 Series : Network interworking
10 Series : Empty - For future use
11 Series : Equipment and Type approval
specifications
12 Series : Operation & Maintenance
MS
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BSC
BSC
PSTN
VL
R
TRAU
HL
R EI
R
OMC
SMSC
BC
AUC
VMSC
MSC
Abis
A
OML
GSM Network Architecture
BTS
BTS
BTS
MS
MS
EIR
AUC
HLR
VLR
MS - Mobile Station
Mobile station provides user access to GSM network for Voice & Data.
All GSM mobiles comply to the GSM standards.
Subscriber data is read from a SIM card that plugs into MS.
Each MS has a unique number called as IMEI number, which is stored in EIR for authentication
purposes.
Mobile camps on to the GSM network through a BTS serving the cell.
Mobile also scans neighbouring cells and reports signal strength.
Network knows whereabouts of mobiles from HLR & VLR databases.
Mobile Transmit and Receive voice at 13 KB/s over air interface.
SIM
H GSM Course
Mobile Station Output Power
CLASS 1 20 watts Vehicle and Portable
CLASS 2 8 watts Portable and Vehicle
CLASS 3 5 watts Hand-held
CLASS 4 2 watts Hand-held
CLASS 5 0.8 watts Hand-held
Output Power determines:
---- Accessibility in areas of coverage
---- Talk time and Standby Time
Output Power on call is varied as commanded by BTS
MS - Mobile Station
H GSM Course
Mobile Station Identities
MSISDN : Human Identity used to call a Mobile Station
CC NDC SN
98 XXX 12345
IMEI: Serial number unique to every Mobile Station
TAC FAC SNR SP
6 digits 2 digits 6 digits 1digit
H GSM Course
SIM - Subscriber Identity Module
GSM
Removable Module inserted when the subscriber wants to use the MS
IMSI : Network Identity unique to a SIM
MCC MNC MSIN
404 XX 12345
3 digits 2 digits 10 digits
Two Sizes
Credit Card
Stamp Size
4-8 digits PIN code
3 false entries - blocks
8 digit PUK
10 false entries - disabled
MS
ROM = 6kb to 16kb
RAM = 128 byte to 256 byte
EEPROM = 3 kb to 8 kb
H GSM Course
SIM - Subscriber Identity Module
Contents of SIM
Serial Number
IMSI, Subscriber Key ( Ki )
Algorithms for Authentication, Ciphering
Network Code
PIN, PUK
Charging Information
Abbreviated Dialling
Supplementary Features ( e.g. call barring )
SIM features and contents are personalized by the Service Activator
MS also stores some temporary data on SIM during operation
H GSM Course
Base Station Cell Site Architecture
Mains
Power
Panel
DC
Power
Supply
Unit Battery
Backup
Abis
BTS
DMR
GSM Antenna System
BTS Cabin/Shelter/Room
AirCon
H GSM Course
BTS - Base Transceiver Station
BTS
MS
BSC MSC
CELL
BTS has a set of Transceivers to communicate with mobile's in its area
One BTS covers one or more than one cell
The capacity of a cell depends upon number of tranceivers in a cell.
BTS is connected to the BSC through Abis Interface, which is a 2Mb/s
BTS transmit and receive voice at 13 kbps over air interface to the mobiles.
BTS commands mobiles to set Tx. power, timing advance and Handovers
RF Channels
Abis - 2 MBits/s
H GSM Course
BTS Architecture 1
BSC
TxRx A Rx B
Splitter
Processor Modules
T
S
B
P P
PC
MInterface
Alar
mInterface
A1
TRX TRX
1 2
B1
A2
B2
T
R
A
U
BTS
COM
RFUBPF
Fr
R
e
f
H GSM Course
BTS Architecture 2
TRX Logic
TRX RF
Power
Amplifier
TRX Unit
PSU & Climate Control
Antenna
ABIS
over G703
Backplane
BTS Cabinet. 3 Channel. Single Sector
I Q
RF
I Q
Combiner / Distribution Unit
Rx FilterLNA
Splitter
Combiner
Duplexer
Coupler
Coupler
Interface
Frequency Reference
Unit
CPU
BTS
Alarms
NEM
Proprietary
Interface
H GSM Course
BSC - Base Station Controller
Several BTS's are connected to one BSC
BSC manages channel allocation,handovers and release of channels at connected BTS's
BSC connects to each BTS on an Abis interface & to the MSC on A interface
BSC has the entire database for all cell parameters associated with the BTS's.
MSC
Abis
A
H GSM Course
Base Station Controller
BTS
Processor Modules
P
C
M
P
C
M
P
C
M
T
S
B
P P
T
M
G
T
R
A
U
MSC
BSC
H GSM Course
Abis Interface
E1 / T1
Abis is a G.703 interface. It could be E1 or T1
Abis carrries Traffic information of all the mobiles in the cells controlled by
the BTS.
Abis also carriers signalling information between BTS and BSC
Signaling over Abis is done by LAPD protocols
LAPD has several modes of implementation
--- LAPD
--- LAPD Concentrated
--- LAPD Multiplexed
H GSM Course
Abis Interface
LAPD Modes
LAPD
Signaling for each TRX is on a dedicated 64 Kbps circuit
Maximum Signalling for 10 Transceivers on 1 E1 link
64 kbps 0 Sync
64 kbps 1 TRX Signaling
64 kbps 2 4 Traffic Channels
64 kbps 3 4 Traffic Channels
64 kbps 4 TRX Signaling
64 kbps 5 4 Traffic Channels
64 kbps 6 4 Traffic Channels
64 kbps 7 TRX Signaling
64 kbps 8 4 Traffic Channels
64 kbps 9 4 Traffic Channels
} 1 TRX
} 1 TRX
} 1 TRX
H GSM Course
Abis Interface
LAPD Modes
LAPD Concentrated mode 1
Signaling for 4 TRX's is on a dedicated 64 Kbps ciruit
Maximum Signalling for 13 Transceivers on 1 E1 link
64 kbps 0 Sync
64 kbps 1 4 x TRX Signaling
64 kbps 2 4 Traffic Channels
64 kbps 3 4 Traffic Channels
64 kbps 4 4 Traffic Channels
64 kbps 5 4 Traffic Channels
64 kbps 6 4 Traffic Channels
64 kbps 7 4 Traffic Channels
64 kbps 8 4 Traffic Channels
64 kbps 9 4 Traffic Channels
64 kbps 10 4 x TRX Signaling
} 1 TRX
} 1 TRX
} 1 TRX
} 1 TRX
H GSM Course
LAPD Modes
LAPD Concentrated mode 2
Signaling for All TRX's is on a dedicated 64 Kbps ciruit
Maximum Signalling for 15 Transceivers on 1 E1 link
64 kbps 0 Sync
64 kbps 1 ALL TRX Signaling
64 kbps 2 4 Traffic Channels
64 kbps 3 4 Traffic Channels
64 kbps 4 4 Traffic Channels
64 kbps 5 4 Traffic Channels
64 kbps 6 4 Traffic Channels
64 kbps 7 4 Traffic Channels
64 kbps 8 4 Traffic Channels
64 kbps 9 4 Traffic Channels
64 kbps 10 4 Traffic Channels
} 1 TRX
} 1 TRX
} 1 TRX
} 1 TRX
Abis Interface
H GSM Course
Abis Interface
LAPD Modes
LAPD Multiplexed
Signaling for each TRX is on 16kbps subchannel.
Maximum signalling for 15 TRX's on
64 kbps 0 Sync
64 kbps 1 TRX Signaling/ 3 Traffic Channels
64 kbps 2 4 Traffic Channels
64 kbps 3 TRX Signaling/ 3 Traffic Channels
64 kbps 4 4 Traffic Channels
64 kbps 5 TRX Signaling/ 3 Traffic Channels
64 kbps 6 4 Traffic Channels
64 kbps 7 TRX Signaling/ 3 Traffic Channels
64 kbps 8 4 Traffic Channels
64 kbps 9 TRX Signaling/ 3 Traffic Channels
64 kbps 10 4 Traffic Channels
} 1 TRX
} 1 TRX
} 1 TRX
} 1 TRX
} 1 TRX
TRAU - Transcoder / Rate Adaptation Unit
The MSC is based on ISDN switching. The Fixed Network is also ISDN based
ISDN has speech rate of 64kbps. Mobile communicates at 13 Kbps
TRAU converts the data rates between 13 KB/s GSM rate to 64 Kbits /s Standard ISDN rate
TRAU can be colocated with the BTS,BSC or MSC or it can be a separate unit.
MS
MS
RF Channels
BTS BSC
MSC
TRAU
Abis
interface
2 MBits/s
A
interface
2 MBits/s
13 KBits/sec
P
S
T
N
16 KBits/sec 16 KBits/sec 64 KBits/secVOICE
H GSM Course
LOCATION OF TRANSCODER
Colocated with MSC,BSC,BTS
Separate Unit
16 kbps
64 kbps
BSCTranscoderMSC
H GSM Course
MSC - Mobile Switching Centre
Exchange where calls are established,maintained and released.
Database for all subcribers and their associated features.
Communicates with BSC's on MS side and with PSTN on fixed line side.
MSC is weighted on the number of subcribers it can support
BSC's
BTS's
HLR
VLR
MSC
H GSM Course
MSC - Mobile Switching Centre
Multiple MSC's
BSC's
BSC's
MSC
MSC
GMSC
More subscribers ? More MSC's !
H GSM Course
HLR - Home Location Register
HLR
MSC has all subscriber database stored in HLR
HLR has all permanent subscriber database
MSC communicates with HLR to get data for subscribers on call
HLR will have the series of all subscriber numbers, which may not be activated or issued .
H GSM Course
VLR - Visiting Location Register
VLR
HL
R
A subscribtion when activated is registered in VLR
VLR has all the subscriber no's which are activated
VLR also has temporary database of all activated subscribers ( on/off, location )
MSC communicates with HLR for susbcribers coming from different MSC's
and if found valid, then registers them in its VLR
H GSM Course
AUC - Authentication Centre
HLR AUCMSC
MS
Authentification is a process by which a SIM is verified
Secret data and the verification process alogorithm are stored at AUC
AUC is the element which carries out the verification of SIM
AUC is associated with the HLR
H GSM Course
EIR : Equipment Identity Register
EIR is the Mobile Equipment Database which has a series of IMEI's
MSC asks the Mobile to send its IMEI
MSC then checks the validity of IMEI with the EIR
All IMEI are stored in EIR with relevant classfications
EI
R
MSC
Classifications of IMEI( Mobile Stations )
White List Grey List
Black List
H GSM Course
BC - Billing Centre
BC
BC Generates the Billing Statement for each Subscriber
BC may be directly connected to the MSC
MSC sents the billing information ( duration of call ) to BC
BC then produces the billing amount based on the units set
H GSM Course
OMC - Operations & Maintenance Centre
It is central monitoring and remote maintenance centre for all network elements
OMC has links to BSC's and MSC
OMC Terminals
BTS's
BTS's
BTS's
OMC System
BSC's
MSC
asasasaaaaa
aqwtttsssdfaa
qwrqrncnceas
asasasaaaaa
aqwtttsssdfaa
qwrqrncnceas
asasasaaaaa
aqwtttsssdfaa
qwrqrncnceas
H GSM Course
OMC - Operations & Maintenance Centre
BTS's
BTS's
OMC System
BSC's
MSC
asasasaaaaa
aqwtttsssdfaa
qwrqrncnceas
asasasaaaaa
aqwtttsssdfaa
qwrqrncnceas
OMC - R
OMC - S
H GSM Course
OMC - RADIO
BTS BTS BTS BTS
BSC BSC
TRANSCODER
MSC
MUX / DEMUX
SERVER OMC - R
X.25 SWITCH
H GSM Course
OMC - Functions
E nvironm ental Alarm s
P ow er , F ire, S ecurity,
Aircons, etc.
E quipm ent F ailure Alarm s
B TS , B S C site F ailures
M S C and pheripheral failures
A larm M on ito ring
Add new hardw are
M odify control param eters
other softw are changes.
C on figuratio n C hang es
C ell Traffic Analysis
N o of calls, o/g ,i/c
P S TN , C all drops etc.
P erfo rm ance A nalysis
O M C Fu nctions
H GSM Course
Equipment Alarms
BTS , BSC , Transcoder Failures
Link Failures
Module Failures ( Transceiver,Processors)
Network
BTS
A
Transceiver 1 Fail
17:35hrs Site A
Transceiver 1 Fail
H GSM Course
Cell Traffic
0
1
2
3
4
5
6
7
8
A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3
cell names
TCH TRAFFIC IN ERLANGS FROM 09:00 to 21:00hrs
1
H GSM Course
SMSC - Short Message Service Centre
Message is sent to a particular mobile.
Message transfer takes place through SMSC
Messages are be sent through a Manual Terminal connected to SMSC
SMSC
MSC
H GSM Course
VMSC : Voice Mail Service centre
VMSC
MSC
It has a database for all Voice Mail Subscribers
It also stores all the Voice Mail - Voice Messages
H GSM Course
GSM Signaling Interfaces
VLR
HLR/AU
C
EIR
PSTN GMSC GSMSC
VLR
HLR/
AUC
Abis A
B
C
F
E
G
D
SS7/R2
MSC
BSC
BTS
OML
OMC
A,B,C,D,E,F,G,H,I = SS7
Abis = LAPD
OML = X.25
SUPP
I
H
A GSM Cell
Broadcast
CHannel
Traffic
CHannel
UPLINK
890-915 MHz
DOW
NLINK
935-960 MHz
BTS
Abis
Interface
To BSC
BCH
TCH
Separate Bands for Uplink and Downlink
Down link : 935 - 960 MHz ( E-GSM 925 - 960 MHz )
Uplink : 890 - 915 MHz
( E-GSM 880 - 915 MHz)
TDMA and FDMA Multiplex
–124 Frequency Channels (ARFCN) for GSM900
– 1 to 124 for current band
– 975 to 1023 for E-GSM
–200kHz Channels
–8 Mobiles share ARFCN by TDMA
0.3 GMSK Modulation
–270.833 kbits/sec. rate
GSM Air Interface
TDMA and FDMA
1 2 3
4
5
6
7
3
4 5 6
7
0
1
2
Time
Frequency
Amplitude
ARFCN
Timeslot
Physical Channel is an
ARFCN and Timeslot
The GSM Burst
Guard
Period
Time
Frequency
Amplitude
Midamble
8.25
bits3
57 bits
1
26
bits
1
57 bits
3
Data
Tail
bits
Data
Control
bit
Tail
bit
Control
bit
Speech Coding
PSTN
Air Interface
PCM Coding - 64 KB/s
RPE-LTP Coding in GSM - 13 KB/s
RPE and LTP Coder ( Regular Pulse
Excited - Long Term Prediction )
RPE-LTP is a combination of RELP
and MPE-LTP codecs.
Coverts Speech to Low Data Rate
20ms Speech makes 260 Bits
Output 13 kbit/s
20 ms Blocks
Speech Coder
Bits Ordered
260 Bits
260 Bits
132 78
Important
Bits
Other
Bits
50
Very Important
Bits
Speech Coder - Defined under GSM TS 6.10
Block Code
132 7850Type Ia Type Ib Type II
Re-ordering
Half rate convolutional code
CRC
50 132 783
Type Ia Type Ib Type II
378 78
Type II
25 25 78466 663
TailCRC Type Ib Type IaType Ia Type Ib Type II
262 Bits in
456 Bits O
456
Bits from 20ms of Speech
Error Correction
Diagonal Interleaving
57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57
456
Bits from 20ms of Speech
456 Bits from 20ms of Speech
57 57 57 57 57 57 57 57 57 57 57 57 57 57
Traffic Channel (TCH) Bursts Carry Two 57 Bit Blocks (114) Each
120ms of Speech = 456x6 = 2736 bits
2736 / 114 = 24 bursts i.e. 24 frames (mobile Tx once per frame)
Multiframe has 26 frames in 120ms
There are 2 spare frames ......One SACCH, One Idle
TCH
Convolutional Coding &
Interleaving
HELLO FOLKS
HHEELLLLOO FFOOLLKKSS
ELSOLHLOFK LEOLSHOLKF
EL SOL HLOFK LEOLSHOLKF
HHEELLL -OO FFO -LLKK -S
HELLO FOLKS
Bits to be Txed:
Convolutionally
Encoded:
Interleaved:
Bits Rxed:
De-Interleaved:
Viterbi Decoded:
Convolutional
Encoder
Interleaver
De-
Interleaver
Decoder
Hello.....
Example:
Speech coding Process
20ms
Speech Coder
260 bits
50 132 78
1a 1b 11
Channel Coder
456 bits
13 kbps
22.8 Kbps
Tranceiver ( BTS )
22.8 Kbps
456 bits
260 bits
13 kbp
Transcoder Handler
260 + 60 = 320 bits
16 kbps
TRAU Frame
Abis
TRAU Frame
260 bits info + 60 TRAU bits = 320 bits/ 20ms = TRAU Frame
60 bits contains Frame Information data which indicates
speech,data,idle,O & M , full-rate/half-rate.
16 KbpsT =
T T T TSynch Sign
T0 T1 T2 T3 T30 T31
Abis
60 bits = 35 synchronization + 21control + 4 timing
8 Midamble Patterns (Colour Codes) of 26 bits
RACH and SCH have Longer 41 and 64 bit Midambles
Equalizer Estimates Channel Impulse Response From
Midamble
Mathematically Construct Inverse Filter
Uses Inverse to Decode Data Bits
Midamble or Training Bits
Timeslot
(normal burst)
Midamble
8.25
bits
357
bits
126
bits
1
57
bits
3
Guard
Period
Data
Tail
bits Data
Control
bit
Tail
bit
Control
bit
GSM TDMA Power Burst
+1.0 dB
-1.0 dB
+4 dB
-6 dB
-30 dB
-70 dB
-6 dB
-30 dB
-70 dB
147 "Useful" Bits
542.8µs
148 "Active" Bits, 546.42µs
3 57 1 26 1 57 3
10µs 8µs 10µs 10µs 10µs8µs
Power
Time
0.3 GMSK Modulation
Data
Frequency
Phase
+67.708 kHz
-67.708 kHz
270.833kB/s
+90deg -90deg
I
Q
Uplink Lags Downlink by 3 Timeslot periods
Uplink and Downlink use same Timeslot Number
Uplink and Downlink use same Channel Number (ARFCN
Uplink and Downlink use different bands (45MHz apart f
GSM900)
Downlink and Uplink
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1
25
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1
Downlink
Uplink
45 MHz
Measurements by MS and BTS
Uplink RXLEV ( - 48 to -110 dbm )
Uplink RXQUAL ( 0 - 7 )
Downlink RXLEV ( - 48 to -110 dbm )
Donwlink RXQUAL ( 0 - 7 )
RXLEV is the received power level
RXQUAL is the received quality.
It is the bit errorr measured on the M idamble
0
1 < 0.2 %
2 0.2 - 0.4 %
3 0.4 - 0.8 %
4 0.8 - 1.6 %
5 1.6 - 3.2 %
6 3.2 - 6.4 %
7 6.4 - 12.8 %
RXQUAL
Measuring Adjacent Cell BCH
Power
UPLINK
DJACENT CELL
BCH
DOWNLINK
RXLEV RXLEV RXLEV RXLEV RXLEV
Mobile Power
Control
Mobile is commanded to change its Transmit Power
Change in Power is proportionate to the Path Loss
Change is Power is done in steps of 2 dbs
Tx Level
5
6
7
.
14
15
Power dBm
33
31
29
.
15
13
Path LossLow RXLEV
Pwr Command
TDMA approach requires signals to arrive at BTS at
the correct time. They must not overlap.
BTS
Timing Advance
Concept of Channels in GSM
1. To pick up employees in the morning
2. To receive company guests from airport
3. To carry material to the site / stores
4. To Collect mail/courier
5. To drop the employees back home
6. To get a doctor in case of emergency
7. To carry company gusts for a dinner
If there were two vehicles, we can allocate a set of tasks
to one , and rest to the other. However, since both are
identicle vehicles, there is greater flexibility in usage.
Concept of Channels in GSM
A company vehicle is used for several purposes in a day..
0 1
5
6
7
4
2 3 4
0
1
2
3
FRAME NUMBER
TIM
E
SLOT
Time Sharing by Channels
FC
C
H
SC
H
B
C
C
H
B
C
C
H
B
C
C
H
TC
H
TC
H
TC
H
TC
H
TC
H
TC
H
TC
H
TC
H
TC
H
TC
H
Concept of Frames
C T T T T T T T
C T T T T T T T
C T T T T T T T
Frame No. 1
Frame No. 2
Frame No. 3
Time slot Number..
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
C T T T T T T T Frame No. 4
CHANNEL ALLOCATIONS IN A CELL
0
1
2
3
4
5
6
7
U1U1 U1 U1
U5 U5 U5 U5 U5 U5 U5 U5 U5
U2 U2 U2 U2 U2
U3 U3 U3 U3 U3 U3 U3
U4 U4 U4 U4 U4 U4 U4 U4
U6 U6 U6 U6 U6 U6 U6 U6
FRAME Number
U7 U7 U7 U7 U7
U8 U8 U8 U8
C CCCC C C C CC C C
Frames and
Multiframes
normal burst)
Control Channel Multiframe
Frame
Timeslot
156.25 Bits
8 Timeslot
Guard
Period
4.615ms
576.92 us
8.25
bits
3
57 bits
1
26
bits
1
57 bits
3 Data
Tail
bits
Data
Control
bit
Midamble
Tail
bit
Control
bit
0 1
2 3 4
5 6 7
0 50 0 26
Traffic Channel Multiframe
Channels in GSM Air Interface
PHYSICAL CHANNELS
ARFCNs - 1 to 124 ( D & U )
Timeslots - 0 to 7 ( D & U )
Total of 124 x 8 = 992 Channels
LOGICAL CHANNELS
ARFCN - X , Timeslot - Y
Frame Number - N
1 2 3
4
5
3
4 5 6
0
1
2
BCH -
BROADCAST
CHANNELS
DCCH -
DEDICATED
CONTROL
CHANNELS
CCCH -
COMMON
CONTROL
CHANNELS
CONTROL CHANNELS TRAFFIC CHANNELS
PCH -
PAGING
CHANNEL
FCCH -
Frequency
Correction
Channel
SCH -
Synchronisation
Channel
BCCH -
Broadcast
Control Channel
BC
H
SDCCH -
Standalone
Dedicated
Control
Channnel
SACCH -
Slow
Associated
Control
Channnel
FACCH -
FAST
ASSOCIATED
CONTROL
AGCH -
ACCESS
GRANT
CHANNEL
RACH -
RANDOM
ACCESS
CHANNEL
TCH - F
FULL RATE
TRAFFIC
CHANNEL
TCH -
TRAFFIC
CHANNEL
TCH - H
HALF RATE
TRAFFIC
CHANNEL
TC
H
One ARFCN, On all the time, in every cell
Uses Timeslot 0 on a channel, in
Downlink.
Allows Mobiles to tune to BTS freq. -
FCCH This channel carries a 142 bit
zero sequence and repeats once in every
10 frames on BCH
Allows Mobile to Synchronise - SCH
This channel carries the Frame
number and BSIC in encrypted data
format. Amidamble of 64 bits helps
mobiles to synchronize. SCH also repeats
once every 10 Frames.
Allows Mobiles to identify Network -
BCH - Broadcast CHannel
BCH
BCH Sub channels
FCCH
SCH
142 bits - all 0's3 3 8.25
Start
Bits
Stop
Bits
Guard
Bits
3
3 8.2539 3964
Training
Sequence
Guard
Bits
Stop
BitsStart
Bits
Encrypted
Data Bits
Encrypted
Data Bits
BCCH
3 3 8.25
Start
Bits
Stop
Bits
Guard
Bits
3 3 8.25
Start
Bits
Stop
Bits
Guard
Bits
3 3 8.25
Start
Bits
Stop
Bits
Guard
Bits
3 3 8.25
Start
Bits
Stop
Bits
Guard
Bits
BCH
57
57
57 57
57
57
57
57
26
26
26
26
CCCH shares Timeslot 0 with BCH on a
Multiframe
CCCH consists of PCH , RACH & AGCH.
PCH - Paging Channel is used to alert mobiles
on incomming calls. PCH carries IMSI to page
for Mobiles in the cell. PCH is Downlink
channel.
RACH - Random Access Channel - is a short
burst sent by mobile to BTS , to initiate a call
request . RACH uses Timeslot 0 on reverse
BCH channel on Uplink.
AGCH - Access Grant Channel - When mobile
sends a RACH to BTS, BTS responds by
CCCH - Common Control CHannel
BCH
Used by the MOBILE to get attention
from BASE STATION in the Uplink.
Several mobiles might originate RACH
simultaneously.
RACH uses a Slotted ALOHA access
scheme.
Mobile doesn't know path delay
–So RACH has to be a special SHORT
BURST
–Mobile sends normal burst only after
RACH - Random Access CHannel
8 3 68.2541 36
Extended
Guard Period
Stop
Bits
Start
Bits
Synchronisation
Bits
Encrypted
Data Bits
88 bits
BCH & CCCH - 51 Frame structure -
DOWNLINKFrame number ( DOWN LINK )
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
FCCH - Frequency correction Channel
SCH - Synchronisation Channel
BCCH - Broadcast Control Channel
AGCH - Access Grant Chan
PCH - Paging Channel
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
F S B B B B A A A A F S P P P P P P P P F S
F S F S I
0
1
2
3
0
1
2
3
Time
slots
BCH & CCCH - 51 Frame structure - UPLINK
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
R
A
C
H
R
A
C
H
R
A
C
H
R
A
C
H
Frame number ( UP LINK )
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
0
1
2
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
0
1
2
RACH - Random Access Channel
( A short burst is transmitted by mobile towards BTS on RACH)
Time
slots
DCCH - Dedicated Control Channel
Dedicated Control Channels have a TCH like allocation.
DCCH have three Sub Channels.
SDCCH - Standalone Dedicated Control Channel This
is used as an interim channel before final assignment of
TCH. SDCCH is used for signalling and Authentication
message transfers.
FACCH - Fast Associated Control Channel . FACCH is
used by BTS to command a handoff to the mobile. A
TCH frame is used up by FACCH , since handoff has to
take place on priority.
SACCH - Slow Associated Control Channel - SACCH
flows at a slower rate on Uplink & Downlink along with
TCH or SDCCH. During a call, SACCH flows once for
every 24 Frames of TCH .
SDCCH - Stand-alone Dedicated Control CHannel
USED DURING CALL SET-UP
Stepping Stone between BCH and TCH
Used for Authentication Etc.
SDCCHSDCCH
TCH
BCH BCH BCH
DOWNLINK ( BTS - MS )
–Mobile Tx Power Commands
–Mobile Timing Advance
–Cell's Channel Configuration
UPLINK ( MS - BTS )
–Received signal quality report
(RXQual)
–Received signal level report
(RXLev)
–Adjacent BCH power measurements
–Mobile's status
SACCH - Slow Associated Control CHannel
INTERRUPTS TCH ON UPLINK AND
DOWNLINK
Rapid message exchange for handovers
Control Bits either side of midamble:
–Indicate TCH ( 0 ) or FACCH ( 1 )
FACCH - Fast Associated Control CHannel
Miidamble
8.25
bits
357
bits
126
bits
1
57
bits
3
Guard
Period
Data
Tail
bits Data
Control
bit
Tail
bit
Control
bit
SDCCH - Combined Channel Config
( Shares Time slot 0 with BCH and CCCH )
Frame number ( DOWN LINK )
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Time
slots
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
F S B B B B A A A A F S P P P P P P P P F S D D D D
D D D D F S D D D D D D D D F S H H H H H H H H I
SDCCH ( D ) : Standalone Dedicated Control Channel
SACCH ( H ) : Slow Associated Control Channel
0
1
2
3
0
1
2
3
BCH & CCCH - 51 Frame structure - UPLINK
S
D
C
C
H
S
D
C
C
H
S
D
C
C
H
S
D
C
C
H
RA
CH
RA
CH
S
A
C
CH
SA
CC
H
SA
CC
H
SA
CC
H
SA
CC
H
SA
CC
H
SA
CC
H
SA
CC
H
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
R
A
C
H
R
A
C
H
R
A
C
H
R
A
C
H
Frame number ( UP LINK )
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
0
1
2
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
RA
CH
SD
CC
H
SD
CC
H
SD
CC
H
SD
CC
H
SD
CC
H
SD
CC
H
SD
CC
H
SD
CC
H
RA
CH
RA
CH
SD
CC
H
SD
CC
H
SD
CC
H
SD
CC
H
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
0
1
2
RACH - Random Access Channel
( A short burst is transmitted by mobile towards BTS on RACH)
Time
slots
8.25bits
357
bits
1
26
bits
1
57
bits
3
Guard
Period
Data
Tail
bits Data
Control
bit
Midamble
Tail
bit
Control
bit
TCH - Traffic Channel
One time burst
Traffic Channel carries the Voice data.
Two blocks of 57 bits contain voice data .
One TCH is allocated for every active call. While call is in
progress if there is degradation in quality of current channel,
BTS may shift the communication to another TCH on a different
Carrier and/or Time slot .
A Full rate TCH carries 13 KB/s voice data , and Half rate TCH
carries a 6.5 KB/s voice data.
156.25 bits or 576.92 uS
TCH Multiframe - TCH Full rate
26 Frames - 120 ms
24 Carry Speech, 1 Idle, 1 SACCH
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
T T A -T T T T T T T T T T T T T T T T T T T T T T
SACCH Idle
TCH Multiframe - TCH Half
rate26 Frames - 120 ms
24 Carry Speech , 2 SACCH
( shared by two mobiles - a & b )
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Ta Tb Aa AbTa Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb
SACCH-a SACCH-b
Click here to type bulleted text
F S B B B B A A A A A A A A F S P P P P D D D D D D
T T T T T T T T T T T T SA T T T T T T T T T T T T Idle
T T T T T T T T T T T T SA T T T T T T T T T T T T Idle
T T T T T T T T T T T T SA T T T T T T T T T T T T Idle
T T T T T T T T T T T T SA T T T T T T T T T T T Idle
T T T T T T T T T T T T SA T T T T T T T T T T T T Idle
T T T T T T T T T T T T SA T T T T T T T T T T T T Idle
T T T T T T T T T T T T SA T T T T T T T T T T T T Idle
Frame number
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
0
1
2
3
4
5
6
7
T - TCH SA - SACCH I - Idle
A delay of (12 * 8)+1 Timeslots
is kept between two successive
SACCH .
TCH and SACCH - FRAMES
Time
Slots
FRAMES
0
0
1
1
2
2
48
23
49
24
50
25
= 6.12 sec
1 Superframe = 51 x 26 CCH MF = 1326 TF
= 26 x 51 TCH MF = 1326 TF
1 Burst = 577usecs
0 1 2 3 4 5 6 7TDMA Frame = 8 bursts = 4.616 ms
0 1 2 23 24 25 0 1 2 48 49 50
Multiframe
TCH Multiframe = 26 TF = 120ms 1 CCH Multiframe = 51 TF = 234.6m
0 1 2 3 204
4
204
5
204
6
204
71 Hyperframe = 2048 Superframes = 2715648 TDMA Frames
= 3 hrs 28 min 53 sec 760 ms
TDMA approach requires signals to arrive at BTS
at
the correct time. They must not overlap.
BTS
Timing Advance
H
Timing Advance
T
B
Synch Seq
41 bits
Encrypted
bits 36
T
B
Guard Period
68.25 bp
63 bits
Timing Adv
5.25 GP
BSS calculates access delay from RACH in terms of bits
Informs Mobile to delay its timing in terms of bits
Maximum Timing Advance of 63 bits
RACH Burst
H
Mobile Maximum Range
Range = Timing Advance x bit period x velocity
2
Range = Distance between Mobile to Base Station
Timing Advance = Delay of Bits ( 0 -- 63 )
Bit period = 577 / 156.25 = 3.693 usecs = 3.693 x 10e-6 secs
Velocity = 3 x 10e5
Range = ( 63 ) x ( 3.693 x 10e-6 ) x (3 x 10e5)
2
= 34.9 kms
Hopping Traffic Channel
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
C1
C2
C3
C1
C2
C3
UPLINK
ADJACENT CELL
BCH
DOWNLINK
IREG
• PURPOSE: To test various call scenarios to provide reliable
Roaming services
• Various Call Scenarios
•Mobile to Mobile
•PSTN to Mobile
•Checking Announcements
•Call Forwarding
•SMS Test
•Combined Test
H
Mobile Searches for Broadcast Channels
(BCH)
Synchronises Frequency and Timing
Decodes BCH sub-channels (BCCH)
Checks if Network Allowed by SIM
Location Update
Authentication
Mobile Turn-On
BSC
MSC
Location Area 1
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BTS
BSC
BSC
BSC
Location Area 3
Location Area 2
Location Area
MCC MNC LAC
Location Area Identity
H
IMPORTANCE OF LOCATION AREA
Reduce Paging Load
Resource Planning
L.Area = 1 L.Area = 2 L.Area = 3
H
What is Location Update
MSC should know the Location of the Mobile for paging.
Mobile is continously changing Location Area.
Mobile when changes Location Area informs the MSC about its new L.A
Process of informing MSC about new Location Area is Location Update
L.Area = 1 L.Area = 2 L.Area = 3
Location Update
H
IMSI ATTACH
Mobile turns off and sends an IMSI Detach to MSC.
Mobile turns on again and compares LAI.
If same,sends an IMSI attach to MSC.
1. Normal Location Update.
2. IMSI Attach.
3. Periodic Location Update.
Types of Location Update
H
NORMAL LOCATION UPDATE
Mobile turns on power.
Reads the new LAI.
If different,does a Location Update.
H
PERIODIC LOCATION UPDATE
Mobile enters non-coverage zone.
MSC goes on sending Pages
Mobile has to inform MSC after a set period.
H
Location Update
Mobile Changes Location Area
Reads the new Location Area from BCCH
Sends a RACH ( request for channel )
Gets a SDCCH on AGCH
Sends its IMSI and new & old LAI in a Location Update Request to MSC on SDCCH
MSC starts Authentication
If successful, Updates the new Location area for the Mobile in the VLR
Sends a confirmation to the Mobile
Mobiles leaves SDCCH , and comes to idle mode
H
Mobile Originated Call
Channel Request
Immediate Assign
Service Request
Authentication
Set Up
Ciphering
Call Proceeding
Assignment
Alerting
Connection
H
MOBILE TERMINATED CALL
Channel Request
Immediate Assign
Authentication
Set Up
Ciphering
Call Confirmed
Assignment
Alerting
Connection
Paging
Paging Response
H
Security Features
Authentication
--- Process to verify the Authenticity of SIM
--- Mobile is asked to perform an operation using an
identity unique to SIM.
Ciphering
--- Process of coding speech for secrecy
--- The speech bits are EXORed with bit stream unique to MS
H
Security Features
TMSI Reallocation
Loc Upd ( IMSI )
TMSI Allocation
Call Setup ( TMSI )
TMSI Reallocation
H
Security Features
Identity Check
Identity Check ( IMEI )
Sends IMEI
EIR
White listed / Grey listed / Black listed ?????
H
HANDOVER
Cell 1 Cell 2
--- Handover is a process by which the control/communication
of a Mobile is transferred from one cell to another
H
CRITERIA FOR HANDOVER
Receive Quality (RXQUAL) on Uplink & Downlink.
Receive Signal Strength (RXLEV) on Uplink & Downlink.
Distance ( Timing Advance ).
Interference Level.
Power Budget.
H
Handover Decision
BSC processes the measurement reported by Mobile
and the BTS.
BSS performs averaging function on these measurements
every SACCH frame ( 480ms).
Handover Decision algorithm is activated after a set number of
SACCH frame periods by comparison against
Thresholds.
H
TYPES OF HANDOVERS
INTRA - CELL HANDOVER
INTER - CELL HANDOVER
INTRA - BSC HANDOVER
INTER - BSC HANDOVER
INTER - MSC HANDOVER
H
INTRA - CELL HANDOVER
- Handover between channels / timeslots of same cell
BTS
H
INTER - CELL HANDOVER
--- Handover between cells of same BTS
C0
C0
BTS
H
INTRA - BSC HANDOVER
MSC BSC
BTS
BTS
--- This type of Handover takes place if the cell to which
which handover is to be done belongs to the sameBSC.
--- In this the BSC handles everything without involving MSC.
--- The MSC will be informed by the BSC after Handover.
H
INTER BSC HANDOVER
MSC
BSC
BSC
BTS
BTS
--- In this type of Handover,the Mobile is handed over
to a cell which belongs to another BSC.
--- The MSC is completely involved in this Handover
H
GMSC
MSC BSC BTS
MSC BSC BTS
--- If the cell belongs to another MSC,then it is
Inter-MSC handover.
--- In this case the handover takes place through the
interconnecting element (PSTN) between the MSC's
INTER - MSC HANDOVER
H
WHAT IS CELL BARRING ?
BTS
H
Every Mobile has an access class .
Every cell defines the Mobile classes which are barred
access.
Cell Barring
USE OF CELL BARRING
--- Reserving Cells for Handovers.
--- Reserving Cells for a certain Mobile Class.
H
Both users talk alternately.
Each direction of Transmission is only 50 %
Transmitter is switched ON for useful information frames.
What is
DTX ?
H
Need for DTX
---- To increase Battery Life
---- To reduce the average interference level
DTX is done by DTX Handlers which
have the following functions.
H
Voice Activity Detector ( VAD )
Senses for speech in 20ms blocks
Removes stationary noise.
VAD is an energy detector.
Compares Energy of filtered speech threshold
H
Evaluation of Background noise
Background noise is always present with speech.
DTX cuts off this noise with speech.
Gives an uncomfortable feeling to the listener.
VAD takes care by inserting comfort noise.
H
CELL BROADCAST
Message is continously broadcasted in cell/or cells
Broadcast is done on SDCCH
BCCH informs the mobile the details of SDCCH for CBCH
Mobile tunes to SDCCH at certain intervals and reads messages
All Mobiles dont support this feature
H
Short Message Service
SMS
Centre
MSC/
VLR
BSC BTS
Short Message is sent to a particular Mobile Station
H
Emergency Calls
-- GSM Specs define ' 112' as emergency number
-- '112' is accessible with or without SIM
-- Without SIM it is sent on the best channel
-- Mobile on sensing '112' sets the establishment
cause to emergency call in the RACH
-- Routing of this call can be done to a desired
location defined in the Switch.
H
GSM Phase 2 features
Extended Frequency Band ( 50 more channels )
Multiple and Alternate Ciphering Algorithm
Half - Rate Coding
Compatibility with DCS 1800 Specifications
Enhancement of SMS and SIM functions
Additional functions for bearer services
H
GSM Phase 2 + features
Data transmission at 64 Kbps and above
DECT access to GSM
PMR/ Public Access Mobile Radio ( PAMR ) - like capabilities
GSM in the local loop
Packet Radio
SIM enhancements
Premium rate services ( e.g. Stock prices sent to your phone )
H
Automatic National Roaming
PLMN "A"
PLMN "B"
PLMN "D"
PLMN "C"
STP
Roamer from "A"
H
Automatic International Roaming
PLMN "A"
PLMN "Z"
Country
Interntl
Gateway
Interntl
Gateway
Country
Interntl
Gateway

More Related Content

What's hot

SRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFB
SRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFBSRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFB
SRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFBVikas Shokeen
 
GSM capacity planning
GSM capacity planningGSM capacity planning
GSM capacity planningDeepak Joshi
 
Complete umts call flow
Complete umts call flowComplete umts call flow
Complete umts call flowsivakumar D
 
Umts network protocols and complete call flows
Umts network protocols and complete call flowsUmts network protocols and complete call flows
Umts network protocols and complete call flowssivakumar D
 
Simplified Call Flow Signaling: 2G/3G Voice Call
Simplified Call Flow Signaling: 2G/3G Voice CallSimplified Call Flow Signaling: 2G/3G Voice Call
Simplified Call Flow Signaling: 2G/3G Voice Call3G4G
 
Basic GSM Call Flows
Basic GSM Call FlowsBasic GSM Call Flows
Basic GSM Call Flowsemyl97
 
Gsm rf interview questions
Gsm rf interview questionsGsm rf interview questions
Gsm rf interview questionsradira03
 
Wcdma physical layer
Wcdma physical layerWcdma physical layer
Wcdma physical layerrajibratan
 
Kpi 2g troubleshootin
Kpi 2g troubleshootinKpi 2g troubleshootin
Kpi 2g troubleshootinAbd Yehia
 
Layer 3 messages
Layer 3 messagesLayer 3 messages
Layer 3 messagesJohn Samir
 
Overview Of Gsm Cellular Network &amp; Operations
Overview Of Gsm Cellular Network &amp; OperationsOverview Of Gsm Cellular Network &amp; Operations
Overview Of Gsm Cellular Network &amp; OperationsDeepak Sharma
 
LTE Training Course
LTE Training CourseLTE Training Course
LTE Training CourseChiehChun
 
VoLTE KPI Performance Explained
VoLTE KPI Performance ExplainedVoLTE KPI Performance Explained
VoLTE KPI Performance ExplainedVikas Shokeen
 
Nokia kpi and_core_optimization
Nokia kpi and_core_optimizationNokia kpi and_core_optimization
Nokia kpi and_core_optimizationdebasish goswami
 
2 g training optimization
2 g training optimization2 g training optimization
2 g training optimizationAhmed Gad
 

What's hot (20)

SRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFB
SRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFBSRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFB
SRVCC (Single Radio Voice Call Continuity) in VoLTE & Comparison with CSFB
 
GSM capacity planning
GSM capacity planningGSM capacity planning
GSM capacity planning
 
Complete umts call flow
Complete umts call flowComplete umts call flow
Complete umts call flow
 
Umts network protocols and complete call flows
Umts network protocols and complete call flowsUmts network protocols and complete call flows
Umts network protocols and complete call flows
 
2G Handover Details (Huawei)
2G Handover Details (Huawei)2G Handover Details (Huawei)
2G Handover Details (Huawei)
 
Simplified Call Flow Signaling: 2G/3G Voice Call
Simplified Call Flow Signaling: 2G/3G Voice CallSimplified Call Flow Signaling: 2G/3G Voice Call
Simplified Call Flow Signaling: 2G/3G Voice Call
 
Basic GSM Call Flows
Basic GSM Call FlowsBasic GSM Call Flows
Basic GSM Call Flows
 
Gsm rf interview questions
Gsm rf interview questionsGsm rf interview questions
Gsm rf interview questions
 
Wcdma physical layer
Wcdma physical layerWcdma physical layer
Wcdma physical layer
 
Kpi 2g troubleshootin
Kpi 2g troubleshootinKpi 2g troubleshootin
Kpi 2g troubleshootin
 
3 g call flow
3 g call flow3 g call flow
3 g call flow
 
Layer 3 messages
Layer 3 messagesLayer 3 messages
Layer 3 messages
 
LTE Air Interface
LTE Air InterfaceLTE Air Interface
LTE Air Interface
 
Overview Of Gsm Cellular Network &amp; Operations
Overview Of Gsm Cellular Network &amp; OperationsOverview Of Gsm Cellular Network &amp; Operations
Overview Of Gsm Cellular Network &amp; Operations
 
LTE Training Course
LTE Training CourseLTE Training Course
LTE Training Course
 
VoLTE KPI Performance Explained
VoLTE KPI Performance ExplainedVoLTE KPI Performance Explained
VoLTE KPI Performance Explained
 
LTE Air Interface
LTE Air InterfaceLTE Air Interface
LTE Air Interface
 
3 g call flow
3 g call flow3 g call flow
3 g call flow
 
Nokia kpi and_core_optimization
Nokia kpi and_core_optimizationNokia kpi and_core_optimization
Nokia kpi and_core_optimization
 
2 g training optimization
2 g training optimization2 g training optimization
2 g training optimization
 

Viewers also liked

How to Intercept a Conversation Held on the Other Side of the Planet
How to Intercept a Conversation Held on the Other Side of the PlanetHow to Intercept a Conversation Held on the Other Side of the Planet
How to Intercept a Conversation Held on the Other Side of the PlanetPositive Hack Days
 
SS7: Locate. Track. Manipulate.
SS7: Locate. Track. Manipulate.SS7: Locate. Track. Manipulate.
SS7: Locate. Track. Manipulate.3G4G
 
Lte security overview
Lte security overviewLte security overview
Lte security overviewaliirfan04
 
Quick Summary of LTE Voice Summit 2015 #LTEVoice
Quick Summary of LTE Voice Summit 2015 #LTEVoiceQuick Summary of LTE Voice Summit 2015 #LTEVoice
Quick Summary of LTE Voice Summit 2015 #LTEVoice3G4G
 
Critical networking using mesh Wi-SUN technology
Critical networking using mesh Wi-SUN technologyCritical networking using mesh Wi-SUN technology
Critical networking using mesh Wi-SUN technology3G4G
 
Narrowband Internet of Things - R&S Whitepaper
Narrowband Internet of Things - R&S WhitepaperNarrowband Internet of Things - R&S Whitepaper
Narrowband Internet of Things - R&S Whitepaper3G4G
 
VoWLAN: Call Quality
VoWLAN: Call QualityVoWLAN: Call Quality
VoWLAN: Call Quality3G4G
 
Andy sutton - Multi-RAT mobile backhaul for Het-Nets
Andy sutton - Multi-RAT mobile backhaul for Het-NetsAndy sutton - Multi-RAT mobile backhaul for Het-Nets
Andy sutton - Multi-RAT mobile backhaul for Het-Netshmatthews1
 
Mobile Network Sharing
Mobile Network SharingMobile Network Sharing
Mobile Network Sharing3G4G
 
Radio Frequency, Band and Spectrum
Radio Frequency, Band and SpectrumRadio Frequency, Band and Spectrum
Radio Frequency, Band and Spectrum3G4G
 
2G/3G Switch off Dates
2G/3G Switch off Dates2G/3G Switch off Dates
2G/3G Switch off Dates3G4G
 

Viewers also liked (11)

How to Intercept a Conversation Held on the Other Side of the Planet
How to Intercept a Conversation Held on the Other Side of the PlanetHow to Intercept a Conversation Held on the Other Side of the Planet
How to Intercept a Conversation Held on the Other Side of the Planet
 
SS7: Locate. Track. Manipulate.
SS7: Locate. Track. Manipulate.SS7: Locate. Track. Manipulate.
SS7: Locate. Track. Manipulate.
 
Lte security overview
Lte security overviewLte security overview
Lte security overview
 
Quick Summary of LTE Voice Summit 2015 #LTEVoice
Quick Summary of LTE Voice Summit 2015 #LTEVoiceQuick Summary of LTE Voice Summit 2015 #LTEVoice
Quick Summary of LTE Voice Summit 2015 #LTEVoice
 
Critical networking using mesh Wi-SUN technology
Critical networking using mesh Wi-SUN technologyCritical networking using mesh Wi-SUN technology
Critical networking using mesh Wi-SUN technology
 
Narrowband Internet of Things - R&S Whitepaper
Narrowband Internet of Things - R&S WhitepaperNarrowband Internet of Things - R&S Whitepaper
Narrowband Internet of Things - R&S Whitepaper
 
VoWLAN: Call Quality
VoWLAN: Call QualityVoWLAN: Call Quality
VoWLAN: Call Quality
 
Andy sutton - Multi-RAT mobile backhaul for Het-Nets
Andy sutton - Multi-RAT mobile backhaul for Het-NetsAndy sutton - Multi-RAT mobile backhaul for Het-Nets
Andy sutton - Multi-RAT mobile backhaul for Het-Nets
 
Mobile Network Sharing
Mobile Network SharingMobile Network Sharing
Mobile Network Sharing
 
Radio Frequency, Band and Spectrum
Radio Frequency, Band and SpectrumRadio Frequency, Band and Spectrum
Radio Frequency, Band and Spectrum
 
2G/3G Switch off Dates
2G/3G Switch off Dates2G/3G Switch off Dates
2G/3G Switch off Dates
 

Similar to Gsm basics

3 g tutorial
3 g tutorial3 g tutorial
3 g tutorialtrimba
 
3gtutorial 130126013738-phpapp02
3gtutorial 130126013738-phpapp023gtutorial 130126013738-phpapp02
3gtutorial 130126013738-phpapp02Hung-Cuong Nguyen
 
3 g tutorial
3 g tutorial3 g tutorial
3 g tutorialshresth88
 
eee264cxxxxxxxxxxxxxxxxxxccccccccccccccc
eee264cxxxxxxxxxxxxxxxxxxccccccccccccccceee264cxxxxxxxxxxxxxxxxxxccccccccccccccc
eee264cxxxxxxxxxxxxxxxxxxcccccccccccccccTDERAISEN
 
Introduction To Cellular Networks
Introduction To Cellular NetworksIntroduction To Cellular Networks
Introduction To Cellular NetworksYoram Orzach
 
Chapter 3v3 Mobile communication systems.pptx
Chapter 3v3 Mobile communication systems.pptxChapter 3v3 Mobile communication systems.pptx
Chapter 3v3 Mobile communication systems.pptxahmadfaisal744721
 
Overview of Wireless Communications
Overview of Wireless CommunicationsOverview of Wireless Communications
Overview of Wireless CommunicationsSuraj Katwal
 
Introduction To Cellular And Wireless Networks
Introduction To Cellular And Wireless NetworksIntroduction To Cellular And Wireless Networks
Introduction To Cellular And Wireless NetworksYoram Orzach
 
Intro to gsm
Intro to gsmIntro to gsm
Intro to gsmabhi12567
 
Tech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdf
Tech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdfTech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdf
Tech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdfSampathFernando12
 

Similar to Gsm basics (20)

3 g tutorial
3 g tutorial3 g tutorial
3 g tutorial
 
3gtutorial 130126013738-phpapp02
3gtutorial 130126013738-phpapp023gtutorial 130126013738-phpapp02
3gtutorial 130126013738-phpapp02
 
3 g tutorial
3 g tutorial3 g tutorial
3 g tutorial
 
3 g tutorial
3 g tutorial3 g tutorial
3 g tutorial
 
eee264cxxxxxxxxxxxxxxxxxxccccccccccccccc
eee264cxxxxxxxxxxxxxxxxxxccccccccccccccceee264cxxxxxxxxxxxxxxxxxxccccccccccccccc
eee264cxxxxxxxxxxxxxxxxxxccccccccccccccc
 
3g tutorial
3g tutorial3g tutorial
3g tutorial
 
5G antenna-Technology
5G antenna-Technology5G antenna-Technology
5G antenna-Technology
 
GSM_Fundamentals_Huawei.pdf
GSM_Fundamentals_Huawei.pdfGSM_Fundamentals_Huawei.pdf
GSM_Fundamentals_Huawei.pdf
 
3 g
3 g3 g
3 g
 
Introduction To Cellular Networks
Introduction To Cellular NetworksIntroduction To Cellular Networks
Introduction To Cellular Networks
 
Gsm (1)
Gsm (1)Gsm (1)
Gsm (1)
 
Chapter 3v3 Mobile communication systems.pptx
Chapter 3v3 Mobile communication systems.pptxChapter 3v3 Mobile communication systems.pptx
Chapter 3v3 Mobile communication systems.pptx
 
Cdma Anjan V1
Cdma  Anjan V1Cdma  Anjan V1
Cdma Anjan V1
 
Overview of Wireless Communications
Overview of Wireless CommunicationsOverview of Wireless Communications
Overview of Wireless Communications
 
2gppt410
2gppt4102gppt410
2gppt410
 
Introduction To Cellular And Wireless Networks
Introduction To Cellular And Wireless NetworksIntroduction To Cellular And Wireless Networks
Introduction To Cellular And Wireless Networks
 
Full gsm overview (modified)
Full gsm overview  (modified)Full gsm overview  (modified)
Full gsm overview (modified)
 
Intro to gsm
Intro to gsmIntro to gsm
Intro to gsm
 
Intro To GSM
Intro To  GSMIntro To  GSM
Intro To GSM
 
Tech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdf
Tech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdfTech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdf
Tech_Talk__Institute_Of_Technology_University_Of_Moratuwa_For_Sales_Team.pdf
 

Recently uploaded

Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...
Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...
Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...IMARC Group
 
Project Brief & Information Architecture Report
Project Brief & Information Architecture ReportProject Brief & Information Architecture Report
Project Brief & Information Architecture Reportamberjiles31
 
AMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdf
AMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdfAMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdf
AMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdfJohnCarloValencia4
 
BCE24 | Virtual Brand Ambassadors: Making Brands Personal - John Meulemans
BCE24 | Virtual Brand Ambassadors: Making Brands Personal - John MeulemansBCE24 | Virtual Brand Ambassadors: Making Brands Personal - John Meulemans
BCE24 | Virtual Brand Ambassadors: Making Brands Personal - John MeulemansBBPMedia1
 
Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)
Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)
Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)tazeenaila12
 
Talent Management research intelligence_13 paradigm shifts_20 March 2024.pdf
Talent Management research intelligence_13 paradigm shifts_20 March 2024.pdfTalent Management research intelligence_13 paradigm shifts_20 March 2024.pdf
Talent Management research intelligence_13 paradigm shifts_20 March 2024.pdfCharles Cotter, PhD
 
NASA CoCEI Scaling Strategy - November 2023
NASA CoCEI Scaling Strategy - November 2023NASA CoCEI Scaling Strategy - November 2023
NASA CoCEI Scaling Strategy - November 2023Steve Rader
 
Chicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdf
Chicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdfChicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdf
Chicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdfSourav Sikder
 
Building Your Personal Brand on LinkedIn - Expert Planet- 2024
 Building Your Personal Brand on LinkedIn - Expert Planet-  2024 Building Your Personal Brand on LinkedIn - Expert Planet-  2024
Building Your Personal Brand on LinkedIn - Expert Planet- 2024Stephan Koning
 
NewBase 25 March 2024 Energy News issue - 1710 by Khaled Al Awadi_compress...
NewBase  25 March  2024  Energy News issue - 1710 by Khaled Al Awadi_compress...NewBase  25 March  2024  Energy News issue - 1710 by Khaled Al Awadi_compress...
NewBase 25 March 2024 Energy News issue - 1710 by Khaled Al Awadi_compress...Khaled Al Awadi
 
To Create Your Own Wig Online To Create Your Own Wig Online
To Create Your Own Wig Online  To Create Your Own Wig OnlineTo Create Your Own Wig Online  To Create Your Own Wig Online
To Create Your Own Wig Online To Create Your Own Wig Onlinelng ths
 
Michael Vidyakin: Introduction to PMO (UA)
Michael Vidyakin: Introduction to PMO (UA)Michael Vidyakin: Introduction to PMO (UA)
Michael Vidyakin: Introduction to PMO (UA)Lviv Startup Club
 
Plano de marketing- inglês em formato ppt
Plano de marketing- inglês  em formato pptPlano de marketing- inglês  em formato ppt
Plano de marketing- inglês em formato pptElizangelaSoaresdaCo
 
The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003
The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003
The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003believeminhh
 
PDT 88 - 4 million seed - Seed - Protecto.pdf
PDT 88 - 4 million seed - Seed - Protecto.pdfPDT 88 - 4 million seed - Seed - Protecto.pdf
PDT 88 - 4 million seed - Seed - Protecto.pdfHajeJanKamps
 
MC Heights construction company in Jhang
MC Heights construction company in JhangMC Heights construction company in Jhang
MC Heights construction company in Jhangmcgroupjeya
 
Borderless Access - Global B2B Panel book-unlock 2024
Borderless Access - Global B2B Panel book-unlock 2024Borderless Access - Global B2B Panel book-unlock 2024
Borderless Access - Global B2B Panel book-unlock 2024Borderless Access
 
A flour, rice and Suji company in Jhang.
A flour, rice and Suji company in Jhang.A flour, rice and Suji company in Jhang.
A flour, rice and Suji company in Jhang.mcshagufta46
 
Developing Coaching Skills: Mine, Yours, Ours
Developing Coaching Skills: Mine, Yours, OursDeveloping Coaching Skills: Mine, Yours, Ours
Developing Coaching Skills: Mine, Yours, OursKaiNexus
 

Recently uploaded (20)

Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...
Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...
Boat Trailers Market PPT: Growth, Outlook, Demand, Keyplayer Analysis and Opp...
 
Project Brief & Information Architecture Report
Project Brief & Information Architecture ReportProject Brief & Information Architecture Report
Project Brief & Information Architecture Report
 
AMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdf
AMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdfAMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdf
AMAZON SELLER VIRTUAL ASSISTANT PRODUCT RESEARCH .pdf
 
Investment Opportunity for Thailand's Automotive & EV Industries
Investment Opportunity for Thailand's Automotive & EV IndustriesInvestment Opportunity for Thailand's Automotive & EV Industries
Investment Opportunity for Thailand's Automotive & EV Industries
 
BCE24 | Virtual Brand Ambassadors: Making Brands Personal - John Meulemans
BCE24 | Virtual Brand Ambassadors: Making Brands Personal - John MeulemansBCE24 | Virtual Brand Ambassadors: Making Brands Personal - John Meulemans
BCE24 | Virtual Brand Ambassadors: Making Brands Personal - John Meulemans
 
Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)
Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)
Harvard Business Review.pptx | Navigating Labor Unrest (March-April 2024)
 
Talent Management research intelligence_13 paradigm shifts_20 March 2024.pdf
Talent Management research intelligence_13 paradigm shifts_20 March 2024.pdfTalent Management research intelligence_13 paradigm shifts_20 March 2024.pdf
Talent Management research intelligence_13 paradigm shifts_20 March 2024.pdf
 
NASA CoCEI Scaling Strategy - November 2023
NASA CoCEI Scaling Strategy - November 2023NASA CoCEI Scaling Strategy - November 2023
NASA CoCEI Scaling Strategy - November 2023
 
Chicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdf
Chicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdfChicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdf
Chicago Medical Malpractice Lawyer Chicago Medical Malpractice Lawyer.pdf
 
Building Your Personal Brand on LinkedIn - Expert Planet- 2024
 Building Your Personal Brand on LinkedIn - Expert Planet-  2024 Building Your Personal Brand on LinkedIn - Expert Planet-  2024
Building Your Personal Brand on LinkedIn - Expert Planet- 2024
 
NewBase 25 March 2024 Energy News issue - 1710 by Khaled Al Awadi_compress...
NewBase  25 March  2024  Energy News issue - 1710 by Khaled Al Awadi_compress...NewBase  25 March  2024  Energy News issue - 1710 by Khaled Al Awadi_compress...
NewBase 25 March 2024 Energy News issue - 1710 by Khaled Al Awadi_compress...
 
To Create Your Own Wig Online To Create Your Own Wig Online
To Create Your Own Wig Online  To Create Your Own Wig OnlineTo Create Your Own Wig Online  To Create Your Own Wig Online
To Create Your Own Wig Online To Create Your Own Wig Online
 
Michael Vidyakin: Introduction to PMO (UA)
Michael Vidyakin: Introduction to PMO (UA)Michael Vidyakin: Introduction to PMO (UA)
Michael Vidyakin: Introduction to PMO (UA)
 
Plano de marketing- inglês em formato ppt
Plano de marketing- inglês  em formato pptPlano de marketing- inglês  em formato ppt
Plano de marketing- inglês em formato ppt
 
The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003
The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003
The Vietnam Believer Newsletter_MARCH 25, 2024_EN_Vol. 003
 
PDT 88 - 4 million seed - Seed - Protecto.pdf
PDT 88 - 4 million seed - Seed - Protecto.pdfPDT 88 - 4 million seed - Seed - Protecto.pdf
PDT 88 - 4 million seed - Seed - Protecto.pdf
 
MC Heights construction company in Jhang
MC Heights construction company in JhangMC Heights construction company in Jhang
MC Heights construction company in Jhang
 
Borderless Access - Global B2B Panel book-unlock 2024
Borderless Access - Global B2B Panel book-unlock 2024Borderless Access - Global B2B Panel book-unlock 2024
Borderless Access - Global B2B Panel book-unlock 2024
 
A flour, rice and Suji company in Jhang.
A flour, rice and Suji company in Jhang.A flour, rice and Suji company in Jhang.
A flour, rice and Suji company in Jhang.
 
Developing Coaching Skills: Mine, Yours, Ours
Developing Coaching Skills: Mine, Yours, OursDeveloping Coaching Skills: Mine, Yours, Ours
Developing Coaching Skills: Mine, Yours, Ours
 

Gsm basics

  • 1. ObjectivesObjectives Understand Concept of Cellular Understand the functional blocks in a GSM Network Understand the Air Interface with Channels Understand Mobile Call Setup Operations Basics
  • 2. Agenda Need for Cellular Introduction to Cellular Channelization Concept GSM Evolution and Markets GSM Network Arhcitecure GSM Air Interface Parameters GSM Speech Coding Physical and Logical Channels Frames and MultiFrames GSM Basic Operations
  • 3. Telephony Communication is today's basic need Telephone has become part of life
  • 4. Fixed Line Telephones What are the drawbacks ?
  • 5. Fixed Line Telephones No Mobility Delay in New Connections Security Hazards Prone to Failures ( Line Disconnection, etc ) Very less value added services
  • 6. Mobile Communications Drawbacks of Fixed Phones have triggered wireless communications "Call People , Not Places ""Call People , Not Places "
  • 7. MCG Spokane Division RTEd Sem, 1000-1268 9/93 Company ConfidentialH First Wireless Signal 3 Postcard: Chicago Daily News Wireless Access Methods
  • 8. Authoring Division Name File Name Security Notice (if required) H Wireless Communication Model Source Display Transmitter Receiver Media of transmission is Radio Frequency
  • 9. Authoring Division Name File Name Security Notice (if required) H Types of Wireless Communications Simplex The direction of transmission is in one direction only BEEP Ex : Broadcast Services ( AM/FM Radios, Television ) Paging Services
  • 10. Authoring Division Name File Name Security Notice (if required) H Types of Wireless Communications Half - Duplex The direction of transmission is alternate in both directions Tx Rx Tx Rx "A " "B " A transmits -- B receives, then B transmits -- A receives Ex : PTT Handsets, Trunked Radios
  • 11. Authoring Division Name File Name Security Notice (if required) H Types of Wireless Communication Duplex The direction of transmission is simultaneous in both directions Ex : Cordless Telephones, Mobile Phones, Microwave Radios Is there separate frequency of transmission at both ends ?
  • 12. Authoring Division Name File Name Security Notice (if required) H The Electromagnetic Spectrum MICROWAVE S AMBROADCASTRADIO SHORT-WAVE RADIO MOBILE RADIO VHF TV FMBROADCAST RADIO MOBILE RADIOVHF TV FIBEROPTICS COMMUNICATION VISIBLE LIGHT 1MH z 10MH z 100MH z 1GHz 10GH z 100 GHz 10 12 1 0 14 1 0 15 M F H F VH F UH F SHF EH F 1µ m 1000 m 100 m 10 m 1 m 10c m 1cm 1m m Wireless Communication !!! At what frequency ?
  • 13. Authoring Division Name File Name Security Notice (if required) H Selection of Band for Wireless Communication MF : 300 KHz - 3 MHz ( Domestic Radios ) HF : 3 MHz - 30 MHz VHF : 30 MHz - 300 MHz ( FM, Paging, PTT ) UHF : 300 MHz - 3 GHz ( Mobile Radios, Cordless Phones ) SHF : 3 GHz - 30 GHz ( Microwave Band ) Properties of Radio Frequencies Low Frequency - Less Loss ,,, High Frequency - More Loss To overcome loss , more power required, More Power - Health hazards Low Frequency - High Beamwidth - Wider and Deeper Coverage Selection of Band will depend on Application Frequency Band is subdivided into Application Band Application Band is further divided into Technology Channels
  • 14. Authoring Division Name File Name Security Notice (if required) H Channelization Frequency Band has several application segments Certain blocks of the Band are reserved for certain applications by regulating authorities and as well by standard Technologies Technologies have decided on fixed bandwidth Channels within these bands Example : Mobile Communications AMPS / DAMPS : 824 MHz -- 894 MHz ( 50 MHz + 20 MHz separation) GSM : 890 MHz -- 960 MHz -- ( 50 MHz + 20 MHz separation) These 50 Mhz are bands are further divided into Channels Channelization can be done by three methods --- FDMA --- TDMA --- CDMA
  • 15. Authoring Division Name File Name Security Notice (if required) H Channelization Methods FDM A Power Frequency Time FDMA Ex: AMPS / DAMPS band is divided into 30 Khz Channels ( 1666 Freq Chs) GSM band is divided into 200 Khz Channels ( 250 Freq Chs ). Television Channels ( Star, Zee, Sony, MTV, BBC, CNN etc. )
  • 16. Authoring Division Name File Name Security Notice (if required) H Channelization Methods Frequency Power Time FDMA/TDMA TDM A Each FDMA Channel is divided into Timeslots Each Timeslot is of fixed period This method increases the number of Channels in a system Ex: DAMPS has 3 timeslots on each 30 Khz Channel ( 4998 Channels) GSM has 8 timeslots on each 200 Khz Channel ( 2000 Channels )
  • 17. Authoring Division Name File Name Security Notice (if required) H Channelization Methods CDMA FrequencyCDMA Power Time Frequency Channel is divided into Code Channels 1.25 MHz of FDMA Channel is divided into 64 Code Channels
  • 18. Authoring Division Name File Name Security Notice (if required) H Mobile Telephony -- Channelization Mobile Telephony needs Duplex Communication How many Channels will be required for one call ? What type of Channels ? -- FDMA, TDMA, FDMA/TDMA , FDMA/CDMA or something else
  • 19. Authoring Division Name File Name Security Notice (if required) H Duplex Access Methods Frequency Division Duplex (FDD) Frequency Amplitude Time F1 F2 Tx Rx Time Division Duplex (TDD) Frequency Amplitude Time F1 Tx Tx Rx Rx
  • 22. Cellular network has cells of different sizes. Bigger cells are used where subcriber density is low. Smaller cells are used where subscriber density is high. Cellular structure High way
  • 24. Frequency Reuse GSM uses concept of cells One cell covers small part of network Network has many cells Frequency used in one cell can be used in another cells This is known as Frequency Re-use F=1 F=2 F=3 F=4,8 F=5,9 F=6,10 F=7 F=1 F=2 F=3 F=4,8 F=5,9 F=6,10 F=7F=1 F=2 F=3 F=4,8 F=5,9 F=6,10 F=7 F= 1,2,3,4,5,6,7,8,9,10 Clusters Co-Channel ( Re-use ) Cells
  • 25. Distance between two cells using same frequencies 1,13,29 D D=R x SQRT( 3 x N ) N= Cluster size ( 7 in this case ) R=Radius of one cell D=Dist between two cells using same channels 1,13,29 1,13,29 1,13,29 D R
  • 27. AuthoringDivisionName FileName SecurityNotice(if required)H Mixed Cell Structure Macrocell base station Indoor Picocell Indoor Picocell Microcell base stations Microcell network Macrocell network
  • 29. Authoring Division Name File Name Security Notice (if required) H GSM TECHNOLOGY - Standards & Implementation. GSM900 DCS1800
  • 30. Authoring Division Name File Name Security Notice (if required) H GLOBAL System for Mobiles GSM900 239 licenses in 109 countries now 44 million subscribers now One New subscriber Every Second ! > 200 million subscribers by Year 2000
  • 31. Authoring Division Name File Name Security Notice (if required) H Personal Communications Networks USA: PCS1900 for new PCS UK: DCS1800 Mercury One-2-One Microtel-Orange Germany: DCS1800 E Net France: DCS1800 For new PCN Australia: DCS1800 for new PCN Thailand: DCS1800 AIS DCS1800 PCS1900 Hong Kong: DCS1800 for 6 New PCNs
  • 32. Authoring Division Name File Name Security Notice (if required) H Evolution of GSM GSM Requirements Good subjective speech quality Encryption of user information Must operate in the entire 890 - 960 Mhz frequency band Spectral efficiency Support for international roaming Minimize modifications to the existing fixed public networks Low handsets and service cost ISDN compatibility Support for range of new services and facilities
  • 33. Authoring Division Name File Name Security Notice (if required) H The Global Standard • Full Urban coverage in Western Europe • WW Roaming available • Subscribers can utilize multiple networks • First dualband networks appearing in Europe and Asia • Full Urban coverage in Western Europe • WW Roaming available • Subscribers can utilize multiple networks • First dualband networks appearing in Europe and Asia • Full Urban coverage in Western Europe • WW Roaming available • Subscribers can utilize multiple networks • First dualband networks appearing in Europe and Asia
  • 34. Authoring Division Name File Name Security Notice (if required) H Other GSM standards GSM 900 and DCS 1800 use the same standards DCS 1800 specs are defined as a delta standard to GSM specs Same GSM switches can be used for DCS 1800 Some software upgrading may be required ( if RR are manged by switch ) Dual Mode handsets will be required to support both PCS 1900 DCS 1800 ETSI has assisted ANSI T1 and TIA TR-46 committees to formulate specs for PCS 1900.
  • 35. Authoring Division Name File Name Security Notice (if required) H Evolution of GSM 1982 : Group Special Mobile formed within CEPT 1986 : A permenent Nucleus formed 1987 : Radio transmission Techniques are chosen.Field trials completed 1987 : GSM becomes ETSI technical committee 1987 : 13 Operators sign a memorandum of uderstanding 1989 : Prototype ( validation ) systems are on the air 1990 : GSM Phase I specifications are finalised 1991 : UK,France,Germany andItaly introduce GSM services 1992 : Motorola cuts over the first commercial system built for COMVIQ on Sept 1 1994 : GSM Phase 2 specifications released 1996 : GSM Phase 2+ specs are now defined GSM Phase I specification document has 5230 pages !!! • Full Urban coverage in Weste Europe • WWRoaming available • Subscribers can utilize multip networks • First dualband networks appearing in Europe and Asia The History
  • 36. Authoring Division Name File Name Security Notice (if required) H Growth • Full Urban coverage in Western Europe • WW Roaming available • Subscribers can utilize multiple networks • First dualband networks appearing in Europe and Asia • Full Urban coverage in Western Europe • WW Roaming available • Subscribers can utilize multiple networks • First dualband networks appearing in Europe and Asia • Full Urban coverage in Western Europe • WW Roaming available • Subscribers can utilize multiple networks • First dualband networks appearing in Europe and Asia
  • 37. Authoring Division Name File Name Security Notice (if required) H Technology Evolution • Full Urban coverage in Western Europe • WW Roaming available • Subscribers can utilize multiple networks • First dualband networks appearing in Europe and Asia • Ful l Ur ban cover age i n Wester n Eur ope • WW Roami ng avai l abl e • Subscr i ber s can uti l i ze mul t i pl e net w or k s • Fi r st dual band netw or k s appear i ng i n Eur ope and Asi a
  • 38. Authoring Division Name File Name Security Notice (if required) H GSM 2G+ • HSCSD - High Speed Circuit Switched Data – Multiple TDMA timeslots allocated for data transmission – Bandwidth on demand, up to 64kBit/s – Compatible with existing GSM network infrastructure • HSCSD - High Speed Circuit Switched Data – Multiple TDMA timeslots allocated for data transmission – Bandwidth on demand, up to 64kBit/s – Compatible with existing GSM network infrastructure • HSCSD - High Speed Circuit Switched Data – Multiple TDMA timeslots allocated for data transmission – Bandwidth on demand, up to 64kBit/s – Compatible with existing GSM network infrastructure
  • 39. Authoring Division Name File Name Security Notice (if required) H IMT-2000 / 3G+ (International Mobile Telecommunications -2000) • HSCSD-HighSpeedCircuitSwitchedData –MultipleTDMAtimeslotsallocatedfordatatransmission –Bandwidthondemand,upto64kBit/s –CompatiblewithexistingGSMnetworkinfrastructure • HSCSD-HighSpeedCircuitSwitchedData – MultipleTDMAtimeslotsallocatedfordatatransmission – Bandwidthondemand,upto64kBit/s – CompatiblewithexistingGSMnetworkinfrastructure
  • 40. Authoring Division Name File Name Security Notice (if required) H GSM Standards structure 01 Series : General 02 Series : Service aspects 03 Series : Network aspects 04 Series : MS-BS interface and protocols ( air interface layer 2 & 3) 05 Series : Physical layer on the Radio path ( air interface layer 1) 06 Series : Speech coding specs.
  • 41. Authoring Division Name File Name Security Notice (if required) H GSM STANDARDS - Continued 07 Series : Terminal adaptation for mobile stations 08 Series : BSS - MSC interfaces ( A & Abis) 09 Series : Network interworking 10 Series : Empty - For future use 11 Series : Equipment and Type approval specifications 12 Series : Operation & Maintenance
  • 43. BTS BTS BTS MS MS EIR AUC HLR VLR MS - Mobile Station Mobile station provides user access to GSM network for Voice & Data. All GSM mobiles comply to the GSM standards. Subscriber data is read from a SIM card that plugs into MS. Each MS has a unique number called as IMEI number, which is stored in EIR for authentication purposes. Mobile camps on to the GSM network through a BTS serving the cell. Mobile also scans neighbouring cells and reports signal strength. Network knows whereabouts of mobiles from HLR & VLR databases. Mobile Transmit and Receive voice at 13 KB/s over air interface. SIM
  • 44. H GSM Course Mobile Station Output Power CLASS 1 20 watts Vehicle and Portable CLASS 2 8 watts Portable and Vehicle CLASS 3 5 watts Hand-held CLASS 4 2 watts Hand-held CLASS 5 0.8 watts Hand-held Output Power determines: ---- Accessibility in areas of coverage ---- Talk time and Standby Time Output Power on call is varied as commanded by BTS MS - Mobile Station
  • 45. H GSM Course Mobile Station Identities MSISDN : Human Identity used to call a Mobile Station CC NDC SN 98 XXX 12345 IMEI: Serial number unique to every Mobile Station TAC FAC SNR SP 6 digits 2 digits 6 digits 1digit
  • 46. H GSM Course SIM - Subscriber Identity Module GSM Removable Module inserted when the subscriber wants to use the MS IMSI : Network Identity unique to a SIM MCC MNC MSIN 404 XX 12345 3 digits 2 digits 10 digits Two Sizes Credit Card Stamp Size 4-8 digits PIN code 3 false entries - blocks 8 digit PUK 10 false entries - disabled MS ROM = 6kb to 16kb RAM = 128 byte to 256 byte EEPROM = 3 kb to 8 kb
  • 47. H GSM Course SIM - Subscriber Identity Module Contents of SIM Serial Number IMSI, Subscriber Key ( Ki ) Algorithms for Authentication, Ciphering Network Code PIN, PUK Charging Information Abbreviated Dialling Supplementary Features ( e.g. call barring ) SIM features and contents are personalized by the Service Activator MS also stores some temporary data on SIM during operation
  • 48. H GSM Course Base Station Cell Site Architecture Mains Power Panel DC Power Supply Unit Battery Backup Abis BTS DMR GSM Antenna System BTS Cabin/Shelter/Room AirCon
  • 49. H GSM Course BTS - Base Transceiver Station BTS MS BSC MSC CELL BTS has a set of Transceivers to communicate with mobile's in its area One BTS covers one or more than one cell The capacity of a cell depends upon number of tranceivers in a cell. BTS is connected to the BSC through Abis Interface, which is a 2Mb/s BTS transmit and receive voice at 13 kbps over air interface to the mobiles. BTS commands mobiles to set Tx. power, timing advance and Handovers RF Channels Abis - 2 MBits/s
  • 50. H GSM Course BTS Architecture 1 BSC TxRx A Rx B Splitter Processor Modules T S B P P PC MInterface Alar mInterface A1 TRX TRX 1 2 B1 A2 B2 T R A U BTS COM RFUBPF Fr R e f
  • 51. H GSM Course BTS Architecture 2 TRX Logic TRX RF Power Amplifier TRX Unit PSU & Climate Control Antenna ABIS over G703 Backplane BTS Cabinet. 3 Channel. Single Sector I Q RF I Q Combiner / Distribution Unit Rx FilterLNA Splitter Combiner Duplexer Coupler Coupler Interface Frequency Reference Unit CPU BTS Alarms NEM Proprietary Interface
  • 52. H GSM Course BSC - Base Station Controller Several BTS's are connected to one BSC BSC manages channel allocation,handovers and release of channels at connected BTS's BSC connects to each BTS on an Abis interface & to the MSC on A interface BSC has the entire database for all cell parameters associated with the BTS's. MSC Abis A
  • 53. H GSM Course Base Station Controller BTS Processor Modules P C M P C M P C M T S B P P T M G T R A U MSC BSC
  • 54. H GSM Course Abis Interface E1 / T1 Abis is a G.703 interface. It could be E1 or T1 Abis carrries Traffic information of all the mobiles in the cells controlled by the BTS. Abis also carriers signalling information between BTS and BSC Signaling over Abis is done by LAPD protocols LAPD has several modes of implementation --- LAPD --- LAPD Concentrated --- LAPD Multiplexed
  • 55. H GSM Course Abis Interface LAPD Modes LAPD Signaling for each TRX is on a dedicated 64 Kbps circuit Maximum Signalling for 10 Transceivers on 1 E1 link 64 kbps 0 Sync 64 kbps 1 TRX Signaling 64 kbps 2 4 Traffic Channels 64 kbps 3 4 Traffic Channels 64 kbps 4 TRX Signaling 64 kbps 5 4 Traffic Channels 64 kbps 6 4 Traffic Channels 64 kbps 7 TRX Signaling 64 kbps 8 4 Traffic Channels 64 kbps 9 4 Traffic Channels } 1 TRX } 1 TRX } 1 TRX
  • 56. H GSM Course Abis Interface LAPD Modes LAPD Concentrated mode 1 Signaling for 4 TRX's is on a dedicated 64 Kbps ciruit Maximum Signalling for 13 Transceivers on 1 E1 link 64 kbps 0 Sync 64 kbps 1 4 x TRX Signaling 64 kbps 2 4 Traffic Channels 64 kbps 3 4 Traffic Channels 64 kbps 4 4 Traffic Channels 64 kbps 5 4 Traffic Channels 64 kbps 6 4 Traffic Channels 64 kbps 7 4 Traffic Channels 64 kbps 8 4 Traffic Channels 64 kbps 9 4 Traffic Channels 64 kbps 10 4 x TRX Signaling } 1 TRX } 1 TRX } 1 TRX } 1 TRX
  • 57. H GSM Course LAPD Modes LAPD Concentrated mode 2 Signaling for All TRX's is on a dedicated 64 Kbps ciruit Maximum Signalling for 15 Transceivers on 1 E1 link 64 kbps 0 Sync 64 kbps 1 ALL TRX Signaling 64 kbps 2 4 Traffic Channels 64 kbps 3 4 Traffic Channels 64 kbps 4 4 Traffic Channels 64 kbps 5 4 Traffic Channels 64 kbps 6 4 Traffic Channels 64 kbps 7 4 Traffic Channels 64 kbps 8 4 Traffic Channels 64 kbps 9 4 Traffic Channels 64 kbps 10 4 Traffic Channels } 1 TRX } 1 TRX } 1 TRX } 1 TRX Abis Interface
  • 58. H GSM Course Abis Interface LAPD Modes LAPD Multiplexed Signaling for each TRX is on 16kbps subchannel. Maximum signalling for 15 TRX's on 64 kbps 0 Sync 64 kbps 1 TRX Signaling/ 3 Traffic Channels 64 kbps 2 4 Traffic Channels 64 kbps 3 TRX Signaling/ 3 Traffic Channels 64 kbps 4 4 Traffic Channels 64 kbps 5 TRX Signaling/ 3 Traffic Channels 64 kbps 6 4 Traffic Channels 64 kbps 7 TRX Signaling/ 3 Traffic Channels 64 kbps 8 4 Traffic Channels 64 kbps 9 TRX Signaling/ 3 Traffic Channels 64 kbps 10 4 Traffic Channels } 1 TRX } 1 TRX } 1 TRX } 1 TRX } 1 TRX
  • 59. TRAU - Transcoder / Rate Adaptation Unit The MSC is based on ISDN switching. The Fixed Network is also ISDN based ISDN has speech rate of 64kbps. Mobile communicates at 13 Kbps TRAU converts the data rates between 13 KB/s GSM rate to 64 Kbits /s Standard ISDN rate TRAU can be colocated with the BTS,BSC or MSC or it can be a separate unit. MS MS RF Channels BTS BSC MSC TRAU Abis interface 2 MBits/s A interface 2 MBits/s 13 KBits/sec P S T N 16 KBits/sec 16 KBits/sec 64 KBits/secVOICE
  • 60. H GSM Course LOCATION OF TRANSCODER Colocated with MSC,BSC,BTS Separate Unit 16 kbps 64 kbps BSCTranscoderMSC
  • 61. H GSM Course MSC - Mobile Switching Centre Exchange where calls are established,maintained and released. Database for all subcribers and their associated features. Communicates with BSC's on MS side and with PSTN on fixed line side. MSC is weighted on the number of subcribers it can support BSC's BTS's HLR VLR MSC
  • 62. H GSM Course MSC - Mobile Switching Centre Multiple MSC's BSC's BSC's MSC MSC GMSC More subscribers ? More MSC's !
  • 63. H GSM Course HLR - Home Location Register HLR MSC has all subscriber database stored in HLR HLR has all permanent subscriber database MSC communicates with HLR to get data for subscribers on call HLR will have the series of all subscriber numbers, which may not be activated or issued .
  • 64. H GSM Course VLR - Visiting Location Register VLR HL R A subscribtion when activated is registered in VLR VLR has all the subscriber no's which are activated VLR also has temporary database of all activated subscribers ( on/off, location ) MSC communicates with HLR for susbcribers coming from different MSC's and if found valid, then registers them in its VLR
  • 65. H GSM Course AUC - Authentication Centre HLR AUCMSC MS Authentification is a process by which a SIM is verified Secret data and the verification process alogorithm are stored at AUC AUC is the element which carries out the verification of SIM AUC is associated with the HLR
  • 66. H GSM Course EIR : Equipment Identity Register EIR is the Mobile Equipment Database which has a series of IMEI's MSC asks the Mobile to send its IMEI MSC then checks the validity of IMEI with the EIR All IMEI are stored in EIR with relevant classfications EI R MSC Classifications of IMEI( Mobile Stations ) White List Grey List Black List
  • 67. H GSM Course BC - Billing Centre BC BC Generates the Billing Statement for each Subscriber BC may be directly connected to the MSC MSC sents the billing information ( duration of call ) to BC BC then produces the billing amount based on the units set
  • 68. H GSM Course OMC - Operations & Maintenance Centre It is central monitoring and remote maintenance centre for all network elements OMC has links to BSC's and MSC OMC Terminals BTS's BTS's BTS's OMC System BSC's MSC asasasaaaaa aqwtttsssdfaa qwrqrncnceas asasasaaaaa aqwtttsssdfaa qwrqrncnceas asasasaaaaa aqwtttsssdfaa qwrqrncnceas
  • 69. H GSM Course OMC - Operations & Maintenance Centre BTS's BTS's OMC System BSC's MSC asasasaaaaa aqwtttsssdfaa qwrqrncnceas asasasaaaaa aqwtttsssdfaa qwrqrncnceas OMC - R OMC - S
  • 70. H GSM Course OMC - RADIO BTS BTS BTS BTS BSC BSC TRANSCODER MSC MUX / DEMUX SERVER OMC - R X.25 SWITCH
  • 71. H GSM Course OMC - Functions E nvironm ental Alarm s P ow er , F ire, S ecurity, Aircons, etc. E quipm ent F ailure Alarm s B TS , B S C site F ailures M S C and pheripheral failures A larm M on ito ring Add new hardw are M odify control param eters other softw are changes. C on figuratio n C hang es C ell Traffic Analysis N o of calls, o/g ,i/c P S TN , C all drops etc. P erfo rm ance A nalysis O M C Fu nctions
  • 72. H GSM Course Equipment Alarms BTS , BSC , Transcoder Failures Link Failures Module Failures ( Transceiver,Processors) Network BTS A Transceiver 1 Fail 17:35hrs Site A Transceiver 1 Fail
  • 73. H GSM Course Cell Traffic 0 1 2 3 4 5 6 7 8 A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3 cell names TCH TRAFFIC IN ERLANGS FROM 09:00 to 21:00hrs 1
  • 74. H GSM Course SMSC - Short Message Service Centre Message is sent to a particular mobile. Message transfer takes place through SMSC Messages are be sent through a Manual Terminal connected to SMSC SMSC MSC
  • 75. H GSM Course VMSC : Voice Mail Service centre VMSC MSC It has a database for all Voice Mail Subscribers It also stores all the Voice Mail - Voice Messages
  • 76. H GSM Course GSM Signaling Interfaces VLR HLR/AU C EIR PSTN GMSC GSMSC VLR HLR/ AUC Abis A B C F E G D SS7/R2 MSC BSC BTS OML OMC A,B,C,D,E,F,G,H,I = SS7 Abis = LAPD OML = X.25 SUPP I H
  • 77. A GSM Cell Broadcast CHannel Traffic CHannel UPLINK 890-915 MHz DOW NLINK 935-960 MHz BTS Abis Interface To BSC BCH TCH
  • 78. Separate Bands for Uplink and Downlink Down link : 935 - 960 MHz ( E-GSM 925 - 960 MHz ) Uplink : 890 - 915 MHz ( E-GSM 880 - 915 MHz) TDMA and FDMA Multiplex –124 Frequency Channels (ARFCN) for GSM900 – 1 to 124 for current band – 975 to 1023 for E-GSM –200kHz Channels –8 Mobiles share ARFCN by TDMA 0.3 GMSK Modulation –270.833 kbits/sec. rate GSM Air Interface
  • 79. TDMA and FDMA 1 2 3 4 5 6 7 3 4 5 6 7 0 1 2 Time Frequency Amplitude ARFCN Timeslot Physical Channel is an ARFCN and Timeslot
  • 80. The GSM Burst Guard Period Time Frequency Amplitude Midamble 8.25 bits3 57 bits 1 26 bits 1 57 bits 3 Data Tail bits Data Control bit Tail bit Control bit
  • 81. Speech Coding PSTN Air Interface PCM Coding - 64 KB/s RPE-LTP Coding in GSM - 13 KB/s
  • 82. RPE and LTP Coder ( Regular Pulse Excited - Long Term Prediction ) RPE-LTP is a combination of RELP and MPE-LTP codecs. Coverts Speech to Low Data Rate 20ms Speech makes 260 Bits Output 13 kbit/s 20 ms Blocks Speech Coder Bits Ordered 260 Bits 260 Bits 132 78 Important Bits Other Bits 50 Very Important Bits Speech Coder - Defined under GSM TS 6.10
  • 83. Block Code 132 7850Type Ia Type Ib Type II Re-ordering Half rate convolutional code CRC 50 132 783 Type Ia Type Ib Type II 378 78 Type II 25 25 78466 663 TailCRC Type Ib Type IaType Ia Type Ib Type II 262 Bits in 456 Bits O 456 Bits from 20ms of Speech Error Correction
  • 84. Diagonal Interleaving 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 456 Bits from 20ms of Speech 456 Bits from 20ms of Speech 57 57 57 57 57 57 57 57 57 57 57 57 57 57 Traffic Channel (TCH) Bursts Carry Two 57 Bit Blocks (114) Each 120ms of Speech = 456x6 = 2736 bits 2736 / 114 = 24 bursts i.e. 24 frames (mobile Tx once per frame) Multiframe has 26 frames in 120ms There are 2 spare frames ......One SACCH, One Idle TCH
  • 85. Convolutional Coding & Interleaving HELLO FOLKS HHEELLLLOO FFOOLLKKSS ELSOLHLOFK LEOLSHOLKF EL SOL HLOFK LEOLSHOLKF HHEELLL -OO FFO -LLKK -S HELLO FOLKS Bits to be Txed: Convolutionally Encoded: Interleaved: Bits Rxed: De-Interleaved: Viterbi Decoded: Convolutional Encoder Interleaver De- Interleaver Decoder Hello..... Example:
  • 86. Speech coding Process 20ms Speech Coder 260 bits 50 132 78 1a 1b 11 Channel Coder 456 bits 13 kbps 22.8 Kbps Tranceiver ( BTS ) 22.8 Kbps 456 bits 260 bits 13 kbp Transcoder Handler 260 + 60 = 320 bits 16 kbps TRAU Frame Abis
  • 87. TRAU Frame 260 bits info + 60 TRAU bits = 320 bits/ 20ms = TRAU Frame 60 bits contains Frame Information data which indicates speech,data,idle,O & M , full-rate/half-rate. 16 KbpsT = T T T TSynch Sign T0 T1 T2 T3 T30 T31 Abis 60 bits = 35 synchronization + 21control + 4 timing
  • 88. 8 Midamble Patterns (Colour Codes) of 26 bits RACH and SCH have Longer 41 and 64 bit Midambles Equalizer Estimates Channel Impulse Response From Midamble Mathematically Construct Inverse Filter Uses Inverse to Decode Data Bits Midamble or Training Bits Timeslot (normal burst) Midamble 8.25 bits 357 bits 126 bits 1 57 bits 3 Guard Period Data Tail bits Data Control bit Tail bit Control bit
  • 89. GSM TDMA Power Burst +1.0 dB -1.0 dB +4 dB -6 dB -30 dB -70 dB -6 dB -30 dB -70 dB 147 "Useful" Bits 542.8µs 148 "Active" Bits, 546.42µs 3 57 1 26 1 57 3 10µs 8µs 10µs 10µs 10µs8µs Power Time
  • 90. 0.3 GMSK Modulation Data Frequency Phase +67.708 kHz -67.708 kHz 270.833kB/s +90deg -90deg I Q
  • 91. Uplink Lags Downlink by 3 Timeslot periods Uplink and Downlink use same Timeslot Number Uplink and Downlink use same Channel Number (ARFCN Uplink and Downlink use different bands (45MHz apart f GSM900) Downlink and Uplink 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 25 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 Downlink Uplink 45 MHz
  • 92. Measurements by MS and BTS Uplink RXLEV ( - 48 to -110 dbm ) Uplink RXQUAL ( 0 - 7 ) Downlink RXLEV ( - 48 to -110 dbm ) Donwlink RXQUAL ( 0 - 7 ) RXLEV is the received power level RXQUAL is the received quality. It is the bit errorr measured on the M idamble 0 1 < 0.2 % 2 0.2 - 0.4 % 3 0.4 - 0.8 % 4 0.8 - 1.6 % 5 1.6 - 3.2 % 6 3.2 - 6.4 % 7 6.4 - 12.8 % RXQUAL
  • 93. Measuring Adjacent Cell BCH Power UPLINK DJACENT CELL BCH DOWNLINK RXLEV RXLEV RXLEV RXLEV RXLEV
  • 94. Mobile Power Control Mobile is commanded to change its Transmit Power Change in Power is proportionate to the Path Loss Change is Power is done in steps of 2 dbs Tx Level 5 6 7 . 14 15 Power dBm 33 31 29 . 15 13 Path LossLow RXLEV Pwr Command
  • 95. TDMA approach requires signals to arrive at BTS at the correct time. They must not overlap. BTS Timing Advance
  • 96. Concept of Channels in GSM 1. To pick up employees in the morning 2. To receive company guests from airport 3. To carry material to the site / stores 4. To Collect mail/courier 5. To drop the employees back home 6. To get a doctor in case of emergency 7. To carry company gusts for a dinner If there were two vehicles, we can allocate a set of tasks to one , and rest to the other. However, since both are identicle vehicles, there is greater flexibility in usage. Concept of Channels in GSM A company vehicle is used for several purposes in a day..
  • 97. 0 1 5 6 7 4 2 3 4 0 1 2 3 FRAME NUMBER TIM E SLOT Time Sharing by Channels FC C H SC H B C C H B C C H B C C H TC H TC H TC H TC H TC H TC H TC H TC H TC H TC H
  • 98. Concept of Frames C T T T T T T T C T T T T T T T C T T T T T T T Frame No. 1 Frame No. 2 Frame No. 3 Time slot Number.. 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 C T T T T T T T Frame No. 4
  • 99. CHANNEL ALLOCATIONS IN A CELL 0 1 2 3 4 5 6 7 U1U1 U1 U1 U5 U5 U5 U5 U5 U5 U5 U5 U5 U2 U2 U2 U2 U2 U3 U3 U3 U3 U3 U3 U3 U4 U4 U4 U4 U4 U4 U4 U4 U6 U6 U6 U6 U6 U6 U6 U6 FRAME Number U7 U7 U7 U7 U7 U8 U8 U8 U8 C CCCC C C C CC C C
  • 100. Frames and Multiframes normal burst) Control Channel Multiframe Frame Timeslot 156.25 Bits 8 Timeslot Guard Period 4.615ms 576.92 us 8.25 bits 3 57 bits 1 26 bits 1 57 bits 3 Data Tail bits Data Control bit Midamble Tail bit Control bit 0 1 2 3 4 5 6 7 0 50 0 26 Traffic Channel Multiframe
  • 101. Channels in GSM Air Interface PHYSICAL CHANNELS ARFCNs - 1 to 124 ( D & U ) Timeslots - 0 to 7 ( D & U ) Total of 124 x 8 = 992 Channels LOGICAL CHANNELS ARFCN - X , Timeslot - Y Frame Number - N 1 2 3 4 5 3 4 5 6 0 1 2 BCH - BROADCAST CHANNELS DCCH - DEDICATED CONTROL CHANNELS CCCH - COMMON CONTROL CHANNELS CONTROL CHANNELS TRAFFIC CHANNELS PCH - PAGING CHANNEL FCCH - Frequency Correction Channel SCH - Synchronisation Channel BCCH - Broadcast Control Channel BC H SDCCH - Standalone Dedicated Control Channnel SACCH - Slow Associated Control Channnel FACCH - FAST ASSOCIATED CONTROL AGCH - ACCESS GRANT CHANNEL RACH - RANDOM ACCESS CHANNEL TCH - F FULL RATE TRAFFIC CHANNEL TCH - TRAFFIC CHANNEL TCH - H HALF RATE TRAFFIC CHANNEL TC H
  • 102. One ARFCN, On all the time, in every cell Uses Timeslot 0 on a channel, in Downlink. Allows Mobiles to tune to BTS freq. - FCCH This channel carries a 142 bit zero sequence and repeats once in every 10 frames on BCH Allows Mobile to Synchronise - SCH This channel carries the Frame number and BSIC in encrypted data format. Amidamble of 64 bits helps mobiles to synchronize. SCH also repeats once every 10 Frames. Allows Mobiles to identify Network - BCH - Broadcast CHannel BCH
  • 103. BCH Sub channels FCCH SCH 142 bits - all 0's3 3 8.25 Start Bits Stop Bits Guard Bits 3 3 8.2539 3964 Training Sequence Guard Bits Stop BitsStart Bits Encrypted Data Bits Encrypted Data Bits BCCH 3 3 8.25 Start Bits Stop Bits Guard Bits 3 3 8.25 Start Bits Stop Bits Guard Bits 3 3 8.25 Start Bits Stop Bits Guard Bits 3 3 8.25 Start Bits Stop Bits Guard Bits BCH 57 57 57 57 57 57 57 57 26 26 26 26
  • 104. CCCH shares Timeslot 0 with BCH on a Multiframe CCCH consists of PCH , RACH & AGCH. PCH - Paging Channel is used to alert mobiles on incomming calls. PCH carries IMSI to page for Mobiles in the cell. PCH is Downlink channel. RACH - Random Access Channel - is a short burst sent by mobile to BTS , to initiate a call request . RACH uses Timeslot 0 on reverse BCH channel on Uplink. AGCH - Access Grant Channel - When mobile sends a RACH to BTS, BTS responds by CCCH - Common Control CHannel BCH
  • 105. Used by the MOBILE to get attention from BASE STATION in the Uplink. Several mobiles might originate RACH simultaneously. RACH uses a Slotted ALOHA access scheme. Mobile doesn't know path delay –So RACH has to be a special SHORT BURST –Mobile sends normal burst only after RACH - Random Access CHannel 8 3 68.2541 36 Extended Guard Period Stop Bits Start Bits Synchronisation Bits Encrypted Data Bits 88 bits
  • 106. BCH & CCCH - 51 Frame structure - DOWNLINKFrame number ( DOWN LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 FCCH - Frequency correction Channel SCH - Synchronisation Channel BCCH - Broadcast Control Channel AGCH - Access Grant Chan PCH - Paging Channel 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 F S B B B B A A A A F S P P P P P P P P F S F S F S I 0 1 2 3 0 1 2 3 Time slots
  • 107. BCH & CCCH - 51 Frame structure - UPLINK RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH R A C H R A C H R A C H R A C H Frame number ( UP LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 0 1 2 RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 0 1 2 RACH - Random Access Channel ( A short burst is transmitted by mobile towards BTS on RACH) Time slots
  • 108. DCCH - Dedicated Control Channel Dedicated Control Channels have a TCH like allocation. DCCH have three Sub Channels. SDCCH - Standalone Dedicated Control Channel This is used as an interim channel before final assignment of TCH. SDCCH is used for signalling and Authentication message transfers. FACCH - Fast Associated Control Channel . FACCH is used by BTS to command a handoff to the mobile. A TCH frame is used up by FACCH , since handoff has to take place on priority. SACCH - Slow Associated Control Channel - SACCH flows at a slower rate on Uplink & Downlink along with TCH or SDCCH. During a call, SACCH flows once for every 24 Frames of TCH .
  • 109. SDCCH - Stand-alone Dedicated Control CHannel USED DURING CALL SET-UP Stepping Stone between BCH and TCH Used for Authentication Etc. SDCCHSDCCH TCH BCH BCH BCH
  • 110. DOWNLINK ( BTS - MS ) –Mobile Tx Power Commands –Mobile Timing Advance –Cell's Channel Configuration UPLINK ( MS - BTS ) –Received signal quality report (RXQual) –Received signal level report (RXLev) –Adjacent BCH power measurements –Mobile's status SACCH - Slow Associated Control CHannel
  • 111. INTERRUPTS TCH ON UPLINK AND DOWNLINK Rapid message exchange for handovers Control Bits either side of midamble: –Indicate TCH ( 0 ) or FACCH ( 1 ) FACCH - Fast Associated Control CHannel Miidamble 8.25 bits 357 bits 126 bits 1 57 bits 3 Guard Period Data Tail bits Data Control bit Tail bit Control bit
  • 112. SDCCH - Combined Channel Config ( Shares Time slot 0 with BCH and CCCH ) Frame number ( DOWN LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25Time slots 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 F S B B B B A A A A F S P P P P P P P P F S D D D D D D D D F S D D D D D D D D F S H H H H H H H H I SDCCH ( D ) : Standalone Dedicated Control Channel SACCH ( H ) : Slow Associated Control Channel 0 1 2 3 0 1 2 3
  • 113. BCH & CCCH - 51 Frame structure - UPLINK S D C C H S D C C H S D C C H S D C C H RA CH RA CH S A C CH SA CC H SA CC H SA CC H SA CC H SA CC H SA CC H SA CC H RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH R A C H R A C H R A C H R A C H Frame number ( UP LINK ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 0 1 2 RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH RA CH SD CC H SD CC H SD CC H SD CC H SD CC H SD CC H SD CC H SD CC H RA CH RA CH SD CC H SD CC H SD CC H SD CC H 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 0 1 2 RACH - Random Access Channel ( A short burst is transmitted by mobile towards BTS on RACH) Time slots
  • 114. 8.25bits 357 bits 1 26 bits 1 57 bits 3 Guard Period Data Tail bits Data Control bit Midamble Tail bit Control bit TCH - Traffic Channel One time burst Traffic Channel carries the Voice data. Two blocks of 57 bits contain voice data . One TCH is allocated for every active call. While call is in progress if there is degradation in quality of current channel, BTS may shift the communication to another TCH on a different Carrier and/or Time slot . A Full rate TCH carries 13 KB/s voice data , and Half rate TCH carries a 6.5 KB/s voice data. 156.25 bits or 576.92 uS
  • 115. TCH Multiframe - TCH Full rate 26 Frames - 120 ms 24 Carry Speech, 1 Idle, 1 SACCH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 T T A -T T T T T T T T T T T T T T T T T T T T T T SACCH Idle
  • 116. TCH Multiframe - TCH Half rate26 Frames - 120 ms 24 Carry Speech , 2 SACCH ( shared by two mobiles - a & b ) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Ta Tb Aa AbTa Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb Ta Tb SACCH-a SACCH-b
  • 117. Click here to type bulleted text F S B B B B A A A A A A A A F S P P P P D D D D D D T T T T T T T T T T T T SA T T T T T T T T T T T T Idle T T T T T T T T T T T T SA T T T T T T T T T T T T Idle T T T T T T T T T T T T SA T T T T T T T T T T T T Idle T T T T T T T T T T T T SA T T T T T T T T T T T Idle T T T T T T T T T T T T SA T T T T T T T T T T T T Idle T T T T T T T T T T T T SA T T T T T T T T T T T T Idle T T T T T T T T T T T T SA T T T T T T T T T T T T Idle Frame number 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 0 1 2 3 4 5 6 7 T - TCH SA - SACCH I - Idle A delay of (12 * 8)+1 Timeslots is kept between two successive SACCH . TCH and SACCH - FRAMES Time Slots
  • 118. FRAMES 0 0 1 1 2 2 48 23 49 24 50 25 = 6.12 sec 1 Superframe = 51 x 26 CCH MF = 1326 TF = 26 x 51 TCH MF = 1326 TF 1 Burst = 577usecs 0 1 2 3 4 5 6 7TDMA Frame = 8 bursts = 4.616 ms 0 1 2 23 24 25 0 1 2 48 49 50 Multiframe TCH Multiframe = 26 TF = 120ms 1 CCH Multiframe = 51 TF = 234.6m 0 1 2 3 204 4 204 5 204 6 204 71 Hyperframe = 2048 Superframes = 2715648 TDMA Frames = 3 hrs 28 min 53 sec 760 ms
  • 119. TDMA approach requires signals to arrive at BTS at the correct time. They must not overlap. BTS Timing Advance
  • 120. H Timing Advance T B Synch Seq 41 bits Encrypted bits 36 T B Guard Period 68.25 bp 63 bits Timing Adv 5.25 GP BSS calculates access delay from RACH in terms of bits Informs Mobile to delay its timing in terms of bits Maximum Timing Advance of 63 bits RACH Burst
  • 121. H Mobile Maximum Range Range = Timing Advance x bit period x velocity 2 Range = Distance between Mobile to Base Station Timing Advance = Delay of Bits ( 0 -- 63 ) Bit period = 577 / 156.25 = 3.693 usecs = 3.693 x 10e-6 secs Velocity = 3 x 10e5 Range = ( 63 ) x ( 3.693 x 10e-6 ) x (3 x 10e5) 2 = 34.9 kms
  • 122. Hopping Traffic Channel 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 C1 C2 C3 C1 C2 C3 UPLINK ADJACENT CELL BCH DOWNLINK
  • 123. IREG • PURPOSE: To test various call scenarios to provide reliable Roaming services • Various Call Scenarios •Mobile to Mobile •PSTN to Mobile •Checking Announcements •Call Forwarding •SMS Test •Combined Test
  • 124. H Mobile Searches for Broadcast Channels (BCH) Synchronises Frequency and Timing Decodes BCH sub-channels (BCCH) Checks if Network Allowed by SIM Location Update Authentication Mobile Turn-On
  • 125. BSC MSC Location Area 1 BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BSC BSC BSC Location Area 3 Location Area 2 Location Area MCC MNC LAC Location Area Identity
  • 126. H IMPORTANCE OF LOCATION AREA Reduce Paging Load Resource Planning L.Area = 1 L.Area = 2 L.Area = 3
  • 127. H What is Location Update MSC should know the Location of the Mobile for paging. Mobile is continously changing Location Area. Mobile when changes Location Area informs the MSC about its new L.A Process of informing MSC about new Location Area is Location Update L.Area = 1 L.Area = 2 L.Area = 3 Location Update
  • 128. H IMSI ATTACH Mobile turns off and sends an IMSI Detach to MSC. Mobile turns on again and compares LAI. If same,sends an IMSI attach to MSC. 1. Normal Location Update. 2. IMSI Attach. 3. Periodic Location Update. Types of Location Update
  • 129. H NORMAL LOCATION UPDATE Mobile turns on power. Reads the new LAI. If different,does a Location Update.
  • 130. H PERIODIC LOCATION UPDATE Mobile enters non-coverage zone. MSC goes on sending Pages Mobile has to inform MSC after a set period.
  • 131. H Location Update Mobile Changes Location Area Reads the new Location Area from BCCH Sends a RACH ( request for channel ) Gets a SDCCH on AGCH Sends its IMSI and new & old LAI in a Location Update Request to MSC on SDCCH MSC starts Authentication If successful, Updates the new Location area for the Mobile in the VLR Sends a confirmation to the Mobile Mobiles leaves SDCCH , and comes to idle mode
  • 132. H Mobile Originated Call Channel Request Immediate Assign Service Request Authentication Set Up Ciphering Call Proceeding Assignment Alerting Connection
  • 133. H MOBILE TERMINATED CALL Channel Request Immediate Assign Authentication Set Up Ciphering Call Confirmed Assignment Alerting Connection Paging Paging Response
  • 134. H Security Features Authentication --- Process to verify the Authenticity of SIM --- Mobile is asked to perform an operation using an identity unique to SIM. Ciphering --- Process of coding speech for secrecy --- The speech bits are EXORed with bit stream unique to MS
  • 135. H Security Features TMSI Reallocation Loc Upd ( IMSI ) TMSI Allocation Call Setup ( TMSI ) TMSI Reallocation
  • 136. H Security Features Identity Check Identity Check ( IMEI ) Sends IMEI EIR White listed / Grey listed / Black listed ?????
  • 137. H HANDOVER Cell 1 Cell 2 --- Handover is a process by which the control/communication of a Mobile is transferred from one cell to another
  • 138. H CRITERIA FOR HANDOVER Receive Quality (RXQUAL) on Uplink & Downlink. Receive Signal Strength (RXLEV) on Uplink & Downlink. Distance ( Timing Advance ). Interference Level. Power Budget.
  • 139. H Handover Decision BSC processes the measurement reported by Mobile and the BTS. BSS performs averaging function on these measurements every SACCH frame ( 480ms). Handover Decision algorithm is activated after a set number of SACCH frame periods by comparison against Thresholds.
  • 140. H TYPES OF HANDOVERS INTRA - CELL HANDOVER INTER - CELL HANDOVER INTRA - BSC HANDOVER INTER - BSC HANDOVER INTER - MSC HANDOVER
  • 141. H INTRA - CELL HANDOVER - Handover between channels / timeslots of same cell BTS
  • 142. H INTER - CELL HANDOVER --- Handover between cells of same BTS C0 C0 BTS
  • 143. H INTRA - BSC HANDOVER MSC BSC BTS BTS --- This type of Handover takes place if the cell to which which handover is to be done belongs to the sameBSC. --- In this the BSC handles everything without involving MSC. --- The MSC will be informed by the BSC after Handover.
  • 144. H INTER BSC HANDOVER MSC BSC BSC BTS BTS --- In this type of Handover,the Mobile is handed over to a cell which belongs to another BSC. --- The MSC is completely involved in this Handover
  • 145. H GMSC MSC BSC BTS MSC BSC BTS --- If the cell belongs to another MSC,then it is Inter-MSC handover. --- In this case the handover takes place through the interconnecting element (PSTN) between the MSC's INTER - MSC HANDOVER
  • 146. H WHAT IS CELL BARRING ? BTS
  • 147. H Every Mobile has an access class . Every cell defines the Mobile classes which are barred access. Cell Barring USE OF CELL BARRING --- Reserving Cells for Handovers. --- Reserving Cells for a certain Mobile Class.
  • 148. H Both users talk alternately. Each direction of Transmission is only 50 % Transmitter is switched ON for useful information frames. What is DTX ?
  • 149. H Need for DTX ---- To increase Battery Life ---- To reduce the average interference level DTX is done by DTX Handlers which have the following functions.
  • 150. H Voice Activity Detector ( VAD ) Senses for speech in 20ms blocks Removes stationary noise. VAD is an energy detector. Compares Energy of filtered speech threshold
  • 151. H Evaluation of Background noise Background noise is always present with speech. DTX cuts off this noise with speech. Gives an uncomfortable feeling to the listener. VAD takes care by inserting comfort noise.
  • 152. H CELL BROADCAST Message is continously broadcasted in cell/or cells Broadcast is done on SDCCH BCCH informs the mobile the details of SDCCH for CBCH Mobile tunes to SDCCH at certain intervals and reads messages All Mobiles dont support this feature
  • 153. H Short Message Service SMS Centre MSC/ VLR BSC BTS Short Message is sent to a particular Mobile Station
  • 154. H Emergency Calls -- GSM Specs define ' 112' as emergency number -- '112' is accessible with or without SIM -- Without SIM it is sent on the best channel -- Mobile on sensing '112' sets the establishment cause to emergency call in the RACH -- Routing of this call can be done to a desired location defined in the Switch.
  • 155. H GSM Phase 2 features Extended Frequency Band ( 50 more channels ) Multiple and Alternate Ciphering Algorithm Half - Rate Coding Compatibility with DCS 1800 Specifications Enhancement of SMS and SIM functions Additional functions for bearer services
  • 156. H GSM Phase 2 + features Data transmission at 64 Kbps and above DECT access to GSM PMR/ Public Access Mobile Radio ( PAMR ) - like capabilities GSM in the local loop Packet Radio SIM enhancements Premium rate services ( e.g. Stock prices sent to your phone )
  • 157. H Automatic National Roaming PLMN "A" PLMN "B" PLMN "D" PLMN "C" STP Roamer from "A"
  • 158. H Automatic International Roaming PLMN "A" PLMN "Z" Country Interntl Gateway Interntl Gateway Country Interntl Gateway

Editor's Notes

  1. Wireless is bouncing in human imagination from the very earlier need of communications. Though the term wireless need not apply in the very earlier stages. The effort was to establish connections without physical resources or connections. Like for example the above picture is an army wireless signaling method. To send a message or a signal to someone away, a very common old method was to shout loudly, make some noise , but then you loose the secrecy behind communication, so to overcome, army started using colourful flags, so the advent of wireless communications.
  2. A basic wireless communication model is shown above. The input to a wireless system is the information source, which could be speech , data, video etc. This information goes to a transmitter which modulates the source information to a Radio Frequency Carrier and it is radiated by a transmitter. On the other hand the information is received by a receive antenna from where it goes to the receiver which demodulated the RF carrier and recovers the original information. This information&apos;s then goes to the receiving destination, like the telephone speaker or display or video terminal.
  3. Wireless communications are of different types : like Simplex, half duplex and Duplex. SIMPLEX : In simplex type of communications, the direction of transmission is only. In very simple words the user terminal is either a transmitter or a receiver. In these types of communication, there will be a transmitter which transmits an information modulated RF carrier which is received by the receiver which demodulates the information. Common examples of Simplex wireless communication are Pagers, AM/FM/ Television Broadcast services etc.
  4. In Half-Duplex communication, the direction of transmission is in both direction but not simultaneous , it is alternate. There will a transmitter plus receiver on both ends of communication terminals. As shown above &quot;A&quot; will transmit information and &quot;B&quot; will receive, when &quot;B&quot; wants to reply , it will indicate &quot;A&quot; to stop transmission and &quot;B&quot; will then start transmitting and &quot;A&quot; will receive. Common examples of this type of systems are Push To Talk Radios etc.
  5. In Duplex communication both the information terminals will transmit and receive simultaneously. Duplex communication is the current trend for wireless mobile application, this is because the Mobile applications require simultaneous communications. Now in the previous two cases both the transmitter and receivers are tuned to a single RF carrier, but what should happen in this case, can I use the same frequency on both ends for simultaneous communication. No I can&apos;t these will interfere with each other. So before we go into the discussion in the frequency domain we need to understand the electromagnetic spectrum.
  6. Let us understand the frequency domain in which wireless communications work. The entire electromagnetic spectrum is divided several Frequency bands like MF, HF, VHF, UHF, SHF and EHF. The common property illustrated above is the wavelength which goes on increasing as the frequency increases. Within this entire band, applications are spread. The spread in applications is based on the properties of electromagnetic waves. Up to 1GHz and also near to 2 Ghz are used for consumer applications like FM radios, Television broadcast, Mobile Telephony etc. From 2 GHz to 100Ghz is the Microwave band. Above 100 Ghz is the Millimeter waves.
  7. Now let us understand why the applications explained on the previous page are spread in specific frequency bands. This is because of the properties of the Radio Frequencies. A common property of Radio frequencies is the loss. Any RF transmission through any media will suffer loss. This loss goes on increasing with higher frequencies. And any RF receiver has a finite sensitivity, the ability to recover the RF signal at its receiver input. So the higher the frequency more will be the loss, and hence low level of signal will come at the receiver, To overcome the poor reception , that is to get level of signal coming at the receiver , the RF frequency should be transmitted at higher power. High Power again increase the health hazards , the effect of which is also proportional to frequency , i.e. the effect of higher frequency transmitted at a certain power X dbm will be higher than a lower frequency transmitted at the sam power of X dbm. So the selection of frequency depends on Application . Based on this the RF spectrum is divided into Application band. The lower frequency bands are used for consumer application where human beings are involved in the transmission and reception of Radio frequencies very closely like Mobile Phones, Domestic Radios , Television broadcast etc. The Application bands are further divided into Technology bands . This is because for certain user applications like Mobile Telephones there are different technologies like Analog , Digital etc., and in many countries different technologies operate simultaneously , so naturally they need to operate in different bands.
  8. As explained earlier the frequency bands are further divided into several application segments. Like Mobile Telephone communications always operates in either the 800- 900 MHz and 1800-1900 MHz band. From these bands, certain specified segments or so called blocks are reserved for certain applications by regulating authorities which reserve this since these blocks are defined by the standard technologies. An example for this is the Mobile Telephone Communications. As mentioned above, these 50 MHz bands are reserved by the regulating authorities as defined by the standards. AMPS/DAMPS band is regulated by TIA , whereas GSM band is reserved by ETSI. What does this mean 50 MHz band to be used for Mobile Communications. But when it is Mobile Communication it is just not one user but several users. This means this needs a further division in the band. So to provide multiple access these 50 MHz bands are further divided into Channels. But how ? Today worldwide there are three channelization methods used , FDMA, TDMA and CDMA.
  9. All the mobile Technologies don&apos;t need very large bandwidth for single user communication. Technologies have well defined the bandwidth required for each call. Like AMPS needs 30 Khz of bandwidth in one direction for communication. Similarly GSM needs 200 Khz for one direction communication. This means if the AMPS band is divided in 30 Khz channels, we can have 1666 Freq channels and similarly for GSM we can have 250 Freq channels. And this is what is practically done. This method of dividing a Frequency band into small bandwidth user channels is termed as Frequency Division Multiple Access ( FDMA ). The term itself specifies Multiple Accesses ( means users ) in a band by dividing into several small Frequency Channels.
  10. It was found later that division by Frequency itself was not sufficient to meet the capacity requirements. So each FDMA channel is further divided into time domain into timeslots. This means now multiple user will use the same FDMA channel , but will not at the same instance. Each user will be given a timeslot, which is of a fixed time period. One user will accomplish communication in that time period and then will remain idle for remaining timeslots which are used by other users. With this the capacity is increased, i.e. now more users can use the same old number of FDMA channels. This method of increasing multiple accesses is termed as Time Division Multiple Access ( TDMA ). For example: AMPS FDMA Channels were divided in 3 timeslots and a new technology was created which was DAMPS. So with DAMPS now we have 4998 Channels. And Similarly in GSM we have 8 timeslots on each FDMA Channel , so we have 2000 Channels.
  11. Code Division Multiple Access is a completely different method of Multiple Access. In CDMA the FDMA Channel is of very large bandwidth i.e. 1.25 MHz. This 1.25 MHz channel is divided into 64 code channels. Each code channel can be used by a different user. All the users will communicate at the same time and will only receive and transmit information correlated to its code. We will discuss CDMA in more details in later sections.
  12. What access methods are we going to use for WLL. First of all WLL as mentioned earlier is not a technology so it uses available wireless telephone technologies with some implementation modifications. WLL needs Duplex Communication . Now lets refresh , in duplex communication the transmission and reception occurs at the same time, so naturally it cannot occur on the same resource or channel. So at least two channels are required for one call. Now what type of two channels. These Duplex channels should be based on the existing Channelization methods.
  13. The above figures illustrates two methods of Duplex Communication. Frequency Division Duplex (FDD) : In this we use the existing the FDMA technique. With FDMA we have divided the application band into several small bandwidth channels. Now for each call, the user will transmit on one FDMA channel and receiver on another FDMA channel. So for each call a pair of FDMA Channels are required . TDD : With this method the transmission and reception takes place on the same frequency but at not at the same time. Each FDMA channel is divided into separate Transmit and Receive Timeslot. The user may first transmit for a specific period and then receive in the next time period. Though this theoretically is not duplex communication but practically it is since the user does not recognize this alternate transmission and reception, since the time periods are very small in microseconds.
  14. To provide wireless communication access to subscribers, we need a pair of RF channels per active call. In a large city , with several thousand subscribers, number of channels required would be so large that they can not be accomodated on one site. Also, there is a limit to availability of spectrum. If an operators get a 5 MHz band, then he has only 25 channels to use !!! With 25 channels loaded at one site, he can offer cellular service to 2000 subscribers at most . ( In GSM , each RF channels accomodates 8 traffic channels ). To overcome this limitation, you have to create zones of coverage, which are called as CELLS.
  15. Each cell has a Base Station Transeiver ( BTS ) at the chosen site. The location of BTS site depends upon several factors.. 1. Coverage in prime localities / hot spots is the most important criteria in choosing the BTS site. 2. Terrain - Type of buildings in the area to be covered. 3. Availability of proper site - COST factor 4. Availability of open space, power supply , security 5. Nearby installations of Cellular / other transmitters. 6. Access to the network - leased lines / Microwave link / Optical link. &quot;Number of BTS&quot; sites is a measure of the size .
  16. As a convention and for simplicity in representation, Cells in Cellular system are shown as Hexagons. The actual cell covered by a Base station takes a very different shape depending upon the terrain, obstuctions and transmitting antenna charecteristics. The cells are of different sizes and shapes. To cover a densly populated areas, smaller cells are used. Where as large cells cover a low subscriber density areas. On the highways and main roads, cell size is optimised to cover larger length of the cell along the road. This is made possible by using a highly directive antenna.
  17. Distance between two cells using same frequency is given by D=R * SQRT(3 * N ). This distance is a deciding factor on what cluster size has to be used. A small cluster size would give a smaller D, which means interference form cell using same freq is going to be higher. A large value of n ( eg. 12 ) would give larger value of D , which is good in terms of interference. But this would affect the number of frequencies available for loading per cell. For N=3 ,
  18. The Global System for Mobile communications (GSM) is a huge, rapidly expanding and successful technology. Less than five years ago, there were a few 10&apos;s of companies working on GSM. Each of these companies had a few GSM experts who brought knowledge back from the European Telecommunications Standards Institute (ETSI) committees designing the GSM specification. Now there are 100&apos;s of companies working on GSM and 1000&apos;s of GSM experts. GSM is no longer state-of-the-art. It is everyday-technology, as likely to be understood by the service technician as the ETSI committee member. GSM evolved as a mobile communications standard when there were too many standards floating around in Europe. Analog cellular was in use for several years in different parts of world. Even today there are few networks of Analog cellular. The experience of analog cellular helped in developing specifications for a Digital Cellular standard. The work on GSM specs took a completed decade before practical systems were implemented using these specs. GSM is quickly moving out of Europe and is becoming a world standard. HP has become expert in GSM through our involvement in Europe. With excellent internal communications, HP is in an excellent position to help our customers, in other regions of the world, benefit from our GSM knowledge. In this presentation we will understand the basic GSM network elements and some of the important features. Since this is a very complex system, we have to do develop the knowledge in a step by step approach.
  19. GSM is truly becoming the GLOBAL System for Mobile Communications. It&apos;s been clear for a long time that GSM would be used across Europe. Now, many countries around the world, who have been delaying their decision, have selected GSM. GSM has become a Pan Asian standard and is going to be used in much of South America.
  20. PCN started in the UK with Mercury One-to-One and Hutchison Microtel (Orange) offering the first two networks to use DCS1800. The UK PCNs have had overwhelming success with their competitive business tariffs and cheap off-peak calls. Germany&apos;s E net followed the UK PCNs. DCS1800 is becoming more widespread with systems in Thailand, Malaysia, France, Switzerland and Australia. Further systems are planned in Argentina, Brazil, Chile, France, Hungary, Poland, Singapore and Sweden. Even the USA, which has shunned the adoption of GSM900, is about to use the GSM based PCS1900 for it&apos;s PCS system. In the USA, GSM will share the allocated bands with other systems based on CDMA, NAMPS and IS-136 TDMA. The PCS1900 licences already cover approximately half of the US population, and we are likely to see this increase to close to full coverage as remaining licences are granted.
  21. GSM Requirements The quality of Voice in the GSM system must be better then that acheived by the 900Mhz analogue systems over all the operating conditions. The system must offer encryption of user information. The system must operate in the entire frequency band 890-915Mhz and 935-960MHz. An international standardized signalling system must be usd to allow the nterconnection of mobile switching centres and location registers. Minimize modifications to the existing fixed public networks. Design the system so handsets costs are minimised Handsets must be able to be used in all participating countries. Maximum flexibility for other services like ISDN System should maximize the functions and services available to cater for the special nature of mobile communications.
  22. evelopment of GSM. The seven companies are: American Personal Communications (APC), American Portable Telecom, Bell South Personal Communications, Intercel, Omnipoint, Pacific Bell Mobile Services and Western Wireless Co. Many of the large GSM manufacturers are also backing PCS1900 including Nokia, Ericsson, Matra, AEG, Northern Telecom. In technical terms PCS1900 will be identical to DCS1800 except for frequency allocation and power levels. The first commercial PCS system was launched by APC, under the name of Sprint Spectrum on 15th November 1995, based on PCS1900. The majority of US PCS licences will becom operational over the next two years. Other systems are also on trial in the US, including DECT.
  23. w services such as data and fax to GSM and DCS1800.
  24. The first generation of mobile telephony systems began with the analogue FM, and frequency division duplex (FDD) systems, AMPS, TACS and NMT. These systems are still heavily subscribed in many parts of the world, but are now rapidly being replaced by second generation systems. The second generations systems, such as GSM, IS-95 CDMA, D-AMPS and PDC offer higher speech quality, higher capacity, data, spectral efficiency, security and better roaming capability. While these systems are still growing, the standards bodies and manufacturers are looking to the future and the third generation (3G). The contenders for third generation systems are: EUROPE - ETSI W-CDMA ASIA - ARIB W-CDMA US - UWCC D-AMPS IS-136 - CDG cdma2000
  25. The concept for a 3G system includes: wireless multimedia, bandwidth on demand, integration of satellite and terrestrial services, and continous worldwide coverage. A broad spectrum of terminal complexity is anticipated, including “machine users”, e.g. vending machines reporting stock status. The International Telecommunications Union (ITU) has been holding discussions on “Future Public Land Mobile Telephony Systems” (FLMTS) since 1978. This acronym has now been replaced by the term IMT-2000. “IMT” stands for International Mobile Telecommunications and the “2000” represents the approximate operating frequency and approximate timescale for deployment
  26. BTS : Base Transceiver Station BSC : Base Station Controller MS : Mobile Station TRAU : Transcoder Rate Adaptation Unit MSC : Mobile Switching Center HLR : Home Location Register VLR : Visiting Location Register AUC : Authentication Centre EIR : Equipment Identity Register SMSC : Short Message Service Center VMSC : Voice Mail Service Center BC : Billing Center OMC : Operation
  27. Mobile Station is rthe gadget used by a GSM subscriber. Mobile Station provides the user the GSM communication services for Voice and Data. GSM Mobile Phones are made according toGSM standards. Each and every Phone produced in the world by any manufacturer complies to GSM standards. Any make Mobile Phone can be used on any GSM Network. GSM phone cannot be used, until it is activated by the Service Provider. This activation is done by providing a SIM card to the user. SIm card is plugged inside the MS. This SIM card has an identification which is unique to the SIM card. MS also has other identification which is its unique IMEI number. IMEI number is also soterd in a central database called EIR . Mobile Sation locks to a Base Station, the one closest to it when it turns ON. Mobile station also scans neigbor cells signals when it is idle and also when it is on call. On the other hand, the network also know the whereabouts of the Mobile and updates it in its databases the VLR and HLR. Mobile transmits and receives voice at 13 kbps over air interface.
  28. Mobile Stations major discrimination is on its Power Class. Power Class of the Mobile is the maximum power which the mobile can transmit under extreme condition when commanded by the BTS. The different power capabilites of the Mobile Phones are 20W, 8W, 5W, 2W and 0.8W. The most commonly used class of mobile is 4, i.e 2Watts . The importance behind the Output Power is that it defines the accessibility of the Mobile Phone in areas of poor coverage. High Power Class may not transmit always at full power , hence this results into excess talk time and standby time. Actual ouptut powr when the Mobile is on call is varied as commanded by the BTS , which is based on the Path Loss
  29. The Mobile Station has two indentities associated with it : MSISDN: Mobile Sation International Dialled Number) : This is the human identitiy associated with the Mobile Phone. This identitiy is used by the users to identify their subscription numbers and also by others to call Mobile Phones. This identity is not stored anywhere in the Mobile Phone. It is availble in the Network database (HLR). The objective of this identity is to route the call over the fixed and Mobile Phone network. It is made up of CC ( Country Code ) which provides uniqueness in routing calls to GSM operations country. Within the country the NDC ( National Destination Code ) provides uniques to the different operators. Finally the SN( Subscriber Number) discriminates each subcriber within a network. IMEI ( International Mobile Equipment Identity ) : This is a unique number stored inside the ROM of the Mobile Phone. Its uniqueness lies in the TAC (Type Approval Code ) which is alloted by the MOU to a new mobile which passed the confrmation specifications. After which the manufacturer may discrimate individual phones by FAC (Final Assemble Code) , SNR (Serial Number) and also by the SP ( Spare digit ) typical used for software version
  30. SIM card as defined by GSM is a removable module which can be insertd inside the Mobile Phone when the user wnats to use the MS. It is available in two sizes the Credit Card size ; known as ISO SIM or the Stamp size ; known as Pug in SIM. SIM card has a unique information on it which is its idnetity the IMSI ( International Mobile Subscriber Identity ). This identity is unique to each SIM used in any of the GSM Networks. this identity si used by the Network to accomplish Signaling with the MS and also to d signaling with other GSM networks for information transfer related toa particular connection. The IMSI is a 15 digit identity which consists of MCC ( Mobile Country Code ) which is unique to each GSM Operations country, the MNC( Mobile Country Code) which discriminates the networks within a MCC , further the MSIN ( Mobile Subscriber Identity Number ) which discriminates individual subscribers ina network. SIM also has a two level protection to prevent misuse. SIM can be optionally by the user be set for a PIN code . Whenever the Mobile is turned ON or the SIM is inserted , the Mobile will ask the user to enter the PIN code. If three false entries of SIM card are entered then the SIM is blocked . The the user needs to enter a Pin Unblocking Key ( PUK) . Ten fakse entries of PUK will permanently disable the SIM card permanently.
  31. Apart from the IMSI, SIM also contains some other essential information which is required to establish successful communication with the network like the subscriber key and algorithms are used for authentication and Ciphering. SIM also contains a list of preferred networks which the Mobile hunts for when it turns on. Ther are several other features and contents on the SIM which are personalized by the Service Provider which activates the SIM card. MS also stores some information on the SIM card EEPROM like its location information and some timer values.
  32. The above figure represents a generic cell site architecture. The BTS is installed ina cabin/shelter or a room. There is an AC Mains Panel to which the AC mains enters and is properly through fuse panels is distributed to the DC Power Supply unit, which rectifies this AC and provides DC power Supply to the Base Station. Typical Operating Voltage Levels of Macro BTS is 48V. There is also a Battery Backup to provide power to the BTS in the event of the Main Power Failure. The swicthing from Mains to Batteries is also done through the Power Supply Unit. All the elements inside the cabinet generate failure alarms and are connected to an Alarm Interface Panel which is then connected to the BTS. The BTS on the other side is connected to the Antenna System, which comprises of Transmit and Receive Antennas. The number of Antennas depends on the loading on the Base Station , basically the number of sectors it controls.The BTS is also connected on a Abis Interface ( E1/T1) to the BSC. The transport media for this could be coaxial, fibre or most commonly used Digital Microwave Radio. We will now in further slides understand the architecture inside the BTS cabinet and also the differenet variations in the Antenna System. Then we will also see the Abis configurations.
  33. Base Transceiver Station which is the key element inside the cell site has set of tanscivers which transmit and receive RF energy with the Mobiles in its area. On BTS will have mimnum cell or more than one cell. The number of transceivers inside the BTs will depend upon the capacity inside the cell. BTS is connected on a G.703 Abis Interface to the BSC. BTS transmits and receivers voice at 13 Kbps over the air interface to the Mobiles. BTS also carries out certain pther functions with the Mobiles like controlling the Transmit Power and Timing instance of the Mobile and also commanding handovers to the Mobile Stations.
  34. re are two TRX&apos;s os tow Receiver Carreir swill also come, and these two receive carrieres will be received b tow Antennas. Each Antenna wil receive two signals, so four signals come to the Splitter. Each trasncverneeds inputs from both antennas , the splitter will split this enerege coming at inout to both the TRX&apos;s. PCM Interface. This is a G.703 interface which connects the BTS to the BSC, and his interface in GSM Trmonlgyy is termed as Abis interface. Alarm Interface. All the external Alamrsm a re connected to this interaface , from hermessages realted to alarm are sen on the )&amp;M interface to the BSC. TRAU :Transcodr Rate Adaptation Unit . If ranscoding is used locally inside the BTS , then this unit will be presnet to code the speech from 13 Kbps to 64 Kbps. If transcoding is to be done at hte BSc or MSC , then this unit will not be present..
  35. The block diagram illustrates a typical architecture for a single sector BTS with three transmitter / receiver pairs (TRXs) - i.e. this BTS has three frequencies on which it will transmit on the downlink and receive on the uplink. Base stations will have their link to the rest of the network, the Abis link, provided either over a standard 2mbits (1.544 in the US) link or via a microwave link. Additionally interfaces may be provided to access internally generated BTS alarms and some troubleshooting information via a propietary NEM specific port. The CPU carries out the processing associated with these links. The frequency reference unit generates the timing to be used by the TRXs. This is normally derived from the Abis link, but may also be an alternate external reference e.g. a GPS receiver, or an internal frequency reference. The TRX can be divided into logic, RF and amplification functions. The logic function is responsible for communication between the TRX and other parts of the BTS. It also performs uplink and downlink digital signal processing such as channel coding, interleaving, ciphering, burst formatting and equalization. The RF function contains the actual radio transmitter and reciever. The combiner / distribution unit is the interface between the TRXs and the antenna system, combining transmitted signals from the TRXs and distributing received signals to all TRXs. By using multiple combiners, antenna diversity can be introduced to reduce the impact of fading.
  36. BSC : Base Station Controller which has several BTS&apos;s connected to it. Depending upon the number of BTS&apos;s there will be BSC&apos;s. The BSC&apos;s will be finally connected to the MSC. So for example, when a call is made from a fixed line to mobile, it is routed from PSTN to MSC, then to BSC and BTS and to Mobile. The BSC controls various functions of BTS and Mobile, like assigning a channel for call, handover etc.
  37. The Base Station Controller though controls the BTS which is a radio equipment, but the BSC itself is not a radio equipment It has no radio elements inside it. The BSC has processor boards and PCM interfaces to provide connections to all the BTS&apos;s and also on the other side to the MSC. The BSC has a major role to play in swithcing traffic ciruits from the Abis to the A interface. The BSC may also have optionally a TRAU, if transcoding is to be done at the BSC.
  38. Abis is the PCM interface between the BSC and MSC. Physically this is a G.703 interface and could be E1 or T1. in all our further dsicussions we will consider E1. Abis carrier the traffic and signalling information for all the transceivers inside the BTS. It also carries O&amp;M information between the BSC and BTS, like the control caommands coming from the BSCand traffic reports orginated by the BTS. Abis used the HDLC protocol for signalling which is LAPD ( Link Access Protocol on D channel ). LAPD has severla modes of operation. What modes means is how the signalling circuits are distributed over the E1 interface, wether each TRX has seperate signalling circuits or several TRX signalling information is concentrated or multiplexed on limited signaling circuits.
  39. The first LAPD mode illustrated above is the LAPD basic mode. In this mode each TRX has a separate signaling circut of 64 Kbps. Each signalling ciruit has two immediate 64 Kbps Traffic ciruits. GSM used 13 kbps of speech rate on the air interface, to which some TRAU information is added and it becomed 16 Kbps. Four such 16 kbps traffic channels are mapped on one 64 Kbps ciruit. EAch TRX has 8 traffic channels. So for each Transceiver two 64 kbps ciruits are required for Traffic and one for Signalling. So with this mode, 10 Transceivers can be accomodated on one E1.
  40. In this mode which is LAPD Concentrated Signaling information for certain number of TRX&apos;s are concentrated on a single 64 kbos circuit. There are two different methods of concentration. The above figure illustratesone method in which on one 64 kbps ciruit the signaling information for 4 TRX&apos;s are concentrated. This is typically done by creating 16 kbps subchannels. So with this metod 13 TRXs signaling as well as speech can be accomodated on a single E1 Link.
  41. In this type of concentrated LAPD mode , signaling for all the Transcevier are concentrated on one 64 kbps circuit. With this 15 TRX&apos;s signaling and Speech can be accomodated on 1 E1 link. This method is becoming very poplular and is adopted by many of the NEMS.
  42. LAPD multiplexed is a mode in which Signaling for each TRX is on a 16 kbps ciruit which is multiplexed wiht 3 speech channels of 16 Kbps. So for each TRX two 64 kbps circuits are required.
  43. TRAU is the Transcoder Rate Adpatation Unit in short referred to as Transcoder which provides the function of coding speech from 13 kbps to 64 kbps and vice versa. The Mobile Switching Center (MSC) is based on ISDN switching. The Fixed network is also ISDN based . ISDN has speech rae of 64 kbp but the GSM Speech rate is 13 kbps, so in order to do the switching the 13 kbps speech channels should be transcoded to 64 kbps and vice versa in the reverse direction. This function is accomplished by the Transcoder. The Trasncoder does not actually gets 13 kbps inputs, because to the 13 kbps the BTS adds 3 kbps of additional information and makes it 16 kbps. The location of the TRAU is implementation dependent, but it is always preferred to locate the TRAU as close to the MSC as possible, since saves on connectivity resources.
  44. The transcoder may be located with the MSC,BSC or BTS.If it is located at the MSC,the 13 kbps channels are transmitted to the BSS by bit stuffing them to a data transfer rate of 16 kbps and then fitting four of them into each 64 kbps circuit. This type of transcoding when done at the MSC is known as remote transcoding since the transcoder device is remote to the BTS.Thus with this type of transcoding each 2.048 Mbps stream from the MSC can carry 120 GSM speech channels.thus increasing channel capacity and thereby reducing cost.
  45. MSC : Mobile Switching Centre is the heart of the GSM network. This element is similar to any PSTN exchange. It does the switching of call, which in other words means connecting , maintaining and release of mobile to mobile and mobile to PSTN and PSTN to Mobile calls. MSC has the database of all the subscribers in the network. It has different sub units for maintaining these databases which are the HLR and VLR. The subscriber database include the subcriber no&apos;s and identities like IMSI , MSISDN etc. It also has the listed subcribed features against each subscriber no. All the BSC&apos;s in the network are connected to the MSC. MSC connects all the calls coming in and going out to PSTN ( fixed line phones ) through the BSC&apos;s. MSC is weighted on the basis of how many subscribers it can support. For example an MSC of 1 lac subscribers means one MSC is enough till subscriber base increases upto 1 lac, beyond which another MSC will be required
  46. As the number of subscribers increase, it will exceed the capcaity of one MSC, so another MSC&apos;s will be require, and another when the subscribers agian doubel up. All the MSC&apos;s in the network have to communicate with other and also with the outside world. It will be very complicated to connect every MSC to each other and also each MSC to PSTN, so the concept of GMSC ( Gateway MSC ) is used which as the name says is a gateway to all the MSC&apos;s to the outside world.
  47. MSC is the entity which establishes calls. To establish calls and other user related services, it needs to know who are users ( list of all subscribers ) and thier secret identitiies, and what services they are allowed. This results into huge database taking into consideration a huge size of GSM subscibers. So to accomplish calls and other services, MSC communicates with HLR and gets some data pertaining to the subscriber. HLR will have a series of subscriber numbers to used in the network, but all all them may not havebeen activated or issued.
  48. VLR has a database of those susbcriber no&apos;s which are activiated , which means those no&apos;s for which the SIM is issued and the subscriber has turned on at least once. So when a SIm is issued , and the Mobile the turns On, the number of the mobile is ckecked with HLR and then registered in VLR. VLR also has temporayr data pertaining to each susbcriber. Temporary data means this data is always changing, which includes the mobile status (like on/off ), and the location of the mobile, that is in which cells is the mobile, so that the incoming calls can be diverted to those cells. In the case where there are more than one MSC, and also in case of raoming , when the mobile comes from some other MSC, it is not known to the visiting MSC, so it is checked with the HLR, and then temporarily registered in the VLR.
  49. When a subcriber takes service from an operator, it is issued with a SIM card, this SIM card as we discussed earlier has an IMSI corresponding to which is the MSISDN ( 98xxx.... ) which is known to the subscriber. Now IMSI is an identity which is used by the network to communicate with the mobile. So it can be easily be captured and a bogus or fraud SIM can be manufactured easily. TO avoid this the process of Authentication is used, which is the verification of SIM before a service is alloted to a subscriber. This is done with the help of a Secret Key ( code ) which is avialble on the SIM. This Key associated with every SIM which means with every IMSI and is different for each SIM. This pair of IMSI and Key is also available at the HLR -AUC. The AUC associated with the HLR does this job of verification of SIM. The Mobile is asked to send its secret key by performing some operations on it by using some number send by AUC. The secret key is then send in this coded form to the MSC , where it is verified.
  50. EIR is the records of the valid IMEI&apos;s . Valid IMEI&apos;s mean those mobile equipments which are type approved. MSC may ask a mobile to send its IMEI, which it checks with the EIR, to find its validity. In the EIR, the IMEI&apos;s are classifiefd into three categories. White List : This contians the IMEI of type approved mobiles. Black List : List of IMEI&apos;s which shold be barred because either they are stolen or are not functioning proprerly Grey List : List of IMEI&apos;s who are to evaluated before they are put in black list.
  51. Billing Centre is the network which generates the billing statement for each subscriber in the network. The MSC sents the billing information of each subscriber to the BC which will have subscriber identity, called number, date and time stamp and duration. The BC then produces the billing amount based on the data received from the MSC. The BC will the information about the units of charge and the susbsidised charge time ( non-peak, midniht hours) , date ( low rate holidays, national holidays, seasonal low rate days , etc ). The BC amy or may not be connected directly to the MSC. If it is connected directly to the MSC, the MSC will send the billing data at regular pre-defined intervals. If it is not connected to the MSC, then the MSC will save the billing data on some tape drive or any other storage device, which will be then fed to the BC, which then generates the billing informatio. In this case the billing operation has manual job, as to remove the stored data and then feed to the BC.
  52. OMC is th operations and maintenance network. Every entity requires some care and maintenance, so are GSM network elements. GSM is a huge network made up of more than 100 BTS&apos;s , several BSC&apos;s and MSC, so there will frequent failure with these elements. It will be very difficult to man all these elements, hence some remote operation is required . OMC is the network element which provides remote access to all the network elements and monitors the performance of each network element.
  53. As seen in the previous diagram, there is one OMC system for both MSC and the radio betwork. In case where the MSC and the Radion network are brought from different suppliers, or otherwise also it can be two types of OMC,. OMC -S : which deals with the switch i.e. MSC OMC - R : which deals with the radio network
  54. The figure shows the structure.Heres the network comprises of BTS,BSC and a remote Transcoder.As per GSM recommendations the OMC signalling for every BSC and transcoder is done over 64 kbps channel.This link is known as OML ( Operations and Maintenance Link) and it uses the X.25 Signalling protocal.All OML&apos;s from different entities are muliplexed at the MUX and the then switched over by the X.25 switch and fed to the various OMC terminals connected to the server.
  55. OMC Fucntions can be in general dived into three categories. Alarm Monitoring : This is the prime function, which continously monitors the alarm reported by all BTS&apos;s, BSC&apos;s, MSC and other elements.It gives an audible alarm for pre-set alarm conditions. Alarms for field sites ( BTS&apos;s and BSC&apos;s ) also include environmental alarms, which are must for field located sites as these are in cabins and rooms which have supporitng accessories like power , airocns, and fire hazards , security problems, since it is not possibel to man hundreds of fields locates sites for these type sof issues, so these alarms are also reported to at the OMCR. Configuartion Changes : All the GSM network elements are highly digital systems, with enormous software control, so there is almost continous requirement of software changes in the existing systems, and also with expansion all the changes are to be done form OMC. Performance Analysis : The OMC also gives the data for network performance which is an indication of quality of service provided to your customer. OMC gives statiscal analysis of traffic like total calls made, no og outging and incoming calls , incoming calls, MS to MS, MS ot PSTN calls etc, no calls dropped , traffic loading on the loading etc. With this data the network quality ia observed, with which further network expansion and other functions could be planned effectively.
  56. The equipment related alarms are generally total failure of the equipment,where the site is totally down but the link to the site is up. The Link Failures are the failure of connectivity between BTS to BSC or BSC to MSC etc.These generally contain some information by which it can be a diagonised that the link at which end has failed. The Module failure is generally failure of any hardware module in the equipment which could be processor,a transceiver,combiner etc. These alarms are generally generated by the equipments and send across to the OMC where the OMC catergorises these and displays it in a systematic manner. These OMC has a database where these alarms are logged and could be reviewed later for analysis.
  57. The above graph represents a performance statistics display for TCH traffic summary report for a 12 hrs period. A1,A2,A3 are the sectorial cells for cell site A.
  58. link and a downlink. It&apos;s interesting to note that while the TCH uses a frequency channel in both the uplink and downlink, the BCH occupies a channel in the downlink band only. The corresponding channel in the uplink is effectively left clear. This can be used by the mobile for unscheduled or random access channels (RACH). When the mobile wants to grab the attention of the base station (perhaps to make a call), it can ask for attention by using this clear frequency channel to send a RACH. Since more than one mobile may want to grab attention at the same time, colliding RACHs are possible, and mobiles may need to make repeated attempt to get heard.
  59. GSM uses TDMA (Time Division Multiple Access) and FDMA (Frequency Division Multiple Access). The frequencies available are divided into two bands. The uplink is for mobile transmission, while the downlink is for base station transmission. The slide shows part of one of these bands. Each band is divided into 200kHz slots called ARFCN (Absolute Radio Frequency Channel Number). As well as slicing up frequency, we also slice up time. Each ARFCN is shared between 8 mobiles, each using it in turn. Each mobile uses the ARFCN for one TS (Timeslot) and then waits for its turn to come round again. Mobiles get the use of the ARFCN once per TDMA frame. The slide illustrates 4 TCH (Traffic CHannels). Each one of the TCH uses a particular ARFCN and Timeslot. Three of the TCH are on the same ARFCN, using different timeslots. The fourth TCH is on a different ARFCN. The combination of a TS number and ARFCN is called a physical channel. There&apos;s not much space between timeslots and ARFCN&apos;s. It&apos;s important for the mobile or base-station to transmit their TDMA bursts at exactly the right time and with exactly the right frequency and amplitude. Too early or too late and a burst may collide with an adjacent burst. Poorly controlled modulation spectrum or spurious will cause interference with adjacent ARFCN.
  60. Most modern digital communications systems use some sort of voice compression. GSM is no exception. It uses a voice coder to model the tone and noise generation in the human throat and the acoustic filtering of the mouth and tongue. These characteristics are used to produce coefficients which are sent via the TCH. The speech coder is based on a residually excited linear predictive coder (RELP), this is enhanced by including a long term predictor (LTP). The LTP improves speech quality by removing the structure from vowel sounds prior to coding the residual data
  61. Speech is captured in blocks of 20ms and coded into 260 bits, which are ordered accordingly into Type 1a - 50 bits,Type 1b - 132 bits and Type 2 - 78 bits.These 260 bits gives out a data rate of 13kbps which is the GSM speech rate. These bits are then channel coded for error correction and converted to 456 bits which yields out a data rate of 22.8kbps which is data rate on Air interface.These 456 bits/20ms is deoded down to 260 bits at the BTS which again gives the original speech rate of 13Kbps. These 260 bits speech is again bit stuffed with 60 bits by the transcoder handler which gives out a rate of 16kbps which is mapped on Abis.
  62. The conection between BTS to BSC is on Abis interface. This is done on 2.048 physical layer which has 32 timeslots of 64kbps each. Time slot 0 is for sybchronization whereas one timeslot for signalling and remaining for speech. The speech timeslot of 64kbps each contains 4 sub channels of 16 kbps each of 4 different circuits. Each 16 kbps subchannel consists of 50 TRAU frames ,with each frame consisting of 260 + 60 bits = 320bits derived from 20ms blocks of speech. These 60 bits contains the TRAU information which has 35 bits for synchronisation between Transcoder unit and TRX, 4 bits for Time Alighnment and 21 control bits which has information about the frame like the frame is of speech,data,idle,O &amp;M,fullrate channel and half rate channel.
  63. In the timeslot structures we saw, there was 26 bits referred to as either a mid-amble or a training sequence. For a normal burst this mid-amble will consist of 8 base station colour codes and these are numbered 0 through 7. They are 26 bits long. Another mid-amble or training sequence is used in the random access channel (RACH) and it is 41 bits long. There is also a 64 bit long sequence that is used on the SCH or synchronisation channel. Mid-ambles are placed in the centre of the burst to minimise the time difference from to any bit in the burst. The mid-amble has a number of different uses, the most important is equalisation to improve bit error rate. The mobile knows the mid-amble it should be receiving (part of the information the MS gets when assigned to a BS). This is a pre-defined sequence is 26 bits in the case of a traffic channel. It receives the mid-amble and compares the it to what it should have been. From the difference it can estimate the impulse response of the transmission path at that instant in time. Once it knows the impulse response it can mathematically calculate an inverse filter, it can apply this filter to the data bits on each side of the mid-amble and clean them up, reducing the chance of detecting a bit wrong. This is referred to as equalisation or the equaliser within the radio. Equaliser mechanisms are a closely guarded design feature of most mobiles. It&apos;s a key area of competition between mobile manufacturers.
  64. Since GSM is a TDMA system and there are 8 users on a frequency pair, each user must only turn his transmitter on at the allowed time and, have his transmitter off in time so that he does not interfere with other users in the adjacent timeslots. Because of this need, GSM has specified an amplitude envelope for the RF burst of the timeslots. There&apos;s also a demanding flatness specification over the active part of the useful bits in the timeslot. The amplitude envelope has greater than 70dB of dynamic range yet needs to measure less than +/-1dB flatness over the active part of the timeslot. All of this is happening over the 577µs period of a timeslot.
  65. ft are tied together by a factor of 4, filtering can not affect the average phase relationships. The filtering does slow down the rate of change of phase velocity (the acceleration of the phase). When Gaussian filtering is applied, the phase makes slower direction changes, but may reach higher peak velocities to catch up again. Without Gaussian filtering, the phase makes instantaneous direction changes, but moves at a constant velocity. The exact phase trajectory is very tightly controlled. GSM radios need to use digital filters and I/Q or digital FM modulators to accurately generate the correct trajectory. The GSM specifications allow no more than 5 degrees rms and 20 degrees peak deviation from the ideal trajectory.
  66. To see how information is transmitted let&apos;s look at an example. We have been assigned timeslot 2 and we&apos;re in a traffic mode, receiving and transmitting information to the base station. The downlink, on which we receive information, will be in the frequency range of 935 to 960MHz. The uplink, the frequency which the mobile will transmit information to the base station, will be in the frequency range of 890 to 915MHz. The uplink and the downlink make up a frequency pair, which for GSM900, is always separated by 45MHz. We can see that the timeslots are offset by 3 between the downlink and the uplink. We receive information in timeslot two in the downlink we have two timeslots in which to switch to the uplink frequency and be ready to transmit information. Then, we have to get ready to receive our next time slot of information in the next frame.
  67. As the mobile moves around the cell, it&apos;s transmitter power needs to be varied. When it&apos;s close to the base station, power levels are set low to reduce the interference to other users. When the mobile is further from the base station, it&apos;s power level needs to increase to overcome the increased path loss. All GSM mobiles are able to control their output power in 2dB steps. The base station commands the mobile to a particular MS Tx Level (Power level). GSM900 mobile have a maximum power of 8W (the specifications allow 20W, but so far, no 20W mobiles exist). DCS1800 mobiles have a maximum power of 1W. Consequently DCS1800 cells need to be smaller.
  68. Besides receiving and transmitting information, the mobile must switch frequency and get ready to receive and measure the level of the adjacent cell&apos;s broadcast channels. It then reports this (RXLev) information to its own base station in order to establish when a handover is appropriate between cells. Again, information is received on timeslot 2, we switch 45MHz to transmit information and then, need to switch back 45MHz +/- a few MHz to monitor and measure the level of the adjacent cell&apos;s broadcast channels. This information will be reported back to the base station at least every 30 seconds so that the base station can determine the appropriate time to do a handoff. The RxLev information is reported back to the base-station on the uplink SACCH (Slow Associated Control CHannel). The mobile uses a list of ARFCN in the BA (Base Allocation) table to know which BCH frequencies to go out and measure. The BA table is coded onto the BCH, and also the downlink SACCH. This is the primary (or non-hopped) mode of operation in the GSM system. If there is an area which has bad multipath, such as urban areas with lots of reflections from buildings, the cell may need to be defined as a hopping cell.
  69. Timing advance is required in GSM because it uses TDMA with cells up to 35 km radius. Since a radio signal take a finite period of time to travel from the mobile to the base-station, there must be some way to make sure the signal arrives at the base-station at the correct time. Without timing advance, the transmitted burst from a user at the edge of a cell would arrive late and overlap (and corrupt) the signal from a user right next to the base station (unless a guard time, between timeslots, greater than the longest signal travel time was used). By advancing the timing of the mobiles, their transmissions arrive at the base station at the correct time. As a mobile (MS) moves, the Base Station (BTS) will signal the MS to reduce its timing advance as it gets closer to centre of the cell, and increase its timing advance as it away from the centre of the cell. Mobile&apos;s in idle mode (not on a call, but still camped to the network) receive and decode the BCH (Broadcast CHannel) from the base station. One element of the BCH, the SCH (Synchronisation CHannel) allows the mobile to adjust it&apos;s internal timing. When the mobile is receiving the SCH, it doesn&apos;t know how far it is from the base station. A distance of 30km will cause the mobile to set it&apos;s internal timing 100µs behind the base-station. When the mobile sends it&apos;s first RACH burst, it will leave 100µs late, after a 100µs transit delay, it will arrive 200µs late, colliding with the bursts from mobile&apos;s closer to the base station. For this reason, the RACH, and other types of access burst are shorter than normal. The mobile only sends normal length bursts once it&apos;s received timing advance information from the base-station. The mobile in our example would need to advance it&apos;s timing by 200µs. We&apos;ll see later how the base station commands the mobile to change it&apos;s timing advance or transmitter power using the SACCH (Slow Associated Control CHannel)
  70. In GSM , concept of channel needs to be understood very thoroughly. There are several types of channesls defined in GSM . If the context is not clear, it could be vry confusing . To introduce you to the concept of time shared channels , we will use an analogy of a Transport Vehicle. Though the vehicle is a common resource, we use it for various purposes in a day on the basis of time sharing. At times of emergency , we allocate a high priority task to the vehicle to achieve the needs of the hour. . In a similar way several channels in GSM are carried by a few common carriers. The timelines for the usage are very accurately defined. A vehicle that is brand new and is quite strong, is used for moving around in the city. If you put your companies name on the front , people in a city would idntify the vehicle with the company.. This is similar to BCH that carries Network Identity and Base station a Identity. Similarly , in GSM , RF Channels and Time slots define total number of available channels . What information is to be carried on these channels and what time periods is defined by GSM stsandards. There is enough flexibility in the standard to allow operators to configure the channels based upon their current needs. To use the analogy again, If the company is small , you may have just a couple of such vehicles. ( Two channels ) . When company grows bigger, you may dedicate one or more vehicles just to carry employees and drop ( Dedicated channels for TCH ).
  71. eeling flags allow the TCH and FACCH to be distinguished. The remainder of the burst carries data (speech for example) and tail/guard bits to fill the gaps between bursts. It&apos;s easy to get confused about the number of bits in a timeslot, are there 148 bits in a timeslot or 147 bits in a timeslot? There are 148 ACTIVE bits in a timeslot, consisting of the mid-amble, the control bits, the data and the tail-bits. There are 147 USEFUL bits from the middle of the first bit to the middle of the last. Effectively 1/2 a bit off each end is lost.
  72. The concept of a BCH is very simple, but the details can get a little complicated. In simple terms, the BCH acts like a beacon, or lighthouse. It&apos;s on all the time and is the first thing the mobile looks for when it&apos;s trying to find service. The BCH ARFCN has to be active in all timeslots to allow mobiles synchronised to other cells to measure it&apos;s power. The useful BCH information is always carried in timeslot 0. The other timeslots are filled with dummy bursts, or are available for TCH. There are a number of interesting parts to the BCH: The FCH (Frequency correction CHannel) uses a special burst which repeats on the BCH, it has a special fixed bit sequence to allow the mobile to tune it&apos;s internal frequency reference when it first turns on. The SCH (Synchronisation CHannel) has a burst with extended midamble. It&apos;s used by the mobile after the FCH to adjust it&apos;s internal timing and get synchronised to the multiframe sequence. The BCCH (Broadcast Control CHannel) has information encoded on it which identifies the network. It also carries lists of the channels in use in the cell (BA and CA tables)
  73. The CCCH (Common Control CHannel) is like a message board. Just like the FCH, SCH and BCCH, it can be received by any mobile. Sub-channels like PCH (Paging CHannel) are posted on the CCCH. When the mobile sees its number on the PCH it recognises that it should respond by requesting service with a RACH. Another CCCH sub-channel is the AGCH (Access Grant CHannel). Once a mobile has sent a RACH, the base station responds by putting an AGCH on the CCCH, bearing the mobiles random number (read from the RACH). The AGCH instructs the mobile to go to an SDCCH or TCH.
  74. When the mobile has become synchronised to the frequency and frame timing of the cell, and looked at the other information on the BCH it is ready to make and receive calls. Once the mobile is in this state it is &apos;camped&apos; to the base station. If the mobile is near the base station their timing will be closely aligned. If the mobile is on the edge of the cell, maybe 30km from the base station, the SCH will have a propagation delay of 100µs. The mobile&apos;s timing will be 100µs in error. When the mobile sends out a RACH, to start a call, the RACH is transmitted 100µs late, with another 100µs transit time to the base station, it arrives 200µs late. To avoid collisions with bursts in adjacent TS, RACH busts are shorter than normal. The RACH is not the only type of short access burst. When a mobile is handed over to another cell, there will be a short period of time before it receives timing advance information on the downlink SACCH from the new cell. During this period, there&apos;s a risk of the mobiles bursts colliding with bursts in the new cell. Until it gets timing advance information from the new cell it sends short access bursts.
  75. The SDCCH is sometimes configured as a logical channel on the BCH, and sometimes on it&apos;s own physical channel. The SDCCH has a different multiframe structure to the TCH. SDCCH bursts repeat less frequently than once per frame. For this reason, more than 8 SDCCH can share a physical channel. As a consequence, the data rate on the SDCCH is lower than on the TCH. The SDCCH is used like a stepping stone. During the call set-up process, there can be a lot of time between the mobile sending a RACH and getting service, to the start of conversation. Time is taken up while the phone is ringing and waiting to be answered. During this period, there&apos;s a need to exchange control information between the mobile and base station. Alerting messages are sent, and authentication takes place, but there&apos;s no need to send speech information. The SDCCH, by using less of the cells resource of physical channels, improves efficiency, and provides a useful holding channel for the mobile until speech data needs to be exchanged. Just like the TCH, the SDCCH has an SACCH associated with it.
  76. One of the two spare frames every 12 TCH frames is used for the SACCH (Slow Associated Control Channel). On the down-link, the SACCH is used to send slowly but regularly changing control information to the mobile. Examples are instructing the mobile to change its transmitter power (MS TX Lev) and burst timing advance (to compensate for RF transit time) as it moves around the cell. It also carries the BA and CA tables. The up-link SACCH carries information about received signal strength (RXLev) and quality (RXQual) of the TCH and the adjacent cell BCH measurement results (also RXLev).
  77. When the SACCH reports coming back to the base station indicate that another cell would offer the mobile better signal quality, a handover is necessary. The SACCH just doesn&apos;t have the bandwidth to transfer all the information associated with a handover (like the new ARFCN and timeslot, or the MA table). For a short period of time, the TCH is replaced by an FACCH. The FACCH uses consecutive bursts, so has a much higher data rate that the SACCH, which uses only one burst in 26. The frame stealing flags (the control bits on either side of the midamble) are set to indicate that the data being sent is an FACCH, not the TCH. In other respects, the FACCH looks just the same as the TCH. It uses the same physical channel (ARFCN and timeslot). When the FACCH steals bursts from the TCH, speech data is lost. It&apos;s often possible to hear a small speech drop-out when handovers take place.
  78. 1 TDMA burst = 577 usec 1 TDMA Frame = 8 bursts = 4.616 ms 1 TCH Multiframe = 26 TDMA frames = 120 ms 1 CCH Multiframe = 51 TDMA frames = 234.6 ms 1 Superframe is over when the TCH and the CCH Frames are alighned. This can only happen after 26 CCH Muliframes(51) or after 51 TCH Multiframes ( 26 ). This means that 1 Superframe = 51 x 26 = 1326 TDMA Frmames = 6.12 sec 1 Hyperframe = 2048 Superframes = 2715648 TDMA frames = 3hrs 28 min 53 sec 760ms The above derivations show that TDMA frames are numbered from 0 to 2715647 . Confused !! What is the significance for this complex frame structure. As we proceed with our further modules ( Advanced GSM ) these concepts will become clear. For the time being, Multiframe are used for distrubution of logical channels. Superframe is used for Mobile synchrnization and Hyperframe is used for Signalling procedures and Ciphering.
  79. BSS calculates the delay from the access burst. Access burst termed as RACH is the GSM burst of 577usec having 88bits of information anf 68.25 bit periods as guard period. This guard period is used
  80. All mobiles must have the capability of hopping. However, not all cells will be hopping cells. Only those cells which have bad multipath problems will be defined as hopping cells. In this example, there are three frequencies pairs to hop among. The mobile still needs to go out and measure the adjacent cells&apos; broadcast channel (BCH). In the first frame, the mobile receives information on channel 1 downlink, then switches to the uplink for channel 1 (45MHz away), transmits it&apos;s information, and finally monitors one of the adjacent cells to measure its level. The mobile must move to the downlink for channel 2 and receive information in timeslot 2, switch 45MHz, and transmit on the uplink for channel 2. Then it monitors another cell&apos;s broadcast channel and measures its level. This continues through the sequence of frequencies that have been assigned to the cell. The hopping sequence is defined by the CA (Cell Allocation) and MA (Mobile Allocation) tables. The CA table is a master list of all the hop frequencies available in a particular cell. It&apos;s sent to the mobile on the BCH and also the downlink SACCH. The MA table is an index into the CA table, and gives a hopping sequence for a particular mobile. The MA table is sent to the mobile as part of the handover or channels assignment process.
  81. Location Area is the area covered by one or more BTS&apos; s where a mobile can move freely without updating the system. One Location Area can be covered by more than one BSC,but only by one MSC.
  82. By dividing a PLMN area into various location areas,paging load reduce since whenever there is page for a mobile it is send by the MSC to those BSC&apos;s which have cells with location areas same as that of the current location area of the Mobile. If entire PLMN area is termed as one location area then the MSC has to page for every mobile in every BSC which increases Paging load and as a result signaling load and hence wastage of resources.
  83. Once a mobile turns on power ,it camps to the BCCH .On the BCCH is broadcasted the Location area identity (LAI) of the cell to in which the mobile is.Mobile reads this LAI and compares this LAI with the LAI which it has store d when it switched off.If this new Lai is different form the one stored,it does a normal location update.
  84. The Mobile many a times may enter a non-coverage zone for a very long period.The MSC has no information about it .The MSC goes on sending Paging messages for the Mobile. In order to avoid this a period is set after which the Mobile has to inform MSC that it is still in the attach state.Now,if the mobile remains in the non-coverage zone for this period,it will not be able to send any message,.As a result of this after the expiry of this period the MSC marks this mobile as detached and rejects all incoming calls to this mobile. This type of update which is done everytime after an expiry of a fixed period is known as Periodic Location Update. Period set ranges from 0 to 255 decihours
  85. TMSI : Temporary Mobile Subscriber Identitiy
  86. Handover is a GSM feature by which the control and communication of a mobile is transferred from one cell to another if certain criteria&apos;s are met.
  87. A mobile on TCH is evaluating the RXLEV &amp; RXQUAL and passing the measurement taken to the cell on the SACCH. The BSS interprets the measurements and determines what actions to be taken to maintain th e link, whether to increase /decrease power output or go for a handover. BSS continously processes the following information : Measurements reported by the Mobile on SACCH ---- RXLEV on Downlink ---- RXQUAL on Downlink ---- Neighbouring Cells RXLEV on Downlink Measurement performed by the BSS ---- RXLEV on Uplink ---- RXQUAL on Uplink ---- Mobile to BSS Distance ---- Interference levels On every SACCH frame ( 480ms) the BSS performs an averaging function on the measurements collected regarding the radio links supported by that cell plus measurements regarding neighbor cells. These averaged values are then processed by the decision algorithms and compared against thresholds to determine whether any action is necessary ( power control or handover ). The period between averaging and decision is user settable with reference to SACCH frame periods.
  88. Cell barring is a GSM Feature by which certain Mobiles could be barred access to certain cells.
  89. Every Mobile has an access class. This access is programmed on the SIM card. These classes range from 0 - 15,in which Classes 0 - 9 are termed as normal class Classes 11 - 15 are emergency classes. Every Cell has a set parameter which defines which access classes are barred for the particular cell.This parameter is broadcasted on the BCCH.
  90. During any conversation it is found that generally one person speaks at a time,that is both users talk alternately. So on an average it is found that transmission in one direction is only for the half the time. DTX is a feature by which the transmitter of the mobile is switched on only for useful information frames.
  91. Voice Activity Detector determines which 20ms blocks contains speech and it only forwards those frames.For case when the mobile is in car,there is background noise of the car which almost stationary.The VAD detects this constant noise and removes it. VAD is an energy detector.It compares the energy of the filtered speech to a threshold and indicates speech whenever the threshold is exceeded.This threshold must be kept above the noise level so as to avoid noise as speech,but it should not be very high so that some speech is lost in the process of avoiding noise.
  92. During any voice transmission there is a background noise which is transmitted with the speech.This noise when received at the other end gives a comfortable feeling to the listener about the progress of the call. With DTX as the speech burst ends,transmission is cut off and with this the background noise also cuts off which gives an annoying feeling to the listener.To resolve this problem the VAD adds an artificial noise known as comfort noise at the receiving end when speech discontinues.
  93. Short Message Service is a broadcast of message to a particular mobile subsrciber. The short message to a mobile is originated at the Short Message Service Centre, and sent to the MSC with the corresponding MSISDN number. The MSC then checks with VLR about the mobile state,whether it is attached or not.If attached the MSC orders the BSS to page the mobile and the message is received by the mobile.