2g(second generation) of cellular system€¦ · in st. louis, 1946 the first mobile telephone...
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2G(Second Generation) of cellular
system
First Mobile Telephone
System ?
In St. Louis, 1946 the first Mobile Telephone
Service (MTS) was introduced.
Only three radio channels were available.
It required manual call set-up
With additional channels and more automatic
handling of calls, in 1964 Improved Mobile
Telephone (IMTS) Service was introduced
IMTS-First Mobile Telephone System
One and only one
high power base
station with which all
users communicate.
Entire Coverage
Area
Normal
Telephone
System
Wired connection
DRAWBACKS OF IMTS ?
Following were the drawbacks of IMTS systems.
– Limited Service Capability
– Poor Service Performance
– Inefficient Frequency Spectrum Utilization
Technology and service affordability
OPTIONS TO OVERCOME LIMITATIONS
OF IMTS(CONVENTIONAL PHONE)
?
Yes, cellular concept ..
In December 1947, Douglas H.Ring and W.
Ray Young, Bell Labs engineers, proposed
hexagonal cell concept for mobile phones.
The coverage region is divided into small cells
Till this stage, the technology to implement the
ideas did not exist nor had the frequencies allocation
method.
Bell Labs developed the electronics to achieve this
concept in 1960s .
In 1970s ,the concepts of frequency reuse and
handoff, as well as a number of other concepts that
formed the basis of modern cell phone technology,
were described.
In December 1971, AT&T submitted a
proposal for cellular service to the FCC.
After years of hearings, the FCC approved the
proposal in 1982 for Advance Mobile Phone
System (AMPS)
AMPS was analog in nature and called 1G.
Later AMPS was eventually superseded by
Digital AMPS in 1990.
First Mobile Cellular System
The technological development that make special
the 1G mobile phones from the previous generation
was the use of Multiple cell sites (cell and
frequency reuse),
Ability to transfer calls from one site to the next as
the user travelled between cells during a
conversation (handoff).
Cellular Concept
?
It started by First Mobile Telephone
System itself.
One and only one
high power base
station with which all
users communicate.
Entire Coverage
Area
Normal
Telephone
System
Wired connection
A new Idea which gave 1G mobile
cellular system
Replace high power transmitter with several low power transmitters to create small “cells”– Multiple low-power base stations ,service
mobile users within their coverage area
– Each cell assigned a set of frequencies
– Neighboring cells assigned different group of frequencies to reduce adjacent-cell interference
– Handoff users to neighboring base stations as users move.
15
First Generation (1G) Cellular System
IG (AMPS)Configuration
Analog in nature
Uses FDD scheme
Down link frequency = 869-894 MHz
Uplink frequency = 824-849 MHz
Spacing between forward and reverse channel = 45 MHz
Channel bandwidth = 30 kHz
Number of full-duplex voice channels = 790
Number of full duplex control channels = 42
Data transmission rate = 10 kbps
Cell size = 2-20km radius
Second Generation (2G) Cellular System
In 1990, the 2G mobile phone systems emerged,
primarily using the GSM standard.
2G differed from the 1G by using digital instead of
analog transmission
In 1991 the first GSM network launched in
Finland.
First GSM mobile phones with
AC adapters
2G Cellular Telephone
Standard
– Global System for Mobile (GSM)
– Interim Standard 136 (IS-136)
– Interim Standard 95 (IS-95)
GSM (Global System for Mobile)
– FDMA/TDMA-based
– Up Link = 890-915 MHz
– Down Link =935-960 MHz
– Channel bandwidth = 200 kHz, 8 users/channel
– Deployed widely in Europe, Asia, Australia, South America,
IS-136
Also known as North American Digital Cellular– Introduced in 1991, TDMA-based
– Transmission range:
– Up Link = 824-849 MHz
– Down Link = 869-894 MHz,
– Channel BW = 30 kHz, 3 users/channel
– Deployed in North & South America, Australia
IS-95
– Also known as cdma One
– Introduced in 1993,
– CDMA-based
– BS and MS transmission bands = same as IS-136
– Channel bandwidth = 1250 kHz, 64 users/channel
– Deployed in North & South America, Korea, Japan, China, Australia
2 G Cellular Standards
Japan Europe Americas
TACS NMT/TACS/Other AMPS
PDC GSM TDMA CDMA
1st Gen
2nd Gen
GSMGLOBAL SYSTEM FOR MOBILE COMMUNICATION
“Brilliant Past, Bright Future”
GSM Criteria ?
– Good subjective speech quality
– Low terminal and service cost
– Support for international roaming
– Ability to support handheld terminals
– Support for range of new services and facilities
– Enhanced Features
– ISDN compatibility
– Enhance privacy
– Security against fraud
GSM Definition ?
GSM is a 2G cellular standard
developed to cater voice and data
delivery services using digital
modulation.
GSM Specifications
GSM RF Spectrum ( 900 MHz)
MS to BTS (uplink): 890-915 MHZ
BTS to MS (downlink): - 935-960 MHZ
Carrier Separation : 200 KHz
Duplex Distance : 45 MHz
No. of RF carriers : 124
Access Method : TDMA/FDMA
Modulation Method : GMSK
Modulation data rate : 270.833 Kbps
GSM Services
GSM has much more to offer than voice telephony.
GSM services are standard collection of applications and
features available to mobile phone subscribers all over the
world.
GSM Services
Three basic types of services offered
through GSM
Tele-services
Bearer or Data Services
Supplementary services
Tele Services • Telecommunication services that enable voice
communication via mobile phones such as
-Telephony (Voice calls)
- Emergency calling( like 911 in USA)- SMS - Group 3 fax- Voice mailbox- Electronic mail- MMS
Bearer Services
Include various data services for information transfer between GSM and other networks like PSTN, ISDN etc at rates from 300 bps to 9.6 k bps
Supplementary services
Supplementary services are provided on top of tele-services or bearer services, and include features such as
caller identification
call forwarding
call waiting
multi-party conversations
barring of outgoing calls
GSM System Architecture
GSM Architecture
PSTN
Data Terminal
HLR/
VLR
MSCBSC
OMC(Operation & Maintenance
Center)
Operation
Terminal
BTS
HandsetA
X.25
A-bis
SS7
Network sub-system PSTNRadio
sub-system
Mobile
station
UM
SIMcard
AUC/
EIR
Cell Site Diagram
Mobile Station (MS)
The Mobile Station is made up of two entities:
1. Mobile Equipment (ME)
2. Subscriber Identity Module (SIM)
Mobile Equipment
Portable, vehicle mounted, hand helddevice
Uniquely identified by an IMEI
Voice and data transmission
Monitoring power and signal quality
of surrounding cells for optimum handover
Power level : 0.8W – 20 W
160 character long SMS.
Digital Cell Phone
cell phones are some of the most intricate
devices people use on a daily basis.
Modern digital cell phones can process millions
of calculations per second in order to compress
and decompress the voice stream.
The parts of a Digital Cell Phone
An amazing circuit board containing the brains
of the phone
An antenna
A Liquid crystal display (LCD)
A keyboard
A Microphone
A speaker
A battery
MS power classes in GSM900
PowerClass MaxPower (Watts)
1 20
2 8
3 5
4 2
5 0.8
Subscriber Indentity Module(SIM)
Smart card contains the International Mobile Subscriber Identity (IMSI)
Allows user to send and receive calls and receive other subscribed services
Encoded network identification details
- Key Ki,Kc and A3,A5 and A8 algorithms
Protected by a password or PIN
Can be moved from phone to phone
contains key information to activate the phone
Base Station Subsystem is composed of
following parts
1. Base Station Controller (BSC)
2. Base Transceiver Station (BTS)
Base Station Controller (BSC)
Communicate with MSC and BTS
Most robust element in the BSS
Provides, the intelligence behind the BTS.
has 16 to 512 of BTS under its control.
One BSC Support ( 20000- 45000 ) subscriber
Function of Base Station Controller
(BSC)
Manages Radio resources for BTS ( Assigns Frequency and time slots for all MS’s in its area )
Handle call set up
Provide Handover to MS
Control Radio Power
Transcoding and rate adaptation functionality
Image of a BSC
Base Transceiver Station (BTS)
Communicates with MS and BSC
BTS is the physical equipment, which provide
radio coverage to a geographical area
Consists of Transceivers (TRX) units
Can support 100 user simultaneously
Encodes, encrypts, multiplexes, modulates and
feeds the RF signals to the antenna.
Frequency hopping – slow (217 hopes/s)
Prize- 15-18 Lac Approx
Image of Typical GSM BTS
What a GSM cell site consist
A Shelter
Tower
BTS Shelter
BTS Shelter Layout
AC-2
AC-1
DDF
BTS
Cabinet
PIU
SMPS Battery
Bank
DO
OR
MCB1
MCB2
Types of Tower
Ground Base Tower(GBT)
Roof Top Tower(RTT)
In Building Solution(IBS)
Types of BTS
Ultra wave BTS
Flexi BTS
Ultra Wave BTS
can support max. of 12 TRx card.
One TRx card supports 8 time slots( i.e. max of 8 users),
Capacity in terms of users can be increased using Half
rate, ( one time slot is assigned to 2 users in Half rate)
It has all Pin connections on back side
Ultra wave BTS
Flexi BTS
Flexi can support max. of 24 TRx.
Easier site construction, with easier implementation
lower installation costs
Reduced demand for power, resulting in smaller power systems
All connections are on front side so it is easy to install every equipment.
FLEXI BTS
NOKIA BTS CABINET 4X4X4
CONFIGURATION
NOKIA BTS CABINET 4X4X4 CONFIGURATION
DVJA
M2HA
M2HA
M2HA
M2HA
M2HA
TRX-0
TRX-6
TRX- 9
TRX-10
TRX-11
TRX-7
TRX-8
TRX-5
TRX-1
TRX-3
TRX-4
TRX-2
M2HA
DVJA
DVJA
DVJA
DVJA
DVJA
BIO
A
PW
SB
PS
WB
PW
SB
BB
F1
BB
F2
BB
F3
BB
F4
BB
F5
BB
F6
VxR
B
VxR
BV
xR
B
VxR
B
Β
Sector
α
Sector
¥
Sector
WCHA
WCHA
WCHA
MS
BTS
BTS
β
ά γ
Each cell is divided into three sectors
TRx-Transmitter/Receiver cards
WCHA-Wide (band) channel Amplifier Duplexer
(Combiner)
PWSB- Power Supply B card
BOIA-Base operation Interface Amplifier
BBF-Base band filter
M2HA-Multi coupler
Vx RB or RRI card (Radio Relay Interface)
DVJA
– Basically does transmission and reception of signals.
– Sending and reception of signals to/from higher network entities (like the BSC)
– Can support 8 user at a time in Ultra BTS and 24 users in Flexi BTS
- Prize 1 Lac approx
Transceiver (TRX)
BOIA-Base operation Interface Amplifier
- Power amplifier
-Brain of BTS
-Amplifies the signal from TRX for transmission through antenna; may be integrated with TRX.
-Support 2TRx
WCHA-Wide band Amplifier Duplexer
– It works as a Combiner
– Combines feeds from several DRXs so that they could be sent out through a single antenna
– allows for a reduction in the number of antenna used.
Base Band Filter(BBF)
– Filter baseband signal coming from user
– Frequency hopping, signal DSP, etc..
– Support 2 TRx
Dual Variable Gain Amplifier(DVGA)
The filtered input signal is level controlled using a variable gain
amplifier (VGA) or a variable attenuator and amplifier
combination.
The signal is then sent to a demodulator RF integrated circuit
(RFIC) where it is demodulated into in-phase (I) and quadrature
phase (Q) baseband signals.
What…?
In case BTS goes down
All of sudden number of user increased in
a particular cell
Well ,Mobile BTS is used
Transcoder/Rate Adaptation Unit
(TRAU)
What is transcoder (TRAU)
TRAU is the data rate conversion unit
Performs trans-coding function for speech
channels and Rate Adaptation (RA) for data
channels in the GSM network.
Convert the data rate from 64 kbps to 16 kbps
from BSC output to MSC input and vice versa..
Transcoder (XCDR)
Need of TRAU
The PSTN/ISDN switch is a switch for 64 kbps
voice.
But current GSM technology permits to
decrease the bit-rate 13 kbps for full rate and 6.5
kbps for half rate.
Since MSC is basically a PSTN/ISDN switch
its bit-rate is still 64 kbps.
That is why a rate conversion is required in
between the BSC and MSC
Transcoder (XCDR)
GSM Antenna
– This is also considered a part of the BTS.
– Antenna is Manufactured by two company
– 1- Catheren
– 2-Andrew
– Cost 1- 0.75 Lac
Micro Wave Antenna
Network Switching Subsystem
(NSS)
NSS carries out switching functions and manages the
communications between MS and the PSTN.
It is owned and deployed by mobile phone operators
PSTN
Data Terminal
HLR/
VLR
MSCBSC
OMC(Operation & Maintenance
Center)
Operation
Terminal
BTS
HandsetA
X.25
A-bis
SS7
Network sub-system PSTNRadio
sub-system
Mobile
station
UM
SIMcard
Function of Network switching subsystem
(NSS)
Nerve Centre of entire GSM network
Manages all call processing subscriber related
functions
Contains
– the core switching component
– a number of databases
– Gateways to other networks
Uses Signaling System Number 7 (SS7)
Components of NSS Network ?
NSS contains following nodes
MSC
VLR
HLR
AUC
EIR
Mobile Switching Center (MSC)
Heart of the network
Manages communication between GSM and other networks
Call setup function and basic switching
Call routing
Billing information and collection
Mobility management
- Registration
- Location Updation
- Inter BSS and inter MSC call handoff
MSC does realize these functions with conjunction of following 4 intelligent data base
– HLR
– VLR
– EIR
– AUC
Mobile Switching Centre
Home Location Registers (HLR)
Contains the administrative information of each of the subscriber registered in the network
Keep permanent copy of the subscriber data
Logically one HLR per PLMN,
HLR maps each IMSI with a unique mobile phone number called Mobile Subscriber ISDN (MSISDN).
HLR also holds most of the information held by the SIM such as IMSI, MSISDN, prepaid/postpaid, roaming restrictions, supplementary services etc.
Visitor Location Registers (VLR)
Temporary database which updates
whenever new MS enters its area, by HLR
database
Controls those mobiles roaming in its area
Database contains IMSI, TMSI, MSISDN,
MSRN, Location Area, authentication key
Authentication Center (AUC)
• AuC is a function to authenticate each SIM card
that attempts to connect to the GSM core network
• Once the authentication is successful, the HLR is
allowed to manage the SIM and services
• Protects against intruders in air interface
• Maintains authentication keys and algorithms and
provides security triplets ( RAND, SRES,Kc)
• Generally associated with HLR
Equipment Identity Register (EIR)
- Database that is used to track handsets using
the IMEI (International Mobile Equipment
Identity)
- Made up of three sub-classes: - The White List,
- The Black List
- The Gray List
- Only one EIR per PLMN
Equipment Identity Register ( EIR )
White List
All Valid
assigned ID’s
Range 1
Range 2
Range n
Black List
Service denied
MS IMEI 1
MS IMEI 2
MS IMEI n
Grey List
Service allowed
but noted
MS IMEI 1
MS IMEI 2
MS IMEI n
EIR
NETWORK COMPONENTS
Other Network Components
Operations & Maintenance Subsystem(OMS)
Enhanced Services Subsystem (ESS)
OMS
OMS is used to configure, control and to
monitor the GSM network.
It comprises of two parts:
– Operation and Maintenance Centre - Switch
– Operation and Maintenance Centre - Radio
OMC-S is used in conjunction with the NSS
used for switching
OMC-R is used in conjunction with the BSS.
The OMC-R controls the traffic load on the
various cells and performs automatic
reconfiguration of the transceivers to cope with
the fluctuation of traffic, load caused due to the
mobility of the customers.
Functions of OMCs
The OMCs provide traffic data measurements, reporting
and analysis.
Store all the data and software for the network elements
Perform as the central maintenance control point for all the
network elements.
Maintain all telecom hardware and network operations
Maintain all charging and billing procedures
VARIOUS ALARM SYMBOL FOR OMCs
Critical :-Immediate action
Major :- As soon as possible
Minor :- Action can be taken when there is time
Warning :-Point out conditions and corrective
Action is then taken during schedule
maintenance
Indeterminate :- shows that an alarm has been
Generated for which there is no alarm severity
In the system.
?
ENHANCED SERVICES SUBSYSTEM
(ESS)
The ESS includes elements such as
– Unified Messaging System (UMS)
– Wireless Application Protocol (WAP) System,
– Intelligent Network (IN) system
– Content and Location Based Services (C&LBS) system
UMS
UMS is the integration of different
electronic messaging and communications media
technologies into a single interface, accessible from a
variety of different devices
Voice Mail
Group 3 Fax
SMS
video messaging
WAP
WAP is a technical standard for accessing
information over a mobile wireless network.
A customer, on move, can surf the web
from his WAP enabled handset .
The WAP system also manages telephony
events such as incoming call etc when a
subscriber connected to the Internet.
Intelligent Network(IN)
The IN Network , is the standard network
architecture specified in the ITU-T Q.1200 series
recommendations.
It is intended for fixed as well as mobile telecom
networks.
It allows operators to differentiate themselves by
providing value-added services in addition to the standard
telecom services such as PSTN, ISDN and GSM
services on mobile phones
Example of IN Network
Tele-voting
Call screening
Telephone number portability
Toll free calls /Free phone/Prepaid calling/Account card
calling
Virtual private networks (such as family group calling)
Prefix free dialing from cell phones abroad
Seamless MMS message access from abroad.
Premium Rate calls
Call queuing
Call transfer
Content and Location Based Services
can offer a variety of PUSH and PULL
services ranging from advising the customer
of the discounts being offered in the shops
near his current ‘location’ to verification of
flight details etc.
BILLING AND CUSTOMER CARE SYSTEM
(B&CCS)
Responsible for obtaining the call details of each of the
customers from the HPLMN as well as from all the VPLMNs
for raising the invoice.
It incorporates a powerful and flexible rating engine that
provide service provider to offer innovative and competitive
tariff packages.
Customer Care module includes an automatic Service
Provisioning Module that will activate / deactivate a customer
account from a Customer Care terminal without the need for any
manual intervention.
Call Flow in Mobile communication
Call Originating from MS
Call termination to MS
PSTN
HLR/
VLR
MSCBSC
BTS
MS
SS7GMSC1
10
1 23 4
5 6
7899
Mobile Originated Call
Mobile Originated Call
1. MS sends dialled number to BSS
2. BSS sends dialled number to MSC
3,4 MSC checks VLR if MS is allowed the requested service . If so, MSC asks BSS to allocate resources for call.
5 MSC routes the call to GMSC
6 GMSC routes the call to local exchange of called user
7, 8,
9,10 Answer back(ring back) tone is routed from called user to MS via GMSC,MSC,BSS
PSTN
HLR/AUC
MSCBSC
MS
SS7GMSC
1
3
4
5
27
9
VLR
68
10
11
12
13
14 15
16
10
13
17
Mobile Terminated Call
Mobile Terminated Call
1. Calling a GSM subscribers
2. Forwarding call to GSMC
3. Signal Setup to HLR
4. 5. Request MSRN from VLR
6. Forward responsible MSC to GMSC
7. Forward Call to current MSC
8. 9. Get current status of MS
10.11. Paging of MS
12.13. MS answers
14.15. Security checks
16.17. Set up connection
A Very Good Afternoon
Security in GSM
Access Control and Authentication
– User should not be able to use the GSM
resources without being authenticated
Confidentiality
– Messages containing user related information
should not be accessible to others
Access Control and Authentication
GSM handsets must be presented with a SIM
A SIM stores
subscriber authentication key(Ki)
authentication algorithm(A3)
cipher key generation algorithm (A8)
encryption algorithm (A5)
Confidentiality
o Temporary encryption key is used for privacy of
data, signaling, and voice
o Information is encrypted before transmission
How Security is provided in GSM ?
Following three algorithms are used to provide
security in GSM
• A3 algorithm for authentication
• A5 algorithm for encryption
• A8 algorithm for key generation
Authentication in GSM
RAND RAND
A3A3
KiKi
128 128128 128
3232SRES SRES
SRESSRES=? SRESSRES
32
SIM
AUC
MSC
Ki =individual subscriber authentication key SRES = signed response number
Key generation and Encryption
RAND RAND
A8A8
A5
KiKi
128 bit 128bit128bit 128bit
64bit64bit
Kc Kc
SIM
AUC
BTS
Kc= cypher key
Encrypted dataA5
MS
Data Data
Have a Nice Day…