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Later AMPS was eventually superseded by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

E-Mail

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…