DR. B.

C ROY ENGINEERING COLLEGE, DURGAPUR

PROJECT TOPIC : USE OF SENSORS IN STAIRCASE

SUBMITTED TO : Dr. Sharmistha De Dutta
DEPARTMENTOF HUMANITIES AND BASIC SCIENCES
SUBJECT CODE : HU-481

SUBMITTED BY : STUDENTS OF ECE-2(X), 4th SEMESTER

: SWATTICK BANERJEE (12000318001)
: SHRADDHA THAPA (12000318005)

: ANKIT PAL (12000318012)

: DEBJYOTI MUKHERJEE (12000317101)

: MANORANJAN SOREN (12000317089)

: MD REHAN ANSARI (12000317086)

SUBMITTED ON :
S

1
 Department of ECE
Dr. B C Roy Engineering College

Acknowledgement
I have taken efforts in this seminar. However, it would not have been possible without the
kind support and help of many books and websites. I would like to extend my sincere
thanks to all of them.

I am highly indebted to Mrs. Moutusi Mondal for his guidance and constant supervision
as well as for providing necessary information regarding the seminar & also for their
support in completing the Seminar.

We also want to thank Mrs. Sharmistha De Dutta of Humanities Department for the help
and guidance given by her which led to the successful completion of this project in a very
efficient manner.

I would like to express my gratitude to Mr. Narendra Nath Pathak, head of department,
for giving us this opportunity and encouraging in completion of this seminar.

I thanks and appreciations also goes to our colleague in developing this seminar and people
who have willingly helped us out with their abilities.

SWATTICK BANERJEE (12000318001)

SHRADDHA THAPA (12000318005)

ANKIT PAL (12000318012)

DEBJYOTI MUKHERJEE (12000317101)

MANORANJAN SOREN (12000317089)

MD REHAN ANSARI (12000317086)

2
 Department of ECE
Dr. B C Roy Engineering College

Certificate
This is to certify that the following students of B.Tech under Electronics
and communication engineering (ECE-1 ‘X’) department of 2nd year
have successfully completed their Seminar Report on topic of
“CELLULAR COMMUNICATION”

SWATTICK BANERJEE (12000318001)

SHRADDHA THAPA (12000318005)

ANKIT PAL (12000318012)

DEBJYOTI MUKHERJEE (12000317101)

MANORANJAN SOREN (12000317089)

MD REHAN ANSARI (12000317086)

Signature:-……………………………………
Mrs. MOUTUSI MANDAL (MENTOR)

Signature:-……………………………………
Mrs. SHARMISTHA DE DUTTA (HU)

Signature:-……………………………………
Mr. NARENDRA NATH PATHAK (HOD)

3
3
 Department of ECE
Dr. B C Roy Engineering College

Abstract

The Global System for Mobile communications, is a digital

cellular communications system which has rapidly gained acceptance
and market share worldwide, although it was initially developed in a
European context. In addition to digital transmission, cellular
communication incorporates many advanced services and features,
including ISDN compatibility and worldwide roaming in other cellular
networks. The advanced services and architecture of cellular
technology have made it a model for future third-generation cellular
systems, such as UMTS. This paper will give an overview of the
services offered by GSM, the system architecture, the radio
transmission structure, and the signalling functional architecture.

Cellular communication basically deals with cell phones and

radio waves. It describes how communication process occurs in cell
phones. What are the basic process for establishment of a call i.e. for
outgoing call and reception of a call. This topic describes the concept
of frequency reuse, the division of cell, types of cell. It also describes
cellular services, cellular components i.e. Base Transceiver Station,
Base Station Controller, Mobile Switching Canter etc. and also
different type of Registers.

4
 Department of ECE
Dr. B C Roy Engineering College

Contents

 Introduction
 Objective
 Methodology
 Generations


 Network Cells


 Frequency Reuse


 Cellular Network Components


 Setting & Making a Call


 Receiving a Call


 Cellular Components & Channels


 GSM & Features


 Cellular Services


 Conclusion
 Advantage & Disadvantage

5
 Department of ECE
Dr. B C Roy Engineering College

List of Figures
Page no.
1. Introduction ……………………………………………...7

2. Objective…………………………………………………8

3. Methodology……………………………………………..9

4. Generation of Phones …………………………………...10

5. Cell………..………………………...……………………13

6. Cluster……………..……………………...………...……13

7. Cellular Network Components…………..……….…...…15

8. Path of Communication………………………………….17

9. Handover…………………………………………………22

10. Roaming…………………………………………………23

11. Control Channels……………………………………...…24

12. TDMA………………………………………………...…25

13. CDMA………………………………………………..…26

14. FDMA…………………………………………………...26

15. GSM……………………………………………………..27

16. Advantage & Disadvantage……………………………...29

6
 Department of ECE
Dr. B C Roy Engineering College

CELLULAR COMMUNICATION

INTRODUCTION :
A hand-held mobile radiotelephone is an old dream of radio engineering. A particularly vivid
and in many ways accurate prediction was presented by Arthur C. Clarke in a 1959 essay, where
he envisioned a "personal transceiver, so small and compact that every man carries one." He
wrote: "the time will come when we will be able to call a person anywhere on Earth merely by
dialing a number." Such a device would also, in Clarke's vision, include means for global
positioning so that "no one need ever again be lost." Later, in Profiles of the Future, he predicted
the advent of such a device taking place in the mid-1980's.
Early predecessors of cellular phones included analog radio communications from ships and
trains. The race to create truly portable telephone devices began after World War II, with
developments taking place in many countries. The advances in mobile telephony have been
traced in successive generations from the early "0G" (zeroth generation) services like the Bell
System's Mobile Telephone Service and its successor, Improved Mobile Telephone Service.
These "0G" systems were not cellular, supported few simultaneous calls, and were very
expensive.

7
 Department of ECE
Dr. B C Roy Engineering College

OBJECTIVE

Mobile technology is a form of technology that is mostly used in cellular communication and
other related aspects. It uses a form of platform where by many transmitters have the ability to
send data at the same time on a single channel. This platform is called Code-division multiple
access (CDMA). This platform allows many users to make use of single frequencies because it
restricts the likelihood of interference of frequencies from two or more sources. This channel has
evolved over the years. The mobile technology is rapidly evolving; over the years, its uses are
becoming diverse and is gradually replacing some similar sources in the market that are also used
for communication e.g. post office and land lines. The mobile technology has improved from a
simple device used for phone call and messaging into a multi-tasking device used for GPS
navigation, internet browsing, gaming, instant messaging tool etc. Professionals argue with the
trend that the future of computer technology is rest on wireless networking and mobile computing.
Mobile technology through tablet and portable computers are becoming more and more popular.

8
 Department of ECE
Dr. B C Roy Engineering College

METHODOLOGY

From a user’s perspective, the two key components of a mobile telecommunication network are an
individual’s mobile phone handset and the mobile tower with an antenna – most often mounted on
a rooftop or on ground based poles.

Mobile phones periodically detect and access the network from wireless signals emitted from an
antenna. The network is divided into geographic areas known as the Cells, each of which is served
by a tower, also known as a base station. To communicate with each other, the mobile phones and
the base stations located at the tower sites exchange radio signals. The user connects to the base
station via a mobile phone and the system ensures that the connection is maintained as the user
moves from one Cell (area) to another.
When a mobile phone is switched on, it responds to specific control signals from the nearby base
stations. Once it has located a suitable base station, the phone initiates a network connection.
When a call is not being made or received, the mobile phone remains in the standby mode.

The mobile connection may also be set up within buildings using an indoor antenna called “In-
building solution”, as is done in the buildings which have a high density of users or where the
signal coverage from the external base station/s is inadequate.
The level of the wireless signal has to comply with the minimum Quality of Service (QoS) levels
specified by the telecom services regulator of the particular country.

9
 Department of ECE
Dr. B C Roy Engineering College

GENERATION :
1G (First generation):
The first automatic analog cellular systems deployed were NTT's system first used in Tokyo
in 1979, later spreading to the whole of Japan, and NMT in the Nordic countries in 1981.
The first analog cellular system widely deployed in North America was the Advanced Mobile
Phone System (AMPS). It was commercially introduced in the Americas in October 1983, Israel
in 1986, and Australia in 1987. AMPS was a pioneering technology that helped drive mass market
usage of cellular technology, but it had several serious issues by modern standards.

It was unencrypted and easily vulnerable to eavesdropping via a scanner; it was susceptible to cell
phone "cloning;" and it used a Frequency-division multiple access (FDMA) scheme and required
significant amounts of wireless spectrum to support.On 6 March 1983, the DynaTAc mobile
phone launched on the first US 1G network by Ameritech. It cost $100m to develop, and took over
a decade to reach the market.

The phone had a talk time of just half an hour and took ten hours to charge. Consumer demand
was strong despite the battery life, weight, and low talk time, and waiting lists were in the
thousands.
Many of the iconic early commercial cell phones such as the Motorola DynaTAc Analog
AMPS were eventually superseded by Digital AMPS (D-AMPS) in 1990, and AMPS service
was shut down by most North American carriers by 2008

2G (Second Generation):

The second generation introduced a new variant of communication called SMS or text
messaging. It was initially available only on GSM networks but spread eventually on all digital
networks. The first machine-generated SMS message was sent in the UK on 3 December 1992
followed in 1993 by the first person-to-person SMS sent in Finland. The advent of prepaid
services in the late 1990s soon made SMS the communication method of choice amongst the
young, a trend which spread across all ages.

2G also introduced the ability to access media content on mobile phones. In 1998 the first
downloadable content sold to mobile phones was the ring tone, launched by Finland's
Radiolinja (now Elisa). Advertising on the mobile phone first appeared in Finland when a free
daily SMS news headline service was launched in 2000, sponsored by advertising.

3G (Third Generation):

3G telecommunication networks support services that provide an information transfer rate of

at least 200 kbit/s. Later 3G releases, often denoted 3.5G and 3.75G, also provide mobile
broadbandaccess of several Mbit/s to smartphones and mobile modems in laptop computers.
3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet
access, video calls and mobile TV.
10
 Department of ECE
Dr. B C Roy Engineering College

This is a set of standards used for mobile devices and mobile telecommunication use services
and networks that comply with the International Mobile Telecommunications-2000 (IMT-
2000)specifications by the International Telecommunication Union. 3G finds application in
wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls and
mobile TV.
A new generation of cellular standards has appeared approximately every tenth year since 1G
systems were introduced in 1981/1982. Each generation is characterized by new frequency
bands, higher data rates and non-backwards compatible transmission technology. The first
release of the 3GPP Long Term Evolution (LTE) standard does not completely fulfill the ITU
4G requirements called IMT-Advanced. First release LTE is not backwards compatible with
3G, but is a pre-4G or 3.9G technology, however sometimes branded 4G by the service
providers. Its evolution LTE Advanced is a 4G technology. WiMAX is another technology
verging on or marketed as 4G.

4G (Fourth Generation):

In telecommunication systems, 4G is the fourth generation of mobile phone mobile

communication technology standards. It is a successor to the third generation (3G) standards.
A 4G system provides mobile ultra-broadband Internet access, for example to laptops with
USB wireless modems, to smartphones, and to other mobile devices. Conceivable applications
include amendedmobile web access, IP telephony, gaming services, high-definition mobile
TV, video conferencing, 3D television, and cloud computing.

Two 4G candidate systems are commercially deployed: the Mobile WiMAX standard (first
used in South Korea in 2006), and the first-release Long Term Evolution (LTE) standard (in
Oslo, Norway and Stockholm, Sweden since 2009). It has however been debated if these first-
release versions should be considered to be 4G or not, as discussed in the technical definition
section below.
In the United States, Sprint (previously Clearwire) has deployed Mobile WiMAX networks
since 2008, and MetroPCS was the first operator to offer LTE service in 2010. USB wireless
modems have been available since the start, while WiMAX smartphones have been available
since 2010, and LTE smartphones since 2011. Equipment made for different continents is not
always compatible, because of different frequency bands. Mobile WiMAX is currently (April
2012) not available for the European market.

5G (Fifth Generation):

Fifth-Generation wireless network or 5G is the latest iteration of cellular technology,

Designed to greatly increase the speed and responsiveness of wireless networks.

5G has the potential to transform the internet and it will be the backbone of other
technologies like Self-Driving Cars, Virtual Reality, Internet of things (IoT).Many
countries are actively working to develop 5G from 2012 and the plan is to provide 5G services
by 2020.5G will be implemented on millimeter waves that is the frequencies between 30 to
300 gigahertz to transmit data over the network, these frequencies have never been used for
mobile devices so opening this up will help accommodate more devices
11
 Department of ECE
Dr. B C Roy Engineering College

5G will be implemented on millimeter waves that is the frequencies between 30 to 300

gigahertz to transmit data over the network, these frequencies have never been used for
mobile devices so opening this up will help accommodate more devices

Using Millimeter waves will improve network speed, reduce latency and avoid network
congestion but the challenge with Millimeter wave is it can be blocked by buildings tree or in
case of bad weather you will not get the network on your phone to overcome this 5G wireless
signals will be transmitted via large numbers of small cell stations located in places like light
poles or building roofs.

5G is primarily built using 5 technologies

• Millimeter Waves: 5G will be using higher frequencies (30 to 300 GHz) and these
frequencies are called millimeter waves

• Small Cell: Since Range of Millimeter waves is less we need to place more call antenna on
street hights, building roofs.

• Massive MIMO (Multiple inputs multiple outputs): This Technology helps in reducing
network interference.

• Beamforming: Define a clear path how network packets should travel from source to
destination.

• Full Duplex: More than one person can talk at a time, that is sent and receive happens on
different frequencies so that there is no interference.

More technologies can be added to implement 5G

DEFINATION :

A mobile phone (also known as a cellular phone, cell phone, and a hand phone) is a device that
can make and receive telephone calls over a radio link while moving around a wide geographic
area. It does so by connecting to a cellular network provided by a mobile phone operator,
allowing access to the public telephone network. By contrast, a cordless telephone is used only
within the short range of a single, private base station.

In addition to telephony, modern mobile phones also support a wide variety of other services
such as text messaging, MMS, email, Internet access, short-range wireless communications
(infrared, Bluetooth), business applications, gaming and photography. Mobile phones that offer
these and more general computing capabilities are referred to as smartphones.

12
 Department of ECE
Dr. B C Roy Engineering College

CELL:
A cellular network or mobile network is a wireless network distributed over land areas called
cells, each served by at least one fixed-locationtransceiver, known as a cell site or base station.
In a cellular network, each cell uses a different set of frequencies from neighboring cells, to
avoid interference and provide guaranteed bandwidth within each cell.
When joined together these cells provide radio coverage over a wide geographic area. This
enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to
communicate with each other and with fixed transceivers and telephones anywhere in the
network, via base stations, even if some of the transceivers are moving through more than one
cell during transmission.
Cellular networks offer a number of desirable features:

 More capacity than a single large transmitter, since the same frequency can be used for
 multiple links as long as they are in different cells
 Mobile devices use less power than with a single transmitter or satellite since the cell
 towers are closer
 Larger coverage area than a single terrestrial transmitter, since additional cell towers can
be added indefinitely and are not limited by the horizon
Major telecommunications providers have deployed voice and data cellular networks over most
of the inhabited land area of the Earth. This allows mobile phones and mobile computing
devices to be connected to the public switched telephone network and public Internet. Private
cellular networks can be used for research or for large organizations and fleets, such as dispatch
for local public safety agencies or a taxicab company.

CLUSTER :
The cells are grouped into clusters. The number of cells in a cluster must be determined so that
the cluster can be repeated continuously within the covering area of an operator. Typical
clusters contain 4, 7, 12 or 21 cells. The number of cells in each cluster is very important. The
smaller the number of cells per cluster is, the bigger the number of channels per cell . The
capacity of each cell will, therefore, increase. However, this must be balanced with the

13
 Department of ECE
Dr. B C Roy Engineering College

reduction of to interference occuring between neighboring clusters. This interference is

produced by the small size of the clusters (cluster size is defined as the number of cells/cluster).
The total number of channels per cell depends on the number of available channels and the
type of cluster used.

FREQUENCY REUSE :
It is a method used by service providers to improve the efficiency of a cellular network and to
serve millions of subscribers using a limited radio spectrum. In the cellular concept, frequencies
allocated to the service are re-used in a regular pattern of areas, called 'cells', each covered by
one base station. In mobile-telephone nets these cells are usually hexagonal. In radio
broadcasting, a similar concept has been developed based on rhombic cells.

To ensure that the mutual interference between users remains below a harmful level, adjacent
cells use different frequencies. In fact, a set of C different frequencies {f1, ..., fC} are used for
each cluster of C adjacent cells. Cluster patterns and the corresponding frequencies are re-used
in a regular pattern over the entire service area.

14
 Department of ECE
Dr. B C Roy Engineering College

TYPES OF CELL :
Macrocell – their coverage is large (aprox. 6 miles in diame ter); used in remote areas, high-
power transmitters and receivers are used. A macrocell is a cell in a mobile phone network that
provides radio coverage served by a high power cellular base station (tower). Generally,
macrocells provide coverage larger than microcell. The antennae for macrocells are mounted
on ground-based masts, rooftops and other existing structures, at a height that provides a clear
view over the surrounding buildings and terrain. Macrocell base stations have power outputs
of typically tens of watt.

Microcell – Their coverage is small (half a mile in diameter) and are used in urban zones; low-
powered transmitters and receivers are used to avoid interference with cells in another clusters.
A microcell is a cell in a mobile phone network served by a low power cellular base station
(tower), covering a limited area such as a mall, a hotel, or a transportation hub. A microcell is
usually larger than a picocell, though the distinction is not always clear. A microcell uses power
control to limit the radius of its coverage area.

Picocell – A picocell is a small cellular base station typi cally covering a small area, such as
in-building (offices, shopping malls, train stations, stock exchanges, etc.), or more recently in-
aircraft. In cellular networks, picocells are typically used to extend coverage to indoor areas
where outdoor signals do not reach well, or to add network capacity in areas with very dense
phone usage, such as train stations. Picocells provide coverage and capacity in areas difficult
or expensive to reach using the more traditional Macrocell approach.

CELLULAR NETWORK COMPONENTS:

15
 Department of ECE
Dr. B C Roy Engineering College

BTS (Base Transceiver System):

A base transceiver station (BTS) is a piece of equipment that

facilitates wireless communication between user equipment (UE) and a network. UEs are
devices like mobile phones (handsets), WLL phones, computers with wireless
Internet connectivity. BTS is also referred to as the radio base station (RBS), node
B (in 3G Networks) or, simply, the base station (BS). For discussion of the LTE standard the
abbreviation eNB for evolved node B is widely used. Though the term BTS can be applicable
to any of the wireless communication standards, it is generally associated with mobile
communication technologies like GSM and CDMA. In this regard, a BTS forms part of the
base station subsystem (BSS) developments for system management. It may also have
equipment for encrypting and decrypting communications, spectrum filtering tools (band pass
filters), etc. antennas may also be considered as components of BTS in general sense as they
facilitate the functioning of BTS. Typically a BTS will have several transceivers (TRXs) which
allow it to serve several different frequencies and different sectors of the cell (in the case of
sectorised base stations). A BTS is controlled by a parent base station controller via the base
station control function (BCF).

BSC (Base Station Controller):

The base station controller (BSC) provides, classically, the intelligence behind the BTSs.
Typically a BSC has tens or even hundreds of BTSs under its control. The BSC handles
allocation of radio channels, receives measurements from the mobile phones, and controls
handovers from BTS to BTS (except in the case of an inter-BSC handover in which case control
is in part the responsibility of the anchor MSC). A key function of the BSC is to act as a
concentrator where many different low capacity connections to BTSs (with relatively low
utilisation) become reduced to a smaller number of connections towards the mobile switching
center (MSC) (with a high level of utilisation). Overall, this means that networks are often
structured to have many BSCs distributed into regions near their BTSs which are then
connected to large centralised MSC sites.

MSC (Mobile Switching Center):

The coordinator of a cellular network, it is connected to several BSCs, it routes calls between
BSCs; links the cellular network with other networks like PSTN through fiber optics,
microwave or copper cable.The mobile switching centre server is a soft-switch variant of the
mobile switching centre, which provides circuit-switched calling mobility management, and
GSM services to the mobile phonesroaming within the area that it serves. MSS functionality
enables split between control (signalling) and user plane (bearer in network element called as

16
 Department of ECE
Dr. B C Roy Engineering College

media gateway/MG), which guarantees better placement of network elements within the
network.

HLR (Home Location Register):

The home location register (HLR) is a central database that contains details of each mobile
phone subscriber that is authorized to use the GSM core network. There can be several
logical, and physical, HLRs per public land mobile network (PLMN),though one international
mobile subscribe identity (IMSI)/MSISDN pair can be associated with
only one logical HLR (which can span several physical nodes) at a time. The HLRs store details
of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called
an IMSI which is the primary key to each HLR record.

VLR (Visitor Location Registor):

A visitor location register (VLR) is a database that contains information about the subscribers
roaming within a mobile switching center’s (MSC) location area. The primary role of the VLR
is to minimize the number of queries that MSCs have to make to the home location register
(HLR), which holds permanent data regarding the cellular network’s subscribers. Ideally, there
should be only one visitor location register per MSC, but it is also possible for a single VLR to
serve multiple MSCs. the VLR also holds the international mobile subscriber identity (IMSI)
and the mobile subscriber integrated services digital network (MSISDN), the services allowed
for a particular IMSI/MSISDN pair, and authentication data, all of which correspond to a
particular subscription.

EIR (Equipment Identity Registor):

Equipment Identity Register (EIR) consults a database to determine if the service of a GSM
mobile station is authorized, unauthorized, or if it should be monitored. EIR allows for the
programming of the decision-making logic and the definition of the course of action to be taken
in each case, taking into consideration e-mail and/or SMS notifications, in addition to the
response required by the MSC. Moreover, it stores information records for their subsequent
processing.

17
 Department of ECE
Dr. B C Roy Engineering College

COMPONENTS OF CELLULAR NETWORK:

Radio transceiver – low power radio transmitter and receiver

Antenna - which is usually located inside the phone
Control circuitry – formats the data sent to and fr om the BTS; controls signal transmission
and reception
Man-machine interface – consists from a keypad and a display; is managed by the control
circuitry
SIM – integrated circuit card that stores the ident ity information of
subscriber Battery - usually Li-ion, the power unit of the phone

SETTING UP A CALL PROGRESS:

In order to gain access to GSM services, a user needs three things:

 A billing relationship with a mobile phone operator. This is usually either where services
are paid for in advance of them being consumed (prepaid), or where bills are issued and
 settled after the service has been consumed (postpaid).
 A mobile phone that is GSM compliant and operates at the same frequency as the
 operator. Most phone companies sell phones from third-party manufacturers.
 A Subscriber Identity Module (SIM) card, which is activated by the operator once the
billing relationship is established. After activation the card is then programmed with the
subscriber's Mobile Subscriber Integrated Services Digital Network Number (MSISDN)
(the telephone number). Personal information such as contact numbers of friends and
family can also be stored on the SIM by the subscriber.
After subscribers sign up, information about their identity (telephone number) and what
services they are allowed to access are stored in a "SIM record" in the Home Location Register
(HLR).
Once the SIM card is loaded into the phone and the phone is powered on, it will search for the
nearest mobile phone mast (also called a Base Transceiver Station/BTS) with the strongest
signal in the operator's frequency band. If a mast can be successfully contacted, then there is
said to be coverage in the area. The phone then identifies itself to the network through the
control channel. Once this is successfully completed, the phone is said to be attached to the
network.
The key feature of a mobile phone is the ability to receive and make calls in any area where
coverage is available. This is generally called roaming from a customer perspective, but also
called visiting when describing the underlying technical process. Each geographic area has a
database called the Visitor Location Register (VLR), which contains details of all the mobiles
currently in that area. Whenever a phone attaches, or visits, a new area, the Visitor Location
Register must contact the Home Location Register to obtain the details for that phone. The

18
 Department of ECE
Dr. B C Roy Engineering College

current cellular location of the phone (i.e., which BTS it is at) is entered into the VLR record
and will be used during a process called paging when the GSM network wishes to locate the
mobile phone.
Every SIM card contains a secret key, called the Ki, which is used to provide authentication
and encryption services. This is useful to prevent theft of service, and also to prevent "over the
air" snooping of a user's activity. The network does this by utilising the Authentication Center
and is accomplished without transmitting the key directly.
Every GSM phone contains a unique identifier (different from the phone number), called the
International Mobile Equipment Identity (IMEI). This can be found by dialing *#06#. When a
phone contacts the network, its IMEI may be checked against the Equipment Identity Register
to locate stolen phones and facilitate monitoring.

MAKING A CALL:

Once a mobile phone has successfully attached to a GSM network as described above, calls
may be made from the phone to any other phone on the global Public Switched Telephone
Network.
The user dials the telephone number, presses the send or talk key, and the mobile phone sends
a call setup request message to the mobile phone network via the nearest mobile phone base
transceiver station (BTS).
The call setup request message is handled next by the Mobile Switching Center, which checks
the subscriber's record held in the Visitor Location Register to see if the outgoing call is
allowed. If so, the MSC then routes the call in the same way that a telephone exchange does in
a fixed network.
If the subscriber is on a prepaid tariff (sometimes known as Pay As You Go (PAYG) or Pay
& Go), then an additional check is made to see if the subscriber has enough credit to proceed.
If not, the call is rejected. If the call is allowed to continue, then it is continually monitored and
the appropriate amount is decremented from the subscriber's account. When the credit reaches
zero, the call is cut off by the network. The systems that monitor and provide the
prepaid services are not part of the GSM standard services, but instead an example of intelligent
network services that amobile phone operator may decide to implement in addition to the
standard GSM ones.
When the HLR receives this query message, it determines whether the call should be routed to
another number (called a divert), or if it is to be routed directly to the mobile.

 If the owner of the phone has previously requested that all incoming calls be diverted to
another number, known as the Call Forward Unconditional (CFU) Number, then this
number is stored in the Home Location Register. If that is the case, then the CFU number
 is returned to the Gateway MSC for immediate routing to that destination.
 If the mobile phone is not currently associated with a Visited Location Register (because
the phone has been turned off) then the Home Location Register returns a number known
as the Call Forward Not Reachable (CFNRc) number to the Gateway MSC, and the call is
forwarded there. Many operators may set this value automatically to the phone's voice

19
 Department of ECE
Dr. B C Roy Engineering College

mail number, so that callers may leave a message. The mobile phone may sometimes
override the default setting.
 Finally, if the Home Location Register knows that the phone is roaming in a particular
Visited Location Register area, then it will request a temporary number (called an MSRN)
from that VLR. This number is relayed back to the Gateway MSC, and then used to route
the call to the MSC where the called phone is roaming.

How speech is encoded during mobile phone calls :

During a GSM call, speech is converted from analogue sound waves to digital data by the
phone itself, and transmitted through the mobile phone network by digital means. (Though
older parts of the fixed Public Switched Telephone Network may use analog transmission.)
The digital algorithm used to encode speech signals is called a codec. The speech codecs used
in GSM are called Half-Rate (HR), Full-Rate (FR), Enhanced Full-Rate (EFR) and Adaptive
Multirate (AMR). All codecs except AMR operate with a fixed data rate and error correction
level.

RECEIVING A CALL :

When the receiver’s phone is in an idle state it listens for the control channel of its
BTS
if there is an incoming call the BSC and BTS sends a message to the cells in the area
where the receiver’s phone is located
the phone monitors its message and compares the number from the message with its
own
if the numbers matches the cell phone sends an acknowledgement to the BTS
after authentication, the communication is established between the caller and the receiver.

20
 Department of ECE
Dr. B C Roy Engineering College

AUC (AUTHENTICATION CENTER):

It is a database that stores the list of authorized subscribers of a GSM network

it is linked to the MSC and checks the identity of each user trying to connect also
provides encryption parameters to secure a call made in the network.
The AuC connects to the following elements:

 The MSC which requests a new batch of triplet data for an IMSI after the previous data
have been used. This ensures that same keys and challenge responses are not used twice
for a particular mobile.
Procedures implemented
The AuC stores the following data for each IMSI:

 the Ki
 Algorithm id. (the standard algorithms are called A3 or A8, but an operator may choose a
proprietary one).
When the MSC asks the AuC for a new set of triplets for a particular IMSI, the AuC first
generates a random number known as RAND. This RAND is then combined with the Ki to
produce two numbers as follows:

 The Ki and RAND are fed into the A3 algorithm and the signed response (SRES) is
 calculated.
 The Ki and RAND are fed into the A8 algorithm and a session key called Kc is calculated.
The numbers (RAND, SRES, Kc) form the triplet sent back to the MSC. When a particular
IMSI requests access to the GSM core network, the MSC sends the RAND part of the triplet

21
 Department of ECE
Dr. B C Roy Engineering College

to the SIM. The SIM then feeds this number and the Ki (which is burned onto the SIM) into
the A3 algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this
SRES matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile
is allowed to attach and proceed with GSM services.
After successful authentication, the MSC sends the encryption key Kc to the base station
controller (BSC) so that all communications can be encrypted and decrypted. Of course, the
mobile phone can generate the Kc itself by feeding the same RAND supplied during
authentication and the Ki into the A8 algorithm.
The AuC is usually collocated with the HLR, although this is not necessary. Whilst the
procedure is secure for most everyday use, it is by no means crack proof. Therefore a new set
of security methods was designed for 3G phones.
A3 Algorithm is used to encrypt Global System for Mobile Communications (GSM) cellular
communications. In practice, A3 and A8 algorithms are generally implemented together
(known as A3/A8, see COMP128). An A3/A8 algorithm is implemented in Subscriber Identity
Module (SIM) cards and in GSM network Authentication Centres. It is used to authenticate the
customer and generate a key for encrypting voice and data traffic, as defined in 3GPP TS
43.020 (03.20 before Rel-4). Development of A3 and A8 algorithms is considered a matter for
individual GSM network operators, although example implementations are available.

HANDOVER :

Moving an ongoing call from one CELL to another CELL due to subscriber’s mobility.

In telecommunications there may be different reasons why a handover might be conducted:

 when the phone is moving away from the area covered by one cell and entering the area
covered by another cell the call is transferred to the second cell in order to avoid call
 termination when the phone gets outside the range of the first cell;
 when the capacity for connecting new calls of a given cell is used up and an existing or
new call from a phone, which is located in an area overlapped by another cell, is

22
 Department of ECE
Dr. B C Roy Engineering College

transferred to that cell in order to free-up some capacity in the first cell for other users,
who can only be connected to that cell;
 in non-CDMA networks when the channel used by the phone becomes interfered by
another phone using the same channel in a different cell, the call is transferred to a different
channel in the same cell or to a different channel in another cell in order to avoid the
 interference;
 again in non-CDMA networks when the user behaviour changes, e.g. when a fast-travelling
user, connected to a large, umbrella-type of cell, stops then the call may be transferred to a
smaller macro cell or even to a micro cell in order to free capacity on the umbrella cell for
other fast-travelling users and to reduce the potential interference to other cells or users
(this works in reverse too, when a user is detected to be moving faster than a certain
threshold, the call can be transferred to a larger umbrella-type of cell in order to minimize
 the frequency of the handovers due to this movement);
 in CDMA networks a handover (see further down) may be induced in order to reduce the
interference to a smaller neighbouring cell due to the "near-far" effect even when the phone
 still has an excellent connection to its current cell;
 etc.
The most basic form of handover is when a phone call in progress is redirected from its current
cell (called source) to a new cell (called target). In terrestrial networks the source and the target
cells may be served from two different cell sites or from one and the same cell site (in the latter
case the two cells are usually referred to as two sectors on that cell site). Such a handover, in
which the source and the target are different cells (even if they are on the same cell site) is
called inter-cell handover. The purpose of inter-cell handover is to maintain the call as the
subscriber is moving out of the area covered by the source cell and entering the area of the
target cell.
A special case is possible, in which the source and the target are one and the same cell and only
the used channel is changed during the handover. Such a handover, in which the cell is not
changed, is called intra-cell handover. The purpose of intra-cell handover is to change one
channel, which may be interfered or fading with a new clearer or less fading channel.

ROAMING :

Roaming helps ensure that a traveling wireless device (typically a cell phone) is kept connected
to a network without breaking the connection. In wireless telecommunications, Traditional
Roaming is a general term referring to the ability for a cellular customer to automatically make
and receive voice calls, send and receive data, or access other services, including home data
services, when travelling outside the geographical coverage area of the home network, by
means of using a visited network. For example; should you travel beyond of your cell phone
company's transmitter range, your cell phone would automatically hop onto another phone
company's service, if available.

23
 Department of ECE
Dr. B C Roy Engineering College

Roaming is divided into "SIM-based roaming" and "Username/password-based roaming",

whereby the technical term "roaming" also encompasses roaming between networks of
different network standards, e.g. WLAN (Wireless Local Area Network) or GSM. Device
equipment and functionality, such as SIM card capability, antenna and network interfaces, and
power management, determine the access possibilities.
Using the example of WLAN/GSM roaming, the following scenarios can be differentiated (cf.
GSM Association Permanent Reference Document AA.39):

 SIM-based (roaming): GSM subscriber roams onto a Public WLAN operated by:

 their GSM Operator, or

  another Operator who has a roaming agreement with their GSM Operator.
 Username/password based roaming: GSM subscriber roams onto a Public WLAN
operated by:

 their GSM Operator, or

 another Operator who has a roaming agreement with their GSM Operator.
Although these user/network scenarios focus on roaming from GSM Network Operator's
network(s), clearly roaming can be bi-directional, i.e. from Public WLAN Operators to GSM
Networks. Traditional roaming in networks of the same standard, e.g. from a WLAN to a
WLAN or a GSM network to a GSM network, has already been described above and is likewise
defined by the foreignness of the network based on the type of subscriber entry in the home
subscriber register. In the case of session continuity, seamless access to these services across
different access types is provided.

GSM Control Channels:

Time Division Multiple Access (TDMA)
Code Division Multiple Access (CDMA)
Frequency Division Multiple Access (FDMA)

24
 Department of ECE
Dr. B C Roy Engineering College

TDMA :

Time division multiple access (TDMA) is a channel access method for shared medium
networks. It allows several users to share the same frequency channel by dividing the signal
into different time slots. The users transmit in rapid succession, one after the other, each using
its own time slot. This allows multiple stations to share the same transmission medium (e.g.
radio frequency channel) while using only a part of its channel capacity. TDMA is used
in the digital 2G cellular systems such as Global System for Mobile Communications (GSM),
IS-136, Personal Digital Cellular (PDC) and iDEN, and in
the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It
is also used extensively in satellite systems, combat-net radiosystems, and PON networks for
upstream traffic from premises to the operator.
TDMA is a type of Time-division multiplexing, with the special point that instead of having
one transmitter connected to onereceiver, there are multiple transmitters. In the case of the
uplink from a mobile phone to a base station this becomes particularly difficult because the
mobile phone can move around and vary the timing advance required to make its transmission
match the gap in transmission from its peers.

25
 Department of ECE
Dr. B C Roy Engineering College

CDMA :

CDMA is an example of multiple access, which is where several tra nsmitters can send
information simultaneously over a single communication channel. This allows several users to
share a band of frequencies (see bandwidth). To permit this to be achie ved without undue
interference between the users, CDMA employs spread-spectrum technology and a special
coding scheme (where each transmitter is assigned a code).
CDMA is used as the access method in many mobile phone standards such as cdmaOne,
CDMA2000 (th e 3G evolution of cdmaOne), and WCDM A(the 3G standard used by GSM
carriers), which are often referred to as simply CDMA.
CDMA is a spread-spectrum multiple access technique. A spread spectrum technique spreads
the bandwidth of the data uniformly for the same transmitted power. A spreading code is a
pseudo-random code that has a narrow ambiguity function, unlike other n arrow pulse codes.
In CDMA a locally generated code runs at a much higher rate than the data to be transmitted.
Data for transmission is comb ined via bitwise XOR (exclusive OR) with the faster code. The
figure shows how a spread sp ectrum signal is generated. The data signal with pulse duration
of (symbol period) is X OR’ed with the code signal with pulse du ration of (chip
period). (Note: bandwidth is proportional to , where = bit tim e.) Therefore, the
bandwidth of the data signa l is and the bandwidth of the sprea d spectrum signal
is . Since is much s maller than , the bandwidth of the spread spectrum signal is
much larger than the band width of the original signal. The ratio is called the spreading
factor or processin g gain and determines to a certain extent th e upper limit of the total number
of users support ed simultaneously by a base station.

FDMA :

Frequency Division Multiple Access or FDMA is a channel access method used in multiple-
access protocols as a channelization protocol. FDMA gives users an indi vidual allocation of
one
ZZ or several frequency ba nds, or channels. It is particularly comm onplace in satellite

26
 Department of ECE
Dr. B C Roy Engineering College

communication. FDMA, like other Multiple Access systems, coordinates access between
multiple users. Alternatives include TDMA, CDMA, or SDMA. These protocols are utilized
differently, at different levels of the theoretical OSI model.

GSM:

GSM (Global System for Mobile Communications, originally Group Spécial Mobile), is a
standard developed by the European Telecommunications Standards Institute (ETSI) to
describe protocols for second generation (2G) digital cellular networks used by mobile phones.
It became the de facto global standard for mobile communications with over 80% market share.
The GSM standard was developed as a replacement for first generation (1G) analog cellular
networks, and originally described a digital, circuit-switched network optimized for full duplex
voice telephony. This was expanded over time to include data communications, first by circuit-
switched transport, thenpacket data transport via GPRS (General Packet Radio Services) and
EDGE (Enhanced Data rates for GSM Evolution or EGPRS).
Subsequently, the 3GPP developed third generation (3G) UMTS standards followed by fourth
generation (4G) LTE Advanced standards, which are not part of the ETSI GSM standard.

Subscriber Identity Module (SIM)

Main article: Subscriber Identity Module

One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM
card. The SIM is a detachable smart card containing the user's subscription information and
phone book. This allows the user to retain his or her information after switching handsets.
Alternatively, the user can also change operators while retaining the handset simply by
changing the SIM. Some operators will block this by allowing the phone to use only a single
SIM, or only a SIM issued by them; this practice is known as SIM locking.

27
 Department of ECE
Dr. B C Roy Engineering College

Network structure:
The network is structured into a number of discrete sections:

 Base Station Subsystem(BSS) – the base stations and their controllers explained
 Network and Switching Subsystem – the part of the network most similar to a fixed
network, sometimes just called the "core network"
 GPRS Core network – the optional part which allows packet-based Internet connection
 Operation support system (OSS) – network maintenance

SIM:

One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM
card. The SIM is a detachable smart card containing the user's subscription information and phone
book. This allows the user to retain his or her information after switching handsets. Alternatively,
the user can also change operators while retaining the handset simply by changing the SIM. Some
operators will block this by allowing the phone to use only a single SIM, or only a SIM issued by
them; this practice is known as SIM locking.

28
 Department of ECE
Dr. B C Roy Engineering College

Benefits or advantages of Cellular Network

Following are the benefits or advantages of Cellular Network:
➨It provides voice/data services even while roaming.
➨It connects both fixed and wireless telephone users.
➨It is used in areas where cables can not be laid out due to its wireless nature.
➨It is easy to maintain.
➨It is easy to upgrade the equipments.
➨The mobile and fixed subscribers are connected immediately with cellular network as soon as
mobile phones are switched on. All the handshake signals between mobile and base station are
automatically exchanged.

Drawbacks or disadvantages of Cellular Network

Following are the disadvantages of Cellular Network:
➨It offers less data rate compare to wired networks such as fiber optics, DSL etc. The data rate
varies based on wireless standards such as GSM, CDMA, LTE etc.
➨Macro cells are affected by multipath signal loss.
➨The capacity is lower and depends on channels/multiple access techniques employed to serve
subscribers.
➨As the communication is over the air, it has security vulnerabilities.
➨It requires higher cost in order to setup cellular network infrastructure.
➨The wireless communication is influenced by physical obstructions, climatic conditions and
interference from other wireless devices.
➨The installation of antennas for cellular network require space and foundation tower. This is
very cumbersome and requires both time and effort

29
 Department of ECE
Dr. B C Roy Engineering College

CELLULAR SERVICES :
 Voice Communication

 Short Message Service

 Multimedia Messaging Service

 Global Positioning System

 Wireless Application Protocol

 Security

CONCLUSION :

The development of GSM is the first step towards a true personal communication
system that will allow communication anywhere, anytime, and with anyone. The
functional architecture of GSM, employing intelligent networking principles, and its
ideology, which provides enough standardization to ensure compatibility, but still
allows manufacturers and operators freedom, has been widely adopted in the
development of future wireless systems.

BIBLIOGRATHY:

M. Mouly and M.-B. Pautet, The GSM System for Mobile Communications,
1992.

M. Mouly and M.-B. Pautet, GSM Protocol Architecture: Radio Sub-system

Signalling,
‘ IEEE 41st Vehicular Technology Conference, 1991.

30