Unit 1

UNIT-1
INTRODUCTION TO MOBILE COMPUTING

Basics of Cell, Cluster and frequency
reuse concept
• Cell
Cell is the basic geographic unit of the cellular communication system.
In reality cell can be of any shape, but generally it is represented in the form of hexagon.
The base station is placed at the center of the cell.

• Cell clusters
Cell cluster is a group of cells in which cells are arranged such that no frequency channels are
reused.
The size of cluster is defined by number of cells in the cluster.
Following figure shows three clusters with size of 7.

• Spectrum and Frequency Re-use
The available spectrum is limited. The design process of selecting and allocating channel groups
for all cellular base stations within a system is called frequency reuse or frequency planning.
To be able to increase the capacity of the system, frequencies must be re-used in the cellular
layout (unless we are using spread spectrum techniques).
 Frequencies cannot be re-used in adjacent cells because of co-channel interference. The cells
using the same frequencies must be dispersed across the cellular layout.

Noise and its effects on Mobile
• What is Noise?
Noise is unwanted disturbances superimposed on a useful signal, which tends to
degrade its information content.
• Types and sources of noise
Thermal noise:
Inter-modulation (IM) noise:
Crosstalk:
Impulse noise:

Thermal noise:
Thermal noise occurs in all transmission media and communication equipment, including passive
devices.
Every equipment element and the transmission medium itself contribute thermal noise to a
communication system if the temperature of that element or medium is above absolute zero.
The more heat generated or applied, the greater the level of thermal noise.

Inter-modulation (IM) noise:
Inter-modulation noise is the result of the presence of inter-modulation products.
If two signals of frequencies F1 and F2 are passed through a nonlinear device or medium, the
result will contain IM products that are spurious frequency energy components.
These components may be inside or outside the frequency band of interest for a particular
device.
Crosstalk:
Cross-talk refers to signals interfering with each other electromagnetically.
Crosstalk refers to unwanted coupling between signal paths.
Electrical coupling between transmission media, like adjacent wires in a multilane serial interface
connection
for example, Ethernet or Fibre Channel;

Impulse noise:
Impulse noise is a discontinuous series of irregular pulses or noise "spikes" of short duration,
broad spectral density and of relatively high amplitude.
In the language of the trade, these spikes are often called "hits. “
Understanding GSM & CDMA
GSM and CDMA refer tocellular communication standards that are adopted by carriers.
GSM
GSM means Global System for Mobile Communications (GSM).
More than 6 billion people worldwide use the GSM Technology.
GSM is the most widely used wireless technology in the world, available in more than 219
countries and territories worldwide, with a market share of more than 90 percent.

GSM, all subscriber and wireless provider information is stored on interchangeable modules
known as SIM(Subscriber Identification Module)cards.
However, the 850MHz and 1900MHz bands are used in North America, while the 900-MHz and
1800-MHz bands are used every where else.
There are several reasons why GSM is so popular among operators and their customers:
Clear voice quality
International roaming
security
Subscriber Identity Module (SIM) cards
Product selection
Research and development

CDMA
The term "CDMA" (Code Division Multiple Access) refers to both a spread spectrum technique
and a cellular standard popular in North America.
What CDMA Means?
Code- encodes and decode process
Division- single channel divided
Multiple Accesses- due to code based information
The goal of CDMA is to break up a finite radio frequency so that multiple users can access it at the
same time.
CDMA networks have greater range and clarity than GSM.
However, it is more difficult for users to switch phones and carriers, since subscriber information
is programmed directly into the phone rather than on a SIM card.
International roaming is also not possible, since CDMA has not been implemented in many
countries

Differentiate CDMA and GSM
CDMA GSM
Code Division Multiple Access Global System for Mobile communication
Storage type: internal memory SIM memory
Global market share: 25% 75%
Dominant standard in the U.S. Dominant standard world wide except the U.S.
There is one physical channel and a special code
for every device in the coverage network. Using
this code, the signal of the device is multiplexed,
and the same physical channel is used to send the
signal.
Every cell has a corresponding network tower,
which serves the mobile phones in that cellular
area.
Less Accessible Most Accessible
Frequency band: Single (850MHz) Multiple (850/900/1800/1900MHz)
Handset specific SIM specific. User has option to select handset of
his choice.
Emits less radiation Emits 28 times more radiations than CDMA

The GSM network can be broadly divided into:
• The Mobile Station (MS)
The Mobile Station is a technical name which is used to
represent Mobile Phones with Subscriber Identity Module
(SIM).
• The Base Station Subsystem (BSS):
• The Base Transceiver Station (BTS)
• The Base Station Controller (BSC)
The BTS and the BSC communicate across the specified Abis
interface, enabling operations between components that are
made by different suppliers.
The radio components of a BSS may consist of four to seven or
nine cells.

• The Base Transceiver Station (BTS)
The BTS houses the radio transceivers that define a cell and
handles the radio link protocols with the MS. In a large urban
area, a large number of BTSs may be deployed.
The BTS corresponds to the transceivers and antennas used in
each cell of the network.
A BTS is usually placed in the center of a cell. Its transmitting
power defines the size of a cell.
functions::
 Encoding, encrypting, multiplexing, modulating, and feeding the RF
signals to the antenna
 Time and frequency synchronizing
 Uplink channel measurements

• The Base Station Controller (BSC)
The BSC manages the radio resources for one or more BTSs.
It handles radio channel setup, frequency hopping, and handovers.
The BSC is the connection between the mobile and the MSC.
 The BSC also translates the 13 Kbps voice channel used over the radio link to the standard 64
Kbps channel used by the Public Switched Telephone Network (PSDN) or ISDN.
Functions
 Control of frequency hopping
 Performing traffic concentration to reduce the number of lines from the MSC
 Time and frequency synchronization
 Power management

• The Network Switching Subsystem (NSS):
The Network switching system (NSS), the main part of
which is the Mobile Switching Center (MSC), performs the
switching of calls between the mobile and other fixed or
mobile network users, as well as the management of
mobile services such as authentication.
 Mobile Switching Centre ( MSC) :
The MSC is the most central unit in the NSS and thus MSC is responsible for controlling the traffic
among all of the present BSCs.
MSC is responsible for
Mobility management and Registration.
Location Updating Process.
Interconnecting BSS and MSC call handoff situations.

• Home Location Register (HLR)
it is the database which is responsible for containing the subscriber information and location
information for each user who reside in the same city as the city of the MSC.
Each subscriber is assigned a Unique international mobile subscriber identity (IMSI) and this is the
number which is used to identify the home user.
• Visitor Location Register (VLR)
VLR is the database which temporarily stores the IMSI an customer information for each roaming
subscriber who is visiting the coverage information for each and a particular MSC.
VLR is always combined with MSC. When a mobile station roams into a new MSC area, VLR
connected to that MSC requests data about the mobile station from HLR.

• Authentication Centre:
Authentication Center is a protected database which is used for storing a copy of the secret key
stored in each subscriber's SIM card.
It is used for authentication and ciphering of the radio channel.
The Authentication center contains a register called Equipment Identity Register (EIR)
• Equipment Identity Register
Equipment Identity Register (EIR) is also known as a database which includes a list of all valid
mobile equipment on the network, where its International Mobile Equipment Identity (IMEI)
identifies each MS.

GSM Services
Short Message Service (SMS)
Multimedia Message Service (MMS)
Location Based Service (LBS)
Value added Service (VAS)
GSM – User Services
Telephony services or teleservices
Data services or bearer services
Supplementary services

• Telephony services or teleservices
 Voice Calls
 Videotext and Facsmile
 Short Text Messages
• Data services or bearer services
Data services or Bearer Services are used through a GSM phone. to receive and send data is the
essential building block leading to widespread mobile Internet access and mobile data transfer.
• Supplementary services
 Conferencing
 Call Waiting
 Call Hold
 Call Forwarding
 Call Barring

Different modes used for Mobile Communication
 Infrared (IR) wireless communication
Infrared wireless communication communicates information in
a device or systems through IR radiation.
IR is electromagnetic energy at a wavelength that is longer
than that of red light.
 Broadcast Radio
The first wireless communication technology is the open radio
communication to seek out widespread use, and it still serves
a purpose nowadays.
Radio uses a transmitter which is used to transmit the data in
the form of radio waves to a receiving antenna (Different
Types of Antennas).

 Microwave Radio
Microwave wireless communication is an effective type of
communication, mainly this transmission uses radio waves, and the
wavelengths of radio waves are measured in centimeters.
Where in satellite method, the data can be transmitted though a
satellite, that orbit 22,300 miles above the earth.
 Communication Satellites
Satellite communication is one type of self-contained wireless
communication technology, it is widely spread all over the world to
allow users to stay connected almost any where on the earth.

Architecture of Mobile Computing
 Presentation Tier
 Application Tier
 Data Tier

Characteristics of Mobile Communication
• Following are some of the characteristics of Mobile Computing:
 User Mobility
 Device Mobility
 Network Mobility
 Bearer Mobility
 Session Mobility

Application of Mobile Communication
• In today’s world almost all the people required mobile computing services in one
or another way.
Manage Personal Record
Social Media and Group Message
Transaction
Mobile Shopping
Tele Banking
Entertainment
Alert & Notification
GPS Based Service
News & Media
Weather Forecast

Middleware & Gateway required for Mobile Computing
• MiddleWare:
Middleware is software that provides a link between separate software applications.
It is a layer that lies between the operating system and applications.
• Types of Middleware:
Communication middleware
Transaction processing middleware
Behavior management middleware
Communication gateways.

Communication middleware
The application will communicate with different nodes and services
through different communication middleware.
Different connectors for different services will fall in this category.
Examples could be TN3270 for IBM mainframe services, or Javamail
connector for IMAP or POP3 services
Transaction processing middleware
In many cases a service will offer session oriented dialogue (SoD).
For a session we need to maintain a state over the stateless
Internet.
This is done through an application server.

Behavior management middleware
For different devices we need different types of rendering.
We can have applications, which are developed specially for different types of rendering.
For example, we can have one application for Web, another for WAP, and a different one for SMS.
Behavior management middleware
Between the device and the middleware there will be network of networks.
Gateways are deployed when there are different transport bearers or networks with dissimilar
protocols.
For example, we need an IVR (Interactive Voice Response) gateway to interface voice with a
computer, or an WAP gateway to access internet over a mobile phone.

Mobile Communication via Satellite
In satellite communication, signal transfer between
sender and receiver through satellite
It requires transmitter station and receiver station to be
setup on earth.
Transmitter station on the earth send signals in the
space towards satellite. This process is known as uplink.
Upon receiving the signal from transmitter station, the
satellite amplifies the signals and send back to receiver
station on the earth. This process is known as downlink.

• Advantages of Satellite Communication
Flexibility
Mobility
Global Coverage
Fast Deployment
• Disadvantages of Satellite Communication
Costly
Propagation Delay
Requirement of Special Terminal

• Types of Satellite
Low Earth Orbit (LEO) Satellite
Medium Earth Orbit (MEO) Satellite
Geostationary Earth Orbit (GEO) Satellite

• Low Earth Orbit (LEO) Satellite
The LEO satellite orbits in the range of 500 to 1500 km
above the surface of earth.
The orbital period of LEO satellite is about 10 to 40
minutes.
As its orbital position is lower from the surface of the
earth, it requires about 40 to 80 satellites to provide
continuous coverage.
LEO is used in telecommunication system to provide
data communication such as email, video
conferencing.

• Medium Earth Orbit (MEO) Satellite
The MEO satellite orbits in the range of 5000 to 12000 km
above the surface of the earth.
It orbits higher than LEO and lower than GEO, so it is
known as Intermediate Circular Orbit (ICO).
The orbital period of the MEO satellite is about 2 to 8
hours.
As its orbital position is higher from the surface of the
earth, it requires about 8 to 20 such satellites to provide
MEO is used for the Navigation.

• Geostationary Earth Orbit (GEO) Satellite
The GEO satellite orbits at the height of 36000 km above the
surface of the earth.
The orbital period of the GEO satellite is about 24 hours.
As its orbital position is very high from the surface of the
earth, it requires about 3 such satellites to provide
GEO satellite is used to handle communication up to large
distance.

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