Introduction to Mobile Computing

Elective III - Code: 414463 A Nitin S Ujgare 1
Introduction to Wireless
Systems & History
Mobile Computing
Prof. Nitin S Ujgare
Department of Information Technology
NDMVPs KBTCOE , Nasik.

Outline
 Motivation
 Introduction
 What is Wireless
 Wireless Network
 History of Wireless of Communication

Recommended Textbooks
 Theodore Rappaport, Wireless
Communications: Principles and Practice,
Second Edition, Prentice Hall, December
2001.
 Yi-Bing Lin, Imrich Chlamtac, Wireless and
Mobile Network Architectures, Wiley
Publication, 2nd edition, 2002.

Grading
 There will be one midterm and one final
exam
 There may be projects. I did not determine
them yet.
 Simulation or implementation projects
 No idea how hard they will be!
 No idea which language(s) they will be
implemented on!
 Attendance is important!

What is Wireless and
Mobile Communication?

Wireless Communication
 Transmitting voice and data using
electromagnetic waves in open space
 Electromagnetic waves
 Travel at speed of light (c = 3x108
m/s)
 Has a frequency (f) and wavelength (λ)
 c = f x λ
 Higher frequency means higher energy photons
 The higher the energy photon the more penetrating is
the radiation

Electromagnetic Spectrum
104
102
100
10-2
10-4
10-6
10-8
10-10
10-12
10-14
10-16
104
106
108
1010
1012
1014
1016
1018
1020
1022
1024
IR UV X-Rays
Cosmic
Rays
Radio
Spectrum
1MHz ==100m
100MHz ==1m
10GHz ==1cm
< 30 KHz VLF
30-300KHz LF
300KHz – 3MHz MF
3 MHz – 30MHz HF
30MHz – 300MHz VHF
300 MHz – 3GHz UHF
3-30GHz SHF
> 30 GHz EHF
Micro
wave
Visible light

Wavelength of Some Technologies
 GSM Phones:
 frequency ~= 900 Mhz
 wavelength ~= 33cm
 PCS Phones
 frequency ~= 1.8 Ghz
 wavelength ~= 17.5 cm
 Bluetooth:
 frequency ~= 2.4Gz
 wavelength ~= 12.5cm

Frequency Carries/Channels
 The information from sender to receiver is carrier
over a well defined frequency band.
 This is called a channel
 Each channel has a fixed frequency bandwidth (in
KHz) and Capacity (bit-rate)
 Different frequency bands (channels) can be used
to transmit information in parallel and
independently.

Example
 Assume a spectrum of 90KHz is allocated over a base
frequency b for communication between stations A and B
 Assume each channel occupies 30KHz.
 There are 3 channels
 Each channel is simplex (Transmission occurs in one way)
 For full duplex communication:
 Use two different channels (front and reverse channels)
 Use time division in a channel
Channel 1 (b - b+30)
Channel 2 (b+30 - b+60)
Channel 3 (b+60 - b+90)
Station A Station B

Simplex Communication
 Normally, on a channel, a station can
transmit only in one way.
 This is called simplex transmision
 To enable two-way communication (called
full-duplex communication)
 We can use Frequency Division Multiplexing
 We can use Time Division Multiplexing

Duplex Communication - FDD
 FDD: Frequency Division Duplex
Base Station
B
Mobile
Terminal
M
Forward Channel
Reverse Channel
Forward Channel and Reverse Channel use different frequency
bands

Duplex Communication - TDD
 TDD: Time Division Duplex
Base Station
B
Mobile
Terminal
M
A singe frequency channel is used. The channel is divided into time
slots. Mobile station and base station transmits on the time slots
alternately.
M B M B M B

Example - Frequency Spectrum
Allocation in U.S. Cellular Radio Service
991 992 … 1023 1 2 … 799 991 992 … 1023 1 2 … 799
824-849 MHz 869-894 MHz
Reverse Channel Forward Channel
Channel Number Center Frequency (MHz)
Reverse Channel 1 <=N <= 799
991 <= N <= 1023
Forward Channel 1 <=N <= 799
991 <= N <= 1023
0.030N + 825.0
0.030(N-1023) + 825.0
0.030N + 870.0
0.030(N-1023) + 870.0
(Channels 800-990 are unused)
Channel bandwidth is 45 MHz

What is Mobility
 Initially Internet and Telephone Networks is
designed assuming the user terminals are
static
 No change of location during a call/connection
 A user terminals accesses the network always from a
fixed location
 Mobility and portability
 Portability means changing point of attachment to
the network offline
 Mobility means changing point of attachment to
the network online

Degrees of Mobility
 Walking Users
 Low speed
 Small roaming area
 Usually uses high-bandwith/low-latency access
 Vehicles
 High speeds
 Large roaming area
 Usually uses low-bandwidth/high-latency access
 Uses sophisticated terminal equipment (cell phones)

The Need for Wireless/Mobile
Networking
 Demand for Ubiquitous Computing
 Anywhere, anytime computing and
communication
 You don’t have to go to the lab to check your email
 Pushing the computers more into background
 Focus on the task and life, not on the computer
 Use computers seamlessly to help you and to make your
life more easier.
 Computers should be location aware
 Adapt to the current location, discover services

More Examples
 You walk into a Conference room or a shopping Mall
with your PDA and your PDA is smart enough to
collect and filter the public profiles of other people
that are passing nearby
 Of course other people should also have smart PDAs.
 The cows in a village are equipped with GPS and
GPRS devices and they are monitored from a
central location on a digital map.
 No need for a person to guide and feed them
 You can find countless examples

How to realize Ubiquitous Computing
 Small and different size computing and
communication devices
 Tabs, pads, boards
 PDAs, Handhelds, Laptops, Cell-phones
 A communication network to support this
 Anywhere, anytime access
 Seamless, wireless and mobile access
 Need for Personal Communication Services (PCS)
 Ubiquitous Applications
 New software

Some Example Applications of Ubiquitous
Computing
 You walk into your office and your computer
automatically authenticates you through your
active badge and logs you into the Unix system
 You go to a foreign building and your PDA
automatically discovers the closest public printer
where you can print your schedule and give to
your friend

22
Introduction to Wireless networks
 Access computing/communication services, on the move
 Wireless WANs
– Cellular Networks: GSM, GPRS, CDMA
– Satellite Networks: Iridium
 Wireless LANs
– WiFi Networks: 802.11
– Personal Area Networks: Bluetooth
 Wireless MANs
– WiMaX Networks: 802.16
– Mesh Networks: Multi-hop WiFi
– Adhoc Networks: useful when infrastructure not available
Elective III - Code:
414463 A
Nitin S Ujgare

414463 A
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Limitations of the mobile environment
• Limitations of the Wireless Network
• limited communication bandwidth
• frequent disconnections
• heterogeneity of fragmented networks
• Limitations Imposed by Mobility
• route breakages
• lack of mobility awareness by system/applications
• Limitations of the Mobile Device
• short battery lifetime
• limited capacities

Mobile communication
 Wireless vs. mobile Examples
  stationary computer
  laptop in a hotel (portable)
  wireless LAN in historic buildings
  Personal Digital Assistant (PDA)
 Integration of wireless into existing fixed networks:
– Local area networks: IEEE 802.11, ETSI (HIPERLAN)
– Wide area networks: Cellular 3G, IEEE 802.16
– Internet: Mobile IP extension
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414463 A
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384 Kbps384 Kbps
56 Kbps56 Kbps
54 Mbps54 Mbps
72 Mbps72 Mbps
5-11 Mbps5-11 Mbps
1-2 Mbps1-2 Mbps 802.11
Wireless Technology Landscape
Bluetooth
802.11b
802.11{a,b}
Turbo .11a
Indoor
10 – 30m
IS-95, GSM, CDMA
WCDMA, CDMA2000
Outdoor
50 – 200m
Mid range
outdoor
200m – 4Km
Long range
outdoor
5Km – 20Km
Long distance
com.
20m – 50Km
µwave p-to-p links
.11 p-to-p link
2G
3G

Reference model
Application
Transport
Network
Data Link
Physical
Medium
Data Link
Physical
Application
Transport
Network
Data Link
Physical
Data Link
Physical
Network Network
Radio

Perspectives
 Network designers: Concerned with cost-effective
design
 Need to ensure that network resources are efficiently utilized
and fairly allocated to different users.
 Network users: Concerned with application services
 Need guarantees that each message sent will be delivered
without error within a certain amount of time.
 Network providers: Concerned with system
administration
 Need mechanisms for security, management, fault-tolerance
and accounting.

Wireless frequency allocation
 Radio frequencies range from 9KHz to 400GHZ (ITU)
 Microwave frequency range
 1 GHz to 40 GHz
 Directional beams possible
 Suitable for point-to-point transmission
 Used for satellite communications
 Radio frequency range
 30 MHz to 1 GHz
 Suitable for omnidirectional applications
 Infrared frequency range
 Roughly, 3x1011
to 2x1014
Hz
 Useful in local point-to-point multipoint applications within confined
areas

Frequencies for mobile communication
 VHF-/UHF-ranges for mobile radio
 simple, small antenna for cars
 deterministic propagation characteristics, reliable connections
 SHF and higher for directed radio links, satellite
communication
 small antenna, focusing
 large bandwidth available
 Wireless LANs use frequencies in UHF to SHF spectrum
 some systems planned up to EHF
 limitations due to absorption by water and oxygen molecules
(resonance frequencies)
 weather dependent fading, signal loss caused by heavy
rainfall etc.

Wireless transmission
 Wireless communication systems consist of:
 Transmitters
 Antennas: radiates electromagnetic energy into air
 Receivers
 In some cases, transmitters and receivers are
on same device, called transceivers.
Transmitter Receiver
Antenna
Antenna

Transmitters
Amplifier
Oscillator
Mixer Filter Amplifier
Antenna
Transmitter
Suppose you want to generate a signal that is sent at 900 MHz and
the original source generates a signal at 300 MHz.
•Amplifier - strengthens the initial signal
•Oscillator - creates a carrier wave of 600 MHz
•Mixer - combines signal with oscillator and produces 900 MHz (also does
modulation, etc)
•Filter - selects correct frequency
•Amplifier - Strengthens the signal before sending it
Source

Satellite Based Mobile Systems
 Categorized as
 Two-way (or one-way) limited quality voice or data
transmission
 Very wide range and coverage
 Large regions
 Sometimes global coverage
 Very useful in sparsely populated areas: rural areas, sea,
mountains, etc.
 Target: Vehicles and/or other stationary/mobile
uses
 Expensive base station (satellites) systems

History of
Wireless and Mobile
Communication

History
 1831: Faraday had first started experimenting with
electromagnetic waves.
 Electromagnetic wave:
 one of the waves that are propagated by simultaneous
periodic variations of electric and magnetic field intensity
and that include
 radio waves
 infrared
 visible light
 ultraviolet,
 X rays
 Gamma rays

History – Mathematics and EM
 1864: Maxwell who had been working on a
mathematical model for electromagnetic waves
finally published his paper on the subject.
 One of the consequences of his theories was that E.M.
waves would travel at near the speed of light.
 This had also been experimentally determined by others
at the time.

History – Existence of EM Waves
 At the same time that Lodge was carrying out his
experiments, Heinrich Hertz in Germany was also
doing some of his own concerning Maxwell’s
equations.
 Hertz's investigations into Maxwell’s equations involved
generation, detection, and measurement of waves in
free space, rather than along wires.
 1887: Hertz proves existence of EM waves; first
spark transmitter generates a spark in a receiver
several meters away
 The units of frequency waves is named after him, 1
cycle/second equals a Hertz.

History – Frequency Tuning
 In 1898: Tesla gave one of the first wireless
demonstrations with a what we would call a
remote control boat.
 He realized that things of this nature would need to only
respond to their own frequency, and remain inactive
otherwise.
 This was Tesla’s fundamental radio tuning invention,
which he had first described several years earlier.

History – Transoceanic
Communication
 1901: Marconi successfully transmits radio signal
across Atlantic Ocean from Cornwall to
Newfoundland
 1902: First bidirectional communication across
Atlantic
 1909: Marconi awarded Nobel prize for physics

History – Voice over Radio
1914: First voice over radio transmission
1930s: Mobile transmitters developed; radio
equipment occupied most of police car trunk
1935: Edwin Armstrong demonstrated frequency
modulation (FM) for the first time. Majority of
police systems converted to FM

History – Mobile Telephony
 1946: First public mobile telephone service was
introduced. First interconnection of mobile users
to public switched telephone
network (PSTN)
 1950-1960: AT&T Bell Labs developed theory and
techniques for cellular telephony

History
 1993: IS-95 code-division multiple-access
(CDMA) spread- spectrum digital cellular system
deployed in US
 1993: CDPD (Cellular Digital Packet Data) over
AMPS was realized
 1994: GSM system deployed in US

History – Bluetooth, PCS
 1994: Ericsson starts investigating a low-power,
low-cost radio technology to remove cables
around cell phones (born of Bluetooth idea)

History – 3G Trials and Progress
 1998: The first call using a Nokia W-CDMA
terminal in DoCoMo's trial network was completed
at Nokia's R&D unit near Tokyo in Japan.
 Jun 1998: CDMA2000 submitted to ITU for IMT-
2000
 Dec 1998: The first meetings of the 3GPP
Technical Specification Groups in France.
 1999: IEEE 802.11b approved (11 Mbps)
 1999: The first open Bluetooth specification 1.0 is
released.

History – 3G Progress
 2001 Ericsson and Vodafone UK claim to have
made the world's first WCDMA voice call over
commercial network.
 Jun 2001: NTT DoCoMo launched a trial 3G
service
 June 2001: CDMA2000 1xEV-DO recognized as
part of the 3G IMT-2000 standard

Elective III - Code: 414463 A Nitin S Ujgare 1.45
Mobile Devices
performanceperformance
Pager
• receive only
• tiny displays
• simple text
messages
Mobile phones
• voice, data
• simple text displays
PDA
• simple graphical displays
• character recognition
• simplified WWW
Palmtop
• tiny keyboard
• simple versions
of standard applications
Laptop
• fully functional
• standard applications
Sensors,
embedded
controllers

References
 Presentation by Shridhar Iyer on Wireless
Communication, KR School of Information Technology,
IIT Bombay.
 Mobile and Wireless Networking İbrahim Korpeoğlu
Computer Engineering Department Bilkent University,
Ankara.
 Yi-Bing Lin, Imrich Chlamtac, Wireless and Mobile
Network Architectures, Wiley Publication, 2 nd edition,
2002
 Wireless communication by Ranjan bose, NPTEL, HRD,
IIT Delhi.

Introduction to Mobile Computing

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