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Chapter One
Introduction to Wireless
Networking
Outline
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•
•
•
•
Basics of Computer Networking
Communication Models
Basics of Wireless Networking
Radiation Patterns and Antenna
Wired vs. Wireless
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Basics of Computer Networking
• Information, defined as a collection of facts
from which conclusions may be drawn is
an important resource
• The need of information has increased
from time
– leads to the need of sharing of information
among different agents
• Data communication is the exchange of
information between two agents
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Basics of Computer Networking
• Old paradigm:
– A single powerful computer serving all the needs of
an organization
– Sneakernet --Method of sharing data by copying it to
a disk and carrying it from computer to computer
• New paradigm
– Computer networks: a large number of separate
(autonomous) but internetworked (being able to
exchange information) computers doing the job
• Merging of computer and communications technologies – no
geographical barrier
• Connection: copper wire, fiber optics, air,…
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Definition: A computer network is an interconnected
collection of autonomous computers
– Interconnected meaning two computers have the ability to
exchange information using some transmission media e.g.,
copper cabling, fibre optics, or air.
– Autonomous meaning where no one computer controls
any other computer (i.e. no computer can forcibly start or
stop another computer)
– Computers can be PC’s, workstations, cellphones and
other “specialized” computers such as hubs, switches and
routers
– The computers can be geographically located anywhere
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•
Overview of Data Communications
• A data communication system has 5 components
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•
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Message: the information to be communicated (text, numbers,
pictures, sound, video - or combinations)
Sender: the device - computer, video camera, …
Receiver: still the device
Medium: the physical path by which a message travels from
sender to receiver
Protocol: the set of rules that govern data communications; an
agreement between the communicating devices
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 Network Categories: based on size, ownership, the distance it
covers
 Local Area Network (LAN): usually privately
owned and links devices in a single office, building or
campus
 Wide Area Network (WAN): covering large
geographic area; may utilize public, leased, or private
communications equipment
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• Metropolitan Area Network (MAN):
designed to extend over an entire city; it
may be a single network or
interconnected LANs
• Personal Area Network (PAN): meant
for one person; e.g. a wireless network
connecting a computer with its mouse,
keyboard and printer
• Body Area Network(BAN): meant to
be used to connect wearable
computing devices. Eg in healthcare
systems
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 Physical Topology
 Refers to the way in which a network is laid out physically
 Refers to the arrangement or physical layout of computers,
cables, and other components on the network
 Two or more devices connect to a link; two or more links form a
topology
 A network's topology affects its capabilities
 The choice of one topology over another will have an impact on
the

Types of equipment that the network needs

Growth of the network – scalability

Way the network managed
 Four basic topologies are possible: mesh, star, bus, ring
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 Mesh
 Star
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 Bus
 Ring
 Hybrid
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• Network Architecture : includes the type
of computers on the network and
determines how network resources are
handled
• Two common models
– Peer-to-peer
– Client/Server
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• Internetwork
– interconnection among or between public, private, commercial,
industrial, or governmental networks
– Called also internet
– Three variants
• Intranet
• Extranet
• Internet
• Intranet
– a set of networks that is under the control of a single administrative
entity
• Extranet
– internetwork that is limited in scope to a single organization or entity
but which also has limited connections to the networks of one or
more other usually, but not necessarily, trusted organizations or
entities
• Internet
– worldwide interconnection of networks
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Transmission media
• Is a physical media that carries a signal from the
transmitter to the receiver
• Two basic categories
– Guided
– Unguided
• Guided – uses a cabling system that guides the
signals along a specific path
– E.g. Fiber Optics, Twisted Pair etc…
• Unguided – consists of a means for the data
signals to travel but nothing to guide them along a
specific path - wireless
– Atmosphere
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• Understanding the characteristics of different
types of transmission media and how they
relate to other aspects of a network is
necessary
for
the
development
of
a
successful network
• Bandwidth – the maximum volume of
information that can be transferred over a
communication medium
– Measured in bits per second (bps) in digital
circuits
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 Mode of transmission
 refers to the direction of signal flow between two linked devices
 It can be
 Simplex: unidirectional, only one of the devices can


transmit
 E.g. TV transmission, pager
Half-duplex: both can transmit and receive, but not at the
same time
 E.g. wireless handset (walkie-Talkie)
Full-duplex: both can transmit and receive at the same
time
 E.g. Telephone transmission
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Outline
•
•
•
•
•
Basics of Computer Networking
Communication Models
Basics of Wireless Networking
Radiation Patterns and Antenna
Wired vs. Wireless
18
Communication Models
• For two computers, in a computer network, to communicate
must talk the same language
– follow the same protocol
• A network protocol is a formal set of rules, conventions and
data structure that governs how computers and other network
devices exchange information over a network
• In earlier days, many of the networks that were built used
different hardware and software implementations
– they were incompatible and it became difficult for
networks using different specifications to communicate
with each other
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Communication Models
• To address the problem of networks being
incompatible and unable to communicate
with each other, we need some way of
model
• The
two
most
widely
known
communication models are:
– OSI
– TCP/IP
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Open System Interconnection
(OSI)
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Transport Control Protocol /
Internet Protocol (TCP/IP)
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Outline
•
•
•
•
•
Basics of Computer Networking
Communication Models
Basics of Wireless Networking
Radiation Patterns and Antenna
Wired vs. Wireless
23
Basics of Wireless Networking
• Wireless networking is the transfer of
information (via electromagnetic signal)
over a distance without the use of wires or
cables
• Guglielmo Marconi invented the wireless
telegraph in 1896
• Sent telegraphic signals across a distance
of about 3200 km in 1901
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• Signal
– any quantity exhibiting variation in time or
variation in space
– electric or electromagnetic representations of
data
– Can be
• Analog
– one in which the signal intensity varies in a smooth fashion
over time
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• Digital
– one in which the signal intensity maintains a constant
level for some period of time and then changes to
another constant level
– Frequency Spectrum:
• Of a signal is the collection of all component frequency
– Bandwidth
– Of a signal is the range of component frequencies or the
width of the frequency spectrum
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• Three characteristics of a signal
– Amplitude
– Frequency
– Phase
• Amplitude
• The value of the signal at any point
• measured in volts, amperes, or watts ….
• Frequency
– The number of periods in one second
– Period – the amount of time, in seconds, a signal needs
to complete one cycle
– Period and frequency have inverse relationship
• Phase
– The position of the waveform relative to time zero
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• The quality of a data transmission depends:
– the characteristics of the medium
– the characteristics of the signal
• Radio
– in the range 30 MHz to 1 GHz
– Omnidirectional
• Microwave
– in the range of about 1 GHz to 100 GHz
– Directional
• Infrared
– roughly, from 3 X 1011 to 2 X 1014 Hz
– Cannot penetrate walls
– No licensing
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Propagation Modes
• Three ways of propagation
– Ground Wave Propagation
– Sky Wave Propagation
– Line of Sight (LoS)
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• Ground Wave Propagation
– follows the contour of the earth
– frequencies up to about 2 MHz
– Eg AM radios
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• Sky Wave Propagation
– 2 - 30MHz
– a signal from antenna is reflected from the
ionized layer of the upper atmosphere
(ionosphere) back down to earth
– Eg BBC and Voice of America
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• Line of Sight (LoS)
– Above 30 MHz
– Eg satellite communication
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Transmission Impairments
• the signal that is received will differ from
the signal that is transmitted
• Transmission impairments
– Attenuation and attenuation distortion
– Free space loss
– Noise
– Atmospheric absorption
– Multipath
– Refraction
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• Multipath
– signal can be reflected by obstacles
• multiple copies of the signal with varying delays
can be received.
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• Atmospheric absorption
– Water vapor and oxygen
– Rain and fog cause scattering of radio waves
– Dependent on frequency
• E.g
– 22 GHz due to water vapor
– oxygen results in an absorption peak in the vicinity of 60
GHz
• Refraction
– caused by changes in the speed of the signal
with altitude
– The signal bent
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Outline
•
•
•
•
•
Basics of Computer Networking
Communication Models
Basics of Wireless Networking
Radiation Patterns and Antenna
Wired vs. Wireless
39
Antenna and Radiation Pattern
• Antenna
– an electrical conductor or system of conductors
used either for radiating electromagnetic
energy or for collecting electromagnetic energy
– Two types
• Dipoles
• Parabolic Reflective Antenna
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• Dipole
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half-wave dipole, or Hertz,
quarter-wave vertical, or Marconi
Omni directional
commonly used for automobile radios and portable
radios
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• Parabolic Reflective Antenna
– directional
– used in terrestrial microwave and satellite
applications
– equidistant from a fixed line (Directrix) and a
fixed point (Focus)
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Radiation Pattern
• graphical representation of the radiation
properties of an antenna as a function of
space coordinates
• common
way
to
characterize
the
performance of an antenna
• An isotropic antenna, ideal antenna, radiates
power in all directions equally
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• Antenna's power gain
– defined as the power output, in a particular
direction, compared to that produced in any
direction by a perfect omnidirectional antenna
– a key performance figure which combines the
antenna’s directivity and electrical efficiency
– measures the directionality of the antenna
•
where
»
»
»
»
»
G = antenna gain
Ae = effective area
f = carrier frequency
c = speed of light (~3 X 108 m/s)
= carrier wavelength
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Example
• For a parabolic reflective antenna with a
diameter of 2m, operating at 12 GHz, what
is the effective area and the antenna gain
– Ae = 0.56 A
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Decibels (dB)
• It is customary to express gains, losses,
and relative levels in decibels
• is a measure of the ratio between two signal
levels
– where
• GdB = gain, in decibels
• Pin = input power level
• Pout = output power level
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• Example
– If a signal with power level of 20mW is
inserted in the transmission system and the
measured power some distance away is
40mW.
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Electromagnetic Spectrum Allocation
• National and international agreements about
who gets to use which frequencies
• The higher frequency spectrum the higher data
rate
• ITU-R international body who sets rules and
regulations
• Four mechanisms
– the beauty contest
– holding a lottery among the interested companies
– auctioning off the bandwidth to the highest bidder
– Not to allocate at all - ISM (2.4GHz, 5.7GHz) 48
Outline
•
•
•
•
•
Basics of Computer Networking
Communication Models
Basics of Wireless Networking
Radiation Patterns and Antenna
Wired vs. Wireless
49
Wired vs Wireless
Wired
• Reliable
• Higher bandwidth
• Immobility
• Infrastructure based
• QoS
• Cheap
• Secure
Wireless
• Less reliable
• Lower bandwidth
• Mobility
• Anytime any anywhere
• Difficult to guarantee QoS
• Expensive
• Insecure
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