Introduction to Wireless

Communication

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 Outline
• Basics of Computer Networking
• Wireless Basics
• Frequency allocation & regulation
• Antennas
• Signal propagation
• Classification of Wireless Network
• Wired Vs Wireless

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 Introduction
• Mobile computing systems are computing systems
that may be easily moved physically and whose
computing capabilities may be used while they are
being moved.
– Examples are laptops, personal digital assistants (PDAs),
and mobile phones
• Wireless communication involves the process of
sending/receiving information through invisible
waves in the air. Information such as text, voice, and
video are carried through the radio frequency of the
electromagnetic spectrum
• Wireless communications is one of the biggest
engineering success
– market size dominating the whole economy
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 Introduction
• Working habits, have been changed “anywhere,
anytime.”
– mobility of workers have increased
• Large number of applications have been developed,
– Wireless sensor networks monitor factories,
– Wireless links replace the cables between computers
and keyboards, mouse and other peripheral devices
– Wireless positioning systems monitor the location of
trucks
• This variety of new applications causes the technical
challenges for the wireless engineers to become
bigger with each day.
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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 to 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
– Sneaker net -- 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, atmosphere
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• Definition: A computer network is an interconnected
collection of autonomous computers
– Interconnected - two computers have the ability
to exchange information using some transmission
media e.g., copper cabling, fiber optics, or
atmosphere.
– Autonomous - where no computer controls any
other computer (i.e. no computer can forcibly
start or stop another computer)
– Computers can be PC’s, workstations, cell phones
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

• 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 8
 General Block Diagram of Communication
The effectiveness of such communication is function of:
• Correct Delivery:-- Delivering to the right recipient
• Accuracy:- Accurate delivery of the actual data
• Timeliness:- Delivering the data at the right time
• Jitter:- Uneven(varying) delay that may occur during
the delivery

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Channel:- is a path between two communication devices
Channel Capacity:- How much data can be passed
through the channel(bit/sec)
• Also called Channel bandwidth
• The smaller the pipe the slower data transfer
Channels are two types
• Physical:- Wired(cables)
• Wireless:- Air interface

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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(a telephone line
assigned to a designated user, usually to provide a permanent connection to the Internet), 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. E.g. 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

Bus

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• Ring

• Hybrid (Tree)
Linear bus + Star

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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
• Internetwork
– Interconnection among or between public, private,
commercial, industrial, or governmental networks
– Also called internet
– Different variants
• Intranet
• Extranet
• Internet
• Ethernet
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• Ethernet
– a network for exchanging messages between computers
on a local area network using coaxial, fiber optic, or
twisted-pair cables
• 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, Coaxial
• Unguided – consists of a means for the data signals to
travel but nothing to guide them along a specific path -
wireless
– Atmosphere
Type of wireless transmission
• Directional: point-to-point. E.g. microwave
• Omni-directional: waves are transmitted equally in all directions.
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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 20
 Wireless communication Medias
Broadcast Radio
• Distribute signals through the air over long
distance
• Uses an antenna
• Typically for stationary locations
Cellular Radio
• A form of broadcast radio used for mobile
communication
• High frequency radio waves to transmit voice or
data
• Utilizes frequency-reuse
Radio frequency (RF) is a measurement representing the oscillation rate of electromagnetic radiation
spectrum, or electromagnetic radio waves, from frequencies ranging from 300 gigahertz (GHz) to as
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low as 9 kilohertz (kHz).
 Wireless communication Medias…
Microwave Channels
• Radio waves providing high speed transmission
• They are point-to-point(can’t be obstructed)
• Used for satellite communication
Infrared(IR)
• Wireless transmission media that sends signals
using infrared light waves

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 What is wireless Communication
• Is basically transmitting/ receiving voice as well as
data using EM waves in open space, basically free
from wires
• The information from sender  receiver usually
carried over A well defined frequency channel
• Wireless communication is one of the fastest
growing segments of the telecommunications
industry
• Wireless communication systems, such as cellular,
cordless and satellite phones as well as wireless
local area networks(WLANs) have found
widespread use
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Ancient Wireless Communication Systems
• Shouts and jungle drums
• Smoke signals
• Flashing lights
• Carrier Pigeons
• Flags, Etc.

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 Evolution of Wireless Networks..
• Marconi invented the wireless telegraph in 1896.
– By encoding alphanumeric characters in analog signals, he
sent telegraphic signals across the Atlantic Ocean.
– This led to a great many developments in wireless
communication networks that support radio, television,
mobile telephone, and satellite systems that have
changed our lives.
• Unidirectional information transmission
– was done for entertainment broadcasting. By the late 1930s,
• The need for bidirectional mobile communications
emerged
– Military ,police departments ,fire station….
• Many sophisticated military radio systems were
developed during and after WW2
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 Evolution of Wireless Networks..
Mobile Telephony System
• The first public telephone system known as Mobile
Telephone System(MTS)
• It was also known as Car-based mobile Telephony
• Mobile Transceivers of MTS were very big and
could be carried only by vehicles.
• MTS was Analog system
• Meaning that it processed voice information as
continuous waveform

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• The system was half-duplex
• Communication parties at a time could either
speak or listen
• To Switch between the two modes, users had
to push a specific button on the terminal
• MTS utilized a Base Station(BS) with a single
high-power transmitter

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 • Base Stations utilized the same frequencies
• Due to Power limitations, mobile units transmitted
not directly to the BS but to receiving sites
• How a call happen in MTS?
• The caller first called a special number to connect
to an MTS operator
• The caller informed the operator of the mobile
subscriber’s number
• Then then the operator searched for an idle
channel in order to relay the call to the mobile
terminal
• Major limitations:
• Manual Switching of calls
• Limited /channels are available (3 channels)
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Improved Mobile Telephone System(IMTS)
• Utilized automatic call switching
• Enhanced its mode of transmission to full – duplex
• The intermediation of the operator in a call is
eliminated
• Number of channel increased to 23
IMTS has also problems:
• Providing a small capacity, because of spectrum
usage
• Interference to adjacent systems due to large power
of BS transmitter

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Analog Cellular Telephony Era
• The first cellular concept issued at AT&T Bell
Laboratories
• The cellular concepts replaces high-coverage BSs with
a number of low-coverage stations
• Area of coverage of each such BS is called
a Cell
• The system was divided into a set of
adjacent, non-overlapping cells
• The available spectrum is partitioned into
channels
• Each BS is connected via wires to a device
in Mobile Switching Center (MSC)
• The first generation of cellular systems(1G
systems) – concept designed
• Analog cellular systems were the first step
for the mobile telephony industry 30
Digital Cellular Telephony
• Analog cellular Eras had Limited performance (which is
alleviated in Digital Cellular era)
• The major issues: Data is represented digitally
• Voices signals through an Analog to Digital(ATD)
converter converted to bit stream to modulate an RF
carrier
The major advantage of Digital Era:
• Privacy and security
• In digital systems, it is possible to apply error
detection and error correction techniques to the voice
bit stream
• RF carrier is shared by more than one user, either by
using different time slots or different codes per user
The Second Generation Cellular(2G) network
conceived here 31
Cordless Phones
• The invention of Phones has
• Primary aim to replace the cord of conventional
telephones with a wireless link
• To enable user move while speaking i.e. to support
Mobility
• Early Cordless telephones were analog which had poor
call Quality, Changed in 1G of digital cordless telephones
• 1G digital cordless telephone was successful, However
there was Handset Usage Restriction
• Tele point system avoid the restriction which is 2G digital
cordless phone
• The other problem is roaming between tele point BSs was
not supported
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Wireless Data System
• The first wireless data system is developed in 1970’s
at university of Hawaii,
• ALOHANET Research project
“the idea of the project was to offer bi- directional
communication between computers spread over four
islands and a central computer on the island of Oahu
without the use of phone lines.”

• Wide Area Data System, Wireless Local Area

Networks(WLANS), Wireless ATM(WATM), etc

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Satellite Communication/Network
• Most Useful wireless communication technology
• Utilize the application of Satellite to enable
communication regardless of geographical location
What Benefits such communication brought:
• No need to bother about the cell phone broadcast
tower
• Avoids the need of physical connection
• Ensure that users are completely free from
telecommunication infrastructure

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 Communication Models
• 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
• 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)

•Physical layer - responsible for movements of bits from one hop (node) to the next
•Data Link layer - responsible for moving frames from one hop (node) to the next
•Network layer - responsible for the delivery of packets from the source to destination
•Transport layer - responsible for the delivery of a message from one process to another
•Session layer – responsible for dialog control and synchronization
•Presentation layer – responsible for translation, compression, and encryption
•Application layer - responsible for providing services to the user
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Transport Control Protocol / Internet Protocol
(TCP/IP)

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 Basics of Wireless Transmission

Antenna Antenna

Transmitter Receiver

• 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 (e.g., cellular phones)

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Signal
– any quantity exhibiting variation in time or
variation in space
– electric or electromagnetic representations of data
(Signals are the physical representation of data)
– Users of a communication system can only
exchange data through the transmission of signals.
• Light ,electric , electromagnetic/radio
– Layer 1 of the OSI basic reference model is
responsible for the conversion of data,
• i.e. bits, into signals and vice versa

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Signal
– 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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• The characteristics of a signal
– Amplitude
– Frequency
– Phase
– Wavelength
• Amplitude
– The value of the signal at any point
– measured in volts, amperes, or watts ….

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• 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

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• Phase
– The position of the waveform relative to time zero

• The quality of a data transmission depends on:

– the characteristics of the medium
– the characteristics of the signal
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• Wavelength
– Describe how long the wave is
– The distance from the “crest”(top) of one wave to the
crest of the next wave or
– We can measure from the “trough” (bottom) of one
wave to the trough of the next wave

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• Hertz (Hz) = number of cycles per second.
Frequency is measured in Hertz.
• Data rate = number of bits sent per second (bps).
• Channel = a logical communication path.
– One physical wire can support multiple
channels; each channel supports one user
• Bandwidth = frequency range used by a signal,
measured in Hz.
• Channel capacity = number of bits that can be
transmitted per second. (same as data rate)

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 Frequency allocation
• Wireless communications use the “radio frequency
(RF)” spectrum for transmitting and receiving
information.
• Several factors are considered while allocating
frequencies
– Cost of components: increases as you go to
higher frequencies.
– Signal losses: also increase as frequencies increase.
– Noise disruption : lower frequencies are disrupted
regularly by man-made noise such as electrical
motors, car ignition, and domestic appliances.

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 The Electromagnetic Spectrum
• The electromagnetic spectrum consists of the full
range of known electromagnetic waves, including
– gamma rays,
– X-rays,
– ultraviolet light,
– visible light,
– infrared light,
– microwaves, and
– radio waves.
• Electromagnetic waves are transverse waves which
travel at the speed of light and involve oscillating
electric and magnetic fields at right angles to each
other.
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 Wireless Frequency Allocation
Radio frequencies range from 9KHz to 400GHZ (ITU)
Major frequency bands
• Microwave frequency range (1 GHz to 40 GHz)
– Directional beams possible
– Suitable for point-to-point transmission
– Used for satellite & terrestrial communications
• Broadcast frequency range(30 MHz to 1 GHz )
– Suitable for Omni-directional applications
– applications : FM radio and UHF and VHF television
• Infrared frequency range(300 GHz to 3000 GHz)
– Useful in local point-to-point multipoint applications
within confined(small) areas.

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 Terrestrial Microwave (1GHz to 40GHz)
• Description of common microwave antenna
– Most common: Parabolic "dish", 3 m in diameter
– Fixed rigidly and focuses a narrow beam
– Achieves line-of-sight transmission to receiving
antenna (relays used in between)
– Located at substantial heights above ground level
• Applications
– Long heave telecommunications service (instead of
fiber, coax) -- requires less repeaters but line of sight
– Short point-to-point links between buildings (e.g, closed
circuit TV, LANs, bypass local telephone companies)
– Most common BW= 4GHZ (can give up to 200 Mbps)

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Satellite Microwave (1GHz to 20 GHz, typically)
• Description of communication satellite
– Microwave relay station
– Used to link two or more ground-based microwave
transmitter/receivers
– Receives transmissions on one frequency band
(uplink), amplifies or repeats the signal, and transmits
it on another frequency (downlink)
• Applications
– Television distribution (e.g., Dstv uses satellites )
– Long-distance telephone transmission between
telephone exchange offices
– Private business networks (lease channels, expensive)

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 Broadcast Radio (30 MHz to 1GHz)
• Description of broadcast radio antennas
– Omni directional (main differentiator from microwave)
– Antennas not required to be dish-shaped
– Antennas need not be rigidly mounted to a precise
alignment
• Applications
– Broadcast radio& TV
• VHF and part of the UHF band; 30 MHZ to 1GHz
• Covers FM radio and UHF and VHF television
– Due to new apps, the frequency range is expanded
frequently

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 Infrared (300 GHz to 3000 GHz)
• Operate in the terribly high frequency (THF)
• Does not penetrate walls
• Used in remote control devices (TV remote
control, garage door openers)
Commonly used frequencies in Wireless Systems
– Cellular networks: Mostly around 900 MHz
– IEEE 802.11 LANs: 2.4 GHz (802.11b, 802.11g) and
5 GHz (802.11a)
– Satellite systems: 3 to 30 GHz
– Wireless local loops: 10 to 100 GHz
– Infrared wireless LANs; 300 GHz to 400 THz
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 Frequency Regulations
Two approaches in using wireless frequencies:
– use an unlicensed band or
– use a frequency that is regulated
• Regulated bands require permission
Regulating Bodies
• ITU (International Telecom Union)
– Responsible for assigning internationally used frequencies
• Local broadcast and telecommunication agencies are also
responsible
• 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)
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 Question
• Which type of frequency do you think is widely
used(or congested) in wireless communication ?
• Lower frequencies or higher? And Why?

Lower frequencies are more congested and highly

competed for because the distance can be longer
and the power requirements are lower.

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 Relationship between Wireless Frequency and
Distance Covered
• A very important relationship exists between frequency and
distance covered. The relationship is
d = k/f
• Where d = distance covered, f = frequency used, and k =
constant that depends on environmental factors.
• Thus, the distance covered is inversely proportional to the
frequency being used.
• This implies that the higher the frequency, the shorter is the
distance covered

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 Signal propagation
• Propagation in free space is always like a light
(straight line)
• In real world Receiving power is influenced by
– fading (frequency dependent)- fluctuation to the
amplitude, phase, wavelength and other
characteristics of the frequency at the receiver
– shadowing
– reflection at large obstacles
– refraction depending on the density of a medium
– scattering at small obstacles
– diffraction at edges

Wave propagation is any of the ways in which waves travel 59

 Signal propagation

shadowing reflection refraction scattering diffraction

• Shadowing a blocking of a receiver by a large object, signal

will be lost totally
• Reflection – occurs when signal encounters large surfaces. The
surface is large relative to the wavelength of the signals.
• Refraction – occurs because the velocity of the wave depend
on the density of the medium ( e.g. from air to water)
• Scattering – occurs when incoming signal hits an object whose
size is in the order of the wavelength of the signal or less.
• Diffraction – occurs at the edge of an impenetrable body that
is large compared to the wavelength of the radio wave. 60
 Multipath
• Signal can take many different paths between sender
and receiver due to reflection, scattering, diffraction

multipath
LOS pulses pulses

signal at sender
signal at receiver

• Time dispersion: signal is dispersed over time

– interference with “neighbor” symbols, Inter Symbol
Interference (ISI)
• The signal reaches a receiver directly and phase shifted
– distorted signal depending on the phases of the different
parts
 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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 Attenuation
• Strength of signal falls off with distance over
transmission medium(loss of energy)
• Attenuation factors for unguided media:
– Received signal must have sufficient strength so
that circuitry in the receiver can interpret the
signal
– Signal must maintain a level sufficiently higher
than noise to be received without error
– Attenuation is greater at higher frequencies,
causing distortion

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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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 Noise
• Additional signals inserted between transmitter
and receiver is known as noise
• It is a major limiting factor in communication
system performance
• Noises can be
– Thermal Noise
– Intermodulation noise
– Crosstalk
– Impulse Noise

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• Thermal Noise
– Due to thermal agitation of electrons in a
conductor
– Is present in all electronic devices and transmission
media
– Is a function of temperature
– Is uniformly distributed across the frequency
spectrum and hence is often referred to as White
Noise
– Cannot be eliminated and therefore places an
upper bound on communication system
performance

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• Crosstalk
– A signal from one line is picked up by another
– Can occur by electrical coupling between nearby twisted
pair or rarely, coax cable lines carrying multiple signals
• Impulse Noise
– is sharp quick spikes on the signal caused from
electromagnetic interference, lightning, sudden power
switching, electromechanical switching, etc
• Inter-modulation noise
– When signals at different frequencies share the same
transmission medium, may result inter-modulation noise.
– The effect of inter-modulation noise is to produce signals
at a frequency that is the sum or difference of the two
original frequencies, or multiples of those frequencies
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 Antenna and Radiation Pattern
• Antenna
– a very important component of communication
systems
– is a device used to transform a RF signal, traveling
on a conductor, into an electromagnetic wave in
free space.
– In two-way communication, the same antenna
can be used for transmission and reception
– Antennas demonstrate a property known as
reciprocity,
• which means that an antenna will maintain the same
characteristics regardless if it is transmitting or receiving.

68
 Antenna and Radiation Pattern
• Types of Antennas
• A classification of antennas can be based on:
– Frequency and size
– Directivity
• Frequency and size
– antennas used for HF are different from the ones used
for VHF, which in turn are different from antennas for
microwave.
– The wavelength is different at different frequencies,
– so the antennas must be different in size to radiate
signals at the correct wavelength.
• Directivity: - antennas can be
– omnidirectional
– sectorial or
– directive
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 Omnidirectional
• Radiate the same pattern all around the antenna in a
complete 360 degrees pattern.
• The most popular types of omnidirectional antennas are
the Dipole-Type and the Monopole type (Ground Plane)
• Dipole
– Two of the simplest and most basic antennas are:
– half-wave dipole, or Hertz,
– quarter-wave vertical, or Marconi
• The half-wave dipole consists of two straight collinear
conductors of equal length, separated by a small gap.
• The length of the antenna is one-half the wavelength
of the signal that can be transmitted most efficiently.
• A vertical quarter-wave antenna is the type commonly
used for automobile radios and portable radios.
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71
Monopole Antenna
– is a class of radio antenna consisting of a straight rod-
shaped conductor, often mounted perpendicularly
over some type of conductive surface, called a ground
plane.
– a ground plane is a flat or nearly flat horizontal
conducting surface that serves as part of an antenna,
to reflect the radio waves from the other antenna
elements.
– The driving signal from the transmitter is applied, or
for receiving antennas the output signal to the
receiver is taken, between the lower end of the
monopole and the ground plane.
– One side of the antenna feed line is attached to the
lower end of the monopole, and the other side is
attached to the ground plane, which is often the
Earth.

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73
 Directive
• Used in terrestrial microwave and satellite applications –
have the highest gain
• A parabola is the locus of all points equidistant from a
fixed line and a fixed point not on the line.
• The fixed point is called the focus and the fixed line is
called the directrix
– E.g. Parabolic Dish, Yagi, Patch

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• Patch Antenna • Yagi

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 Sectorial
• Beam can be as wide as
180 degrees or as
narrow as 60 degrees
• Common in Cellular
networks

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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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 Decibels (dB)
• It is customary to express gains, losses, and relative levels
in decibels
• is a measure of the ratio between two signal levels
– Positive: amplified
– Negative: attenuated

– where
• GdB = gain, in decibels
• Pin = input power level
• Pout = output power level
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 Signal propagation and Propagation Modes
• Transmission range
– communication possible
– low error rate
• Detection range
– detection of the signal
possible
– no communication
sender
possible
• Interference range
transmission
– signal may not be
distance
detected
detection
– signal adds to the
background noise interference

A signal radiated from an antenna travels along one of three routes:

– Ground Wave Propagation
– Sky Wave Propagation
– Line of Sight (LoS)
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• Ground Wave Propagation
– follows the contour of the earth
– can propagate considerable distances, well over
the visual horizon.
– frequencies up to about 2 MHz
• Electromagnetic waves in this frequency range are
scattered by the atmosphere
• In such a way that they do not penetrate the upper
atmosphere.
– e.g 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
– can travel through a number of hops, bouncing back
and forth between the ionosphere and the earth's
surface
– a signal can be picked up thousands of kilometers
from the transmitter.
• E.g. amateur radio, BBC and Voice of America

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• Line of Sight (LoS)
– Above 30 MHz, neither ground wave nor sky wave
propagation modes operate, and communication
must be by line of sight
– For ground-based communication, the transmitting
and receiving antennas must be within an effective
line of sight of each other.
• E.g. Satellite Communication

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 Summary of Wireless Frequency Ranges,
Applications, and Propagations
Frequency Range Type of Waves Typical Applications Propagation
Extremely Low to
Ground-Wave
< 2 MHz Medium frequencies AM radio
propagation
(power and Voice Waves

Amateur radio, and

High frequency international radio
2 MHz to 30 MHz Sky-Wave propagation
(Broadcast radio waves) services such as BBC and
VOA (Voice of America)
VHF television, FM
Very high frequency
30 MHz and 300 MHz broadcast and two-way Line-of-Sight propagation
(Broadcast radio waves)
radio
UHF television, cellular
300 MHz to 3000 MHz Ultra high frequency Line-of-Sight propagation
phone, wireless LANs
Satellites, wireless local
Super high frequency
3 to 30 GHz loops, terrestrial Line-of-Sight propagation
(Microwaves)
microwave links
Extremely high Wireless local loops,
30 to 300 GHz Line-of-Sight propagation
frequency experimental links
300 GHz to 400 THz Infrared Infrared LANs Line-of-Sight propagation
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 Classification of Wireless Network
Wireless Networks

Wireless LANs Wireless MANs Wireless WANs

Wireless Cellular Satellite Paging

Personal Business Local Loops Networks Systems Networks
Area LANs (Fixed Wireless)
Networks

Example1: Example1: Example1: Example1: Example1: Example1:

Bluetooth 802.11b LMDS GSM, 9.6 Kbps, Motorola
11 Mbps,
FLEX,
1 Mbps, 37 Mbps, wide coverage Iridium
10 Meters 100 Meters 1.2 Kbps
2-4 Km up to 64 Mbps
Example2: globally
Other examples: Other Example2: 3G, 2 Mbps, Example2:
wireless sensor examples: FSO wide coverage Example 2: ReFLEX,
networks, UWB 802.11g, 1.25 Gbps Deep space 6.4Kbps
HiperLAN2 1-2 KM communication

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 Wired vs Wireless
Wired Wireless
• Reliable • Less reliable
• Higher bandwidth • Lower bandwidth
• Immobility • Mobility
• Infrastructure based • Anytime any anywhere
• QoS • Difficult to guarantee
• Cheap QoS
• Secure • Expensive
• Insecure

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 Reference
• William Stallings
– Chapter 2
• 2.1, 2.2, 2.4
– Chapter 3
• 3.1
– Chapter 4
• 4.1, 4.2, 4.3
– Chapter 5
• 5.1, 5.2, 5.3
• wireless.ictp.trieste.it/handbook/C4.pdf

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