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Master of Computer Science & IT (MCIT)
Fall Semester 2013
Elec1ve Course (CT-531) Wireless & Mobile Communica:on
Lecture 2
Dr. Muhammad Mubashir Khan [email protected]
Department of Computer Science & IT, NED University of
Engineering & Technology, Karachi
September 2013
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Background Topics Informa1on Signals Frequency and Frequency
Bands Channel Capacity Mul1plexing Frequency Division Mul1ple
Access (FDMA) Time Division Mul1ple Access (TDMA) Propaga1on Modes
Ground wave, Sky wave, Line of sight transmission
Spread Spectrum Frequency Hopping Spread Spectrum (FHSS) Direct
Sequence Spread Spectrum (DSSS) Code Division Mul1ple Access
(CDMA)
Other points will be explained as needed
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Electromagne1c signals Electromagne1c waves can be imagined as a
self-propaga1ng transverse oscilla1ng wave of electric and magne1c
fields.
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Frequency and Wavelength The rela1ve wavelengths of the
electromagne1c waves of three different colors of light (blue,
green, and red) with a distance scale in micrometers along the
x-axis.
Greater wavelength Smaller frequency
Smaller wavelength greater frequency
Frequency (f): Rate, in cycles per second, or Hertz (Hz) at
which the signal repeats
Peak amplitude (A) - maximum value or strength of the signal
over 1me; typically measured in volts
Wavelength () - distance occupied by a single cycle of the
signal Or, the distance between two points of corresponding phase
of two consecu1ve cycles
Phase () - measure of the rela1ve posi1on in 1me within a single
period of a signal
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Analog & Digital Signals Analog signal - signal intensity
varies in a smooth fashion over 1me
No breaks or discon1nui1es in the signal Digital signal - signal
intensity maintains a constant level for some period of 1me and
then changes to another constant level
Periodic signal - analog or digital signal pa`ern that repeats
over 1me s(t +T ) = s(t ) -< t < +
where T is the period of the signal
A digital signal waveform: (1) low level, (2) high level, (3)
rising edge, and (4) falling edge.
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William Stallings Book
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Frequency, Spectrum, Bandwidth Fundamental frequency - when all
frequency components of a signal are integer mul1ples of one
frequency, its referred to as the fundamental frequency (the lowest
frequency of a periodic waveform)
Spectrum - range of frequencies that a signal contains Absolute
bandwidth - width of the spectrum of a signal Effec:ve bandwidth
(or just bandwidth) - narrow band of frequencies that most of the
signals energy is contained in
The greater the bandwidth, the higher the informa:on-carrying
capacity
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EM Spectrum
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EM Spectrum = Gamma rays HX = Hard X-rays SX = Sok X-Rays EUV =
Extreme-ultraviolet NUV = Near-ultraviolet Visible light (colored
bands) NIR = Near-infrared MIR = Moderate-infrared FIR =
Far-infrared EHF = Extremely high frequency (microwaves) SHF =
Super-high frequency (microwaves) UHF = Ultrahigh frequency (radio
waves) VHF = Very high frequency (radio) HF = High frequency
(radio) MF = Medium frequency (radio) LF = Low frequency (radio)
VLF = Very low frequency (radio) VF = Voice frequency ULF =
Ultra-low frequency (radio) SLF = Super-low frequency (radio) ELF =
Extremely low frequency (radio)
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Fundamental Frequency Any electromagne1c signal can be shown to
consist of a collec1on of periodic analog signals (sine waves) at
different amplitudes, frequencies, and phases
The period of the total signal is equal to the period of the
fundamental frequency
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A`enua1on The gradual loss in intensity of any kind of signal
(wave) through a medium. sunlight is a`enuated by dark glasses,
X-rays are a`enuated by lead, and light and sound are a`enuated by
water.
In electrical engineering and telecommunica1ons, a`enua1on
affects the propaga1on of waves and signals in electrical circuits,
in op1cal fibers, as well as in air (radio waves).
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Rela1onship b/w Data Rate and Bandwidth The greater the
bandwidth, the higher the informa1on-carrying capacity
Conclusions Any digital waveform will have infinite
bandwidth
BUT the transmission system will limit the bandwidth that can be
transmi`ed
AND, for any given medium, the greater the bandwidth transmi`ed,
the greater the cost
HOWEVER, Limi1ng the bandwidth creates distor1ons making it
difficult to interpret the received signal
The only way to get finest steep edge is by adding an infinite
number of harmonics.
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Data, Signal, Transmission Data - en11es that convey meaning, or
informa1on Signals - electric or electromagne1c representa1ons of
data
Transmission - communica1on of data by the propaga1on and
processing of signals
Analog data Video Audio
Digital data Text Integers
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Analog Signals A con1nuously varying electromagne1c wave that
may be propagated over a variety of media, depending on
frequency
Examples of media: Copper wire media (twisted pair and coaxial
cable) Fiber op1c cable Atmosphere or space propaga1on
Analog signals can propagate analog and digital data
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Digital Signals A sequence of voltage pulses that may be
transmi`ed over a copper wire medium
Generally cheaper than analog signaling Less suscep1ble to noise
interference Suffer more from a`enua1on Digital signals can
propagate analog and digital data
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Different combina1ons are possible Digital data, digital signal
Equipment for encoding is less expensive than digital-to-analog
equipment
Analog data, digital signal Conversion permits use of modern
digital transmission and switching equipment
Digital data, analog signal Some transmission media will only
propagate analog signals
Examples include op1cal fiber and satellite Analog data, analog
signal Analog data easily converted to analog signal
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Analog and Digital transmission Transmit analog signals without
regard to content A`enua1on limits length of transmission link
Cascaded amplifiers boost signals energy for longer distances but
cause distor1on Analog data can tolerate distor1on Introduces
errors in digital data
Digital Signal Repeaters achieve greater distance Repeaters
recover the signal and retransmit
Analog signal carrying digital data Retransmission device
recovers the digital data from analog signal
Generates new, clean analog signal
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Channel Capacity Channel (A specific radio frequency, pair or
band of
frequencies) Impairments, such as noise, limit data rate that
can be
achieved For digital data, to what extent do impairments limit
data
rate? Channel Capacity the maximum rate at which data can be
transmi`ed over a given communica1on path, or channel, under
given condi1ons
Related concepts Data rate - rate at which data can be
communicated (bps) Bandwidth - the bandwidth of the transmi`ed
signal as constrained by the transmi`er and the nature of the
transmission medium (Hertz)
Noise - average level of noise over the communica1ons path Error
rate - rate at which errors occur Error = transmit 1 and receive 0;
transmit 0 and receive 1
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Signal to Noise Ra1o Ra1o of the power in a signal to the power
contained in the noise thats present at a par1cular point in the
transmission
Typically measured at a receiver Signal-to-noise ra1o (SNR, or
S/N)
A high SNR means a high-quality signal, low number of required
intermediate repeaters
SNR sets upper bound on achievable data rate
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Shannon's Capacity Formula Equa1on:
Represents theore1cal maximum that can be achieved
Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24
dB
Using Shannons formula
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Transmission Media Transmission Medium Physical path between
transmi`er and receiver
Guided Media Waves are guided along a solid medium E.g., copper
twisted pair, copper coaxial cable, op1cal fiber
Unguided Media Provides means of transmission but does not guide
electromagne1c signals
Usually referred to as wireless transmission E.g., atmosphere,
outer space Transmission and recep1on are achieved by means of an
antenna
Configura1ons for wireless transmission Direc1onal
Omni-direc1onal
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General Frequency Ranges Microwave frequency range 1 GHz to 40
GHz Direc1onal beams possible Suitable for point-to-point
transmission Used for satellite communica1ons
Radio frequency range 30 MHz to 1 GHz Suitable for
omnidirec1onal applica1ons
Infrared frequency range Roughly, 3x1011 to 2x1014 Hz Useful in
local point-to-point mul1point applica1ons within confined
areas
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Terrestrial Microwave Descrip1on of common microwave antenna
Parabolic "dish", 3 m in diameter Fixed rigidly and focuses a
narrow beam Achieves line-of-sight transmission to receiving
antenna Located at substan1al heights above ground level
Applica1ons Long haul telecommunica1ons service Short
point-to-point links between buildings
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Satellite Microware Descrip1on of communica1on satellite
Microwave relay sta1on Used to link two or more ground-based
microwave transmi`er/receivers
Receives transmissions on one frequency band (uplink), amplifies
or repeats the signal, and transmits it on another frequency
(downlink)
Applica1ons Television distribu1on Long-distance telephone
transmission Private business networks
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Broadcast Radio Descrip1on of broadcast radio antennas
Omnidirec1onal Antennas not required to be dish-shaped Antennas
need not be rigidly mounted to a precise alignment
Applica1ons Broadcast radio VHF and part of the UHF band; 30 MHZ
to 1GHz Covers FM radio and UHF and VHF television
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Mul1plexing Capacity of transmission medium usually exceeds
capacity required for transmission of a single signal
Mul1plexing - carrying mul1ple signals on a single medium More
efficient use of transmission medium
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Why Mul1plexing? Cost per kbps of transmission facility declines
with an increase in the data rate
Cost of transmission and receiving equipment declines with
increased data rate
Most individual data communica1ng devices require rela1vely
modest data rate support
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Basic Mul1plexing Techniques Frequency-division mul1plexing
(FDM) Takes advantage of the fact that the useful bandwidth of the
medium exceeds the required bandwidth of a given signal
Time-division mul1plexing (TDM) Takes advantage of the fact that
the achievable bit rate of the medium exceeds the required data
rate of a digital signal
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FDM
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TDM
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Get in touch
Course homepage
h`ps://sites.google.com/site/WirelessMobileCommunica1on/
Best way to contact me is to email: [email protected]