e-signlas slides electronic communication.ppt
TRANSCRIPT
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Electronic
Communication: Electronic communication is thetransmission, reception, and processing of
information b/w two or more Ends / Stations
using electronic circuits. Information (Message) can be Analogous
(continuous) form such as voice, music, or
igital (discrete) form such as binar!"coddednumbers.
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Electronic
Communication: In #$%&, Samuel Morse developed the firstelectronic communication s!stem that was called
'elegraph.
In #$&, Aleander *raham +ell and 'homas A.atson developed the first electronic
communication s!stem that was able to transmit
conversation called 'elephone s!stem.
In #$-, *uglielmo Marconi transmitted the firstwireless signals through Earths atmosphere.
0ommercial 1adio broadcasting began in #-23.
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Major e-communication
types: Analog communication s!stem4 Information / messages are transmitted and
received in analogous (continuous) signals.
igital communication s!stem4 Information / messages are transmitted and
received in digital (discrete) signals.
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A Simple igital 0ommunication Model
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Electronic Signals
0ommunication
Signals '!pes
Analogous Digital
5ature 6 0omposition
Simple Composite Periodic Aperiodic
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Y(t)=A sin (2ft +)
Y(t)=A cos (2ft +
)
A Simple Signal (Sine Wave):
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7ourier Anal!sis4
7ourier showed that a composite
signal is a sum of a set of sine waves of
different fre8uencies, phases, and
amplitudes.
In other words, we can write a composite
signal as4
Y(f)=A1Sin (2f1t+1) + A2Sin (2f2t+2) + A3Sin (2f3t+3) + . . .
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Required all the odd harmonics up toRequired all the odd harmonics up to
infinity:infinity:
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+! adding these three harmonics, we do notget a s8uare wave9we get something
which is close, but not eact.
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0omposite Signal and 'ransmission Medium
A signal needs to pass through atransmission medium (cable or air).
A medium ma! pass some
fre8uencies and ma! bloc: orwea:en others.
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'his means that when we send our
s8uare wave signal through a
medium, we get something at the
other end which is not a s8uare
wave at all.
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Example
If a periodic signal is decomposed into five sine
waves with fre8uencies of #33, %33, ;33, &33,and -33 raw the
spectrum, assuming all components have a
maimum amplitude of #3 ?.
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'he spectrum has onl! five spi:es, at #33, %33,
;33, &33, and -33
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Eample
A signal has a bandwidth of 23
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'he spectrum contains all integral
fre8uencies. e show this b! a series of
spi:es.
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DIGITAL SIGNALS
A # can be encoded as a positive voltage and a
3 as =ero voltage4
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+it interval and +it rate 'he bit interval is the time re8uired to send one
single bit.
'he bit rate is the number of bit intervals per
second. 'his means that the bit rate is thenumber of bits sent in # s, or bits per second
(bps).
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Eample
A digital signal has a bit rate of 2333 bps. hat
is the duration of each bit (bit interval)> Solution
'he bit interval is the inverse of the bit rate.
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igital Signal4 0omposite AnalogSignal having an infinite number
of fre8uencies. In other words,
the bandwidth of a digital signalis infinite.
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Distortion:
istortion means that the signal changes its
form or shape.
istortion occurs in a composite signal, made
of different fre8uencies.
Each signal component has its ownpropagation speed through a medium and,
therefore, its own dela! in arriving at
the final destination.
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W! D" #"D$LATI"N %
#" 7or allowing multiple signals to share
a single ph!sical media.
2" 5ecessar! for wireless communication
where the antenna diameter must be at
least e8ual to the wavelength of the
carrier signal. @ c/f B
%" 7or a medium not suitable for digitaltransmission.
"
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Sine Wave as a CARRIER
'hin: of a Sine ave as a Carrier Signal,
i.e. the signal onto which the information is
loaded for sending to the end user. A 0arrier Signal is used as the basis for sending
e.m. signals between a transmitterand a
receiver, independentl! of the fre8uenc!.
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Carrier signals
A 0arrier Signal ma! be considered to travel
at the speed of light, c, whether it is in free
space or in a metal wire.
It travels more slowl! in most substances.
'he ?elocit!, 7re8uenc!, and avelength of
the carrier signal are uni8uel! connected b!4
c = f Wavelength
Frequency
Velocity of light
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5oise Effects on igital Signal
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Attenuation in an Analog Signal
Attenuation in an igital Signal