e-Signlas slides Electronic communication.ppt

7/26/2019 e-Signlas slides Electronic communication.ppt

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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

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