advance communication system lectures part 1

8/2/2019 Advance Communication System Lectures Part 1

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Text Book: Electronic Communication Systemby Kennedy and Davis

Reference Text: Modern Digital and AnalogCommunication System by B.P. Lathi

(Soft/photo copy will be provided)


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Explain the principles of a communicationsystems

Discuss the nature of information, different typesof signals involved and their characteristics

Make the distinction between Analog and Digitalcommunication systems

Determine the need of modulation anddifferentiate various type of modulation

techniques in time, frequency domain Important steps in analog to digital conversion,

PCM, PAM, PPM etc


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Basic Communication System (Chp 1 Kennedy)

Concept of time and frequency domain

Different types of Signals (Chp 2 Reference)

Baseband vs Passband Communication

Modulation and its needs (Chp 1 Kennedy)


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5

How do you want to senddata/information tosomeone who is far from

you?


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6

Communication : To transfer information from one place toanother


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7

1837 Samuel Morse invented telegraph. 1858 First telegraph cable across Atlantic (Canada Ireland) 1876 Alexander Graham Bell invented telephone. 1988 Heinrich Hertz introduce electromagnetic field theory. 1897 Marconi invented wireless telegraph. 1906 Radio communication system was invented. 1923 Television was invented. 1938 Radar and microwave system was invented for World War II. 1950 TDM was invented. 1956 First telephone cable was installed across Atlantic. 1960 Laser was invented 1962 Satellite communication 1969 Internet DARPA 1970 Corning Glass invented optical fiber. 1975 Digital telephone was introduced. 1985 Facsimile machine. 1988 Installation of fiber optic cable across Pacific and Atlantic. 1990 World Wide Web and Digital Communication. 1998 Digital Television.


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The Real AimIf the information that you want to send is your voice, how tomake sure that what you are saying is understood by your friend?

Basic Parts of a Communication System


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TransmitterTransmissionMedium

ReceiverInputTransducer

OutputTransducer

Noise

wired / wireless

mtx(t)

s(t) r(t)

ptx(t)

n(t)

mrx(t)prx(t)

s(t) Input signal; audio, video, image, data etc.

mtx(t) Modulating signal; input signal that has been converted to electrical

signal.ptx(t) Modulated signal transmit by the transmitter.

n(t) Noise signal.

prx(t) Modulated signal receive by the receiver.

mrx(t) Modulating signal at the receiver.

r(t) Output signal.


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Input Transducer convert input signal, s(t) in electrical forms. eg:microphone.Transmitter involve modulation process convert modulatingsignal,mtx(t) to modulated signal,ptx(t). And finally transmit thesignal.Transmission medium connecting the transmitter and the receiverthat enable the modulated signal,ptx(t) propagate through themedium.Receiver receive the modulated signal,prx(t) and then convert thesignal to modulating signal,mrx(t) through the process calleddemodulation.Output Transducer convert the modulating signal,mrx(t) to itsoriginal forms (output signal), r(t) that is useful to the users. eg:loud speaker.


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12

Twisted pair Unshielded Twisted Pair (UTP) Shielded Twisted Pair (STP)Coaxial

Fiber Optic

Waveguide


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100 Mbps is how many bits per sec?Which is bigger:10,000 Mbps, 0.01Tbps or 10Gbps?

Wireless channel capacity:


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Data(nonelectrical)

ElectricalWaveform

Without any shift in the range of frequencies of the signalThe signal is in its original form, not changed by modulation.

Basebandis the original information that is to be Sent.

It starts from zero and to some specific frequency

WHAT IS BASEBAND ?


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After modulation, the original baseband

signal is moved to a range of frequency whichfar more higher than the baseband signal

So its a range of frequency shifted aftermodulation


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MODULATION IS THE PROCESS OFCHANGING SOME PROPERTYOF THEINFORMATION SOURCES INTO SUITABLEFORM FOR TRANSMISSION THROUGH THEPHISICAL MEDIUM/CHANNEL

Process of coverting baseband signal intopassband signal is called modulationIt is performed in the Transmitter bya device calledModulator.

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Transmitter

Carrier

Information tobe transmitted

(Baseband signal)

Transmitted

signal

Channel

Received

signal

Receiver

Recovery ofinformation


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18


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Amplitude Modulation (AM)Frequency Modulation (FM)Phase Modulation (PM)

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Channel assignment (various informationsources are not always suitable for directtransmission over a given channel)Efficient Utilization of bandwidth andmultiplexingReduce noise &interferenceReduction in antenna size

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DEMODULATION IS THE REVERSE PROCESSOF MODULATION BY CONVERTING THEMODULATED INFORMATION SOURCES BACKTO ITS ORIGINAL INFORMATION (ITREMOVES THE INFORMATION FROM THECARRIER SIGNAL).

It is performed in the Receiver bya device calledDemodulator.22


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IT CONSISTS OF ALL FREQUENCIESCONTAINED IN THE WAVEFORM ANDTHEIR RESPECTIVE AMPLITUDE IN THEFREQUENCY DOMAIN.

23


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24

100MH

z

WaveguideCoaxial CableTwisted PairCable

Infrared

Visible

Ultraviolet

Optical Fiber

ExtraHigh

Frequency

EHF

SuperHigh

Frequency

SHF

UltraHigh

Frequency

UHF

VeryHigh

Frequency

VHF

High

Frequency

HF

Medium

Frequency

MF

Low

Frequency

LFVery

Low

Frequency

VLF

Audio

Line-of-sightradio

Skywaveradio

Groundwaveradio

Wavelength

Frequencydesignations

Transmissionmedia

Propagationmodes

Representativeapplications

Frequency

Laser beam

100km 10km 1km 100m 10m 1m 10cm 1cm 10-6m

Tele

phone

Tele

graph

Mobilradio

VHFTVandFM

Mobiland

Aeronautical

UHFTV

CBradio

Ama

teurradio

AMbroadcasting

Aerona

utical

Submarinecable

Navigation

Transoc

eanicradio

Broadband

PCS

Wirelesscommunication

Cellular,Pager

Satellite-satellite

Microwaverelay

Earth-satellite

Radar

Widebanddata

1kHz

10kHz

100kHz

1MHz

10MHz

1GHz

10GHz

1G0Hz

1014Hz

1015Hz


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IT IS THE DIFFERENCE BETWEEN THEHIGHEST FREQUENCIES AND THE LOWESTFREQUENCIES OF THE INPUT SIGNALFREQUENCIES (fB = 2fm ). The bandwidth of a communication signal bandwidth of the information signal.

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If human voice frequencies containsignals between 300 Hz and 3000 Hz,

a voice frequency channel should havebandwidth equal or greater than 2700Hz. a communication channel cannot propagate asignal that contains a frequency that ischanging at a rate greater than the ChannelBandwidth.

27


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Lecture 27 28

Signal

SourceModulator

Power

Amplifier

Antenna


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Block diagram In Modulator the audio modulates the RF

amplitude

ModulatorLow-pass

filter

AFamplifier

Microphone

RF

oscillator

Power

amplifier


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Lecture 27 30

The modulator converts the frequency of theinput signal from the audio range (0-5kHz) tothe carrier frequency of the station (i.e..

605kHz-615kHz)

frequency5kHz

Frequency domainrepresentation of input

Frequency domainrepresentation of output

frequency610kHz


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Lecture 27 31

RF

Amplifier

IF

Mixer

IF

Amplifier

Envelope

Detector

Audio

Amplifier

Antenna

Speaker


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A signal g(t) in the intervalt1tt1+T0 can be represented by

1

000 )sin()cos()(n

nn tnbtnaatg 011 Tttt

01

1

)(1

0

0

Tt

t

dttgT

a

01

1

)cos()(2

0

0

Tt

t

n dttntgT

a

01

1

)sin()(2

0

0

Tt

t

n dttntgT

b T0 = 2 /0


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Or, in the compact form

Ifg(t) is even then bn = 0 for all n

Ifg(t) is odd then an=0 for all n.

1

00 )cos()(

n

nn tnCCtg

;22

nnn baC

n

nn

a

b1tan

011 Tttt

C0 = a0 ;


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The frequency 0= 2/T0 is called thefundamental frequency and the multiple of thisfrequency n0 is called the nth harmonic.

FS ofg(t) is equal to g(t) over the interval t1tt1+T0 only.

The FS for all tis a periodic function of periodT0 in which the segment ofg(t) over the intervalt1tt1+T0 repeats periodically.

If the function g(t) itself is periodic with periodT0 then the FS represents g(t) for all t.


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Dn is related to Cn and n as

| Dn | is called the amplitude spectrum of the signal.

Dn is called the phase spectrum of the signal.They provide a frequency-domainrepresentation of the

signal.

)0(

000)(

nn

tjn

n

n

tjn

n eDDeDtg

dtetg

T

DT

tjn

n

0

0)(1

0

nnn CDD2

1||||

011Tttt

nnnDD

advance communication system lectures part 1

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