copy of ee 303 letures old format

7/30/2019 Copy of EE 303 Letures Old Format

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EE 303 Communication SystemsSemester 12012-2013


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Do

Readone of the many books available multiple sources

Work on your English time is running out

Pay attention to scientific language, units, symbols, diagrams, captions,axis labels etc

Write your name on any form of submission

Ask for an appointment faculty are always busy email is the best

Feel free to say you disagree - but please be polite

You can disagree without being disagreeable


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Expect class notes

Come late

Sleep in class

Do work related to other courses

Expect extension of deadlines

Do not

Do not write Respected Sir in your emails Use Dear Sir or Sir if youmust use Sir, Dear Dr Chakraborty is perfectly alright with me.


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Course Details

Books:

Modern Digital and Analog Communications B. P. Lathi & Z. Ding

Communications Systems - by A Bruce Carlson

Principles of Communications Systems H. Taub & D. Schilling

References

www.ieee.org get a student membership long-term benefits

IEEE Spectrum great resource for all electrical engineers

IEEE Communications Society IEEE Photonics Society

Evaluation

Several quizzes all will count

Assigmts,Matlab programs,

Project

Mid sem

End sem

No invigilation take responsibility dont moan later Only EE has this tradition
http://www.ieee.org/http://www.ieee.org/


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Altamira Caves

Source Wikipedia


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Telegraphy

Hi f T l i i


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History of Telecommunications

1996 CDMA cellular service and HDTV broadcastin

1837 Morse code Samuel Morse earliest digital comms? Transatlantic comms

1864 Maxwell EM theory dies before verification

1876 Alexander Graham Bell telephone and photophone

1878 First telephone exchange in Connecticut

1887 Heinrich Hertz detects EM waves

1896 Wireless telegraphy patented by Marconi

BUT 1894 Jagadish Chandra Bose - wireless signalling in CalcuttaFormally recognized Bose as a father of radio by IEEE

1901 First transatlantic radio telegraph by Marconi Bose not acknowledged!

1906 First AM radio broadcast

1925 First TV system demonstrated

1935 First FM radio Edwin Armstrong

1947 Cellular concept from Bell Labs

1948 Shannons paper on information theoryTransistor invented by Shockley, Brattain and Bardeen

1958 Integrated circuits proposed by Texas Instruments

1960 Reed-Solomon error correcting code Mariner and Pioneer use it

1971 First wireless computer network: AlohaNet

1973 First portable mobile device - Motorola

1984 First handheld (analog) cellular phone Motorola

1991 First GSM (digital) cellular service in Finland - first LAN

J di h Ch d B


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Jagadish Chandra Bose

9 pioneered the investigation of radio and microwave optics

9 very significant contributions to plant science

9 laid the foundations of experimental science in the Indian subcontinent

9 first person from the Indian subcontinent to receive a US patent, in 1904

9 He is also considered the father of Bengali science fiction

9 IEEE named him one of the fathers of radio science

30 Nov 1858 23 Nov 1937

A Polymath: a physicist, biologist, botanist, archaeologist, an early writer of science fiction

Books:

1. Response in the Living and Non-Living (1902)

2. The Nervous Mechanism of Plants (1926)

At that time, sending children to English schools was an aristocratic status symbol. In the vernacular school, to which I

was sent, the son of the Muslim attendant of my father sat on my right side, and the son of a fisherman sat on my left.

They were my playmates. I listened spellbound to their stories of birds, animals and aquatic creatures. Perhaps these

stories created in my mind a keen interest in investigating the workings of Nature. When I returned home from school

accompanied by my school fellows, my mother welcomed and fed all of us without discrimination. Although she was an

orthodox old-fashioned lady, she never considered herself guilty of impiety by treating these untouchables as her own

children. It was because of my childhood friendship with them that I could never feel that there were creatures who

might be labelled low-caste. I never realised that there existed a problem common to the two communities, Hindus and

Muslims.


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Evolution of the modern communications ageEvolution of the modern communications age 1842 Samuel Morse submerged a wire in New York Harbour, and telegraphed through it.

1850s - 1911, British submarine cable systems - North Atlantic

1870 Bombay - London submarine cable

1872, Australia - Bombay link via Singapore and China

1902 - US mainland to Hawaii, Canada, Australia, New Zealand and Fiji also linked

Construction - layer of iron and later steel wire, wrapped in rubber

Problems high capacitance & inductance, very limited bandwidth

1956 - TAT-1, from Oban, Scotland - Newfoundland, Canada 36 telephone channels Moscow-Washington hotline

As of 2006, overseas satellite links - only 1% of international traffic

http://www.ieeeghn.org/wiki/index.php/Milestones:The_First_Submarine_Transatlantic_Telephone_Cable_System_%28TAT-1%29,_1956

1988 - TAT-8 40k telephone circuits - AT&T, France Telecom & BT


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KaoKapany

Ren Descartes - cable layer ship

1980s OPTICAL FIBER comms

Electromagnetic Spectrum


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Electromagnetic Spectrum

3-30 kHz VLF Sonar, navigation, whale song

30-300 kHz LF Navigation

300-3000 kHz MF AM radio 3-30 MHz HF, SW SW radio

30-300 MHz VHF FM radio, TV, mobile

0.3-3GHz UHF TV, radar, sat comm, mobile

3-30GHz SHF Sat Comm, Microwave links

30-300GHz EHF radar, research

300-3000GHz Terahertz hot topic

1. In which region do the best modern

communications systems operate?

2. Future? Mid-IR comms

Transmission media / Channels


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Transmission media / Channels Open wire lines

telephone and telegraph 0.05dB/km loss for voice frequencies

susceptible to noise pick-up from the environment cross-talk

Coaxial cables central wire conductor MHz bandwidth

Radio frequencies striplines

Waveguides

Optical fibre low loss 0.1dB/km

huge bandwidth immune to electromagnetic interference low cross-talk flexible and low cost

Signals must be tailored to the requirements of the channel

Communications frequency bands


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Communications frequency bands

Terahertz, mm wave


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German troops installing a

field telegraph in WWI.

Elements of a Communications system


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Source Transmitter Channel Receiver Sink

Transmitter

Channel

Receiver

Elements of a Communications system

Some aspects of communication


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Some aspects of communication

Power of the signal

Bandwidth of the signal

Rate of Information transmitted decides the Bandwidth required.

Audio and Data signals require less amount of Bandwidth.

Video transmission requires higher bandwidthe.g.: human speech, 300 to 3.3kHz, requires approximately 4kHz of bandwidth

Noise

External sources interfering channels, man-made noise due to switches, poor power supplies,lightning

Internal sources thermal motion of electrons (Johnson noise), random emissions, diffusion and

recombination in electronic devices

Channel physical medium a filter - generally attenuates and distorts Dispersion

frequency-dependent gain, multipath effects, Doppler shift

Information Claude Shannon

C = B log2 (1+SNR) bits/s


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Analog and Digital Signals

Analog signals are continuously defined on time and their amplitude is

continuous

Digital Signals are discretely time defined and their amplitude can be either

quantized or not.


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Modeling of Communication systems

Signals are represented as sum of complex sinusoids or

Weighted impulse responses

Systems are approximated to Linear Time Invariant systems.

Unwanted effects of transmitter, channel and receiver on the

signal are modeled into channels LTI.


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Signals and Spectra

Fourier Series and Discrete Spectra


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Fourier Series and Discrete Spectra

02( )j nf t

nv t c e

= By definition, Fourier series

0

0

2

0

1( )

j nf t

n

T

c v t e dt T

=

A periodic signal has a discrete (line) spectrum

Properties of the Fourier transform

1. All frequencies are harmonics of the fundamental frequency, f0

= 1/T0

.

2. c0 at 0 is the DC value

3. If v(t) is real, then , therefore and

0

0

0

1( )

T

c v t dt T

=

arg* n

j c

n n nc c c e

= = arg argn nc c = n nc c =

even amplitude symmetry odd phase symmetryV(f) exhibits Hermitian symmetry

Coefficients cn

are the weights of the various

exponentials

cn

are in general complex numbers

arg nj c

n nc c e=

All physically realizable signals are real signals

Fourier Transforms and Continuous Spectra


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F u f m u u p

2( ) [ ( )] ( ) j ftV f v t v t e dt

= function of the continuous variablef

1 2( ) [ ( )] ( ) j ftv t V f V f e df

=

By definition, Fourier transform

Conversely, inverse Fourier transform

A non-periodic signal has a continuous spectra

Properties of the Fourier transform

1. The Fourier transform is a complex function,

so |V(f)| is the amplitude spectrum and arg V(f) is the phase spectrum

2. The value of V(f) at 0 equals the net area of v(t), since

3. If v(t) is real, then and and

(0) ( )V v t dt

=

( ) *( )V f V f = arg ( ) arg ( )V f V f = ( ) ( )V f V f =

even amplitude symmetry odd phase symmetryV(f) exhibits Hermitian symmetry

All physically realizable signals are real signals

Duality Theorem


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2( ) ( ) j ftV f v t e dt

= 2( ) ( ) j ftv t V f e df

= and

differ only in sign of the exponent & variable of integration

Ifv(t) and V(f) constitute a known transform pair, and if there exists a time functionz(t) related to the

function V(f) by then where( ) ( )z t V t= [ ( )] ( )z t v f = ( ) ( )v f equals v t with t f =

Superposition Theorem

Note that

( ) ( )k k k k k k

a v t a V f = Practical viewpoint greatly facilitates spectral analysis when the signal in

question is a linear combination of functions whose individual spectra are

known

Theoretical viewpoint underscores the applicability of the Fourier

transform for the study of linear systems

Apply the duality to the Sinc pulse: ( ) sinc(2 )z t A Wt= to get frequency-domain function

Task:

Application: Way of generating new transform pairs without the labour of integration

Time Delay Theorem


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Time Scaling

1( ) ( ), 0

fv t V

Time-scaling produces a horizontally scaled image ofv(t)

Scaled signal is expanded in time if

and is compressed if

0

Time-scaling produces a reciprocal scaling in the frequency domain,

Hence compressing a signal expands its frequency spectrum and vice versa

Note: Femtosecond laser pulses use this vice versa

Also, refer to Shalabh Guptas work

y

2( ) ( ) d

j ft

dv t t V f e

Generate other waveforms from time-shifted copies of an original waveform.

In frequency domain, time shift causes an added phase with slope of

Direction of time-shift determined by sign of delay td

Note that the magnitude response remains unaffected because

2 dt

2 2

( ) ( ) ( )d dj ft j ft

V f e V f e V f

= =

Applicable to the analysis of undistorted signal transmission take the example

Comb Filter


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( ) ( ) ( )h t t t T =

Delay

T

+( )x t ( )y t

2( ) 1 j fTH f e =

( )22 2

2

( ) 1

4sin 2 ( ), where 2

j fT

c c

H f e

f f f T

=

= =

Impulse response

Frequency response

Magnitude response

2 2( ) 4sin 2 ( ), where 2c cH f f f f T= =

Comments:

Periodically varying frequency response

Fibre ring resonator widely used to form a frequency scale in sensing and metrology applications

Lock-in amplifier

If input PSD is known,the output PSD can be

calculated

2( ) 4sin 2 ( ) ( )y c x

G f f f G f =

Frequency Translation and Modulation


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( ) ( )cj t

cv t e V f f

Apply Duality to Time Delay theorem

Multiplying in time function by causes its spectrum to be translated by +fc

Complex modulation Frequency translation

cj te

Observe

1.Clustering around fc

- highly significant

2.Translation doubles the spectral width - though V(f) was bandlimited to W, V(f- fc) has spectral width of 2W.

Alternatively, the negative frequency portion ofV(f) now appears as at positive frequencies

3.V(f - fc) is not Hermitian but does have symmetry with respect to translated origin atf=fc

But is not a real function of time.Why then do we bother about this?

( ) cj tv t e

( ) cos( ) ( ) ( )2 2

j j

c c c

e ev t t V f f V f f

+ + +

Multiplying in time function by a sinusoidtranslates its spectrum up and down by fc.Other observations above also apply here

In addition the spectrum is now Hermitian, which it must be because is a real function of time( )cos cv t t

Differentiation and Integration


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( )2 ( )

dv tj f V f

dt

Certain signal processing technique involve differentiating or integrating a signal

and by iteration,

Suppose we generate another function by integrating v(t) over all past time.

1( ) ( )

2

t

v d V f j f

Conversely, integration suppresses the high frequency components

Other observations above also apply here

In addition the spectrum is now Hermitian, which it must be because is a real function of time( )cos cv t t

( )( 2 ) ( )

nn

n

d v tj f V f

dt Differentiation theorem

2 ( ) ( ) 1 2j f V f V f for f > >Differentiation enhances the high frequency components in a signal since

Convolution Integral


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The convolution of two functions of the same variable is defined as,

( )* ( ) ( ) ( )v t w t v w t d

Note:

1.Independent variable is t, the same as the independent variable of the function being convolved

2.Integration performed with respect to a dummy variable; t is a constant insofar as the integration is concerned

3.Graphical interpretation of convolution is helpful if one or both functions is defined in a piecewise fashion

Convolution Theorems

( )* ( ) ( )* ( )

( )*( ( )* ( ) ) ( ( )* ( ))* ( )

( )*( ( ) ( ) ) ( )* ( ) ( )* ( )

Commutative v t w t w t v t

Associative u t v t w t u t v t w t

Distributive u t v t w t u t v t u t w t

=

=

+ = +

( )* ( ) ( ) ( )

( ) ( ) ( )* ( )

v t w t V f W f

v t w t V f W f

Convolution in time domain becomes multiplication in frequency domain

Multiplication in time domain becomes convolution in frequency domain

Utility filtering operations in time domain a described by convolution of signal and impulse response of filter. This is

much easier to address in the frequency domain.


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Signal Transmission and Filtering

Signal Distortion in Transmission


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When do we get distortionless transmission?

( ) ( )dy t K x t t=

Implies that shape of the signal remains unchanged

2( ) ( ) d

ftY f K X f e

= 2( )

( )

( )

dftY f

H f K e

X f

= =

In words The output is undistorted if it differs from the inputonly by a multiplying constant and a finite time delay

Note - shape is due to the Fourier components of the signal Therefore, the delicate balance of the harmonic components must not be disturbed during transmission

Frequency-domain view

Time-domain view

t = tdt = 0

transmission

Mathematically,

Interpretation A distortionless channel must have

( )H f K=

arg ( ) 2 180dH f ft m= D

9 a constant amplitude response

9 negative linear phase shift

Types of distortion


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( )H f K

arg ( ) 2 180dH f ft m D

Amplitude distortion

Delay distortion

Nonlinear distortion

Low-pass, high-pass or bandpass

filtering elements in channelFrequency-domain effect manifests

itself as a time-domain distortion

Successive echoes of transmitted signal can

overlap at receiver causing inter-symbolinterference (ISI)

Limits bit rate in digital communications

Generation of new frequencies due tononlinearity of channel

Assignment/Tutorial task


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g

Obtain Fourier series expression for a square wave up to 7 harmonics

Use Matlab to plot each harmonic in a single figure

Investigate the effect of suppression of one or more harmonics look at low-pass and high-

pass effects of the channel

Investigate the effect of nonlinear phase delay

Linear Distortion


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0 0 0( ) cos 1 3cos3 1 5cos5x t t t t = +

If the amplitude response of a system H(f), is not constant over the spectrum of interest, the various

Fourier components are not in the correct proportion to add up to the original wave.

Common causes low-pass or high-pass filtering effects of electronics circuits and channel

Less commonly disproportionate response to a band of frequencies hence Gain flattening required

Show the effect of unequal gain for different frequency components

Delay distortion alone can result in increase or decrease of peak values of a signal

Comments

Amplitude distortion

Consider a signal

Linear Distortion

l ( h ) d


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arg ( )

Time delay, ( ) 2d

H f

t f f=

If phase shift is nonlinear, various frequency components suffer different amounts of time delay, and

the delicate balance of the Fourier components is disturbed

Constant time delay is desired constant phase delay is not.

Time delay is constant only if arg H(f) varies linearly with frequency

Delay distortion alone can result in increase or decrease of peak values of a signalComments

Delay (phase) distortion

Musicians love it!!

A closer look at phase delay of a modulated signal


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0 0( 2 ) 2

( ) g gj ft j ftj

H f Ae Ae e + = =

Transfer function of a channel with a flat frequency response and a linear phase shift is given by,

0

arg ( )( ) 2

2d g

H ft f t f

f

= =

1 2( ) ( ) cos ( )sinc cx t x t t x t t = If the input signal is,

The time delay is given by,

1 0 2 0( ) ( )cos[ ( ) ] ( )sin[ ( ) ]g c g g c gy t Ax t t t t Ax t t t t = + +

1 2( ) ( ) cos ( ) ( )sin ( )g c d g c d y t Ax t t t t Ax t t t t =

Group delay

Modulation Envelope Information

Phase delay

Very profound implications for communications and optics

Output given by,

Slow light

Nonlinear distortionLet the linearized transfer characteristics for a system be given by,

nonlineardistortion


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y g y

1 2 3( ) ( ) ( )* ( ) ( )* ( ) ...Y f a X f a X f X f a X f X f = + + +

Output spectrum found by invoking convolution theorem,

32 4 2 41 0 0

33( ) ... ... cos ... cos 2 ...

2 8 4 2 4

aa a a ay t a t t

= + + + + + + + + +

2 3

1 2 3( ) ( ) ( ) ( ) ...y t a x t a x t a x t= + + +terms

Nonlinear distortion is desirable in many cases!!!e.g. nonlinear optics for generation of newwavelengths (mid-infrared)

Recall the diode

For single input tone,

2f0 component3

1nd

2 4

3...

42 harmonic distortion 100%

...2 4

aa

a a

+ +

=

+ +

Quantified by,

Nonlinear transfercharacteristics

Nonlinearity leads to cross-modulation

1f

12 f

22 f

1 2f f+1 2f f2f

dc

d 1500 V fi 0 9 i (2* i*f* 0 94* i)

Illustration of nonlinear modulation of laser diode


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1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 18500

0.1

0.2

0.3

0.4data 1500mV ; fit = avg +0.9amp sin(2*pi*f*n - 0.94*pi)

1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 1850

-0.01

0

0.01

d t 1500 V fit 0 9 i (2* i*f* 0 94* i)



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1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 18500

0.1

0.2

0.3


1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 1850

-0.01

0

0.01

d t 2000 V fit 0 985 i (2* i*f* 0 95* i)



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1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 18500

0.1

0.2

0.3


index

1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 1850

-0.01

0

0.01

data 2500mV ; fit avg 0 985amp sin(2*pi*f*n 0 96*pi)



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1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 18500

0.1

0.2

0.3


data index

sig

nal(V)

1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 1850

-0.01

0

0.01

data index

signal(V)

data 3000mV ; fit = avg +0 985amp sin(2*pi*f*n 0 95*pi)



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1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 18500

0.1

0.2

0.3

0.4data 3000mV ; fit = avg +0.985amp sin(2 pi f n - 0.95 pi)

1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 1850

-0.01

0

0.01

data for 3500mV



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1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 18500.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

data index

sig

nal(V)

data for 3500mV

1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 1850

-0.01

0

0.01

data index

signal(

V)

data 4000mV; fit = avg +0 985amp sin(2*pi*f*n - 0 97*pi)



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1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 18500

0.1

0.2

0.3

0.4

data index

sig

nal(V)

data 4000mV; fit = avg +0.985amp sin(2 pi f n 0.97 pi)

1750 1760 1770 1780 1790 1800 1810 1820 1830 1840 1850

-0.01

0

0.01

data index

signal(

V)

Analog Communication


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CarrierModulations

LinearModulation

Non-LinearModulation

Amplitude

Modulations AngleModulations

PAM,PWM,PPMPCM

Modulations

BasebandCommunication

Ex: LAN, TvVCR, Gameconsole, etc.

AngleModulationsFreq, Angle

AngleModulationsFreq, Angle

PAM, PWM, PPM and PCM signals use digital pulse coding schemes.Despite of the word modulation in their name they are baseband

communications.

Amplitude modulation-Types


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Double Side Band-Suppressed Carrier

Double Side Band-With Carrier

Single Side Band and Vestigial Side Band

Notations

m(t) Message or Modulating signal

M(f) Fourier transform of m(t)

c(t) Carrier SignalC(f) Fourier transform of c(t)

s(t) Modulated signal

S(f) Fourier transform of s(t)

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