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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)
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 2000 V fit 0 985 i (2* i*f* 0 95* 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 2000mV ; fit = avg +0.985amp sin(2*pi*f*n - 0.95*pi)
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)
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 2500mV ; fit = avg +0.985amp sin(2*pi*f*n - 0.96*pi)
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)
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 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
Illustration of nonlinear modulation of laser diode
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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)
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
0.4
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)