Post on 15-Jul-2015
MODULATION:MODULATION: Modulation is the process of varying one Modulation is the process of varying one
or more properties of a high-frequency or more properties of a high-frequency periodic waveform, called the carrier periodic waveform, called the carrier signal, with a modulating (message) signal signal, with a modulating (message) signal which typically contains information to be which typically contains information to be transmitted.transmitted.
TYPES OF MODULATIONTYPES OF MODULATION Amplitude Modulation.Amplitude Modulation. Frequency Modulation.Frequency Modulation. Phase Modulation. Phase Modulation.
OUR OBJECTIVEOUR OBJECTIVE Our objective is to implement amplitude Our objective is to implement amplitude
modulation using Matlab. modulation using Matlab.
AMPLITUDE MODULATIONAMPLITUDE MODULATION A type of modulation in which the A type of modulation in which the
amplitude of the carrier wave (signal) amplitude of the carrier wave (signal) changes according to the amplitude of changes according to the amplitude of message (modulating) signal.message (modulating) signal.
In this modulation the frequency of the In this modulation the frequency of the carrier signal remains same.carrier signal remains same.
SPECIFICATION AND SPECIFICATION AND IMPORTANT TERMENOLOGIESIMPORTANT TERMENOLOGIES
SAMPLING FREQUENCY (fs)SAMPLING FREQUENCY (fs) The The sampling ratesampling rate , , sample ratesample rate , ,
or or sampling frequencysampling frequency (fs) defines the (fs) defines the number of number of samplessamples per unit per unit of time (usually seconds) taken from of time (usually seconds) taken from a continuous signal to make a discrete a continuous signal to make a discrete signal. signal.
Here in our code we use fs =1000Here in our code we use fs =1000
SAMPLING TIME (ts)SAMPLING TIME (ts) The time interval after which we take the The time interval after which we take the
sample of our message signal.sample of our message signal. It is the reciprocal of sampling frequency It is the reciprocal of sampling frequency
(fs).(fs). Here in our code we use ts =1/1000Here in our code we use ts =1/1000
Nyquist–Shannon sampling Nyquist–Shannon sampling theorem theorem
states that perfect reconstruction of a states that perfect reconstruction of a signal is possible when the sampling signal is possible when the sampling frequency is greater than twice the frequency is greater than twice the maximum frequency of the signal being maximum frequency of the signal being sampled.sampled.
fs ≥ 2fmfs ≥ 2fm
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-4
-3
-2
-1
0
1
2
3
4The Modulating Signal
n
x1
-500 -400 -300 -200 -100 0 100 200 300 400 5000
200
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The Modulating Signal in Frequency Domain
Frequency
Mag
nitu
de o
f X
1F
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-5
0
5The Carrier Signal
n
xc
-500 -400 -300 -200 -100 0 100 200 300 400 5000
200
400
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The Carrier Signal in Frequency Domain
Frequency
Mag
nitu
de o
f X
cF
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
-8
-6
-4
-2
0
2
4
6
8
The Modulated Signal
n
X
-500 -400 -300 -200 -100 0 100 200 300 400 5000
200
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1400
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The Modulated Signal in Frequency Domain
Frequency
Mag
nitu
de o
f X
F
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-4
-2
0
2
4The Modulating Signal
n
x1
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45-5
0
5The Carrier Signal
n
xc
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
-5
0
5
The Modulated Signal
n
X
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90
1
2
3
4
5
6
7
8
9Xint
n
Xin
t
-500 -400 -300 -200 -100 0 100 200 300 400 5000
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2500Xint in Frequency Domain
Frequency
Mag
nitu
de o
f X
intF
0 50 100 150 200 250 300 350 400 450 5000
500
1000
1500
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2500Xint (Before DC Offset Elimination) in Frequency Domain
Frequency
Mag
nitu
de o
f X
intF
0 50 100 150 200 250 300 350 400 450 5000
200
400
600
800
1000
Xint (After DC Offset Elimination) in Frequency Domain
Frequency
Mag
nitu
de o
f X
intF
0 100 200 300 400 500 600 700 800 900 1000
-2
-1
0
1
2
3
4
5
6
Xint (After DC Offset Elimination) in Time Domain
n
Xin
tT