saprojectreport1

A
Project Based Lab Report

On
DSB-SC modulation and demodulation with phase and

frequency deviations
Submitted in partial fulfilment of the
Requirements for the award of the Degree of

Bachelor of Technology
in

COMPUTER SCIENCE ENGINEERING
By

T.KUNDANA (150030897)
V.SAI SANTOSH(150030947)
V.LIKITHA (150030950)

Under the guidance of
Guide Name: S.VARA KUMARI

Designation: ASST.PROF., Dept. of ECE

Dept. of Computer Science Engineering,
K.L. UNIVERSITY

Green fields, Vaddeswaram-522502
Guntur Dist.
2016-17

1

K L University

DEPARTMENT OF COMPUTER SCIENCE ENGINEERING

CERTIFICATE

This is to certify that this project based lab report entitled “DSB-SC modulation and
demodulation with phase and frequency deviations” is a bonafide work done by
T.kundana(150030897), V.Sai Santosh (150030947) and V.Likitha (150030950) in partial
fulfilment of the requirement for the award of degree in Bachelor of Technology in
Computer Science Engineering during the academic year 2016-2017.

I also declare that this project based lab report is of our own effort and it has not been

submitted to any other university for the award of any degree.

Signature of the Project Guide Signature of Course Coordinator

Head
Dep. Of ECE

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ACKNOWLEDGMENT

It is great pleasure for me to express my gratitude to our honorable President Sri. Koneru
Satyanarayana, for giving the opportunity and platform with facilities in accomplishing
the project based laboratory report.

I express the sincere gratitude to our principal for his administration towards our
academic growth.

I express sincere gratitude to our Coordinator Mr.P.Sasi Kiran for his leadership
and constant motivation provided in successful completion of our academic semester.

I record it as my privilege to deeply thank our pioneer Dr. V.Srikanth HOD-CSE
for providing us the efficient faculty and facilities to make our ideas into reality.

I express my sincere thanks to our project supervisor S.Vara Kumari madam
for his novel association of ideas, encouragement ,appreciation and intellectual zeal
which motivated us to venture this project successfully.

Finally, it is pleased to acknowledge the indebtedness to all those who devoted
themselves directly or indirectly to make this project report success.

Place: KL University
Date:

S.No Name of the Student
1 T.Kundana(150030897)
2 V.Sai Santosh(150030947)
3 V.Likitha(150030950)

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CONTENTS

Content Page No
Abstract 5
Problem statement: 6,7
Chapter 1: Introduction 8,9
Chapter 2: Tasks Simulation Results and Discussion
10-13
(a) Task1: 14-16
(b) Task2 : 17-26

(c) Task3: 27
Chapter 3: Conclusions and future scope 28
References

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ABSTRACT

In full AM (DSB-AM), the carrier wave c(t) is completely independent of the message
signal m(t), which means that the transmission of carrier wave represents a waste of
power. This points to a shortcoming of amplitude modulation, that only a fraction of
the total transmitted power is affected by m(t) . To overcome this shortcoming, we may
suppress the carrier component from the modulated wave, resulting in double sided-
suppressed carrier (DSB-SC) modulation. A double-sideband, suppressed carrier AM
signal is obtained by multiplying the message signal m(t) with the carrier signal. Thus
we have the amplitude modulated signal. The spectrum of DSB-SC modulated wave
consists of impulse functions located at ωc ±ω m −ωc ±ω m . and Note: Suppression of
the carrier has a profound impact on the waveform of the modulated signal and its
spectrum. (See Fig3. page 19 for DSB (full) and Fig 11. page 29 for DSB-SC) When
the message signal m(t) is limited to the interval −ω m ≤ ω ≤ ω m ( not a single tone
but it is a spectrum ) the DSB-SC modulation process simply translates the spectrum of
the message signal by ±ωc The transmission bandwidth required for DSB-SC
modulation is the same as that for full amplitude modulation, namely 2 . ω m The
generation of a DSB-SC modulated wave consists simply of the product of the message
signal m(t) and the carrier wave ) A cos( t c ωc . A device for achieving this requirement
is called a product modulator, which is another term for a straightforward multiplier.

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Problem statement:

OBJECTIVES:

(a) Generation of a double sideband suppressed carrier (DSB-SC) modulated signal.
(b) To investigate the phase and frequency deviations (offset errors) in the demodulation of
DSB- SC signals.
(c) Exposure to simulation on modulation/demodulation systems for DSB-SC using
MATLAB for synthetic & real signals (such as speech).

Fig 1. Block diagram of DSB-SC modulation and noise free demodulation system.

A base band signal m(t) is used to generate DSB-SC modulated
signalDSBSC(t) m(t) c(t) , where c(t) is a carrier signal c(t) Ac cosct as shown in
the Fig.1. The objective is to explore the theoretical concepts of DSB-SC signal by
modeling and simulation using Matlab and Simulink.

Task1: Consider a single tone modulating signal m(t) cos1000t , and carrier
signalwith frequency of 5000 Hz.
1. Determine the expression for DSB-SC modulated signal in both time domain and
frequency domain.
2. Sketch the modulating signalm(t) and its spectrum.
3. Sketch the carrier wave c(t) and its spectrum.
4. Sketch the DSB-SC modulated signal DSBSC(t) and its spectrum.
5. Identify the USB and LSB spectra.
6. Determine the maximum and minimum amplitudes of the envelope.
7. Find the powers of USB, LSB, total sideband and modulated waves.

Task2: Now consider a multi tone modulating signal
m(t) 2cos1000t sin1500t+1.5cos2000t and repeat the steps (1) to (7) above from the
Task1 .

Task 3: Assume that the demodulation process is shown in Fig.1. The objective is to
study the effect of phase and frequency offset errors in demodulation of DSB-SC
wave. Now consider a single tone case.
1. The phase angle , denoting the phase difference between c(t) andm(t) at time t

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= 0, is variable. Derive the expression for the demodulated wave and sketch for
the following values of =0 ,45 ,90 and 135.Comment on the results..
2. Assume that the local oscillator frequency Fc generated in the demodulation
process is not synchronized with the carrier frequency generated at transmitter.
Let F is an offset frequency deviated from the local oscillator and is variable.
Derive the expression for the demodulated wave and sketch for the following
values of F = 50 Hz, 100 Hz, 300 Hz and 500 Hz. Comment on the results.
Task 4: Repeat above tasks for real speech signals.

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CHAPTER-1:
INTRODUCTION:-

Double-sideband suppressed-carrier transmission (DSB-SC) is transmission in which
frequencies produced by amplitude modulation (AM) are symmetrically spaced above and
below the carrier frequency and the carrier level is reduced to the lowest practical level, ideally
being completely suppressed.

 Double sideband-suppressed (DSB-SC) modulation, in which the transmitted wave
consists of only the upper and lower sidebands.

 Transmitted power is saved through the suppression of the carrier wave, but the
channel bandwidth requirement is same as in AM .

 Basically, double sideband-suppressed (DSB-SC) modulation consists of the product
of both the message signal m (t) and the carrier signal c(t),as follows:

 S (t) =c (t) m (t)
 S (t) =Ac cos (2пfc t) m (t)
 The modulated signal s (t) undergoes a phase reversal whenever the message signal m

(t) crosses zero.
 The envelope of a DSB-SC modulated signal is different from the message signal
 The transmission bandwidth required by DSB-SC modulation is the same as that for

amplitude modulation which is twice the bandwidth of the message signal,
2W.Assume that the message signal is band-limited to the interval –W ≤f≤ W.
 The standard time domain equation for the DSB-SC modulation is given by

S (t) =Ac cos (2 fct) m(t). Assume m (t) =Amcos(2fmt) .
 We will get S (t) =Ac Am cos (2 fct) cos (2 fmt) S (t) = Ac Am/2[cos 2π (fc-fm) t +

cos 2π (fc+fm) t].The Fourier transform of s (t) is S (f) =Ac Am/4[δ (f-fc-fm) + δ
(f+fc+fm)] + Ac Am/4[δ (f-fc+fm) + δ (f+fc+fm)]

Modulation :
 In electronics and telecommunications, modulation is the process of varying one or

more properties of a periodic waveform, called the carrier signal, with
a modulating signal that typically contains information to be transmitted.

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Demodulation :

 Demodulation is extracting the original information-bearing signal from a modulated
carrier wave. A demodulator is an electronic circuit (or computer program in a
software-defined radio) that is used to recover the information content from the
modulated carrier wave.

Signal Tone Signal:
 Any signal having single frequency.

ex: sin5t ,in this ex there is only 1 freq 5rad/sec..... thats why its single tone msg
signal.

Multi-Tone Signal:
 A composite of several sine waves, where each sine wave can have distinct amplitude,

phase and frequency.
 A Multitone signal is useful for testing the frequency response of a system quickly.
 Stepped sine or swept sine measurements can have significant setting time issues.
 A quick visual observation or simple level measurement can be used for production

testing.

ADVANTAGES:
Lower power consumption The modulation system is simple.
DISADVANTAGES:
Complex detection
APPLICATION:
Analog TV systems: to transmit color information.

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CHAPTER-2:-

TASK:1 :-

Matlab Codes:

% task 1
fc=5000;
fm=fc/10;
fs=100*fc;
t=0:1/fs:4/fm;
xc=cos(2*pi*fc*t);
xc1=cos(2*pi*fc*t + (pi/180)*45); %for phase variations
xc2=cos(2*pi*(fc+500)*t); %for frequency variations
xm=cos(2*pi*fm*t);

% task 1.2 spectrum of message signal

figure(1)
subplot(3,1,1),plot(t,xm);
title('message signal of 0.5 khz in time domain');
xlabel('time (sec)');
ylabel('amplitude');
l2=length(xm);
f1=linspace(-fs/2,fs/2,l2);
XM=fftshift(fft(xm,l2)/l2);
subplot(3,1,2),plot(f1,abs(XM));
title('DSB SC MODULATION IN FREQUENCY DOMAIN magnitude spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 0.5]);
subplot(3,1,3);plot(f1,angle(XM));
title('DSB SC MODULATION IN FREQUENCY DOMAIN phase spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-10000 10000 -5 5]);

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% task 1.3 spectrum of carrier signal

figure(2);
subplot(3,1,1),plot(t,xc);
title('carrier signal of 5 khz in time domain');
xlabel('time (sec)');
ylabel('amplitude');
l3=length(xc);
f2=linspace(-fs/2,fs/2,l3);
XC=fftshift(fft(xc,l3)/l3);
subplot(3,1,2),plot(f2,abs(XC));
title('DSB SC MODULATION IN FREQUENCY DOMAIN magnitude spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 0.5]);
subplot(3,1,3);plot(f2,angle(XC));
title('DSB SC MODULATION IN FREQUENCY DOMAIN phase spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-10000 10000 -5 5]);

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% DSB-SC MODULATION

z1= xm.*xc;
figure(3)

% task 1.4 spectrum of DSB-SC modulated signal

subplot(3,1,1),plot(t,z1);
title('DSB-SC MODULATION IN TIME DAOMAIN');
xlabel('time (sec)');
ylabel('amplitude');
l1=length(z1);
f=linspace(-fs/2,fs/2,l1);
Z1=fftshift(fft(z1,l1)/l1);
subplot(3,1,2),plot(f,abs(Z1));
title('DSB SC MODULATION IN FREQUENCY DOMAIN magnitude spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 0.3]);
subplot(3,1,3);plot(f,angle(Z1));
title('DSB SC MODULATION IN FREQUENCY DOMAIN phase spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-10000 10000 -5 5]);

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TASK-2:
MATLAB CODES:
% task 2 DSB-SC modulation for multi tone signal
fc=5000;
fm=fc/10;
fs=100*fc;
t=0:1/fs:4/fm;
xc=cos(2*pi*fc*t);
xm=(2*cos(2*pi*fm*t))-sin(1500*pi*t)+(1.5*cos(2000*pi*t));
% task 2.2 spectrum of multi tone signal
figure(1)
subplot(3,1,1),plot(t,xm);
title('message signal of 0.5 khz in time domain');
xlabel('time (sec)');
ylabel('amplitude');
l2=length(xm);
f1=linspace(-fs/2,fs/2,l2);
XM=fftshift(fft(xm,l2)/l2);
subplot(3,1,2),plot(f1,abs(XM));
title('DSB SC MODULATION IN FREQUENCY DOMAIN magnitude spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-7000 7000 0 1]);
subplot(3,1,3);plot(f1,angle(XM));
title('DSB SC MODULATION IN FREQUENCY DOMAIN phase spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-10000 10000 -5 5]);

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% task 2.3 spectrum of carrier signal

figure(2);
subplot(3,1,1);
plot(t,xc);
title('carrier signal of 5 khz in time domain');
xlabel('time (sec)');
ylabel('amplitude');
l3=length(xc);
f2=linspace(-fs/2,fs/2,l3);
XC=fftshift(fft(xc,l3)/l3);
subplot(3,1,2),plot(f2,abs(XC));
title('DSB SC MODULATION IN FREQUENCY DOMAIN magnitude spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 0.6]);
subplot(3,1,3);
plot(f2,angle(XC));
title('DSB SC MODULATION IN FREQUENCY DOMAIN phase spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-10000 10000 -5 5]);

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% DSB-SC MODULATION of multi tone signal

z1= xm.*xc;
figure(3)
% task 2.4
subplot(3,1,1),plot(t,z1);
title('DSB-SC MODULATION IN TIME DAOMAIN');
xlabel('time (sec)');
ylabel('amplitude');
l1=length(z1);
f=linspace(-fs/2,fs/2,l1);
Z1=fftshift(fft(z1,l1)/l1);
subplot(3,1,2),plot(f,abs(Z1));
title('DSB SC MODULATION IN FREQUENCY DOMAIN magnitude spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-10000 10000 0 1]);

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subplot(3,1,3);plot(f,angle(Z1));
title('DSB SC MODULATION IN FREQUENCY DOMAIN phase spectrum');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-10000 10000 -5 5]);

TASK-3:
MATLAB CODES:

% task 3.1 demodulation with phase variations

s1=z1.*xc;
S1=fftshift(fft(s1,length(s1))/length(s1));
figure(4);
subplot(3,1,1);
plot(t,s1);
title('DEMODULATED signal IN TIME DAOMAIN');
xlabel('time (sec)');
ylabel('amplitude');

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subplot(3,1,2);
plot(f,abs(S1));
title(' demodulated signal IN FREQUENCY DOMAIN before filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 0.5]);
hold on;
Hlp=1./sqrt(1+(f./fc).^(2*100));
subplot(3,1,3);
plot(f,abs(S1));
title(' demodulated signal IN FREQUENCY DOMAIN before filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 1]);hold on
plot(f,Hlp,'g');
title(' demodulated signal frequency response of low pass filter');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 1.2]);

% task 4 RECOVERY OF THE SIGNAL

E1=Hlp.*S1;
figure(5)
subplot(2,1,1),plot(f,E1);
title(' Recover signal IN FREQUENCY DOMAIN after filtring');
xlabel('frequency(hz)');

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ylabel('amplitude');
axis([-50000 50000 0 0.3]);
e1=ifft(ifftshift(E1))*length(E1);
subplot(2,1,2),plot(t,(1/0.5)*e1);
title(' Recover signal IN Time DOMAIN after filtring');
xlabel('time(sec)');
ylabel('amplitude');

% task 3.1 demodulation with phase=45'

s2=z1.*xc1;
S2=fftshift(fft(s2,length(s2))/length(s2));
figure(6);
subplot(3,1,1);
plot(t,s2);
title('DEMODULATED signal IN TIME DAOMAIN with phase=45');
xlabel('time (sec)');
ylabel('amplitude');
subplot(3,1,2);
plot(f,abs(S2));
title(' demodulated signal IN FREQUENCY DOMAIN before filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 0.5]);
hold on
Hlp=1./sqrt(1+(f./fc).^(2*100));

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subplot(3,1,3);
plot(f,abs(S2));
title(' demodulated signal IN FREQUENCY DOMAIN before filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 1]);
hold on
plot(f,Hlp,'g');
title(' demodulated signal frequency response of low pass filter');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 1.2]);

% task 4 RECOVERY OF TE SIGNAL

E2=Hlp.*S2;
figure(7)
subplot(2,1,1),plot(f,E2);
title(' Recover signal IN FREQUENCY DOMAIN after filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 -0.3 0.3]);
e2=ifft(ifftshift(E2))*length(E2);
subplot(2,1,2),plot(t,(1/0.5)*e2);
title(' Recover signal IN Time DOMAIN after filtring');
xlabel('time(sec)');

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ylabel('amplitude');

demodulation with phase=90'

demodulation with phase=135'

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%task 3.2 demodulation for frequency variations
s3=z1.*xc2;
S3=fftshift(fft(s3,length(s3))/length(s3));
figure(8);
subplot(3,1,1);
plot(t,s3);
title('DEMODULATED signal IN TIME DAOMAIN with phase=45');
xlabel('time (sec)');
ylabel('amplitude');
subplot(3,1,2);
plot(f,abs(S3));
title(' demodulated signal IN FREQUENCY DOMAIN before filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 0.5]);
hold on
Hlp=1./sqrt(1+(f./fc).^(2*100));
subplot(3,1,3);
plot(f,abs(S3));
title(' demodulated signal IN FREQUENCY DOMAIN before filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 1]);
hold on
plot(f,Hlp,'g');

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title(' demodulated signal frequency response of low pass filter');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 0 1.2]);

% task 4 RECOVERY OF TE SIGNAL

E3=Hlp.*S3;
figure(9)
subplot(2,1,1),plot(f,E3);
title(' Recover signal IN FREQUENCY DOMAIN after filtring');
xlabel('frequency(hz)');
ylabel('amplitude');
axis([-50000 50000 -0.3 0.3]);
e3=ifft(ifftshift(E3))*length(E3);
subplot(2,1,2),plot(t,(1/0.5)*e3);
title(' Recover signal IN Time DOMAIN after filtring');
xlabel('time(sec)');
ylabel('amplitude');

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demodulation for df=50hz
24

demodulation for df=100hz
demodulation for df=300hz

demodulation for df=500hz

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Recovery of the signal
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Chapter 3: Conclusions and Future scope
Conclusions:

By using matlab codes we can modulate and demodulate the signals easily. The complication
of demodulation will be decreased

Future scope:

Even matlab have some limitations so by improving the code we can overcome it by Matlab
coding for this type of modulations are very large we can reduce it

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REFERNCES:

• https://www.google.com/search?q=dsb-
sc%20modulation%20and%20demodulation&oq=DSB-SC&ie=UTF-
8&aqs=chrome.1.69i57j0j69i60j0l3.6871j0j7&sourceid=chrome-
instant&ion=1&bav=on.2,or.r_cp.&bvm=bv.136593572,d.cWw&biw=1448&bih
=736&dpr=0.9&ech=1&psi=l18OWPuSFMP4-
AGDzaKYCg.1477336989223.3&ei=l18OWPuSFMP4-
AGDzaKYCg&emsg=NCSR&noj=1

• https://subjects.ee.unsw.edu.au/tele3113/lecture_notes/TELE3013_week3.pdf

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