The document describes simulations of various digital modulation and demodulation techniques using MATLAB software, including: 1. AM, DSB-SC, FM, SSB, PWM, sampling and reconstruction, PPM modulation and demodulation. 2. For each technique, the document provides the MATLAB code used for the simulation as well as plots of the output signals to demonstrate the modulation/demodulation process. 3. The techniques are executed using the MATLAB communication toolbox and involve generating modulated signals, adding noise, and recovering the original signal through demodulation.

1. 1. AM MODULATION AND DEMODULATION
AIM: To simulate am modulation with different modulation index using MATLAB
SOFTWARE
EQUIPMENT REQUIRED:
1. MATLAB SOFTWARE
2. PC
PROGRAM:
fc=50000;
fs=1000000;
f=1000;
m=0.5;
a=1/m;
opt=-a;
t=0:1/fs:((2/f)-(1/fs));
x=cos(2*pi*f*t);
y=modulate(x,fc,fs,'amdsb-tc',opt);
subplot(221);plot(x);grid;title('modulating signal');
subplot(222);plot(y);grid;title('am signal with m=0.5'); % am with m=0.5
m=1.0;opt=-1/m;y=modulate(x,fc,fs,'amdsb-tc',opt);%am with m=1.0
subplot(223);plot(y);grid;title('am with m=1.0');
m=1.2;opt=-1/m;y=modulate(x,fc,fs,'amdsb-tc',opt);%am with m=1.2
subplot(224);plot(y);grid;title('am with m=1.2');
z=demod(y,fc,fs,'amdsb-tc');figure(2);plot(z);
title('demodulated output');grid;

2. modulating signal am signal with m=0.5
1 4
0.5 2
0 0
-0.5 -2
-1 -4
0 500 1000 1500 2000 0 500 1000 1500 2000
am with m=1.0 am with m=1.2
2 2
1 1
0 0
-1 -1
-2 -2
0 500 1000 1500 2000 0 500 1000 1500 2000
demodulated output
2
1.5
1
0.5
0
-0.5
0 200 400 600 800 1000 1200 1400 1600 1800 2000

3. Result : The AM modulation and demodulation is executed using MATLAB
software.

4. 2. DSBSC MODULATION AND DEMODULATION
AIM: To simulate dsbsc modulation and demodulation using MATLAB SOFTWARE.
EQUIPMENT REQUIRED:
1. MATLAB SOFTWARE
2. PC
PROGRAM:
fc=50000;
fs=1000000;
f=1000;
m=0.5;
a=1/m;
opt=-a;
t=0:1/fs:((2/f)-(1/fs));
x=cos(2*pi*f*t);
s=cos(2*pi*fc*t);%carrier signal
y=modulate(x,fc,fs,'amdsb-sc',opt);
subplot(411);plot(x);grid;title('modulating signal');
subplot(412);plot(s);grid;title('carrier signal');
subplot(413);plot(y);grid;title('DSB-SC signal');
z=demod(y,fc,fs,'amdsb-sc');subplot(414);plot(z);
title('demodulated output');grid;

5. Result : The DSB-SC modulation and demodulation is executed using MATLAB
software.

6. modulating signal
1
0
-1
0 200 400 600 800 1000 1200 1400 1600 1800 2000
carrier signal
1
0
-1
0 200 400 600 800 1000 1200 1400 1600 1800 2000
DSB-SC signal
1
0
-1
0 200 400 600 800 1000 1200 1400 1600 1800 2000
demodulated output
1
0
-1
0 200 400 600 800 1000 1200 1400 1600 1800 2000

7. 3. FM MODULATION AND DEMODULATION
AIM: To simulate FM modulation and demodulation using MATLAB SOFTWARE.
EQUIPMENT REQUIRED:
1. MATLAB SOFTWARE
2. PC
PROGRAM:
%FM generation
close all;
fc=input('Enter the carrier signal freq in hz,fc=');
fm=input('Enter the modulating signal freq in hz,fm =');
m=input('Modulation index,m= ');
t=0:0.0001:0.1;
c=sin(2*pi*fc*t);%carrier signal
M=sin(2*pi*fm*t);% modulating signal
subplot(3,1,1);plot(t,c);
ylabel('amplitude');xlabel('time index');title('Carrier signal');
subplot(3,1,2);plot(t,M);
ylabel('amplitude');xlabel('time index');title('Modulating signal');
y=cos(2*pi*fc*t+(m.*sin(2*pi*fm*t)));
subplot(3,1,3);plot(t,y);
ylabel('amplitude');xlabel('time index');
title('Frequency Modulated signal');

8. Result : The FM modulation and demodulation is executed using MATLAB software.

9. Carrier signal
1
amplitude
0
-1
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
time index
Modulating signal
1
amplitude
0
-1
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
time index
Frequency Modulated signal
1
amplitude
0
-1
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
time index

10. 4. SSB MODULATION AND DEMODULATION
AIM: To simulate SSB modulation and demodulation using MATLAB SOFTWARE.
EQUIPMENT REQUIRED:
1. MATLAB SOFTWARE
2. PC
PROGRAM:
plot_frequency = 1000;
t = 0:1/plot_frequency:10;
% Choose a maximum frequency for our signal in Hertz
f_max = 10;
% Use a sinusoidal signal
A = 1;phi = 0;v = cos(2*pi*f_max*t);
% Choose a modulation sensitivity
k_am = 1;
% Choose a carrier frequency in Hertz
f_c = 100;
% Perform SSBSC modulation
u = k_am*v.*cos(2*pi*f_c*t) - k_am*imag(hilbert(v)).*sin(2*pi*f_c*t);
% Choose a noise power
N_0 = 0;
% Add some noise to our signal
u_received = u + sqrt(N_0)*randn(size(u));
% Perform coherent demodulation
u_mixed = u_received.*cos(2*pi*f_c*t);
% Choose a cutoff frequency in Hertz
f_cutoff = f_c/2;
% Low pass filter the signal
v_reconstructed = func_low_pass_filter(t, u_mixed, f_cutoff);
% Plot the results
figure(1)
subplot(2,2,1,'box','on');
holdon
plot(t(1:1000),v(1:1000));
xlabel('t [s]');ylabel('amplitude');title('Message signal');
subplot(2,2,2,'box','on','YLim',[-
ceil(max(abs(u(1:1000)))),ceil(max(abs(u(1:1000))))]);
holdon
plot(t(1:1000),u(1:1000));
xlabel('t [s]');ylabel('amplitude');title('SSBSC signal');
subplot(2,2,3,'box','on','YLim',[-
ceil(max(abs(u(1:1000)))),ceil(max(abs(u(1:1000))))]);
holdon
plot(t(1:1000),u_mixed(1:1000));
xlabel('t [s]');ylabel('amplitude');title('Mixed signal');
subplot(2,2,4,'box','on');
holdon
plot(t(1:1000),v_reconstructed(1:1000));

11. xlabel('t [s]');ylabel('amplitude');title('Reconstructed message signal');
figure(2)
subplot(2,2,1,'box','on');
pwelch(v,[],[],[],plot_frequency);
title('Message signal');
subplot(2,2,2,'box','on');
pwelch(u,[],[],[],plot_frequency);
title('SSBSC signal');
subplot(2,2,3,'box','on');
pwelch(u_mixed,[],[],[],plot_frequency);title('Mixed signal');
subplot(2,2,4,'box','on');
pwelch(v_reconstructed,[],[],[],plot_frequency);
title('Reconstructed message signal');figure(1)

12. Result : The SSB-SC modulation and demodulation is executed using MATLAB
software.

13. Message signal SSBSC signal
1 2
0.5 1
amplitude
amplitude
0 0
-0.5 -1
-1 -2
0 0.5 1 0 0.5 1
t [s] t [s]
Mixed signal Reconstructed message signal
2 0.5
1
amplitude
amplitude
0 0
-1
-2 -0.5
0 0.5 1 0 0.5 1
t [s] t [s]

14. Message signal SSBSC signal
0 0
Power/frequency (dB/Hz)
Power/frequency (dB/Hz)
-50 -50
-100 -100
0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4
Frequency (kHz) Frequency (kHz)
Mixed signal Reconstructed message signal
0 0
Power/frequency (dB/Hz)
Power/frequency (dB/Hz)
-50 -50
-100 -100
0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4
Frequency (kHz) Frequency (kHz)

15. 5. PWM MODULATION AND DEMODULATION
AIM: To simulate PWM modulation and Demodulation using MATLAB SOFTWARE.
EQUIPMENT REQUIRED:
1. MATLAB SOFTWARE
2. PC
PROGRAM:
%PWM wave generation
t=0:0.001:1;
s=sawtooth(2*pi*10*t+pi);
m=0.75*sin(2*pi*1*t);
n=length(s);
for i=1:n
if (m(i)>=s(i))
pwm(i)=1;
elseif (m(i)<=s(i))
pwm(i)=0;
end
end
plot(t,pwm,'-r',t,m,'--k',t,s,'--b');grid;
title('PWM wave');axis([0 1 -1.5 1.5]);

16. Result : The PWM modulation and demodulation is executed using MATLAB software.

17. PWM wave
1.5
1
0.5
0
-0.5
-1
-1.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

18. 6. ANALOG SIGNAL SAMPLING AND RECONSTRUCTION
AIM: To simulate analog signal sampling and reconstruction using MATLAB
SOFTWARE.
EQUIPMENT REQUIRED:
1. MATLAB SOFTWARE
2. PC
PROGRAM:
%creating "analog" signal
clear; %clears all variables
t=0:.1:20;F1=.1;F2=.2;
x=sin(2*pi*F1*t)+sin(2*pi*F2*t);
%plotting
figure(1);subplot(2,1,1);plot(t,x);
title('Original signal')
xlabel('t');ylabel('x(t)');subplot(2,1,2);
x_samples=x(1:10:201); %gets 21 samples of x.
stem(x_samples,'filled');
title('Sampled signal');xlabel('n');ylabel('x_s(n)');
axis([0 20 -2 2]);
%starting reconstruction process
figure(2);
subplot(2,1,2);plot(t,x,'black');
holdon;
plot([0 20],[0 0],'black');
holdoff;
xlabel('t');ylabel('x(t)');title('Original signal');
grid;
x_recon=0;subplot(2,1,1);
for k=0:length(x_samples)-1
stem(0:length(x_samples)-1,x_samples,'filled');
if k==length(x_samples)-1
title('Reconstruction finished');
else
title('Sample by sample reconstruction');
end
gridon;
l=k:-.1:-20+k;
x_recon=x_recon+x_samples(k+1)*sinc(l);
axis([0 20 -2 2]);
hold;
plot(t,x_samples(k+1)*sinc(l),'r')
plot(t,x_recon);
holdoff;
waitforbuttonpress;
end

19. Result : The Analog signal sampling and reconstruction is executed using MATLAB software.

20. Original signal
2
1
x(t)
0
-1
-2
0 2 4 6 8 10 12 14 16 18 20
t
Sample by sample reconstruction
2
1
0
-1
-2
0 2 4 6 8 10 12 14 16 18 20
Reconstruction finished
2
1
0
-1
-2
0 2 4 6 8 10 12 14 16 18 20
Original signal
2
1
x(t)
0
-1
-2
0 2 4 6 8 10 12 14 16 18 20
t

21. 7. PPM MODULATION AND DEMODULATION
AIM: To simulate PPM modulation and demodulation using MATLAB SOFTWARE.
EQUIPMENT REQUIRED:
1. MATLAB SOFTWARE
2. PC
PROGRAM:
fc=50;
fs=1000;
f1=200;f2=300;
t=0:1/fs:((2/f1)-(1/fs));
x1=0.4*cos(2*pi*f1*t)+0.5;
subplot(311);plot(x1);title('message signal');GRID;
subplot(312);y=modulate(x1,fc,fs,'ppm');plot(y);
title('PPM MODULATION');
GRID;
z=demod(y,fc,fs,'ppm');
subplot(313);plot(z);title('demodulated o/p');grid;

22. Result : The Pulse Position modulation and demodulation is executed using MATLAB
software.

23. message signal
1
0.5
0
1 2 3 4 5 6 7 8 9 10
PPM MODULATION
1
0.5
0
0 20 40 60 80 100 120 140 160 180 200
demodulated o/p
1
0.5
0
1 2 3 4 5 6 7 8 9 10