**%% Amplitude Modulation And Demodulation**

% Name:

%

% R.No:

%% closing and clearing commands

close all

clear all

clc

%% Initialization

fs=8000; % sampling frequency

fm=20; % message signal frequency

fc=500; % carrier signal frequency

t=[0:.1*fs]/fs; % time index

%% Message signal Generation

Am=1; % message signal amplitude

m=Am*cos(2*pi*fm*t); % message signal

subplot(4,3,1:3);

plot(t,m);

xlabel('time-->'), ylabel('amplitude')

title('Modulating or Message signal(fm=20Hz)');

%% Carrier signal Generation

Ac=1; % carrier signal amplitude

c=Ac*cos(2*pi*fc*t); % carrier signal

subplot(4,3,4:6);

plot(t,c);

xlabel('time-->'), ylabel('amplitude')

title('Carrier signal(fc=500Hz)');

%% Under Modulation

ka=0.5; % modulation sensitivity

u=ka*Am; % modulation Index

s1=Ac*(1+u*cos(2*pi*fm*t)).*cos(2*pi*fc*t);%AM

subplot(4,3,7);

plot(t,s1);

xlabel('time-->'), ylabel('amplitude')

title('Under Modulated signal(ka.Am=0.5)');

%% Critically Modulated signal

Am=2; % message signal amplitude

ka=0.5; % modulation sensitivity

u=ka*Am; % modulation index

s2=Ac*(1+u*cos(2*pi*fm*t)).*cos(2*pi*fc*t);

subplot(4,3,8);

plot(t,s2);

xlabel('time-->'), ylabel('amplitude')

title('Critically Modulated signal(ka.Am=1)');

%% Over Modulated signal

Am=5; % message signal amplitude

ka=0.5; % modulation sensitivity

u=ka*Am; % modulation index

s3=Ac*(1+u*cos(2*pi*fm*t)).*cos(2*pi*fc*t);

subplot(4,3,9);

plot(t,s3);

xlabel('time-->'), ylabel('amplitude')

title('Over Modulated signal(ka.Am=2.5)');

%% Demodulation

% for under modulated signal

r1= s1.*c; %detection

[b a] = butter(1,0.01);% LPF design

mr1= filter(b,a,r1);% demodulation

subplot(4,3,10);

plot(t,mr1);

xlabel('time-->'), ylabel('amplitude')

title('Demodulated signal')

% for critically modulated signal

r2= s2.*c;%detection

[b a] = butter(1,0.01);% LPF design

mr2= filter(b,a,r2);% demodulation

subplot(4,3,11);

plot(t,mr2);

xlabel('time-->'), ylabel('amplitude')

title('Demodulated signal')

% for overmodulated signal

r3= s3.*c;%detection

[b a] = butter(1,0.01);% LPF design

mr3= filter(b,a,r3);% demodulation

subplot(4,3,12);

plot(t,mr3);

xlabel('time-->'), ylabel('amplitude')

title('Demodulated signal')

**%% Pre emphasis and De emphasis**

% Name:

%

% R.No:

%% closing and clearing commands

close all

clear all

clc

%% Initialization

f1=10;

for f=1:50

x(f)=(1/sqrt(1+(f1/f)^2));

f2(f)=f;

end

subplot(2,1,1);

plot(f2,x);

title('pre-emphasis filter response');

for f=1:50

y(f)=(1/sqrt(1+(f/f1)^2));

f3(f)=f;

end

subplot(2,1,2);

plot(f3,y);

title('de-emphasis filter response');

**%% Time Division Multiplexing**

% Name:

%

% R.No:

%% closing and clearing commands

close all;

clear all;

clc

%% Signal generation

x=0:.5:4*pi; % signal taken upto 4pi

sig1=8*sin(x); % generate 1st sinusoidal signal

l=length(sig1);

sig2=8*triang(l);% Generate 2nd traingularSignal

%% Display of Both Signal

subplot(2,2,1);

plot(sig1);

title('Sinusoidal Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

subplot(2,2,2);

plot(sig2);

title('Triangular Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

subplot(2,2,3);

stem(sig1);

title('Sampled Sinusoidal Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

subplot(2,2,4);

stem(sig2);

title('Sampled Triangular Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

l1=length(sig1);

l2=length(sig2);

for i=1:l1

sig(1,i)=sig1(i); % Making Both row vector to a matrix

sig(2,i)=sig2(i);

end

% TDM of both quantize signal

tdmsig=reshape(sig,1,2*l1);

% Display of TDM Signal

figure

stem(tdmsig);

title('TDM Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

% Demultiplexing of TDM Signal

demux=reshape(tdmsig,2,l1);

for i=1:l1

sig3(i)=demux(1,i);% Converting the matrix into row vectors

sig4(i)=demux(2,i);

end

% display of demultiplexed signal

figure

subplot(2,1,1)

xlabel('Time--->');

%Display of Both Sampled Signal

plot(sig3);

title('Recovered Sinusoidal Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

subplot(2,1,2)

plot(sig4);

title('Recovered Triangular Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

**%% DSBSC Modulation And Demodulation**% Name:

%

% R.No:

%% closing and clearing commands

close all

clear all

clc

%% Initialization

Vm= 1; % message signal amplitude

Vc= 1; % carrier signal amplitude

fm = 20;%message signal frequency

fc= 500; %carrier signal frequency

fs=2*fc; % sampling frequency

t =0:inv(fs):2*pi; %time index

m_t = Vm*sin(2*pi*(fm/fs)*t);% message signal

subplot(4,1,1);

plot(t,m_t);

xlabel('time-->'), ylabel('amplitude')

title('message signal')

c_t = Vc*sin(2*pi*(fc/fs)*t); % carrier signal

subplot(4,1,2);

plot(t,c_t);

xlabel('time-->'), ylabel('amplitude')

title('carrier signal')

s_t = m_t.*c_t; %DSB-SC signal

subplot(4,1,3);

hold on;

plot(t,s_t);

plot(t,m_t,'r:');

plot(t,-m_t,'r:');

hold off;

xlabel('time-->'), ylabel('amplitude')

title('DSB-SC modulated signal')

%% Demodulated signal

r = s_t.*c_t;% detection

[b a] = butter(1,0.01);%LPF design

mr= filter(b,a,r);%demodulation

subplot(4,1,4);

plot(t,mr);

xlabel('time-->'), ylabel('amplitude')

title('Demodulated signal')

**%% SSB-SC Modulation And Demodulation**

% Name:

%

% R.No:

%% closing and clearing commands

close all

clear all

clc

%% Initialization

fs=8000; % sampling frequency

fm=20;%message signal frequency

fc=50;%carrier signal frequency

Am=1;% message signal amplitude

Ac=1;% carrier signal amplitude

t=[0:.1*fs]/fs;%time index

%% message signal generation

m1=Am*cos(2*pi*fm*t);% message signal 1

subplot(4,2,1);

plot(t,m1);

xlabel('time-->'), ylabel('amplitude')

title('Message Signal 1');

m2=Am*sin(2*pi*fm*t);% Message signal 2

subplot(4,2,2)

plot(t,m2);

xlabel('time-->'), ylabel('amplitude')

title('Message Signal 2');

%% carrier signal generation

c1=Ac*cos(2*pi*fc*t);% carrier signal 1

subplot(4,2,3)

plot(t,c1)

xlabel('time-->'), ylabel('amplitude')

title('Carrier Signal 1');

c2=Ac*sin(2*pi*fc*t);% carrier signal 2

subplot(4,2,4)

plot(t,c2)

xlabel('time-->'), ylabel('amplitude')

title('Carrier Signal 2');

%% SSB-SC generation

Susb=0.5*m1.*c1-0.5*m2.*c2;

subplot(4,2,5);

plot(t,Susb);

xlabel('time-->'), ylabel('amplitude')

title('SSB-SC Signal with USB');

Slsb=0.5*m1.*c1+0.5*m2.*c2;

subplot(426)

plot(t,Slsb);

xlabel('time-->'), ylabel('amplitude')

title('SSB-SC Signal with LSB');

%% Demodulation

r1 = Susb.*c1;% Detection

[b a] = butter(1,0.0001,'low');%LPF design

mr1= filter(b,a,r1);% demodulation

subplot(4,2,7);plot(t,mr1);

xlabel('time-->'), ylabel('amplitude')

title('Demodulated signal 1')

r2 = Slsb.*c2;% Detection

[b a] = butter(1,0.0001,'low');%LPF design

mr2= filter(b,a,r2);% demodulation

subplot(4,2,8);plot(t,mr2);

xlabel('time-->'), ylabel('amplitude')

title('Demodulated signal 2')

**%% Frequency Modulation And Demodulation**

% Name:

%

% R.No:

%% closing and clearing commands

close all

clear all

clc

%% Initialization

%fm=35HZ,fc=500HZ,Am=1V,Ac=1V,B=10

fs=10000; % sampling frequency

Ac=1;% carrier signal amplitude

Am=1;% message signal amplitude

fm=35;%message signal frequency

fc=500;%carrier signal frequency

B=10;

t=(0:.1*fs)/fs;%time index

%% MESSAGE SIGNAL GENERATION

m_t=Am*cos(2*pi*fm*t);

subplot(4,1,1);

plot(t,m_t);

title('Modulating or Message signal(fm=35Hz)');

%% carrier signal generation

c_t=Ac*cos(2*pi*fc*t);

subplot(4,1,2);

plot(t,c_t);

title('Carrier signal(fm=500Hz)');

%% Frequency modulated signal generation

s_t=Ac*cos(2*pi*fc*t+B*sin(2*pi*fm*t));

subplot(4,1,3);

plot(t,s_t);

title('Frequency Modulated signal');

%% Demodulated signal generation

d=demod(s_t,fc,fs,'fm');

subplot(4,1,4);

plot(t,d);

title('demodulated signal');

**%% Pulse Amplitude Moulation And Demodulation**

% Name:

%

% R.No:

%% ALGORITHM:

% STEP1: Start

% STEP2: define modulating and carrier frequency.

% STEP3: define time axis

% STEP4: define modulating signal and carrier signal

% STEP5: modulate the signals using FFT Algorithm to get PAM signal

% STEP6: demodulate the signal using IFFT Algorithm to get back the original signal.

% STEP7: Stop

%% PROGRAM:

%% clearing and closing commands

close all

close all

clc

%% Initialization

t=0:1/6000:((10/1000)-(1/6000));% time index

xa=sin(2*pi*100*abs(t));

subplot(3,1,1)

plot(xa);

grid

Ts=32;

x=sin(2*pi*600*(Ts*t));

X=fft(xa,abs(x));

subplot(3,1,2);

stem(t, abs(X));

grid

Y=ifft(xa,X);

subplot(3,1,3)

plot(t,abs(Y))

**%% PPM Generation And Demodulation**

% Name:

%

% R.No:

% Choose the sampling frequency fs and modulating frequency f1 such that Nyquist criteria are satisfied.

% Generate the message signal using f1 andfs .

% Modulate the message signal using the carrier frequency.

% FFT is applied to the modulated signal to get frequency spectrum.

% Demodulate the modulated signal using the same carrier frequency.

% Plot the graphs for the original message signal, modulated, frequency spectrum and demodulated signal.

%% clearing and closing commands

close all;

clear all

clc

%% Initialization

fc=100; % carrier signal frequency

fs=1000; % sampling frequency

f1=80;%f2=300

t=0:1/fs:((2/f1)-(1/fs));

x1=0.4*cos(2*pi*f1*t)+0.5;

%x2=0.2*(cos(2*pi*f1*t)+cos(2*pi*f2*t))+0.5 ;

subplot(4,2,1)

plot(x1)

title('original msg signal')

y1=modulate(x1,fc,fs,'ppm')

subplot(4,2,2)

plot(y1)

axis([0 50 -0.2 1.2])

title('ppm one of f1,fc=1000,f1=80 ')

fx1=abs(fft(y1,1024))

fx1=[fx1(512:1024) fx1(1:513)]

f=[(511*fs/1024):(fs/1024):(512*fs/1024)]

subplot(4,2,3)

plot(fx1)

title('freq des ppm signal tone,fc=1000')

x1_recov = demod(y1,fc,fs,'ppm')

subplot(4,2,4)

plot(x1_recov)

title('time domain recovered signal')

**%% PWM MODULATION AND DEMODULATION**

% Name:

%

% R.no:

%% clearing and closing commands

clear all

close all

clc

%% Initialization

fc=1000; % carrier signal frequency

fs=10000; % sampling frequency

f1=200;

t=0:1/fs:((2/f1)-(1/fs));

x1=0.4*cos(2*pi*f1*t)+0.5;

subplot(421);

plot(x1);

title('original signal tone mesage,f1=500,fs=10000')

%% modulation

y1=modulate(x1,fc,fs,'pwm');

subplot(422);

plot(y1);

axis([0 500 -0.2 1.2]);

title('PWM')

%% demodulation

x1_recov=demod(y1,fc,fs,'pwm');

subplot(423);

plot(x1_recov);

title('time domain recoverd signal tone,f1=200')