Modulation and Demodulation

clear all;
close all

fm=120;%Frequency of message signal
fc=1200;%frequency of carrier signal
T=1/fm;% period of message signal
Fs=120000;%Sampling frequency

t=0:1/Fs:5*T;% time domain

m=5*cos(2*pi*fm*t);%message signal;

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

plot(t,m);

hold on ;
plot(t,c);
title('Message signal and Carrier signal ');
N=length(m);
%///////////////Modulation
f=linspace(-Fs/2,Fs/2,N);% frequency domain
Modsi=m.*c;% modulated signal
% Plotting the Modulated Signal in time domain And
% in frequency domain.
figure(2);
subplot(2,1,1);
plot(t,Modsi);
title('Modulated Signal');
Xmosi=fftshift(fft(Modsi,N))/length(Modsi);
subplot(2,1,2);
plot(f,abs(Xmosi));
xlim([-2000 2000]);
title('Modulated Signal in Frequency domain ');

%//////////////Part2
Wn=(2*fc)/Fs;%Normalizing factor of filter
order=5;% order of filter
dene=2*cos(2*pi*t*fc);% to demodulate we multiply our
%modulated signal with cos(2*pi*t*fc);
dene2=dene.*Modsi;
[a,b]=butter(order,Wn,'low');%creating low pass signal
Filtereddemod=filter(a,b,dene2);%Sending our
%signal which we multiply modulated signal by cos(2*pi*t*fc)

%Plotting Message signal and Demodulated Signal
figure(3);
plot(t,m);
hold on;
plot(t,Filtereddemod);

title('Demodulated and Original Signals');