SSB Amplitude Modulation With Audiosignal

clear all;
close all;
Fs=8000;
fc=3000;

duration=4.9902;
t=0:1/Fs:duration;
me=audioread('speech_dft_8kHz.wav');
me=me';
len=length(me);
f=linspace(-Fs/2,Fs/2,len);

%Message signal in time domain
plot(t,me);
title('Sound Signal');
%/////////////////////////
% frequency response of message signal
ffme=fftshift(fft(me,len))/len;
figure(5);
plot(f,abs(ffme));
title('Frequency response of message signal');
%///////////////////////////////////////

carrie=5*cos(2*pi*t*fc);%carrier
modulated=me.*carrie;%modulation



%construtc a filter in order to obtain Upper side
%band of modulation signal.
n=10;
Wn=2*fc/Fs;
[b,a]=butter(n,Wn,'high');
%filter magnitude response
[h,w]=freqz(b,a,len);
h=freqz(b,a,w);
figure(12);
plot(f,abs(h));
title('Magnitude Response of Filter');
%//////////////////////////////

%Frequency response of modulated signal;
ffmodulated=fftshift(fft(modulated,len))/len;
figure(3);
plot(f,abs(ffmodulated));
title('frequency response of modulated signal');
%///////////////////////////////////////////


%Obtaining the USB signal by hilbert transform
hil=imag(hilbert(me,len));
%You might ask yourself why we use imag function
%here the answer is very simple and easy just
% write hilbert to the help and read it
%it is easy to understand.

USB=me.*cos(2*pi*t*fc)-hil.*sin(2*pi*fc*t);
ffUSB=fftshift(fft(USB,len))/len;


%Frequency response of upper side band signal
%with two different method
upperside=filter(b,a,modulated);
ffupperside=fftshift(fft(upperside,len))/len;
figure(4);
subplot(211)
plot(f,abs(ffupperside));
title('Frequency response of upper side band with filter');
subplot(212)
plot(f,abs(ffUSB));
title('Frequency response of upper side band with Hilberet');
%////////////////////////////////////////////

%//////////////////DEMODULATION PART///////////
%////////Construct a low pass filter//////////
fm=800;% this cutoff frequency is adjusted by checking the frequency response of message signal.
Wn2=2*fm/Fs;
[c,d]=butter(n,Wn2,'low');
upperside=upperside.*carrie;
USB=USB.*carrie;
%before filtering we have to multiply with a
% signal whose frequency same as carrier signal
%In this lab phase are assumed to be same.
reconme=filter(c,d,upperside);%with hilbert
reconme2=filter(c,d,USB);%with filter
%////////////////////Filter Magnitude Response
figure(1552);
[h1,w1]=freqz(c,d,len);
h1=freqz(c,d,w1);% return the frequency response
plot(abs(h1));
title('Magnitude response of filter');



%Message signal and demodulated signal freq resp
figure(1523);
ffreconme2=fftshift(fft(reconme2,len))/len;
subplot(211);
plot(f,abs(ffreconme2));;
title('Demodulated Signal frequency response');
subplot(212);
plot(f,abs(ffme));
title('Message signal frequency response');
%////////////////////////////////////////////

figure(263);
subplot(311)
plot(t,reconme);
title('With Hilbert');
subplot(312);
plot(t,reconme2);
title('With Filter');
subplot(313);
plot(t,me);
title('Original Message Signal');
sound(reconme2);