communicationSystem.m

function [outputSignal,noiseSignal] = communicationSystem(channel,fs,sigma,i,impulseResponse)
% Note the if before every plot is because we plot only the 
%first chanell
% 1) Transmision 
%------------------------------------------%
x = channel;
t_end = length(x)./fs;
t = linspace(0,t_end, t_end*fs);

%plot in time domain
if (i==1)
    figure(1)
    subplot(3,1,1)
    plot(t,x)
    title('Signal in time domain')
end

X = fftshift(fft(x));
Xmg = abs(X);
Xphase = angle(X);
N = length(x);
fvec = linspace(-fs/2,fs/2,N);


%plot in frequency domain
if (i==1)
    subplot(3,1,2)
    plot(fvec,Xmg)
    title('Signal Magnitude in frequency domain')
end

if (i==1)
    subplot(3,1,3)
    plot(fvec,Xphase)
    title('Signal Phase in frequency domain')
end

% 2) Channel
%------------------------------------------%
% A) Delta
% the output signal is the same as the input
if (impulseResponse ==1)
    H1 = [1 zeros(1,N-1)];
    y = conv(x,H1);

    t_end = length(y)./fs;
    t_conv = linspace(0,t_end, t_end*fs);
    
    y = y';
end

% B) exp(-2pi*5000t) 
% the system amplifies the signal volume by approximately 2
if (impulseResponse == 2)
    H2 = exp(-2*pi*5000*t);
    y = conv(x,H2);
    
    t_end = length(y)./fs;
    t_conv = linspace(0,t_end, t_end*fs);
 
    y = y';
end

% C) exp(-2pi*1000t) 
% the system amplifies the signal volume by approximately 4
if(impulseResponse == 3)
    H3 = exp(-2*pi*1000*t);
    y = conv(x,H3);
    
    t_end = length(y)./fs;
    t_conv = linspace(0,t_end, t_end*fs);
   
    y = y';
end

% D) The channel has the following impulse response
% the system somehow disturbe the signal (overlab)
if (impulseResponse == 4)
    H4 = [2 zeros(1,1*fs -2) 1];
    y = conv(x,H4);
    
    t_end = length(y)./fs;
    t_conv = linspace(0,t_end, t_end*fs);
end

% ploting the signal after applying system
if (i==1)
        figure(2)
        subplot(3,1,1)
        plot(t_conv, y)
        title('Signal in time domain after applying system')
        
        Y = fftshift(fft(y));
        Ymg = abs(Y);
        Yphase = angle(Y);
        N = length(Y);
        fvec = linspace(-fs/2,fs/2,N);
        
        subplot(3,1,2)
        plot(fvec, Ymg)
        title('Signal Magnitude in freq. domain after applying system ')
        
        subplot(3,1,3)
        plot(fvec, Yphase)
        title('Signal phase in freq. domain after applying system ')
end
% 3) noise
%------------------------------------------%
% play sound file after adding noise

z = sigma*randn(length(x),1);
noiseSignal = y(1:length(x)) + z;
x = noiseSignal;

% plot the sound file after adding noise in time domain
t_endN=length(x)./fs;
t=linspace(0,t_endN,t_endN*fs);

if (i==1)
    figure(3)
    subplot(2,1,1)
    plot(t,x)
    title('sound file after adding noise in time domain')
end

% plot the sound file after adding noise in frequency domain
xf=fftshift(fft(x));
xfmg=abs(xf);
N=length(x);
fvec=linspace(-fs/2,fs/2,N);

if (i==1)
    subplot(2,1,2)
    plot(fvec,xfmg)
    title('sound file after adding noise in frequency domain')
end
% 4) Receiver
%------------------------------------------%
N = length(x);
n = N/fs;
right_band = round((fs/2-3400)*n);
left_band = (N-right_band+1);
xf([1:right_band left_band:N]) = 0;

x = real(ifft(ifftshift(xf)));

% plot the sound file at receiver in time domain
t_end = length(x)./fs;
t=linspace(0,t_end,t_end*fs);

if (i==1)
    figure(4)
    subplot(2,1,1)
    plot(t,x)
    title('sound file at receiver in time domain')
end

% plot the sound file at receiver in frequency
Xmg=abs(xf);
N=length(x);
fvec=linspace(-fs/2,fs/2,N);

if (i==1)
    subplot(2,1,2)
    plot(fvec,Xmg)
    title('sound file at receiver in frequency domain')
end

outputSignal = x;
end