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# Demodulate FSK signal Matlab

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#### lynx_z3

##### Newbie level 1
hi i need help in writing the demodulation code for the FSK system below any help would be appreciated. cause i have no idea how to move forward with this

Code:
function bfsk_project(g,f0,f1)
if nargin > 3
error('Too many input arguments')
elseif nargin==1
f0=1;
f1=2;
elseif nargin==2
f1=2;
end

val0=ceil(f0)-f0;
val1=ceil(f1)-f1;
if val0 ~=0 || val1 ~=0;
error('Frequency must be an integer');
end

if f0<1 || f1<1;
error('Frequency must be bigger than 1');
end

t=0:2*pi/99:2*pi;
cp=[];
cp1=[];
sp=[];
sp1=[];
mod=[];
mod1=[];
bit=[];
bit1=[];
noise_amp = 0.1;% set noise level 0.1~=6dB=SNR=Eb/No

%Channel Coding using repetition Code (3,1)
h = repmat(g,3,1); % to repeat the matrix
res = reshape(h, 1,3*(length(g)));% to resize the matrix

%Binary Pulse Shaping
for n=1:length(g);
if g(n)==0;
die1=ones(1,100);
c1=sin(f0*t);
se1=zeros(1,100);
else g(n)=1;
die1=ones(1,100);
c1=sin(f1*t);
se1=ones(1,100);
end
cp1=[cp1 die1];
mod1=[mod1 c1];
bit1=[bit1 se1];
end

%Binary Pulse Shaping for Encoded Signal
for n=1:length(res);
if res(n)==0;
die=ones(1,100);
c=sin(f0*t);
se=zeros(1,100);
else res(n)=1;
die=ones(1,100);
c=sin(f1*t);
se=ones(1,100);
end
cp=[cp die];
mod=[mod c];
bit=[bit se];
end

%FSK Modulation
fsk=cp.*mod;

% Add White Noise to Modulated FSK Signal
noise_awgn = noise_amp*randn(1,length(fsk));% noise generator
fsk_noise = fsk + noise_awgn;%modulated carrier plus noise

% Graphics
subplot(6,1,1);plot(bit1,'LineWidth',1.5);grid on;
title('Binary Signal');
axis([0 100*length(g) -2.5 2.5]);

subplot(6,1,2);plot(bit,'LineWidth',1.5);grid on;
title('Binary Signal w/ Error Correction (3,1) Repetition Code');
axis([0 100*length(res) -2.5 2.5]);

subplot(6,1,3);plot(fsk,'LineWidth',1.5);grid on;
title('FSK modulation');
axis([0 100*length(res) -2.5 2.5]);

subplot(6,1,4);plot(noise_awgn,'LineWidth',1.5);grid on;
title('Additive White Gaussian Noise');
axis([0 100*length(res) -2.5 2.5]);

subplot(6,2,7);plot(fsk_noise,'LineWidth',1.5);grid on;
title('FSK modulation w/ white noise');
axis([0 100*length(res) -2.5 2.5]);

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