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Hi currently im doing a mod and demod of FSK signals and i have to add AWGN into it but cant figure it out can someone help and identify the error, currently im using the code below:

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Shaun Tay
Shaun Tay on 16 Oct 2020
Answered: Chaitanya Mallela on 19 Oct 2020
x=[1 0 0 1 1 0 1]; binary information
bsp=0.000001; bit period
disp(‘Binary information at Transmitter:’);
disp(x);
%Noise
SNR = 0:4:40;
Noise_Power = 1./(10.^(SNR./10));
K_rice = 5;
num_bits = 5000000;
%Representation of transmitting binary information as digital signal
bit=[];
For n=1:1 length(x)
If x(n)==1;
se=ones(1,100);
Else x( n)==0;
se=zeros(1,100);
End
bit=[bit se];
End
t1=bp/100:bp/100:100*length(x)*(bp/100);
subplot(3,1,1);
plot(t1, bit, ‘lineWidth’, 2.5); grid on
axis([0 bp*length(x)-.5 1.5]);
ylabel(‘Amplitude(volt)’);
xlabel(‘Time(sec)’)
title(‘Transmitting information as digital signal’);
%Binary-FSK modulation
A=5; amplitude of carrier signal
br=1/bp; bit rate
f1=br*8; carrier frequency for info as 1
f2=br*2; carrier frequency for info as 0
t2=bp/99:bp99:bp;
ss=length(t2);
m=[];
For (i=1:1:length(x)
if(x(i)==1);
y=A*cos(2*pi*f1*t2);
Else
u=A*cos(2*pi*f2*t2);
end
m=[m y];
end
t3=bp/99:bp/99:bp*length(x);
subplot(3,1,2);
z=awgn(t3,m); ,- this is the part i am not so sure about
plot(z,m);
xlabel('time(sec)');
ylabel('amplitude(volt)');
title('waveform for binary FSK modulation corresponding binary information');
%XXXXXXXXXXXXXXXXXXXX Binary FSK demodulation
mn=[];
for n=ss:ss:length(m)
t=bp/99:bp/99:bp;
y1=cos(2*pi*f1*t); % carrier signal for information 1
y2=cos(2*pi*f2*t); % carrier signal for information 0
mm=y1.*m((n-(ss-1)):n);
mmm=y2.*m((n-(ss-1)):n);
t4=bp/99:bp/99:bp;
z1=trapz(t4,mm) % integration
z2=trapz(t4,mmm) % integration
zz1=round(2*z1/bp)
zz2= round(2*z2/bp)
if(zz1>A/2) % logic lavel= (0+A)/2 or (A+0)/2 or 2.5 ( in this case)
a=1;
else(zz2>A/2)
a=0;
end
mn=[mn a];
end
disp(' Binary information at Reciver :');
disp(mn);
%XXXXX Representation of binary information as digital signal which achived
%after demodulation XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
bit=[];
for n=1:length(mn);
if mn(n)==1;
se=ones(1,100);
else mn(n)==0;
se=zeros(1,100);
end
bit=[bit se];
end
t4=bp/100:bp/100:100*length(mn)*(bp/100);
subplot(3,1,3)
plot(t4,bit,'LineWidth',2.5);grid on;
axis([ 0 bp*length(mn) -.5 1.5]);
ylabel('amplitude(volt)');
xlabel(' time(sec)');
title('recived information as digital signal after binary FSK demodulation');
%
Sorry if the error is stupid as im still a beginner to matlab,
furthermore could someoen explain the following:
t3=bp/99:bp/99:bp*length(x); what does this line do?

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Shaun Tay
Shaun Tay on 16 Oct 2020
or is there a more efficient way to compute my code for modulation and demodulation of FSK systems. thank you in advanced!

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Answers (1)

Chaitanya Mallela
Chaitanya Mallela on 19 Oct 2020
awgn function considers input vector signal, Signal to Noise Ratio (SNR) and Signal power as a general valid attributes.
Refer the documentation https://www.mathworks.com/help/comm/ref/awgn.html for more insights on using awgn function.
t3=bp/99:bp/99:bp*length(x);
This line generates a vector with start value bp/99 and end value bp*length(x) incrementing at bp/99.

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