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:

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?

[Shaun Tay]

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

Answer 1

[Chaitanya Mallela]

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.