Kindly help with fsk demodulation

Hello,

This is my code for fsk modulation and demodulation in MATLAB. I am able to do it upto modulation.However fskdemod command is throwing up an error saying that "nsamp" has to be greater than 1.This despite the fact that I am using a number greater than 1.Kindly help me.I am at my wits end :(

clc;
clear ;
close all;

% For Plots : 

set(0,'DefaultAxesFontSize',20);      % Default font size for plots
set(0,'DefaultLineLineWidth',2.0);    % Default line width for plots
set(0,'DefaultTextInterpreter','latex'); % Default text interpreter

%-----------------------START OF PROGRAM-----------------------%
b = [1 1 0 0 1 1 0 1];
n = length(b);
t = 0:.01:n;
F=1:n;
N1=800;
SNR=30;

b_p = 2*b - 1;
bw = zeros(size(t));
N = N1/n;
for idx = 1:n
    bw(N*(idx-1)+1:idx*N) = b_p(idx);
end

wo = 4*pi*t;
W = 2*pi*t;

sinHt = sin(wo+W); %--First Carrier Wave--%
sinLt = sin(wo-W); %--Second Carrier Wave--%

st = sin(wo+(bw).*W); %--Modulated Wave--%

%-----------------------PLOTTING MODULATED SIGNALS-----------------------%

figure;
plot(t,bw);
title('Given Bit Input');
xlabel('time');
ylabel('amplitude');
grid on ;

figure('Name','Carriers');

subplot(2,1,1);
plot(t,sinHt);
title('First Carrier Wave');
xlabel('time');
ylabel('amplitude');
grid on ; 

subplot(2,1,2);
plot(t,sinLt);
title('Second Carrier Wave');
xlabel('time');
ylabel('amplitude');
grid on ; 

figure('Name','Modulated Wave');
plot(t,st);
title('Modulated Waveform');
xlabel('time');
ylabel('amplitude');
grid on ; 

%-----------------------ADDING NOISE-----------------------%

swn=awgn(st,SNR);
figure('Name','Modulated Signal with Noise');
plot(t,swn);
xlabel('time');
ylabel('amplitude');
grid on ; 

%-----------------------DEMODULATION-----------------------%

   fd=fskdemod(swn,2,8,1);
   figure;
   plot(F,fd);
   grid ON;

%-----------------------------------------------------------------------------%

Answer 1

[John D'Errico]

Hmm. I'll accept that you THINK you passed in a number greater than 1.

This is the calling sequence, copied directly from the help for fskdemod:

z = fskdemod(y,M,freq_sep,nsamp)

You should see that the 4th argument is nsamp.

Here is your call to that function:

   fd=fskdemod(swn,2,8,1);

It looks like a 1 to me - that symbol that appears after the third comma in the argument list. :)

So, when I read the statement: "fskdemod command is throwing up an error saying that "nsamp" has to be greater than 1.", well I assume that you might do better if you pass in a number greater than 1. It is only a guess on my part of course.

[Aditi Moudgalya Sreeroop]

Heya,

Thanks for replying.My bad I dint check the value.However even after modifying the fskdemod command ,it is still not working.I have attached a picture.Please have a look at it.

Thanks and Regards, Aditi Moudgalya Sreeroop :)

[John D'Errico]

Lacking that toolbox, I'd read the help.

https://www.mathworks.com/help/comm/ref/fskdemod.html

It seems to indicate that fskdemod works down the rows of y, that with multiple columns, it process each column independently. I cannot test that fact however. You are passing it a row vector, which might seem to cause problems.

[Aditi Moudgalya Sreeroop]

Heya,

It is still not working :( I have attached the pic :(