MATLAB Answers

Using obw to solve for the bandwidth of a signal

3 views (last 30 days)
Hello everyone,
I have a bunch of symbols in the time domain and I am trying to do the fft of them and then calculate their bandwith. I have been trying to use the obw function to do this but the values do not seem to be right. My code is below:
clear
Fs = 1000;
Ts= 1/Fs;
symbol_duration= 1;
t= 0:Ts:symbol_duration;
%% number of functions is degree. Only one for testing
degree = 1;
p(1,:) = (2/symbol_duration)*cos(2*pi*15*t) + (2/symbol_duration)*cos(2*pi*50*t);
for i = 1:degree
%%%%% https://www.mathworks.com/help/matlab/math/fourier-transforms.html
xform=(1/Fs) .* fft( p(i,:) );
n=length(p(i,:));
fshift = (-n/2:n/2-1)*(Fs/n);
yshift(i,:) = abs( fftshift(xform) );
bw(i)= obw( yshift(i,:) )
plot(fshift,yshift(i,:))
xlim([0 Fs/2])
hold on
end
bw = 3.0991
The plot of my fft appears to be correct, but bw always seems to be some very small number that seems incorrect. Any help would be appreciated!

Accepted Answer

Ashutosh Singh Baghel
Ashutosh Singh Baghel on 24 Sep 2021
Edited: Ashutosh Singh Baghel on 24 Sep 2021
Hi Russell,
I understand that 'obw' function is used for returning the 99% occupied bandwidth of the input signal. The function 'obw' uses input signal instead of 'fft' of that input signal. Also, it is good practise to give sampling frequency 'Fs' as second input to 'obw' function.
Please try in the following way -
Fs = 1000;
t= 0:1/Fs:1;
x = cos(2*pi*10*t) + cos(2*pi*60*t);
obw(x,Fs);
Please see MATLAB Documentation page on 'obw' for further references.
  2 Comments
Russell Geschrey
Russell Geschrey on 24 Sep 2021
I see why I was not getting a graph. I was setting the output to a variable. If I just call the function alone it gives a graph. This is indeed a powerful function. Thank you for your help.

Sign in to comment.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!