how to calculate the coherence bandwidth

I need to calculate the coherence bandwidth of the channel which the Frequency Correlation Function FCF is defined by :

here is my code

    % code
H=[501,24]; % 24 measured transfer function 
for i = 1:n
  r(:,i) = xcorr(H(:,m));
  R(i)=max(r(i))
  B=min(r/R);
end