function [R_true] = True_r(h1,h2,r_length)

%--------------------------------------------------------------------------------
%	True_r.M
%	Calculate the True Cross correlation of two system driven by the same input
%
%  Usage:
%     [R_true] = True_r(h1,h2,r_length);
%  Where
%  R_true    : the True Correlation R(m) of a system driven by white noise.
%	h1        : Impulse Response of system 1
%	h2        : Impulse Response of system 2
%              h1 and h2 must have the same length
%	r_length  : the range of correlation, should be larger than the ORDER of h1,h2
%
%  This function is verified to be correct for both real and complex systems.
%
%  Binning Chen
%  Communications and Signal Processing Laboratory
%  ECE Department, Drexel University
%  Philadelphia, PA 19104, USA
%  http://www.ece.drexel.edu/CSPL
%--------------------------------------------------------------------------------

ORDER=length(h1)-1;

R_true=zeros(2*r_length+1,1);

for ii=r_length+1-ORDER:r_length+1+ORDER
   for kk=max(1,-(ii-r_length-1)+1):min(ORDER+1,ORDER-(ii-r_length-1)+1)
      R_true(ii,1)=R_true(ii,1)+conj(h1(kk))*h2(kk+ii-r_length-1);
   end
end