ip_09_05.m

The matlab source code for book of "digital communications"

% MATLAB script for Illustrative Problem 5, Chapter 9.
echo on
% first determine the maximal length shift register sequences
% We'll take the initial shift register content as "00001".
connections1=[1 0 1 0 0];
connections2=[1 1 1 0 1];
sequence1=ss_mlsrs(connections1);
sequence2=ss_mlsrs(connections2);
% cyclically shift the second sequence and add it to the first one
L=2^length(connections1)-1;;
for shift_amount=0:L-1,
  temp=[sequence2(shift_amount+1:L) sequence2(1:shift_amount)];
  gold_seq(shift_amount+1,:)=(sequence1+temp) - floor((sequence1+temp)./2).*2;
end;
% find the max value of the cross correlation for these sequences
max_cross_corr=0;
for i=1:L-1,
  for j=i+1:L,
    % equivalent sequences
    c1=2*gold_seq(i,:)-1;
    c2=2*gold_seq(j,:)-1;
    for m=0:L-1,
      shifted_c2=[c2(m+1:L) c2(1:m)];
      corr=abs(sum(c1.*shifted_c2));
      if (corr>max_cross_corr),
        max_cross_corr=corr;
      end;
    end;
  end;
end;
% note that max_cross_corr turns out to be 9 in this example...