%-------------------------------------------------------------
%  Compute auto-correlation of a Gold sequence
%-------------------------------------------------------------

%--- compute Gold sequence of length 2^7-1 ---
N = 7;
m = 2^N -1;   % length
G1seq = [ones(1,N-1), -1];
for n=N+1:m 
    G1seq(n)=G1seq(n-N)*G1seq(n-3); 
end
G2seq = [ones(1,N-1), -1];
for n=N+1:m 
    G2seq(n)=G2seq(n-N)*G2seq(n-5)*G2seq(n-4)*G2seq(n-3)*G2seq(n-2)*G2seq(n-1); 
end

Goldseq = G1seq.*G2seq;

%--- oversample by 4 ---
osMseq = ones(4,1)*Goldseq;
osMseq = osMseq(:);

%--- compute auto-correlation ---
h12 = xcorr([osMseq' osMseq' osMseq'], osMseq');
plot([-3*4*127:3*4*127-2]-507,(h12)/(4*127)); grid on
axis([-500 500 -.25 1])
ylabel('Normalized Auto-correlation')
xlabel('Delay(samples)')