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# How to obtain the coordinate of the maximum value in the Cross ambiguity function

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John Lee on 19 Feb 2021
Commented: John Lee on 19 Feb 2021
I am trying to find delay and doppler shift between two received signals by using the cross ambiguity function as follows.
prf = [1/1e-3 1/1e-3];
Fs = 1/1e-5;
[afmag,dly,dpp] = ambgfun(r1,r2,Fs,prf); % two received signals: r1 and r2
So, I obtain 2D array of afmag besides dly and dpp.
I think the coordiate where afmag is the maximum is what I want.
I may be able to find afmag, but I am not sure how to find the corresponding "dly" and "dpp" at that point of "afmag".
So, I want to know the maximum value of "afmag", the values of "dly" and "dpp" at that maximum point.
Thank you for your help.
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### Answers (1)

David Goodmanson on 19 Feb 2021
Hi John,
Not having the phased array system toolbox I don't know how the plot axes are oriented, but I think one of the two possibilities below should work, assuming the basic idea is correct. You would have to check on a plot.
[afmag,dly,dpp] = ambgfun(r1,r2,Fs,prf); % two received signals: r1 and r2
[~,k] = max(afmag(:))
[i j] = ind2sub(size(afmag),k)
% either this
dly0 = dly(i)
dpp0 = dpp(j)
% or this
dly0 = dly(j)
dpp0 = dpp(i)
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John Lee on 19 Feb 2021
Thanks, David,
Yes, but the problem is that we are not sure it is correct.
I don't know how to verify it because how the plot axes are oriented as you said.
Thnk you, anyway.

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