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How to calculate standard deviation?

  1. May 5, 2017 #1
    I have 2 signals:

    signal1: https://www.dropbox.com/s/zr04pff9skeh8cn/TX.dat?dl=0

    signal2: https://www.dropbox.com/s/h436a915dd99hln/RX1.dat?dl=0

    signal2 represents for 20 measurements, each measurement combines with signal1 to get time delay estimation using xcorr.

    So, I will have 20 delays and put them in the vector delay (1x20),then calculate the Standard deviation

    The expectation of the Standard deviation is few nanoseconds, but I still got in microseconds, I could not figure out what are issues?

    I am not sure I did right and need help from experience people, if you see something wrong or not make sense to you, please let me know.

    Thank you.

    <Moderator's note: please use code tabs when posting code>
    Code (Matlab M):

    format long;
    %% initial values:
    nsamps = inf;
    nstart = 0;
    Fs = 8e6; % sample rate
    c = 3e8; % speed of light

    %% input data
    file_tx = 'TX.dat';
    file_rx = 'RX1.dat';
    x_tx = readcplx(file_tx, nsamps,nstart);
    x_rx = readcplx(file_rx, nsamps,nstart);

    %% condition for selected gain
    mav_rx = maxabs(x_rx);

    if ((mav_rx >= 1e3) && (mav_rx <= 1e4))

        fprintf('satisfy condition! maximum absolute value inside [1000 10000] range. \n');
        %% calculate the seconds of the rx data
        data_time = length(x_rx)/(Fs/10) - 1; % seconds

        %% split every single second window
        factor = data_time/10;
        matric = reshape(x_rx, [Fs/data_time*factor, data_time + 1]);
        size_matric = size(matric);
        delay = zeros(1, size_matric(2));

      %% add noise and extend the length for x_tx = length of 1 second window of each pulse
        len = size_matric(1) - length(x_tx);
        tx_extend = zeros(1, len);
        matric1 = matric(1:end, 1);
        matric1 = matric1.';
        x_tx = [x_tx matric1(length(x_tx):end-1)];

      for i = 1:size_matric(2)
        signal1 = x_tx;
        signal2 = matric(1:end, i);
        signal2 = signal2.';
        [cc_correlation,lag] = xcorr(signal2, signal1);
        [cc_maximum, cc_time] = max(abs(cc_correlation));
        cc_estimation = abs(length(signal1) - cc_time);
        delay(i) = cc_estimation / Fs; % in second
        lagDiff = lag(cc_time);
        s2 = signal2(abs(lagDiff)+1:end);
        t2 = (0:length(s2)-1)/Fs;
      end % for i = 1:size_matric(2)

        fprintf('look and adjust the gain from RX and TX to make sure the Maximum Absolute Value (MAV) in the range of 1000 to 10000 !\n');

    end % if ((mav_rx >= 1e3) && (mav_rx <= 1e4))

    S = std(delay);
    mean1 = mean(delay);
    delay1 = mean1 - delay;
    SNR = 20*log(mean1/S);

    fprintf('\n Done! \n\n');


    function x = readcplx(filename,nsamps,nstart);
        fid = fopen(filename);
        fseek(fid,4 * nstart,'bof');
        y = fread(fid,[2,inf],'short');
        x = complex(y(1,:),y(2,: ));
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. May 6, 2017 #2
    Try to present the RX and TX files in pdf or word or excel. I could translate the Matlab language in excel of VB but these files are not accessible in .dat format.
  4. May 8, 2017 #3
    I also attached this function readcplx below, it works for .dat file, have you tried it? if you tried it and did not work, i will send you the the excel format, because these are long data in complex. it will take time to convert into excel format.
  5. May 10, 2017 #4
    are you still there?
  6. May 11, 2017 #5
    Sorry Nate Duong.At first I am not familiarized with Matlab. I'm using only Microsoft Excel and Visual Basic programs "hand made" so I cannot open .dat files nor in Excel neither in Visual Basic.Standard deviation it is a standard calculation and I could do it in Visual Basic 6 for instance if I would open the files.:sorry:
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