# How to calculate standard deviation?

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>
Matlab:
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';

%% 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)
else

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');
%%%%%%%%%%%

%%%%%%%%%%%

fid = fopen(filename);
fseek(fid,4 * nstart,'bof');
fclose(fid);
x = complex(y(1,:),y(2,: ));
end
%%%%%%%%%%%

Last edited by a moderator:

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.

Nate Duong
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.
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.

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.
are you still there?

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.