read data from txt file and do FFT in matlab

I currently have a txt file data of complex number but it includes some other useless information in the file.

There are 4 chirps numbered as 1,2,3,4 and each chirp has 64 data.

I want to read the data from the file chirp by chirp.

And arrange the samples of the chirps as an array of dimensions (number of chirps) x (samples per chirp) which means 4 x 64 array.

And do the FFT to show the graph.

But I do not know how to process the data in the matlab.

The txt file is in the attachment.

Is there any method to achieve it?

Thank you for the help.

[Mathieu NOE]

hello

I see in your txt file that the 4 chirps data of 64 samples are repeated 12 times . do we have to use all those repetitions or are you interested in only the first ietration of the 4 chirps ?

this is the first attempt to read the data; it needs to be expanded further to get it into your sepcifi output format

C = readmatrix("data1.txt");
% all chirps data stored in one C matrix 
[m,n] = size(C);

% first rearrange data real / imag parts
data = real(C(:,1)) + j*imag(C(:,n));
% then remove NaN lines (correspond to lines with blanls or (:,:,:) text
data = data(~isnan(data));
% remove last line data ("193 end")
data(end) = [];
% this contains 4 chirps (1/2/3/4) of 64 samples each (complex data)
% this is repeated 12 times , so total amont of data is 4*64*12 = 3072
% samples

[Huijie Zhang]

Hi,

Thank you very much for the help.

I want to use all the data in the txt file not only the first ietration of the 4 chirps.

[Mathieu NOE]

hello again

I wonder if your data (chirp) is already the FFT output (as it is complex ?)

so plotting the data for first iteration block is simple :

C = readmatrix("data1.txt");
% all chirps data stored in one C matrix 
[m,n] = size(C);

% first rearrange data real / imag parts
data = real(C(:,1)) + j*imag(C(:,n));
% then remove NaN lines (correspond to lines with blanls or (:,:,:) text
data = data(~isnan(data));
% remove last line data ("193 end")
data(end) = [];
% this contains 4 chirps (1/2/3/4) of 64 samples each (complex data)
% this is repeated 12 times , so total amont of data is 4*64*12 = 3072
% samples

% one single (first) iteration retrieval
iter1_data = data(1:4*64);
out_data = (reshape(iter1_data,64,4))';

% fft plot
fft_mag = 20*log10(abs(out_data));
figure(1),plot(1:64,fft_mag);
title('FFT data block 1');
ylabel('dB');
legend('chirp 1','chirp 2','chirp 3','chirp 4')

[Huijie Zhang]

hi hello,

I am not sure whether the complex number data is already FFT or not. What you have said is also an idea to do it.

I'm trying to use complex numbers to do FFT

[Mathieu NOE]

Regarding you first comment, I modified a bit the code to display all data (i.e 4 chirps x 12 iterations = 48 chirps of 64 samples) . the plot below shows 48 traces that overlay quite well.

So I wonder what you want to do when you say you want to use all data - does it mean you average for each chirp accross the 12 iterations ?

C = readmatrix("data1.txt");
% all chirps data stored in one C matrix 
[m,n] = size(C);

% first rearrange data real / imag parts
data = real(C(:,1)) + j*imag(C(:,n));
% then remove NaN lines (correspond to lines with blanls or (:,:,:) text
data = data(~isnan(data));
% remove last line data ("193 end")
data(end) = [];
% this contains 4 chirps (1/2/3/4) of 64 samples each (complex data)
% this is repeated 12 times , so total amont of data is 4*64*12 = 3072
% samples

% % one single (first) iteration retrieval
% iter1_data = data(1:4*64);
% out_data = (reshape(iter1_data,64,4))';
% 
% % fft plot
% fft_mag = 20*log10(abs(out_data));
% figure(1),plot(1:64,fft_mag);
% title('FFT data block 1');
% ylabel('dB');
% legend('chirp 1','chirp 2','chirp 3','chirp 4')
% 
% all iterations retrieval
out_data = (reshape(data,64,4*12))';

% plot
figure(1),
subplot(2,1,1),plot(1:64,real(out_data));
ylabel('real part');
subplot(2,1,2),plot(1:64,imag(out_data));
ylabel('imag part');

[Huijie Zhang]

What I mean all data is that using data point by point not the average value. The chirps number 1,2,3,4 I think is one series of each number of chirp. May I ask why need to split the real part and image part?

[Mathieu NOE]

hello

my previous answer was to show (see plot) that the 12 iterations of the 4 chirps give more or less the same results. The plot confirms that all 48 real traces overlay well , and so for the imaginary parts. But it is still unclear to me what you intend to do with the 12 iterations. I was thinking you wanted to do avearge of the 12 iterations , but maybe it's not right.

[Huijie Zhang]

hi

Thank you for your help at first.

I want to make the data to an array which size will be 4 by number of samples. For example, in this data1.txt, there are 12 sets of 4x64 complex number data. So I want to make the array to be size maybe 4x768. After doing 2D-FFT. In my understanding is that doing range-FFT along each row and doing doppler-FFT along each column.