Can someone help me with performing range fft on FMCW Radar ADC data?

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Pratham 2024-2-13

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https://ww2.mathworks.cn/matlabcentral/answers/2081583-can-someone-help-me-with-performing-range-fft-on-fmcw-radar-adc-data

评论： William Rose 2024-2-23

I have a dataset of raw ADC data from an FMCW Radar which is in the form where for each radar frame, its raw data (*.mat) has 4 dimension:

samples (128), chirps (255), receivers (4), transmitters (2). I am unable to perform range FFT analysis on such data. Can someone help me with the same?

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Pratham 2024-2-20

编辑：Walter Roberson 2024-2-20

在 MATLAB Online 中打开

000003.mat

Hi @William Rose,

I am attatching below a sample .mat file for your reference. I am actually refering to the dataset on this github repo to perform range fft analysis. The code I have written so far is :

function [range_profiles] = perform_range_fft(adcData, fs, c)
if ~isequal(size(adcData), [128, 255, 4, 2])
    error('Data dimensions must be (samples, chirps, receivers, transmitters)');
end
% Create empty array for range profiles
range_profiles = zeros(size(adcData, 2), size(adcData, 3), size(adcData, 4));
% FFT parameters
N = size(adcData, 1); % Number of samples per chirp
% Loop through chirps, receivers, and transmitters
for chirp_index = 1:size(adcData, 2)
    for receiver_index = 1:size(adcData, 3)
        for transmitter_index = 1:size(adcData, 4)
            % Extract single-antenna data for this chirp and receiver-transmitter pair
            single_data = adcData(:, chirp_index, receiver_index, transmitter_index);
            % Apply windowing (optional, uncomment if desired)
            %window = hamming(N);
            %single_data = single_data .* window;
            % Perform FFT with zero-padding for improved resolution
            fft_output = fft(single_data, length(single_data) * 2, 1);
            % Shift result to center frequencies (optional)
            fft_output = fftshift(fft_output);
            % Calculate frequency axis (linearly mapped with zero-padding)
            f_axis = linspace(-fs/2, fs/2 - fs/N, N * 2);
            % Calculate range axis (convert frequency to range using speed of light)
            range_axis = c / (f_axis);
            % Take magnitude (absolute value) for range profile
            range_profile = abs(fft_output);
            % Store range profile
            range_profiles(chirp_index, receiver_index, transmitter_index) = range_profile;
        end
    end
end
end

I am getting an error message at the line "range_axis=c/f_axis" :

Error using /

Matrix dimensions must agree.

Error in perform_range_fft (line 34)

range_axis = c / (f_axis);

I am trying to find out the range fft for all the provided files in the dataset.

William Rose 2024-2-20

编辑：William Rose 2024-2-20

@Pratham

[Edit: fix spelling errors]

Now I see that you answered my question about zero-padding in your comments: you zero pad to improve the range resolution. I am not convinced that this gives a real improvement in range resolution. You have not added any additional data, so how can it improve real resolution? Some people zero-pad time-domain signals, to improve frequency resolution. It is true that this will give you a finer grid along the frequency axis, which makes it look like you have improved the frequency resolution. What really happens is that the prior spectral data gets interpolated, in a slightly complicated way, to a finer grid. Therefore the apparent improvement in frequency resolution is illusory. I syspect this is true for radar signal procressing also, but I could bre wrong.

I wrote script radarRanging.m, to call your function. I modified your function "perform_range_fft", to avoid an error, and gave it a new name (I added "_wr"), to distinguish it from your original posting. Script radarRanging.m plots the 8 complex traces for chirp 1 (four receivers, two transmitters). The script reads the data from the file you posted earlier, 000003.mat. The script makes the figure below. I am not sure what the results mean, but I was curious to know what the traces look like. The script and your modified function are attached.

Pratham 2024-2-22

If we reshape the adcData into 3 dimensions then the code provided would not work because we are iterating through three loops where we go through chirp_index,reciever_index and transmitter_index.

My final intent is to find out the range,velocity and angle of approach of the cycle.I have never worked on radar data before hence this is very new to me.

I have read through those cited papers, and from my understanding plotting the magnitudes of the range_profile that we obtained in the perform_range_fft_wr.m file should work right? What is the mistake due to which we are getting a wrong plot?

William Rose 2024-2-23

@Pratham,

"I have never worked on radar data before hence this is very new to me. " That makes two of us.

"From my understanding, plotting the magnitudes of the range_profile that we obtained in the perform_range_fft_wr.m file should work, right?" I have a different understanding. I think the signal analysis in that function, as it appears above, does not implement the method of Gao et al. Therefore I am not surprised that the function above does not give the desired result.

I think I know what the issue is, but it's complicated. If you wish to discuss this further, please email me by clicking on the envelope icon that appears when you click on the "WR" next to my comments.

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