FMCW FFT processing (range time plot)

I'm working on the processing of raw FMCW radar data.

In my case the radar works in the [6.014-7.76] GHz band (I have 187 frequency points starting from 6.014 GHz and ended with 7.76GHz) and the data that I collect are organized in a complex-double numbers (I&Q) matrix [Number of frame x 187] per each couple tx-rx antennas.

Unfortunately the radar company doesn't want to provide me so much information about how the radar works and I am not much of an expert. They said that the collected data are the channel response in the frequency domain.

Now if I plot one received frame I get the results shown in the figure1 and if I do 1D fft on the detrended raw data I get the figure2 ( RTI (range time intensity) plot where you can see two humans moving forth and back in front of the radar).

I'm a little bit confused: I thought that the fft processing were to do on the dechirped time domain data to get the RTI plot but I'm doing it on frequency domain and I'm getting result that makes sense, what am I missing here? To me is not clear:

1. Are the received I&Q data (as you said: output of the FMCW matched filter) in time domain? If yes, as I think, why the radar company said that the received data are the channel response in the frequency domain?
2. If the received I&Q data are in frequency domain does make sense to FFT them to obtain the target's range; I'm not expert but I known that the FFT in signal processing od FMCW radar has to be applied to traslate the radar signal from the time domain to the distance estimation.

[Learning Dadada]

Hello, may I know how do you plot out the range time plotting? I'm a beginner in radar signal processing and is that possible to have a look at your mat lab code? Thanks!

[ahmed lamiri]

Hi, can you post your code ?

Answer 1

[Honglei Chen]

I'm just speculating but if your processing result matches the ground truth, it will be hard to argue against it.

For a FMCW, the frequency shift can be translated to the time information due to the sweep slope, which in turn can be translated to the distance.

HTH