# how get the range from FFT on FMCW radar data

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The data from an FMCW radar is 256x128, so I got 256 samples of every of the 128 ramps. There is only one target being scanned.

Now I would just use fft(), calculate the magnitude and then find the index peak. But when I know where the peak is, which Im not too sure how to do as well, how do I use that index to then calculate the range and also the velocity of the target with matlab code?

##### 2 Comments

Pratham
on 15 Feb 2024

HI @Simeon, were you able to solve the problem. I am trying to perform the same fft analysis on FMCW radar data which is for each radar frame, its raw data (*.mat) has 4 dimension: samples (128), chirps (255), receivers (4), transmitters (2).

Please let me know if you were able to perform fft analysis.

### Answers (1)

William Rose
on 11 Feb 2024

You need to specify exactly what the signal that you have consists of. It could be the received signal mixed with a reference signal with a constant frequency. YOu say it is 256 by 128, representing 128 ramps. It this is a time domain signal, then can we think of it as one continuous signal with diraiton 256x128 (a vector instead of an array)? The reaon I am asking is that if you have a time domain signal, you will want to do a time-dependent =Fourier transform, using Matlab's stft(). But if the signal has already been frequency-analyzed, then what you have is frequency versus time, already.

To get range and velocity, your "ramp" signal should be a triangle, not a sawtooth. YOu said you have 128 ramps. Does that mean 64 up-ramps and 64 down-ramps, each of which is 256 points long? Or 128 round-trip ramps, where the up is 128 points long and the down is 128 points long? IT affects the signal processing.

YOu also need the transmitted signal for reference.

It will help if you post the signal you have. Innclude the transmitted signal too if you have it.

##### 4 Comments

William Rose
on 14 Feb 2024

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