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Thread: Distance2Go Doppler evaluation

  1. #1
    New Member New Member radaruser is on a distinguished road
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    Distance2Go Doppler evaluation

    Hey there,

    I'm using the Distance2Go board with the Doppler and FMCW firmware (Radar_D2G_Doppler_FMCW in DAVE) and in /Algorithm/src/doppler.c line 130 it is said:

    g_doppler_velocity = g_doppler_frequency / 44.4f;

    where

    g_doppler_frequency = maxBin * doppler_Hz_per_bin

    is defined the line above.

    doppler_Hz_per_bin = sampling_freq / (float32_t)FFT_SIZE; which would be 20 kHz / 1024 = 19.53125 Hz per bin in my case (FFT size is 1024).

    This gives a g_doppler_velocity of maxBin * 19.53125 Hz / 44.4.

    What does the 44.4 stand for? Does it have to do with the velocity resolution? How is that calculated? What is the unit of 44.4? Since the result needs to be in km/h, Hz is 1/s and maxBin is just a value with no unit, the 44.4 should be in 1/km if the factor 3.6 for m/s to km/h is already included.
    But where does that come from? And is that even valid? Isn't it that I converted 1/km in m/s which is not possible?

    I'd appreciate your help to find out about the 44.4. Too bad there isn't any comment in the source code...

    In addition I'd like to know how long is the Doppler CW chirp? Does it have the same duration as the global variable for the chirp time for the FMCW chirps?

    Thanks!
    Last edited by radaruser; Dec 26th, 2018 at 07:05 AM.

  2. #2
    New Member New Member radaruser is on a distinguished road
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    Update:

    I now realised that the 44.4 is the signal frequency (24 GHz) divided by 1.8 times the speed of light c. So it has to do with the velocity resolution and it has the unit 1/m. The factor 1.8 is from 3.6/2 where the 3.6 is from the conversion m/s to km/h.
    Maybe you can add a comment there with the next update

    As far as I know the chirp time is 1/doppler_Hz_per_bin so it should be 1/19.53 Hz=51.2 ms. If that is true, how can the minimum frame time for CW+FMCW evaluation be lower than the chirp time of only the doppler CW chirp?

  3. #3
    Beginner Beginner unnabi is on a distinguished road
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    https://www.infineon.com/dgdl/Infine...671c76d2a00614

    I believe that 44 is to convert doppler frequency to velocity in m/s

    I wanted to take a look at the minimum frame for FMCW vs CW but I damaged the USB connector used for GUI

  4. #4
    New Member New Member radaruser is on a distinguished road
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    Yeah thanks, figured that out now with that 44.4

    Sounds bad, hope you get a new connector soon.

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