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IWR6843ISK-ODS: 68XX_3D_people_counting

user6256355
Prodigy 220 points
Part Number: IWR6843ISK-ODS

hello，

I am following the 68xx_3D_people_counting demo of people counting lab. and Design Guide: TIDEP-01000 People Tracking and Counting Reference Design Using mmWave Radar Sensor show that the process of

Static Clutter Removal is as below, but i can not understand the process.  the 1D FFT data is abot the information of range, why it can be used as below to remove static point?  thank you.
Best wishes
  • 0
    TI__Mastermind 28055 points

    Hi,

    Are you familiar with the doppler calculation process? We look for phase differences between the same range bins on different chirps. This phase difference is a difference in distance, but is small so we typically don't care about it for range calculation in most use cases. However, this change in range correlates to velocity. 

    Now assume you take the average value of a range bin for all chirps - if the object at that range bin is not moving, then there is no phase difference, all the bins have exactly the same value. So the average = the bin value, so bin value - average = 0. Static object energy is now removed.

    Now, assume a moving object. It's phase is different across chirps, so for any given chirp, bin value != average value. After removing the average value from the range bin, we will have some energy left over, which only corresponds to the moving objects.

    This formula is used in most of the mmWave demos - you can run the Out of Box demo with the online visualizer to plot the Range FFT and Noise. Then you can toggle on and off static clutter removal to see how this effects the Range FFT for a quick visualization.

    Regards,

    Justin

  • 0 in reply to Justin Curewitz
    Prodigy 220 points

    Hello，

    I understand your statement,  but a range bin contains both moving and nonmoving points.  If I take the average value of a range bin for all chirps including static and dynamic points. 

    Is the "After removing the average value from the range bin, we will have some energy left over, which only corresponds to the moving objects."  also applied ?

    I mean the bin value = average value may occur for a moving point, then the moving point is also removed.

    Thank you

    Best

  • 0 in reply to user6256355
    TI__Mastermind 28055 points

    Hi,

    Assume a configuration with 32 chirps. If an object is static, same value for each bin, object is removed. If an object is moving, each bin has a different value. So if a bin = the average, then yes, that bin will be zero. But remember we do an FFT on this data set to find the doppler energy. After FFT we will see which frequency (which correlates to doppler) the energy is clustered at.

    Regards,

    Justin