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AWR2944EVM: Velocity computations DDMA

Mark Passia
Prodigy 250 points
Part Number: AWR2944EVM

Tool/software:

Hi,

I have noticed that the velocity resolution inside the default HECR demo (value from the automotive visualizer) is computed as: 

dopplerStep = 0.106392793

I wonder how is this quantity computed? The standard formula: delta_v = lambda_start / (2 * N_chirps * T_chirp) = c / (2 * N_chirps * f_start * T_chirp) yields the following when using default HECR values for the legacy frame:

delta_v = (3e8) / (2 * (128 * 6) * 77e9 * (3.5 + 17.33)e-6) = 0.121481129 m/s

Also when it comes to the max unambiguous velocity v_unambiguous = lambda_start / (4 * T_chirp), yields:

v_unambiguous = lambda_start / (4 * T_chirp) = c / (4 * T_chirp * f_start) = 3e8 / (4 * (3.5 + 17.33)e-6 * 77e9) = 46.76 m/s

Which is more than it is hardcoded into the chirp_design_HECR.h file which has: HECR_GTRACK_MAX_RAD_VEL  40.8781 

I do understand that this is the DDMA mode so that these quantities are perhaps computed differently than in standard TDM? But either way, please let me know how to properly compute these quantities for DDMA, so that I understand where do these values used in the demo come from. 

Thanks in advance,
Mark

  • 0
    TI__Mastermind 20810 points

    Hi Mark,

    You can check MmwDemo_RFParser_parseCtrlConfig function in C:\ti\radar_toolbox_<ver>\source\ti\examples\Automotive_ADAS_and_Parking\high_end_corner_radar\src\demo\utils\mmwdemo_rfparserDDMA.c.

    chirpRepeatPeriod_sec = idleTime_sec + rampEndTime_sec;

    frameActiveTime_sec = chirpRepeatPeriod_sec * numChirps

    dopplerResolution_meters_per_sec = lambda / ( 2 * frameActiveTime_sec);

    maxVel_meters_per_sec = lambda/(4 * chirpRepeatPeriod_sec);

    Mark Passia said:
    Which is more than it is hardcoded into the chirp_design_HECR.h file which has: HECR_GTRACK_MAX_RAD_VEL  40.8781 

    GTRACK parameters are to be set by the user based on their configuration. Do update this parameter based on your requirement.

    Regards,

    Samhitha

  • 0 in reply to Samhitha Bobba
    Prodigy 250 points

    Thanks for you reply!

    Is there any convention for lambda, whether to take the starting wavelength or the wavelength at the centre frequency? 

    Also with the formula that you have provided for the default HECR frame we get:

    dopplerResolution_meters_per_sec = lambda / ( 2 * frameActiveTime_sec) = c / (2 * frameActiveTime_sec * f) = 3e8 [m/s] / (2 * (3.5 + 17.33)e-6 [s] * 128 (chirps) * 6 (chirp loops) * 77e9 Hz) = 0.1217727 [m/s]

    But by default the trackers setting is:

    #define HECR_GTRACK_RAD_VEL_RESO 0.1065

    So is this a mistake? Or do I miss something?

    Regards,
    Mark

  • 0 in reply to Mark Passia
    TI__Mastermind 20810 points

    Mark,

    Mark Passia said:
    Is there any convention for lambda, whether to take the starting wavelength or the wavelength at the centre frequency? 

    In HECR, we use centre frequency to compute doppler resoultion.

    Mark Passia said:

    But by default the trackers setting is:

    #define HECR_GTRACK_RAD_VEL_RESO 0.1065

    So is this a mistake? Or do I miss something?

    As mentioned in my previous response, gTrack parameters are to be set by the user based on their configuration. We haven't adjusted gTrack parameters as per the default configuration used. Note: gTrack algorithm is provided for reference.

    Regards,

    Samhitha

  • 0 in reply to Samhitha Bobba
    Prodigy 250 points

    Hello Samhitha,

    Samhitha Bobba said:
    We haven't adjusted gTrack parameters as per the default configuration used.

    So how should I understand this. Does it mean that the default chirp_design_HECR.h file as provided by the toolbox is simply incorrect (with respect to frame design vs. gtrack parameters)?

    Regards,
    Mark

  • +1 in reply to Mark Passia
    TI__Mastermind 20810 points

    Hi Mark,

    Samhitha Bobba said:
    We haven't adjusted gTrack parameters as per the default configuration used. Note: gTrack algorithm is provided for reference.

    We have verified the basic functionality of the tracker algorithm. I meant that it can be finetuned further.

    HECR_GTRACK_RAD_VEL_RESO value is not used anywhere in the algorithm. So, the value populated here will be a don't care input. HECR_GTRACK_RAD_VEL_RESO is assigned to radialVelocityResolution but this field of the structure is not utilized. You can refer to "C:\ti\mmwave_mcuplus_sdk_04_07_01_03\mmwave_mcuplus_sdk_04_07_01_03\ti\alg\gtrack\docs\Tracking radar targets with multiple reflection points.pdf" document for details related to gTrack.

    Regards,

    Samhitha