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Relationship and the formula between the threshold in cfarcfg and the SNR

Mohamed Naceur Hassine
Intellectual 460 points
Other Parts Discussed in Thread: AWR1843

Hello,

I'm using the OOB demo with the AWR1843 and yesterday I did some tests by modifying the thresholds in cfarcfg to filter the points detected with a snr > 200. In fact, I did tests first with 15db then with 25, 30, 35 db.

At 15db I get points with snr < 200 but at 25db, 30db and 35db I get only points with snr > 200.

I'd like to know what the relationship and the formula is between the threshold in cfarcfg and the snr so that I can change the threshold non-randomly ???

Regards,

Ben Hassine

  • 0
    TI__Mastermind 20605 points

    Hi Ben,

    Users are expected to understand this by going through the source code. Please follow on how cfar is implemented in the code so as to derive thresholds accordingly.  You can also look online for theory on CFAR algorithm and understand how the threshold plays a part based on given signals. That being said, the SNR is going to be dependent on the scene and CFAR adaptively calculates the comparison value against the threshold. For a given scene, there is a lot of unpredictability with respect to what lies in the range spectrum. Trial and error would be an easier approach when it comes to setting the appropriate CFAR threshold in the cfg.

    Regards,

    Kaushik

  • 0 in reply to Kaushik Gowda
    Intellectual 460 points

    Hello Kaushik,

    Thank you for your answer. I have been researching the CFAR algorithm and have figured it out.
    I found in the document that :

    CUT > (threshold scale converted from dB to Q8) + (noise sum / 2^x).

    According to this comparison, when I increase the threshold scale, I get points with a high snr and this is logical, but I would like to know what the direct relationship is between snr and threshold in OOB demo so that I can filter certain points by snr using the threshold scale, as I can modify it directly from cfarcfg.

    cfarCfg -1 0 2 8 4 3 0 15 0

    Regards,

    Ben Hassine

  • 0 in reply to Mohamed Naceur Hassine
    TI__Guru 69960 points

    Hi Ben,

    Expert is out of office today, please expect a reply next week.

    .

    Regards,

    Jitendra