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AWR1443BOOST: Radar Range calculation in mmWavesensing Estimator

Siva Vinay
Prodigy 155 points
Part Number: AWR1443BOOST
Other Parts Discussed in Thread: AWR1443, AWR1243

Hi,

Appreciate if you could explain below from range equation got from sensing estimator tool at TI web

max_range_for_typical_detectable_object  is given as 
Math.sqrt(Math.sqrt((0.001*rcs_value*combined_factor_linear*Math.pow(lambda,2)*num_virtual_rx*chirp_time*min_num_of_chirp_loops)/(0.9*cube_4pi*kB*ambient_temperature*1e12)))
};

1. I would expect num_virtual_rx can be max of 8 even for AWR1443 for range calculation purpose since only 2 Tx can be on at a time. Is my understanding correct?

2. How Non Coherent combining loss estimated ?

3. Any explanation for the factor 0.9 at denominator  as it can't be seen any classical radar equation?

Thanks

Siva

  • 0
    TI__Expert 4720 points

    Hi Siva,

    1. I would expect num_virtual_rx can be max of 8 even for AWR1443 for range calculation purpose since only 2 Tx can be on at a time. Is my understanding correct?

    'num_virtual_rx' can be as high as 12 in AWR1243. This is because, when using the radar equation, we are interested in computing the 'total active frame time' which is 'the total duration during which the device is transmitting'. In the above equation, it would come out to 'num_virtual_rx*chirp_time*min_num_of_chirp_loops'.

    2. How Non Coherent combining loss estimated ?
        It is 10*log10(Number of non-coherent sums).

    3. Any explanation for the factor 0.9 at denominator  as it can't be seen any classical radar equation?
        I think you can ignore it. It might be a mistake on our side.

    Regards
    Anil




  • 0
    TI__Expert 5235 points
    1. Number of virtual antennas is not necessarily based on simultaneous tx, e.g if you enable only one tx antenna in a chirp, you can have up to 12 virtual antennas (3 tx * 4 rx). The product [number of virtual receive antennas * physical one chirp time * number of chirp loops] represents total integration time, it is the same as [number of receive antennas * number of physical chirps * physical one chirp time]. Physically the time is only number of ]physical chirps * physical single chirp time] but because we receive number of rx worth of physical antennas of data every chirp, so that factor is there.

    2. Non coherent combining loss is based on empirical data (the non-coherent summation is over number of virtual antennas)

    3. See e2e.ti.com/.../689147
  • 0 in reply to Anil Mani
    Prodigy 155 points
    Hi Anil,
    Thanks for the answers. On the non coherent combining loss I see different logic in TI estimator .js script and below is given for that purpose. Could you pls explain it to me. It is given as and not aligning with 10*log10(Number of non-coherent sums)
    var non_coherent_combining_loss = function(num_virtual_rx) {
    //F78 =IF(F77=8;3;IF(F77=4;2;(IF(F77=2;1;0))))
    // Math.log2(x)
    if (num_virtual_rx == 8) {
    return 3;
    } else if (num_virtual_rx == 4) {
    return 2;
    } else if (num_virtual_rx == 2) {
    return 1;
    } else {
    return 0;
    }
  • 0 in reply to Siva Vinay
    TI__Expert 5235 points
    It is not 10*log10(number of virtual antennas), the js code you quoted is reflecting the empirical results. The 10*log10(N) formula you are quoting is actually coherent combining gain (i.e gain due to combining coherently N terms over using only one (N=1) term or no-combining). The coherent gain is already reflected in the integration time but because actual combining is non-coherent, there is a loss and this needs to be accounted, this loss is based on empirical data which is coded in the if/else logic for different number of virtual antennas (the number of terms in the non-coherent combining).
  • 0 in reply to Piyush_
    Prodigy 155 points
    Thanks for clarifying
  • 0 in reply to Piyush_
    Prodigy 155 points
    Thanks I got it that combining gain is added to integration time by multiplying by number of virtual antennae. I would expect empirical non coherent combining loss will be applicable when more than one TX is ON simultaneously in this context since receive chains process the signals independently ( Correct me if I am wrong here) . But if else logic appears deciding based on number of virtual antennae and also if number of virtual antennae are more than 8 the logic returns 0dB which is not clear to me. Please help me to understand what I am missing here.
    Thanks
    Siva
  • 0 in reply to Siva Vinay
    TI__Expert 5235 points

    Firstly, you correctly noticed the problem when virtual antennas is beyond 8, there is a legitimate case of 12 virtual antennas for 14xx. It seems this happened because empirical data wasn't available for 12 case but at least we should not have it coded to 0 loss. We will look into addressing this.

    Consider the case of TDM-MIMO where we activate a single tx antenna in each transmission and repeat e.g if there are 2 tx selected and 4 rx selected, then it will be first chirp tx1, 2nd chirp tx2, 3rd chirp tx1, ...and for each chirp we get 4 rx physical receive antennas worth of data. We construct the radar cube from this data. Doppler processing needs to be done on data corresponding to the same tx because different txes are separated in space (to create a virtual array of rx separated by lambda/2 for angle estimation purposes) so the doppler dimension is half the number of physical chirps in this case (i.e doppler dimension = number of physical chips/ numTx). So each range-doppler cell contains 2*4 = 8 virtual rx antenna of data. These 8 virtual antenna data for each range-doppler cell are aggregated in energy by doing a sum of the log of their magnitudes in a typical implementation and this is the non-coherent combining we are talking about, the CFAR processing is done on this aggregated data. Thus the non-coherent combining order is number of virtual antennas [if you did not do TDM-MIMO this will be same as number of physical antennas]. You can see this processing chain implemented in the out of box demo of the SDK, the details of the processing chain are explained in the doxygen documentation of the demo.

  • 0 in reply to Piyush_
    Prodigy 155 points
    Thanks Piyush for detail explanation. This help me to clarify my understanding for most part. Lastly will there be any additional loss factor if we enable BPM on simultaneous TX channels due to interference or any nonideality?
    Thanks
    Siva
  • 0 in reply to Siva Vinay
    TI__Guru 58035 points
    Hello Siva,
    The main thing you need to consider while using multiple TX simultaneously is the delay matching on two TX. This includes the PCB traces, antenna etc. Any mismatch there would cause a slightly different gain pattern from the idle 180 phase shift of the two TX.

    Regards,
    Vivek
  • 0 in reply to Vivek Dham
    Prodigy 155 points

    Thanks Vivek