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AWR1843BOOST: Vehicle Occupancy and Vital Signs demo with RX beamforming

Marcelina
Prodigy 80 points
Part Number: AWR1843BOOSTIWR6843AOP
Other Parts Discussed in Thread: IWR6843AOP, AWR1843

Hello,

I am currently using AWR1843 and IWR6843AoP platforms.

What I am working on is to measure vital signs of Object of Interest which can move around the room.

My current goal is to improve SNR, by removing clutter surrounding Object of Interest. According to https://ieeexplore.ieee.org/document/8378778 it can be done by using beamforming techniques.

As far as I know, TX beamforming might not be the best option in this case, as the object is not far from the radar and is moving around.

If I understand correctly, RX beamforming is mostly used for improving angular resolution for better object separation in the same range bin. In the paper linked above, it is used to differentiate between two targets and retrieving individual breathing and heart displacements. As I can see in Figure 8, signals seem to be clearly separated from each other, with no noticeable correlation between them.

To test this I've tried out Vital Signs and Occupancy Detection demo from Automotive Toolbox 3.2.0 with default chip configuration provided for AWR1843 (10fps). I have used this board for Vital Signs demo and it worked well (plots had breathing and heart components clearly visible). In case of this demo, presence of object is perfectly visible on heatmap, but its presence doesn't seem to have impact on displacement and phase plots. From what I have noticed, signals from both zones looks similar. If there is another person in second zone, signals are still similar. I am not able to resolve if there is any person in any zone from phase signal shape (which is not a problem in standard Vital Signs demo). Me and my colleague made experiment in which we were breathing with different, but stable rate (12 and 20 breaths per minute respectively). Calculated breathing rates were completely off and frequency content in breathing signal did not show expected results. As the example, in the figure below I have plotted displacement data from zone 1.

 

 

  1. For IWR6843AoP - due to different antenna geometry than non-AoP board, my guess is that this demo won't work properly with provided 68xx configuration. Although, it should work if I use TX2 and TX3 combined with RX2 and RX4 or RX1 and RX3, however angular resolution will be reduced due to lowering virtual antennas number from 8 to 4. Is that right?
  2. To Q1: how much would combining two strings of 4 virtual antennas (similarly to Overhead Occupancy demo) improve SNR in this case?
  1. What is done differently between VOD demo and the paper?
  2. Is my understanding valid, that RX beamforming is a good way to improve SNR and isolate signal from surrounding noise (not only for improving angular resolution)?

Looking forward to your reply.

Regards,
Marcelina

  • 0
    TI__Guru*** 149044 points

    HI,

    I have assigned this thread to the teams that owns this demo.

    They will be able to get back to you soon

    thank you

    Cesar

  • 0 in reply to Cesar
    Prodigy 80 points

    Hi, 

    Have you had the time to look into this?

    Thanks

    Marcelina

  • 0 in reply to Marcelina
    TI__Mastermind 40495 points

    HI, there:

    I will try to cover your first two questions: 

    1. For IWR6843AoP - due to different antenna geometry than non-AoP board, my guess is that this demo won't work properly with provided 68xx configuration. Although, it should work if I use TX2 and TX3 combined with RX2 and RX4 or RX1 and RX3, however angular resolution will be reduced due to lowering virtual antennas number from 8 to 4. Is that right?

    Yes, you can use partial antenna of AOP to create the range-azimuth heatmap, like the antennas you mentioned above. And yes, the antenna resolution will be half compare to ISK antenna pattern.  And you will have to change the code to make this demo works for AOP board.  

    1. To Q1: how much would combining two strings of 4 virtual antennas (similarly to Overhead Occupancy demo) improve SNR in this case?

    When you say improve SNR, what is the base you compare with?  Do you compare with using 1TX-1RX for vital sign detection?

    We do not support paper in our e2e forum, you will need to figure our yourself. The demo has all the source code for you to figure out.

    Best,

    Zigang

  • 0 in reply to zigang Yang
    Prodigy 80 points

    Hi,

    thank you for your answer.
    I consider my first question as resolved.

    For the other one - yes, my base is Vital Signs demo - how much SNR is improved?

    How does it affect phase noise of reflected signal?

    Will the phase measurement improve with beamforming or are there some limitations?

    Also, I have found formula for TX beamforming SNR - is there analogous formula for RX beamforming?

    Lets put aside the paper (it was written by TI employees and I just guessed it is connected with VS and VOD demos, as the steps of signal processing are similar). My main question is how does signal processing such as beamforming or combining of two virtual antenna strings should affect phase signal? VS demo, which does not contain beamforming works well and the phase signal reflects object breathing and heart rate. On the other hand, VS and VOD demo which has RX beamforming  does not show any sensible data - phase signal no longer reflects object breathing or heart rate. Further signal processing also does not reveal any meaningful results.

    Thank you,

    Marcelina

  • 0 in reply to Marcelina
    TI__Mastermind 40495 points

    HI, Marcelina:

    When the target is an ideal point target, then combining the signal from different antenna should increase the SNR by 10*log10(N) dB, where N is the number of antennas.  

    Best,

    Zigang