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IWR6843ISK-ODS: Dithering the phase of each chirp for mitigation of parallel interference

Grigor Mardiyan
Prodigy 240 points
Part Number: IWR6843ISK-ODS
Other Parts Discussed in Thread: DCA1000EVM

Tool/software:

Dear colleagues,

In "Interference Management in Radar Systems":

/cfs-file/__key/communityserver-discussions-components-files/1023/Managing_5F00_Interference_5F00_in_5F00_TI_5F00_Radar_5F00_FAE2019.pdf

We can read that "Dithering the phase of each chirp"

"Extremely Useful. Especially in a parallel interferer scenario."

I have IWR6843ISK-ODS. I want to use two or more devices in one room with the same radar configuration.

So I face with parallel interference (the same bandwith, frequency slope for agressor and victim radars).

I see the interference like a moving peak across range from chirp to chirp in affected radar frame.

Let us consider an example. I use two pairs of IWR6843ISK-ODS + DCA1000EVM. One is victim another one - agressor.

I use 255 chirps per frame, I set two unique pseudo random sequences for phase shifters of aggressor and victim. The phase of chirps in a frame is 0 or 180 degrees.

If we look at the interference in picture with coordinates "range profile bins vs number of chirp", we see the behavior of interference (64 samples per chirp, 255 chirps per frame):

Here you can see the strong declined line corresponded to interference and weak horizontal line corresponded to standing human.

When I calculate Range-Doppler map after per chirp phase correction to compensate the transmitter's phase shifting I get a picture (vertical line is a range in meters, horizontal line - velocity):

Here you can see the point on 0 velocity and 1.3 m range which is corresponded to standing human.

As you can see there is no suppression of interference.

Could you advice, should phase dithering be effective in my case?

Best regards,

Grigor Mardiyan

  • 0
    TI__Genius 14290 points

    Hello Grigor.

    Nathan is out of office and will provide a response once he is back.

    Sincerely,

    Santosh

  • 0 in reply to Santosh Krishnan
    Prodigy 240 points

    Dear colleagues,

     

    Gentle reminder,

    Best regards,

    Grigor Mardiyan

  • 0 in reply to Grigor Mardiyan
    TI__Mastermind 33930 points

    Hi Grigor,

    Dithering will help reduce the likelihood of multiple chirps within a frame interfering with one another. However, your plot here indicates that the range of the interference signal is changing over chirps. This is not the expected behavior for parallel chirp interference. Parallel chirp interference is supposed to be seen as an object at a constant range, since the intermediate frequency should be constant (assuming both the interferer device and interfered device use the same chirp slope). Is there a reason you think the range of the object is changing over chirps?

    See section 2.3.3.

    https://www.ti.com/lit/an/swra662a/swra662a.pdf?ts=1732203728973&ref_url=https%253A%252F%252Fwww.google.com%252F

    Best,

    Nate

  • 0 in reply to Nathan Block
    Prodigy 240 points

    Dear Nate,

    First of all, I use following parameters of radar signal:

    There are two identical radars with the equal parameters in the room opposite each other.

    I conducted plenty of experiments, and can say that the interference which is directly came from one radar to another always shifts across the range bins. As was depicted above.

    As far as I understand the interference will have fixed range in one particular case - when two radars are synchronized. While they are not synchronized, every radar have its own local oscillators with slightly different frequencies (and slightly different period of signal for every radar) which results to such behavior of parallel interference. It happens once per several minutes.

    Best regards,

    Grigor Mardiyan

  • 0 in reply to Grigor Mardiyan
    TI__Mastermind 33930 points

    Hi Grigor,

    I think I understand the picture now - I wonder if the chirping sequence is coming in/out of overlap, like the picture below. (red chirp = one radar, blue chirp = second radar).

    If the interferer radar's start time is increasing slightly every chirp, it would give an IF tone that increases in frequency over chirp #. Dithering would still probably help you here by decreasing the likelihood of this scenario. Have you tried using it?

    Best,

    Nate