nRF5340 Distance Measurement test

[remtec]

Hi. I did some testing with two nrf5340DK boards to check the accuracy of distance measurement with Nordic's nrf_dm app.
Even in non-high precision mode the reading with ifft is quite accurate even at various distances. I inserted a median filter on the data to cut out non-compliant readings.
As you can see in the image below, the reading with ifft is good, but there are those two sudden drops that happen every now and then and I don't understand what they are due to!

Has anyone ever had something similar happen? How did you solve it?
Thank you

[remtec]

Sorry for the little info: the upper line is with phase_slope method and the lower is ifft method. The boards have always been about 8 meters away.

[Michal]

Hello,

How often are those drops happening?

What unit are you using for the x-axis?

Best regards,

Michal

[remtec]

Hi Michal.
On the X axis are the seconds, on the Y axis are the meters.
These drops fall randomly: if it's 1 or 2 I can filter them, but if it stays for 10-20 seconds I can't eliminate them.
I also tried changing the timeslots parameters but it doesn't change.

[Michal]

Ah, okay, that makes the issue worse, I agree.

So you are continuously moving the devices apart and this is the result, is that correct?

[remtec]

No. In that test the two boards remained stationary at 8 meters! But not the measurement!
Today I noticed that the measurement seems to be significantly influenced by the proximity of the human body to the boards, even if these have their own small antenna on the PCB: I thought that this type of measurement was not as affected as the RSSI.
What do you think about this?

[remtec]

These 'disturbances' seem to be present at small distances, under 10 meters.
I'm doing tests around 20 meters and the results seem much more stable.

[remtec]

Ok. Maybe I understood the problem.

I was using a nRF52840DK + a custom board based on nRF52840, but with slightly different antennas and the measurement changes depending on who is the initiator and who is the reflector.

With identical cards the uncertainty is not so evident!

Question: Is it possible to constantly set the initiator and reflector?

[Michal]

remtec said:

Question: Is it possible to constantly set the initiator and reflector?

From the documentation:

This scanner/advertiser interaction is used as a synchronization point. After a configurable delay, Device A and Device B try to range each other.

• If a Device acts as an advertiser in synchronization, it will act as the reflector in the ranging procedure.

• If a Device acts as a scanner in synchronization, it will act as the initiator in the ranging procedure.

Best regards,

Michal