Questions about the principles and applications of Nordic Distance Measurement Toolbox

[Sho_Ri]

Hello,

I am using nrf52833-DK to test the Nordic Distance Measurement Toolbox.

And now I have the following 3 questions about Toolbox.

1. In this article: Using the Nordic Distance Toolbox to measure the distance between short-range radios, mentions the Toolbox uses an estimation of multipath channel impulse response from frequency spectrum measurements. But since I have no relevant knowledge about this technology, could you provide some introductory article about that?
2. In the Nordic Distance Measurement library Changelog: Nordic Distance Measurement library Changelog, Changes of nRF Connect SDK v2.0.0 mentions that ”Removed distance offset compensation of fixed user-configurable offsets. This now needs to be done in the application”.  Do you have any suggestions on how to implement distance offset compensation settings in applications?
3. In this video: Measuring distance with the Nordic Distance Toolbox, mentions used median 3 filter in IFFT and High Precision. Could you please tell me what is the median 3 filter and how to use it to filter data?

Best regards,

Sho

[Simonr]

Hi

1. This is advanced technology that we don't have a specific introductory articles on, but there are some articles on this when searching on Google for it.

2. I will have to ask internally if we have any specific suggestions on how to do this on newer NCS 2.0.0 versions.

3. Median 3 filtering is the algorithm choosing the median value between the three results from the techniques (Friis, Phase and IFFT) and thus finding the "best" estimate of the distance to the other device.

Best regards,

Simon

[Simonr]

Update to Q2: Distance offset compensation can be done by measuring the performance of the design (with multiple units) and then determining if there is any offset in the system. This can then be compensated for in each reading by the application.

Best regards,

Simon

[Sho_Ri]

Hi Simon

Thanks for your answers.

1. This is advanced technology that we don't have a specific introductory articles on, but there are some articles on this when searching on Google for it.

Thanks for the keywords you provided, I will confirm the relevant articles.

Update to Q2: Distance offset compensation can be done by measuring the performance of the design (with multiple units) and then determining if there is any offset in the system. This can then be compensated for in each reading by the application.

In the subsection "Zero-distance calibration", it is mentioned: "To determine the offset value, place the devices at a reference distance of 60 cm from each other and collect a batch of measurement data". Does this mean that if there is a 10cm error between the two devices at 60cm, then I need to subtract this 10cm error from the measurement results at other distances?

3. Median 3 filtering is the algorithm choosing the median value between the three results from the techniques (Friis, Phase and IFFT) and thus finding the "best" estimate of the distance to the other device.

On pages 28 and 30 of the presentation in the video, the median filter seems to be used to deal with outliers in IFFT and High Precision algorithms. Is the principle also choosing the median value between the three results?

[Simonr]

Hi

Sho_Ri said:

Does this mean that if there is a 10cm error between the two devices at 60cm, then I need to subtract this 10cm error from the measurement results at other distances?

Correct!

Sho_Ri said:

On pages 28 and 30 of the presentation in the video, the median filter seems to be used to deal with outliers in IFFT and High Precision algorithms. Is the principle also choosing the median value between the three results?

Yes.

Let me know if you have any follow-up questions.

Best regards,

Simon