Subject: Clarification on Correct Distance Parameter in nRF52840 Measurements

[Usha]

Dear Nordic Semiconductor Support Team,

I am using the nRF52840 for distance measurement and have observed multiple distance-related parameters in my output, including RSSI, Best, Openspace, and IFFT. However, I am unsure which parameter represents the most accurate distance measurement.

Could you please clarify:

1. Which parameter (RSSI, Best, Openspace, or IFFT) should be considered as the correct distance measurement?

2. How do these parameters relate to each other in terms of accuracy and reliability?

3. Are there any recommended filtering techniques to improve the measurement accuracy?

Your guidance would be greatly appreciated.

Best regards,

[Simonr]

Hi

1. The "Best" parameter is the best estimate of the distance measurement, as this take all parameter into consideration.

2. In general, the RSSI parameter is the least reliable/accurate, since it's so heavily influenced by interference and obstruction of line of sight, RTT/Openspace is more accurate, but still can be affected by obstructions of line of sight, while IFFT (Multi-carrier phase difference) is the most accurate of these in most cases. This is best described here: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrfxlib/nrf_dm/doc/nrf_dm_overview.html 

3. The best ways to improve accuracy is to enable High-precision calculation as well as doing the Zero-distance calibration suggested in the sample documentation: https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/samples/bluetooth/nrf_dm/README.html 

Best regards,

Simon