Title: Best Method for Accurate BLE Distance Measurement Between Two Devices

[Usha]

Description:

Hello,

I want to measure the distance between two BLE devices with high accuracy. I have already tried using nRF52840 modules, but the results are not very precise.

Questions:

1. What is the best approach for accurate BLE-based distance measurement?
2. Does Nordic provide any recommended algorithms or libraries for this purpose?
3. Would nRF Distance Measurement (nRF DM) with MCPD or RTT be suitable for achieving better accuracy?
4. Are there any specific hardware configurations or external components that can improve the accuracy?

I would appreciate any guidance or recommendations. Thank you! 

[Simonr]

Hi

1. We're getting started with development of the Bluetooth Channel Sounding solution now, and that will be the best way to do BLE based distance measurement going forward. As of yet it's experimental, but more SW support is coming. Note that only the nRF54L15 supports Bluetooth Channel sounding as of yet. For nRF52/53 series the Distance measurement sample can be used.
2. The Distance Measurement subsystem and service is available from the Distance Measurement sample linked to.
3. Enabling CONFIG_DM_HIGH_PRECISION_CALC in the nRF Distance Measurement sample will impact the MCPD ranging mode to provide a more high-precision ranging result. However the best result will be combining RTT and MCPD and find a best estimate from the two.
4. Not for the Distance Measurement sample, but for Channel sounding, an option is to use antenna arrays to get a more precise ranging with multiple antenna points.

Best regards,

Simon

[Usha]

"I have enabled CONFIG_DM_HIGH_PRECISION_CALC in the nRF Distance Measurement sample, but the measured distance is not accurate. The actual distance is 1 meter, but the readings I get are around 1.70 or 2.05 meters. Is there any additional calibration or configuration needed to improve accuracy?"

[Simonr]

Have you done the Zero-distance calibration that's mentioned and recommended in the sample documentation as well? https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/samples/bluetooth/nrf_dm/README.html#zero-distance_calibration 

Best regards,

Simon

[Usha]

"I haven't performed the zero-distance calibration yet, and I'm not entirely sure what it entails. Could you please clarify what steps are involved in the zero-distance calibration process?"

[Simonr]

The documentation is rather brief, but it is basiacally explaining what's necessary. You need to compensate the zero-calibration offset and by performing a manually calibration. To determine the offset, place the devices at a known reference distance (we recommend 60cm) from antenna to antenna. Then collect a batch of measurement data. The difference between the average measurement and the actual distance can then be used as an offset. Whether you implement this offset to be deducted/added in the calculation on either of the devices is entirely up to you. 

Best regards,

Simon