Channel Sounding on nRF54L15DK – Accuracy of IFFT Value

[Major Tom]

Dear Nordic Support,

I am currently performing initial tests for distance measurement using Channel Sounding with the nRF54L15 Development Kit.

Here are the details of my setup:

• I am using two nRF54L15DK boards.

• One board is configured as the initiator, the other as the responder.

• I am using nRF Connect SDK version 3.0.2.

• I am working with the sample applications from the SDK:

  • nrf/samples/bluetooth/channel_sounding_ras_initiator

  • nrf/samples/bluetooth/channel_sounding_ras_reflector

I have a few questions and observations:

1. Can you please confirm that the IFFT value provided by the sample corresponds directly to the distance in meters?

2. At a physical distance of 45 cm between the two boards, the IFFT value seems reasonably accurate. It consistently gives a value of around 0.59. Please see the attached image:
    

3. However, at a distance of 150 cm, the IFFT value becomes less accurate. The reported value averages around 2.1 cm. Please see the attached image:
    

Question:
Are such deviations in the IFFT-based distance measurement known to Nordic?
If not, are there any parameters we can tweak to improve the accuracy?
Do you have any experience or recommendations in this regard?

Looking forward to your insights.

Best regards

[Ressa]

Hi, 

Regarding the distance measurement accuracy of channel sounding, we recommend to use IFFT method for short distance measurements and RTT for long distance.  IFFT method has a usable resolution of 50 cm. For RTT it is 5 m. So there are variation and deviation in the measured numbers. While most of the measurement should fit into these resolutions, under harsh condition it can fall out of these numbers. It should be noted that channel sounding distance measurements are sensitive to channel condition (surrounding environment under test) and also the algorithm being used. So a good approach for real applications of ranging would be to see what is the accuracy needed for the application and then looking at channel sounding measurements to see if it can be used for such use cases.