Question about identifying active antenna indices and IQ sample logging impact on ranging (nRF54L15 Channel Sounding)

[Firo_187]

I am currently working with the Channel Sounding sample on the nRF54L15 DK boards (SDK and toolchain v3.1.1) and using Nordic’s multiple-antenna support as described here: docs.nordicsemi.com/.../channel_sounding.html

I am operating in multiplexing mode with four antennas on the Initiator and one antenna on the Reflector. However, I am struggling to determine which specific antenna on the Initiator side is used for each path. I have already identified the antenna permutation and successfully logged it, but I would like to know if it is also possible to log the index of the currently active antennas.

This becomes particularly interesting in a 2-to-2 antenna configuration, where it would be very useful to see which antenna is used at a given time. The antennas I am using have different polarizations, so knowing the active antenna is especially important for my analysis.

I have also applied the recommendations and updates mentioned in this DevZone thread:
https://devzone.nordicsemi.com/f/nordic-q-a/124064/channel-sounding-and-more-antenna-paths  for channel sounding with multiple antennas.

One more question: if I additionally log the IQ samples from both the Initiator and the Reflector, could this affect the ranging performance in any way, since logging these samples might take additional time?

Any guidance or insight on how to access or log the active antenna index — and whether IQ sample logging has any measurable impact on the ranging process — would be greatly appreciated.

[Edvin]

Hello,

Sorry for the late reply. I am discussing this with our channel sounding team to see whether it is possible. I will get back to you when I know more. I am sorry for the delay.

Best regards,

Edvin

[Firo_187]

I would also like to mention that I am using the 4×4 antenna array CoreHW CHW1010-ANT 2-1.0 with different polarizations. I am testing various configurations to study the effect of polarization and how it affects the ranging, and therefore I would like to know which antenna is currently active...

[Edvin]

Hello,

This should be where you can find the IQ data:

https://github.com/nrfconnect/sdk-nrf/blob/a7e36dcbea5d835baea5e96ea80d0b7955e296fd/include/bluetooth/cs_de.h#L78-L79

You should be able to hook onto those using the NCS\nrf\samples\bluetooth\channel_sounding_ras_[initiator/reflector] samples.

Best regards,

Edvin

[Firo_187]

Hi edvin,

Thanks for the reply but is it now possible to log the current active antenna index or not with an multi antenna Configuration?

[Firo_187]

I’m already familiar with the struct and I’m logging the antenna_permutation_index. However, it’s still not entirely clear to me where in the code I can actually see which antenna is being used.

In the file cs_de.c, inside the process_step_data function, I’m working with the struct
bt_hci_le_cs_step_data_mode_2, since my main focus is on Mode 2.
There, I can access the antenna_permutation_index and tone_info.

While I understand the order of the selected antenna paths from the antenna_permutation_index, I still don’t see how to determine which specific physical antenna was active at a given moment.

Could you please clarify how to derive the currently active antenna based on the antenna_permutation_index or any related data?