Channel Sounding: which antennas get used

[Gush9]

Hi,

I am currently working with 2 nrf54L15-DK and a seperate 4 antenna array.

For my tests i run a 2x2 antenna config with preferred peer set to 1 and 4.

I was now wondering how strict this config is and what antennas get used for my initiator?

Is the preferred peer a hard setting or more of a suggestion which can be overruled by the BLE controller?

Will my initiator also follow the config for antenna 1 and 4 or does it randomly select 2 antennas each procedure?

Best regards

[Elfving]

Hi

From the spec:

The Preferred_Peer_Antenna parameter indicates the preferred peer-ordered antenna elements to be used by the remote device for the antenna configuration denoted by the Tone_Antenna_­Config_­Selection parameter. The number of bits set in this field shall be greater than or equal to the number of antenna elements denoted by the Tone_Antenna_­Config_­Selection parameter.

"Shall" means its mandatory.

Regards,

Elfving

[Gush9]

Hi,

I did read the specs, but this quote does not answer my question. It states that you need an equal or greater number of preferred peers set than the number of antennas. The same struct also contains some timing parameters, but these are treated as suggestions which the BLE controller can completely ignore. Therefore, I was not sure whether the preferred peer parameters would also work as suggestions.

I finally got my hands on an oscilloscope and was able to confirm how it works:

The local device will always use the lowest-indexed antennas. For a device with 4 antennas in a 2×2 configuration, this means antennas with index 0 and 1 will be used. Antennas 2 and 3 are never used.

For the peer device, the same logic is followed, with the additional constraint that it can only use antennas set in the preferred peer configuration. This also means the preferred peer configuration is a hard configuration and not a suggestion. For a device with 4 antennas in a 2×2 configuration and preferred peer set to 1 and 2, the antennas with index 1 and 2 will be used. If the preferred peer is set to 0, 2, and 3, the antennas with index 0 and 2 will be used.

Best regards