Inquiry on Proper Use of tx_power_delta in Channel Sounding Configuration

Dear Nordic Specialist,

I would like to ask about the correct usage of the power recommendation parameter in the channel sounding configuration.

In bt_le_cs_set_procedure_parameters_param, the description of tx_power_delta appears to indicate the transmit power difference between the two devices. If the initiator’s TX power is 8 dBm and I would like the reflector to transmit at 6/4/0 dBm, should I adjust this parameter accordingly? For example, does setting tx_power_delta = 4 configure the reflector’s transmit power to 4 dBm?

This is how I am currently configuring it, but I am not entirely sure whether the reflector is actually transmitting at the power level implied by my tx_power_delta setting. Is there a recommended method to verify this?

My setup uses two 54L15 DK boards placed approximately 50 cm apart, without external antennas. I am observing that the local and remote measurement magnitudes are not significantly different. I tested tx_power_delta values of 4 dBm and 0 dBm, and compared them with the initiator’s 8 dBm. I did not see a substantial change in the measured magnitudes. Intuitively, an 8 dBm transmitter should have about six times the power of a 0 dBm transmitter.

Thank you very much for your guidance and support.

Best regards,
Cheng

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  • Hi Simonr,

    Thank you for your reply. I revisited the Bluetooth Core Specification v6.0, Vol 4, Part E, page 2835. It indicates that this parameter represents the delta relative to the current PHY transmit power. In addition, the value should be provided in hexadecimal and interpreted as a signed value.

    For example, if my initiator TX power is 8 dBm and I want the peer to use 6 dBm, I should set the parameter to −2 (0xFE). In other words, 8 − 2 = 6.

    After applying this setting, it appears to be working as expected. If I have misunderstood anything, please let me know. Thank you.

    Best,

    Cheng

  • That should be correct Cheng. Glad to hear it's working as expected now.

    Best regards,

    Simon

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