Max TX power for channel sounding

[witc]

Hi,

In the example ras_initiator for channel sounding, there is a macro set for maximum TxPower:

const struct bt_le_cs_set_default_settings_param default_settings = {
		.enable_initiator_role = true,
		.enable_reflector_role = false,
		.cs_sync_antenna_selection = BT_LE_CS_ANTENNA_SELECTION_OPT_REPETITIVE,
		.max_tx_power = BT_HCI_OP_LE_CS_MAX_MAX_TX_POWER,
	};

where
#define BT_HCI_OP_LE_CS_MAX_MAX_TX_POWER 20

In the datasheet for nRF54L15, I see that the maximum possible TX power is +8 dBm.

But when I run the example, the log shows TX power: 0 dBm

[00:00:02.301,953] <inf> app_main: CS config creation complete. ID: 0
[00:00:02.501,909] <inf> app_main: CS security enabled.
[00:00:02.752,027] <inf> app_main: CS procedures enabled:
 - config ID: 0
 - antenna configuration index: 0
 - TX power: 0 dbm
 - subevent length: 28198 us
 - subevents per event: 1
 - subevent interval: 0
 - event interval: 2
 - procedure interval: 10
 - procedure count: 0
 - maximum procedure length: 1000

So what is really valid?
What TX power is really used for CS procedures?
How can I set the highest possible TX power for channel sounding on nRF54L15?

Thank you.

[Amanda Hsieh]

Hi, 

Could you share you bt_le_cs_set_procedure_parameters_param values? While the .max_tx_power shows the maximum power possible, it is the combination of  tx_power_delta and phy in the bt_le_cs_set_procedure_parameters_param that decides the tx_power. To get +8 dB, setting the power delta to 0x7F will generally transmit at maximum TX power as long as the PHY value is equal to the current ACL PHY.

Regards,
Amanda H.

[Patrick49]

Hello, 

By default, it is set like this :

 

If we want do decrease (or increase for this case) the Tx power to lower the consumption, how can we do that ? Is there a table of values to change the tx_power_delta so we can set the Tx power accordingly ? 

Best regards, 

Patrick

[Amanda Hsieh]

Patrick49 said:

If we want do decrease (or increase for this case) the Tx power to lower the consumption, how can we do that ? Is there a table of values to change the tx_power_delta so we can set the Tx power accordingly ? 

You can change the TX power of the ACL or use the tx power delta parameter, which only affects the CS activity.

1. Set the TX power statically through Kconfig options in your project configuration file (prj.conf) to change  the TX power of a Bluetooth connection:

CONFIG_BT_CTLR_TX_PWR_PLUS_3=y

The available power levels depend on your specific Nordic device: nRF54L15: -40 to +8 dBm (note: max TX power depends on package variant)

See Changing TX power for Bluetooth LE provides a comprehensive reference for the available power levels.

2. Changing the tx power delta parameter: https://github.com/nrfconnect/sdk-nrf/blob/main/samples/bluetooth/channel_sounding_ras_initiator/src/main.c#L615 API documentation: https://github.com/nrfconnect/sdk-zephyr/blob/63c239c946d1686c51ee0f0d2c2f05badcdc67fb/include/zephyr/bluetooth/cs.h#L790