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.

[witc]

I am very sorry, but I do not understand how to do this.
I took the clean code from the example channel_sounding_ras_initiator and changed:

• .cs_sync_phy = BT_CONN_LE_CS_SYNC_2M_PHY in config_params

• .phy = BT_LE_CS_PROCEDURE_PHY_2M in procedure_params

• .tx_power_delta = 0x7f

It is great that the error CS procedure enable failed no longer happens, but the TX power is still 0 dBm - nothing has changed:

[00:00:02.755,636] <inf> app_main: CS procedures enabled:
 - config ID: 0
 - antenna configuration index: 0
 - TX power: 0 dBm
 - subevent length: 25282 us
 - subevents per event: 1
 - subevent interval: 0
 - event interval: 2
 - procedure interval: 10
 - procedure count: 0
 - maximum procedure length: 1000

Also I have tried to call bt_le_set_phy after connecting to change the PHY to 1M with CONFIG_BT_AUTO_PHY_UPDATE=n, but even this did not help.

[witc]

I tried to set Tx power 8 dBm on the reflector and now in the LOG I can see +8 dBm

<inf> app_main: CS procedures enabled:
 - config ID: 0
 - antenna configuration index: 0
 - TX power: +8 dBm

This +8 dBm is valid for refelctor and also initiator? 

[Amanda Hsieh]

The log indicates the TX power on that device, your reflector.

[witc]

Amanda, I'm even more confused -> I don't think you're right, but please correct me if I'm wrong.

To clarify, I'm using pure examples of ras_initiator and reflector. You surely know that reflector doesn't have this CS procedure LOG output at all – it outputs something slightly different when running the CS procedure. Basically, the +8dBm listing is logged from the initiator device, and I ask again: is this the power for the CS procedure, meaning that both sides must use this power, or can each side use a different power?

Another thing is that what you advised me last time regarding the +8 dBm setting did not work. Does it work for you? If so, can you share the code?

The goal is to have the full power that nrf54L15 supports on both the initiator and the reflector.

[Amanda Hsieh]

The tx_power_delta parameter of the procedure parameters command affects the remote device's TX power as documented here https://github.com/nrfconnect/sdk-zephyr/blob/d24c26f9852942beb447cd6a352aa95873fb6b7a/include/zephyr/bluetooth/cs.h#L794-L798 

 

But TX power for CS is something the controllers can negotiate to some extent. So to know what TX power each device uses post-negotiation, you need to check the selected_tx_power field, documented here https://github.com/nrfconnect/sdk-zephyr/blob/d24c26f9852942beb447cd6a352aa95873fb6b7a/include/zephyr/bluetooth/conn.h#L1750-L1751. Each side may select a different output power, so to ensure it is correct on both sides, the event needs to be checked on both devices.