Direction Finding Tx transmit power

[Marcous]

Hi, I am developing my own application based on the newest demo direction _finding_connectionless_tx and direction_finding_connectionless_rx with Dev board nrf52833. 

I am wondering that if there is a api or something for me to set the tx power, like 0dbm,+4dbm. I see from other question that the api function sd_ble_gap_tx_power_set()  do actually set the tx power. But in demo direction _finding_connectionless_tx  i did not find the similar code. Can you help me?

[Edvin]

Hello,

You can't use the "old" softdevice (Bluetooth stack) API sd_ble_gap_tx_power_set() as this is not defined in NCS. That being said, it is actually a good question how to set the TX power during runtime. 

I remember seeing some TX power configurations that you can set in the prj.conf file, but is that something that would work for you, or do you need to be able to change it dynamically during runtime?

Best regards,

Edvin

[Marcous]

Actually I do not need to change it dynamically while running. Obviously, with a higher Tx power, rx side would get the signal with a higher rssi value. I'd like to conduct an experiment to find out the relationship between BLE AoA direction finding performance and Rssi value ( in other word, tx power).

Besides, in the direction finding rx side, I can obtain some cte information like intervals, cte type, rssi value and so on. Only not to find the parameter of tx power.  So I wondering is this Tx power feature available in the direction finding ? Maybe I have missed something in the whilepaper of ble direction finding?

Best regards,

Marcous 

[Edvin]

Hello Marcous,

I believe this is what you are looking for:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/softdevice_controller/doc/api.html#c.sdc_hci_cmd_vs_zephyr_write_tx_power

Marcous said:

Only not to find the parameter of tx power

I am not familiar with direction finding particularly, but I would not be surprised if the TX power is not part of the advertisement packet. There have been a few attempts of standardizing beacons the past decade, including iBeacon and eddystone, and there one option was to include the TX power in the advertisement packet, to give some sense of idea of how close you were when you receive the advertisement, and compare the RSSI and TX power. However, the RSSI is a very bad indicator of distance, so it may very well be that the TX power is not part of the advertisement packet in direction finding.

Best regards,

Edvin