ESP32 Forum

Hello!
How shall the power back off configuration parameters be used?

For band edge compliance I need to lower the output power on the lowest and top channels but I can't measure any difference when I change the backoff settings.

For testing backoff configurations I have used channel 13. I enable backoff and set the backoff power with the following lines of code:
.chan_backoff_en = 1;
.chan13_power_backoff_qdb = 8;
This however is not working, what am I missing?

Additionally - how shall the chanX_rate_backoff_index settings be used?
I do not understand the mapping to rate or see any effect in measurements. The bit set maps to a target_power_qdb_i value but I guess this is for all rates.

In do_phy_init() I print the full init_data struct before it is passed to esp_phy_init() so I know the expected values are used. To verify that the settings have any effect I tried to lower output power set by .target_power_qdb_0 and can see that the settings are applied using measurements.

Any help is appreciated!
An example configuration in the form of a "phy_init_data" constant that shows a backoff configuration would be great!

The channel power backoff configuration has 3 steps:

1) set .chan_backoff_en = 1 to enable backoff.
2) set .chanX_power_backoff. For example, setting .chanX_power_backoff=8, means setting channel x backoff to 2dB
3) Set .chanX_rate_backoff_index. Bits from low to high correspond to target_power_qdb_0 to target_power_qdb_5. For instance, when setting .chanX_rate_backoff_index=3, binary code is 00000011, it means the target_power_qdb_0 and target_power_qdb_1 have 2dB backoff.
target_power_qdb_N values correspond to data rates (table attached below).

An example:
.chan_backoff_en = 1
.chan13_power_backoff=4 (backoff 1dB)
.chan13_rate_backoff_index=12 (binary code:00001100)
It means target_power_qdb_2 and target_power_qdb_3 have 1dB backoff on channel 13.



Edit: sorry, I was just informed that the above will only work with a version of PHY library more recent than what we have in ESP-IDF at this point. We'll update IDF to use latest PHY library in a few days.