The 802.11ax standard which adheres to OBSS PD operation should also conform to certain minimum and maximum OBSS PD levels and transmit power constraints. The station should conform to operate within the OBSS PD min/max values and also cannot transmit at the maximum power it is possible to transmit a packet. The transmit power is also calculated to be below or at TX_PWR_max.

The above restrictions are placed so that though the 802.11ax station re-uses the air medium, the current transmission from the 802.11ax station should not actively interfere with the OBSS transmission. It should attempt to minimize any interference caused or cause no interference.

The OBSS PD level maintained by the non-AP 802.11ax station is provided below:

The TX_PWR_ref values are defined as provided in the table below

TX_PWRref Value	Description (as per standard)
21 dBm	non-AP STAs
21 dBm	For an AP with the Max HE-MCS For 3 SS subfield in the Tx HE-MCS Map ≤ 80 MHz subfield in the Supported HE-MCS and NSS Set field of its HE Capabilities element field set to 3.
25 dBm	For an AP with the Max HE-MCS For 3 SS subfield in the Tx HE-MCS Map ≤ 80 MHz subfield in the Supported HE-MCS and NSS Set field of its HE Capabilities element field set to a value other than 3

The TX_PWR value is defined as the combined transmit power at the tranmsit antenna connector of all antennas in dBm. Check sections 11.7.6 in 802.11-2020 and section 27.3.15.2 for 802.11ax for details of TX_PWR calculation.

The PPDU_BW is calculated as per below table

The 802.11ax station should adjust the OBSS_PD levels so that the equation provided above (equation 26-5) should be conformant. The adjustment rule conformance is depicted pictorially below:

The standard defines the following for OBSS PD minimum and maximum level values for an SRG and non-SRG OBSS

For an Access Point which transmits a Spatial Reuse Parameter Set element, the below constraints are enforced

Transmit Power Restriction period and TX power level for OBSS PD operation