Another method of Spatial Reuse that has been defined in the standard is Parameterized Spatial Reuse (PSR) operation. The operation is dependent on the receive of a PSRR PPDU packet. It is important to understand the definition of PSRR PPDU.

What is a PSRR PPDU?

The full-form of the PSRR PPDU stands for Parameterized Spatial Reuse Reception (PSRR) Physical Layer Protocol Data Unit (PPDU). As the name suggests, if a non-AP station receives a PSRR PPDU from an OBSS AP, the non-AP station can utilize the opportunity to perform an UpLink (UL) transmission to its own Acess Point as long as it conforms to certain transmit power constraints.

A PPDU that contains a trigger frame which has a valid value in the UpLink (UL) Spatial Reuse Subfield of the common info subfield is termed as a PSRR PPDU. The Spatial reuse sub-field is shown below:

The spatial reuse sub-field is set to the same values are as the HE-SIG-A field (Refer section Table 27-1 of 802.11ax) of the HE TB PPDU. The Spatial reuse values should not be set to PSR_DISALLOW or PSR_AND_NON_SRG_OBSS_PD_PROHIBITED. The below table from the standard defines the different PSR values for HE-SIG-A spatial reuse fields and for UL Spatial Reuse fields in the common info field.

What is a PSR opportunity?

If a non-AP 802.11ax station receives a PSRR PPDU and the PPDU is an Inter-BSS PPDU, then the station can avail the opportunity to discard the OBSS transmission and to send its own Uplink packet to its AP as long as it meets certain transmit power constraints – i.e. Transmit power level is less than PSR – RPL.

1. PSR – value from above table
2. RPL – Received Power level at the the receive antenna connector over the entire bredth of the PSRR PPDU Bandwith

The above methodology when a non-AP Station grabs the opportunity to transmit even if an OBSS PD transmission is seen by the station is termed PSR opportunity. The PSR Transmission cannot be longer than the duration from the Common Info field. It is shown pictorially below

In the following article, we see which MAC parameters should be enabled to allow PSR based spatial reuse

PSR-based Spatial Reuse operation MAC settings