Hi Liangxiao,
Thank you for initiating the discussion on the BSS color collision issue on the NPCA primary channel.
First, I believe that the approaches considered in Option 2 and Option 3 of 11-25/1991r1—using different BSS colors on the BSS primary channel and the NPCA primary channel—are not the preferred direction, as they would increase the operational complexity of NPCA STAs.
Therefore, the Option 1 approach, which uses the same BSS Color on both the BSS primary channel and the NPCA primary channel, appears to be the more appropriate direction.
The text proposed in 11-25/1991r1 is also aligned with Option 1, and I support this direction. However, additional consideration is needed for scenarios in which a BSS color collision occurs that the NPCA AP cannot directly detect. As you may be aware, when an OBSS that is hidden from the AP uses the same BSS color, only the non-AP STA can detect the collision. In IEEE 802.11ax, a BSS color collision report mechanism (26.17.3.5, Detecting and reporting BSS color collision) was defined to address such cases.
One possible approach would be to reuse the legacy mechanism for the NPCA primary channel. However, the current mechanism is defined only for collisions detected on the BSS primary channel. Even if the legacy mechanism were extended to the NPCA primary channel, the AP would still have no way to determine which primary channel actually experienced the collision, as the current report format lacks a field to identify the originating channel.
To address this ambiguity, changes have been proposed in 11-26/0398 to enable non-AP STAs to report collisions occurring on the NPCA primary channel and to allow the AP to identify the channel on which the collision occurred. Since CID 8011 is closely related to this issue, it may be more efficient to address CID 8011 together with the CIDs in 11-26/0398.
Best regards,
Shawn
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