A non-AP 802.11ax station will maintain 2 NAVs. An 802.11ax Access Point may maintain 2 NAVs. The two NAVs are defined as below:

1. Basic NAV – NAV maintained and updated by an Inter- PPDU packet reception
2. Inter-BSS NAV – NAV maintained and updated on receipt of an Inter-PPDU packet reception or an 802.11 packet reception which cannot be classified as Inter-PPDU or Intra-PPDU

Maintaining two separate NAVs help in the following manner

1. The Intra-BSS NAV is only updated on receipt of an intra-BSS frame. This provides protection to the station from collision due to other packet transmission in the same BSS
2. The Basic NAV is only updated on receipt of an Inter-BSS frame or any frames that cannot be termed as Intra/Inter-BSS. Basically, the Basic NAV is updated for receipt of packets from neighbouring BSSes. This NAV helps in mitigating interference from the neighbouring BSSes.

Only when both NAVs are Zero is the Virtual CS indication for the station is that the medium is idle. Else, the medium is termed to be busy. The 802.11ax standard defines the rules for updating Inter-BSS and Intra-BSS NAV as below:

Since, Basic NAV is only updated for transmissions from neighboring BSSes and intra-BSS NAV is only updated for intra-BSS transmissions, this method solves one of the problems caused due to co-channel interference, i.e., accidental updation of the NAV (in single NAV 802.11 stations) on receipt of non-BSS frames leading to collision and interference.

Spatial Reuse Operation