an AP can perform simultaneous transmissions to multiple
receiving STAs by using the Group ID. Note that MU-TXOP
requires at least a single STA, regardless of its access category
(AC), to receive traffic from the AC that successfully obtained
the TXOP instead of the original EDCA requirement where
only transmission originating from the AC that won the TXOP
is allowed. Finally, VHT TXOP power save is introduced so
that a non-AP VHT STA could enter power save mode when
it ascertains that it is not the intended recipient during that
TXOP by filtering based on the RXVECTOR parameter of
Group ID or partial association identifier (AID).