Opportunistic power save in P2P

Opportunistic power save allows P2P Group Owner to save power when all its associated clients are sleeping.

P2P Power Management protocol defines an availability period, called the CTWindow(Client Traffic Window), during which a P2P Group Owner is present.  P2P Clients are allowed to transmit during CTWindow period. If at the end of the CTWindow all associated P2P Clients are sleeping, the P2P
Group Owner is allowed to sleep until the next Beacon time. However, if any P2P Client stays in active mode at the end of the CTWindow the P2P Group Owner is forced to remain awake
until the next Beacon time.

The P2P Group Owner is responsible for selecting an appropriate value for
CTWindow. The CTWindow shall be an integral number of TU and shall always
be less than the beacon interval. For a P2P Group Owner that desires to be
discoverable, the CTWindow should be at least 10 TU. A CTWindow shall start
at each TBTT and extend for the chosen duration.

Opportunistic power save:
The P2P  Group Owner shall indicate that Opportunistic Power Save is enabled by setting  the OppPS bit to 1 in the CTWindow and OppPS Parameters field of the Notice of Absence attribute in beacon.

With OppPS set to 1:

 If at the end of the CTWindow all associated P2P Clients are sleeping, the P2PGroup Owner is allowed to sleep until the next Beacon time. Here's a Null function set with
power management bit set to 1 to indicate that STA is going to sleep.

However, if any P2P Client stays in active mode at the end of the CTWindow the P2P Group Owner is forced to remain awake until the next Beacon time.