What is Wifi's Power Management?
As long as wifi preempts the air interface according to the predetermined channel access strategy, why is there a thing called Power Management? After all, if there is no need to seize the air, each client can rest on its own.
The problem is that each client does not know when they will receive the data, so this provides space for power management. When there is no data to receive, then the clients will doze (doze), but they can't doze all the time, because if there is data in the middle, what should I do?
This is what Power management has to do.
Complete three things:
1>clients tell AP, when do I sleep (Power save mode),
2>Tell AP, when will I wake up
3>How to send the data cached by AP to clients.
1>Enter the Power Save state through Null frame Power Management bit set 1
2.1>Tell AP to wake up at regular intervals through Listen Interval field in Association Request. This does not include DTIM. In other words, if there is DTIM after the last Listen but before the next Listen, then the Interval will not be reset.
2.2> Another way is U-APSD (Unschedueled Auto Power Save Dilivery), which is adopted as the specification for Wireless Multimedia Power Save, WMM-PS, STA expresses waking up through trigger frame.
3>There are many ways.
The way of Ps-Poll is: STA uses a Ps-Poll frame, which is a control frame, to ask whether its own data is buffered, and repeat this process until More Data == 0.
The U-APSD method is: After waking up, the STA sends a trigger frame. The trigger frame here is not the 802.11ax trigger frame, but the data frame that triggers the AC. It asks whether there is buffered data. If the AP has it, then Send all data in burst, set more data to '0' in the last frame, if not, return a null frame.
PSMP, this is an agreement about when data is sent/received, and there is no stipulation on whether to receive doze, so there is no stipulation on how to wake up. AP sends PSMP frame, a kind of action frame. To allocate UTT and DTT of each STA in this PSMP sequence.
4> Dynamically switch the antenna.
Clients tell the AP to use only one antenna next time. Or use two antennas.
Use RTS/CTS to enter the single antenna, and then the clients judge by themselves whether the data reception is over, and if it is over, switch to multiple antennas.