无线power save

对于无线客户端，节电非常重要，除了传统的节电，还有WMM节电，对于802.11n的推出，还有一种特殊的控制空间流的节电方式，具体大家看看下面吧：

 

 

（1）Legacy 802.11 Power Save
             Active mode：客户端总处于上电状态，默认模式。

              Power Save mode：客户端在两个信标帧之间进入休眠状态以节电，可选模式。

（2）WMM Power Save、

             客户端和AP都要通过Wi-Fi CERTIFIED WMM-PS认证。

              实时性要求高的业务必须支持WMM-PS，这是因为WMM-PS的设计目的之一就是减小实时性要求高的业务在电源管理过程中的延迟。

（3）802.11n Power Save

           SMPS

           PSMP

 

原文如下：

1. Legacy Power Save Mode (Pre 802.11e, now rolled into 802.11-2007)There are only two power save modes.
• Active mode
o This is when the STA is awake and the AP isn’t
buffering data for the STA. This can be referred to
as Constant Aware Mode. In this state the STA
device saves no battery power.

• Power save mode
o When in power save mode, it doesn’t mean that the
STA is asleep. It just means that it is in a mode to
conserve battery life.

Awake State
• The STA can send and receive frames.
Doze state
• The STA radio cannot send or receive frames.

注意：关于传统节电方式legacy Power Save Mode
• The Power Management bit（电源 管理比特位）, found in the header of every
Wi-Fi frame is used to notify the AP of the STA’s power
management state. If the bit is set to 1, the STA is in
Power Save Mode and the AP will buffer data. If the bit is
set to 0, the STA is not in Power Save Mode.
• The More Data bit（更多 数据比特位）, found in the header of every Wi-Fi
frame, is used only by the AP (it’s always 0 when sent by a
STA). When the AP is delivering buffered data to a STA,
the AP sets the More Data bit to 1 until the buffer is empty.
When the buffer is empty, the More Data bit is set to 0.
• Inside of every Becon is a Traffic Indication Map (TIM)（流量指示图）.
The TIM is a list of STA’s that have data buffered. Each
STA is referred to not by MAC address in the Beacon, but
by Association Identifier (AID). This is because MAC
addresses are too large and would make for large Beacon
frames. AID’s are much smaller and more efficient.
• ATIMs are TIMs for an Ad Hoc network.（用于adhoc的特殊TIM，ATIM）
• Power Save Poll (PS-Poll) �C Used in legacy power save
mode. When a STA sees its AID in a Beacon frame, it will
Tx a PS-Poll frame to the AP, indicating it is ready to
receive frame(s).

2. 802.11e (802.11-2007) Power Save Mode (WMM-PS)
Automatic Power Save Delivery (APSD)
• STAs do not use PS-Poll frames to retrieve buffered data
• STAs switch from Power Save Mode to Active Mode when
they want to retrieve buffered data. This is done by
sending a frame (Any data frame or Null Data frame) to flip
the Power Management bit. When the STA is awake, the
AP sends all data in the buffer.

3. HT Power Save Modes

Spatial Multiplexing Power Save (SMPS)
• 802.11n (HT-OFDM) uses multiple data streams to
increase throughput. One form of 11n power save, SMPS,
can selectively shut down all but one radio. This conserves
battery life so that 11n STAs can mimic the battery
performance of legacy single radio devices in active mode.

Power Save Multi Poll (PSMP)
• Similar to 802.11-2007’s APSD