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SMPS (Spatial multiplexing power save) is a mechanism to conserve power in an 802.11n implementation. For details on the mechanism and rationale, please refer to 802.11 (as amended by 802.11n-2009) “11.2.3 SM power save”.
The mac80211 implementation is capable of sending action frames to update the AP about the station's SMPS mode, and will instruct the driver to enter the specific mode. It will also announce the requested SMPS mode during the association handshake. Hardware support for this feature is required, and can be indicated by hardware flags.
The default mode will be “automatic”, which nl80211/cfg80211 defines to be dynamic SMPS in (regular) powersave, and SMPS turned off otherwise.
To support this feature, the driver must set the appropriate
hardware support flags, and handle the SMPS flag to the
operation. It will then with this mechanism be instructed to
enter the requested SMPS mode while associated to an HT AP.