The interested reader can refer Spatial Multiplexing Power save here <Spatial Multiplexing Power Save>
The SM Power-Save Action frame can be used to change the current SM Power-Save Configuration
When the 802.11 Station needs to change the Antenna configuration – it sends a SM Power-Save action frame to the Access point indicating a change in its configuration. The action frame format is depicted pictorially below
Static SM Power-Save handshake
Dynamic SM power-Save Handshake
FIG COURTESY: CWAP – official study guide