The interested reader can get an overview of the Spatial Multiplexing feature here <Spatial Multiplexing Power Save>.

Dynamic SMPS

In Dynamic SMPS mechanism, an 802.11 station enables its multiple receive chains on receiving a frame addressed to it.

The First frame so received shall be a single spatial stream individually addressed frame that requires immediate acknowledgement. Hence an RTS/CTS mechanism is normally used for this purpose.

The 802.11 station should be able to receive a multiple stream frame a SIFS time after the transmission of the CTS frame by it.

The 802.11 station can determine the end of the frame sequence by using the below rules

• It receives an individually addressed frame addressed to another STA.
• It receives a frame with a TA that differs from the TA of the frame that started the TXOP.
• The CS mechanism indicates that the medium is idle at the TxPIFS slot boundary

The Dynamic SM Power Save Mechanism is depicted pictorially below

Static SMPS

In Static SMPS mechanism, the 802.11 Station keeps the number of receive Antennas constant. It will keep the number of antennas as a single chain system or as a multiple antenna system. When the 802.11 Station wants to change its Antenna configuration (when the 802.11 Station desires to send/receive at Multiple Spatial stream), it can indicate to the Access point of the change in configuration using an SM Power Save action frame by indicating that it is no longer in power save mode.

Spatial Multiplexing Power Save Action Frame