Spatial Multiplexing Power Save (SMPS)
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Spatial Multiplexing Power Save (SMPS)
- The purpose of SM power save is to allow a MIMO 802.11n device to power down all but one of its radios.
- For example, a 4×4 MIMO device with four radio chains would power down three of the four radios, thus conserving power.
- SM power save defines two methods of operation:
- Static
- a MIMO client station powers down all the client’s radios except for one single radio.
- Effectively, the MIMO client station is now the equivalent of a SISO radio that is capable of sending and receiving only one spatial stream.
- The client uses an SM power save action frame to inform the access point that the MIMO client is using only one radio and is capable of receiving only one spatial stream from the AP.
- The SM power save action frame is also used to tell the AP that the client station has powered up all of its radios and now is capable of transmitting and receiving multiple spatial streams once again.
- Dynamic
- MIMO client can also power down all but one of the client’s radios but can power up the radios again much more rapidly.
- The client station disables all but one of the radios after a frame exchange.
- An access point can trigger the client to wake up the sleeping radios by sending a request-to-send (RTS) frame.
- The client station receives the RTS frame, powers up the sleeping radios, and sends a clear-to-send (CTS) frame back to the access point.
- The client can now once again transmit and receive multiple spatial streams.
- The client uses an SM power save action frame to inform the AP of the client’s dynamic power save state.
- Static
Reference:
Coleman, David D.,Westcott, David A. CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106 Wiley.
Coleman, David D.,Westcott, David A. CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106 Wiley.
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