MU-MIMO They're not calling you names, they're speeding up your Wi-Fi! #Aerohive #WFD5

The thing I always vividly remember from an Aerohive session at Wireless Field Day, is the presentation by Matthew Gast. I love how he intertwines fun facts and figures into a slide deck AND uses matrix math to explain things that are still (somewhat) theoretical in nature.

At the WFD5 event, Matthew Gast presented on MU-MIMO in 802.11ac. I tried to take notes, but the  information flow was more than my brain buffer can process in real-time.


802.11ac Wave-2 and its enablers

• explicit beamforming in 802.11ac
• matrix math
• implementation
• null steering
• acknowledgement and queueing

4 features of 802.11ac

• wider channels (80 & 160MHz)
• more spatial streams (up to 8 in a single user tx, 4 in a multi-user tx)
• 256-QAM
• downlink MU-MIMO

null data packets

• not even a L2 construct
• it's a phy layer data plane to describe the way the energy will be steered

Multiple devices connected at the 64 QAM rates will be able to send/receive more data than a single 256 QAM device will tx/rx.


Several matrices are used in matrix math:

• H is the channel matrix that describes the path between transmitter and receiver
• Q is the steering matrix that alters the distribution of energy along a path
• V is the feedback matrix, sent as part of the measurement process to derive Q

The feedback loop based on speeds now is "Did you get an ACK or not?", it's not a matrix describing the connectivity. You can mix data rates inside a feedback matrix data result.

The block ack protocol is used when transmitting to multiple devices at the same time. This is a layer on top of sending beamformed frames. Data rates within a beamformed frame can be mixed. Block ACKs get used as a distributed acknowledgment system along with the RTS-CTS mechanism.

Multi-user MIMO is trading total overall throughput for individual peak throughput, and only works downstream.

The GCMP encryption requires AES but has fewer trips through the AES block and is still only optional in 802.11ac. 

I know all of that is quite a mouthful of acronyms! If you haven't watched the Aerohive presentation series, you'd be doing yourself a favor if you did.



Aerohive ID Manager Demonstration at WFD5 from Stephen Foskett on Vimeo.


Aerohive Client Management Demonstration from Stephen Foskett on Vimeo.


Aerohive Application Visibility and Control Demonstration from Stephen Foskett on Vimeo.


Aerohive Application Visibility and Control Presentation at WFD5 from Stephen Foskett on Vimeo.