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Blog

How MU-MIMO Can Supercharge Wi-Fi

By Laurent Pierrugues

MU-MIMO is going strong and offered in many devices. Although, 100’s of Millions MU-MIMO Clients like Galaxy S8 and S9, Moto Z series, Google Pixel 2 and 3XL are being deployed today, many users are yet to know their devices are offering MU-MIMO capabilities.

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A Client can be either SU-MIMO or MU-MIMO. Single User (SU) MIMO provides each user 1 time slot with full band but they share channel capacity while, several Multi-User (MU) MIMO users share the same full band time slot but with increased channel capacity for existing 11ac (Wi-Fi 5) and upcoming 11ax (Wi-Fi 6) Clients. Another time slot sharing option is OFDMA, which allows several users to use a partial band in 1 time slot and share channel capacity. However, OFDMA does not offer any channel capacity increase and this option will be available only in upcoming 11ax Clients.

Configuration options

Steering with Transmit (Tx) Precoders plays an important role in maximizing the receive signal SNR. Below pictures show how signals are directed in different scenarios.

Antenna Steering

MU-MIMO capabilities include:

  • Sending more data during a fixed time slot proportional to the number of Clients in the group
  • Splitting airtime between Multi-User groups and Single-User nodes so SU clients win as well from Multi-User MIMO traffic
  • Reducing packet overhead impact while maximizing data size in Tx packet

Another important factor is Client feedback. The new 8 stream feedback Clients can make the most of MU-MIMO capabilities, due to their ability to receive the highest number of feedbacks. Eight stream feedback from Clients like LG G7 or Sony XPERIA XZ to 8x8 access points such as Quantenna’s QSR10GU/GA (8x8 5GHz 11ac + 4x4/2x2 2.4GHz 11n) or QSR10GU-AX (8x8 5GHz 11ax + 4x4 2.4GHz 11ax) allows three 2x2 Clients to be supported at the same time in one MU-MIMO group. This allows a peak TCP throughput of 1.5Gbps, which is up to 2.5x improvement over SU-MIMO.

To wrap up, MU-MIMO ecosystem has definitely matured and is the main method to increase total system capacity and performance. Downlink MU-MIMO is also a mandatory feature in the IEEE 802.11ax (Wi-Fi 6).

For more information please view our webinar recording on Light Reading’s website.