What is MU MIMO

Multi-user MIMO

MIMO is the generic term for processes that improve radio connections with several simultaneous data streams on several antennas.

Multi-User-MIMO (MU-MIMO) is an extension to send different data streams on several antennas to individual WLAN clients at the same time. Four or more antennas are useful here for base stations that have to supply several clients. In order for this to work, all clients must also be MU-MIMO-capable.

  • SU-MIMO - single user, multiple input, multiple output (multiple antennas for one user)
  • MU-MIMO - Multi User, Multiple Input, Multiple Output (multiple antennas for multiple users)

With IEEE 802.11ac, a single-stream client achieves 433 Mbit / s gross or 300 Mbit / s net. If an access point serves 3 clients at the same time, the data rate per client is reduced to less than 100 Mbit / s. This means that single-stream clients give away capacity on the radio channel.

With MU-MIMO, an access point can serve several single-stream clients with several data streams at the same time. The idea is to distribute several MIMO streams to several clients via MU-MIMO. On as many clients as the access point has antennas.

MU-MIMO only works in the downlink direction with WLANs from IEEE 802.11ac (optional). The opposite direction, the uplink, is only supported from IEEE 802.11ax (optional).

MU-MIMO in practice

  • MU-MIMO is optional and therefore not included in all devices. But for MU-MIMO to work, the WLAN access point and all clients must support MU-MIMO. This means that in the future (from IEEE 802.11ax) when purchasing WLAN-capable devices, you have to make sure that they are also MU-MIMO-capable.
  • Another limitation is the wireless connection. MU-MIMO only works with a good wireless connection. Usually over short distances. So only in the same room. If the distance or the attenuation of the radio signals through walls and ceilings is too great, MU-MIMO is deactivated.
  • Another limitation arises if not all WLAN clients work with the same data rate. Then the data rate of all clients is based on the slowest client.

Speed ​​increase through MU-MIMO

What speed increase can be expected with MU-MIMO? If MU-MIMO works, you can expect about 50 percent more data throughput per individual connection. But only if all clients can handle MU-MIMO. But even without full MU-MIMO support, the radio channel is freed up more quickly with partial use of MU-MIMO, which also benefits the clients without MU-MIMO.
If several clients download data at the same time, MU-MIMO provides more reserve. This means that MU-MIMO improves the total throughput in the radio cell.

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