Multiuser MIMO (MU-MIMO)
- in basic 802.11 operation modes, bandwidth is shared between all stations
- because of CA contention protocol
- AP can communicate with only one AP at a time
- multiple station requests go into a queue
- Wi-Fi 5 and 6 address this problem using beamforming or multiuser MIMO (MU-MIMO)
Download MU-MIMO (DL MU-MIMO) allows the AP to use its multiple antennae to process a spatial stream of signals in one direction separately from other streams.
- means that a group of stations on a different alignment can connect simultaneously and obtain more bandwidth
- e.g., if four stations are position north, west, south, east of a 4x4:4 AP
- AP can allow each of them to connect at close to the max speed
- if another station is added to the north
- the two north stations will share the available bandwidth along that beam path
- both stations and AP must support MU-MIMO
- e.g., if four stations are position north, west, south, east of a 4x4:4 AP
- Wi-Fi 5 supports up to four stations communicating in parallel over 5 GHz only
- Wi-Fi 6 supports up to eight stations in 2.4 GHz, 5 GHz, and 6 GHz bands
- gives better performance in congested areas
- only AP can initiate beamforming
- so only available on the downlink from AP to station
Uplink MU-MIMO (UL MU-MIMO allows stations to initiate beamforming with the access point.
- supported by Wi-Fi 6
Info
- Wi-Fi 5 and 6 improvements are released to market in waves
- e.g.,
- UL MU-MIMO was released in wave 2 Wi-Fi 6 products
- also added support for 6 GHz band
Info
MU-MIMO and OFDMA are different but complimentary technologies.
- MU-MIMO makes use of spatial streams
- OFDMA makes flexible use of subcarriers within a channel
- both work together to increase parallelism
- supporting communication with more devices simultaneously