IEEE 802.11ac supports multi-user MIMO
(MU-MIMO) as well as single-user MIMO (SUMIMO).
SU-MIMO as shown in Fig. 2a is a
method by which an AP can transmit multiple
independent streams at the same time to a single
device. MU-MIMO as depicted in Fig. 2b is a
technique by which the AP can transmit multiple
independent streams at the same time to multiple
devices. In 802.11ac, MU-MIMO system supports
four users with up to four spatial streams
per user with the total number of spatial streams
not exceeding eight.