Multi-user multiple-input multiple-output (MU-MIMO) is a multi-user technology that plays an important role in the wireless communications field. This technology allows one AP to communicate with multiple terminals simultaneously, fully utilizing space resources and improving wireless throughput. MU-MIMO is mainly applicable to cellular networks and Wi-Fi (also known as WiFi) networks.
MU-MIMO vs. MIMO
Before we can delve into MU-MIMO, we must first understand how MIMO works. Simply put, MIMO technology divides network resources spatially, which are transmitted simultaneously through multiple antennas.
MIMO system
MIMO technology greatly improves the data transmission efficiency of a single device without occupying extra spectrum resources. MIMO has greatly contributed to the surge of Wi-Fi transmission rates — for example, evolving from 54 Mbit/s (802.11g) to 300 Mbit/s or even 600 Mbit/s (802.11n).
In a MIMO system, an AP can communicate with only one terminal at a time. This is why MIMO is sometimes also known as single-user MIMO (SU-MIMO). When the number of antennas on a terminal is the same as that on an AP, space resources of the AP can be fully effective. Practically speaking, we cannot require the APs and terminals on a Wi-Fi network to have the same number of antennas. This is because APs typically have three or four antennas, whereas most terminals (such as mobile phones) have only one or two. As a result, the APs and terminals are unable to make the most of channel resources. Case in point is a Wi-Fi 5 AP that supports 4x4 (4T4R) MIMO can provide a maximum theoretical speed of 1.732 Gbit/s. When it communicates with a mobile phone (1x1 MIMO), the maximum theoretical speed can reach only 433 Mbit/s, one quarter of the AP's speed peak. Three antennas stay idle during communication, meaning a speed of 1.3 Gbit/s is unused.
To address this issue, MU-MIMO technology is introduced. It enables an AP to communicate with multiple terminals simultaneously, thereby fully utilizing the AP capacity.
For more information, see MU-MIMO.
