multi-user MIMO

What is multi-user MIMO?

Multi-user MIMO, or MU-MIMO, is a wireless communication technology that uses multiple antennas to improve communication by creating multiple connections to the same device at the same time. MIMO is an acronym that stands for multiple input, multiple output.

MU-MIMO is commonly used in devices such as routers, and it works with mobile devices such as smartphones and laptops. The technology supports environments where multiple users access the same wireless network at once.

Typically, when multiple users connect to the same router, congestion will begin to build up as the router services the first device's requests while the other devices wait to be serviced. The amount of time each device waits is generally not long, but can build up with enough devices. MU-MIMO helps relieve this potential congestion by creating multiple connections to a device at the same time, which increases network efficiency.

MU-MIMO takes advantage of multi-path, which is when a radio signal gets reflected and bounces around surrounding objects to be picked up by a receiver in a user's device at slightly different times and angles. MU-MIMO will typically have multiple antennas at the transmit end and one antenna at the receiving end of the signal.

MU-MIMO devices separate bandwidth into individual streams that share an equal connection. These streams typically divide as 2x2, 3x3, 4x4 or 8x8, which refers to the number of streams. The data streams directly to one device, which means an MU-MIMO router can only send and receive data from one device at a time.

Network pros typically use algorithms to enable fair access to multiple devices to an access point (AP). Initially, only routers supported MU-MIMO, but as time went on, other endpoint devices started catching up.

Types of MU-MIMO

Each type of MU-MIMO has its own use case. Examples of MU-MIMO include the following:

• MIMO multiple-access channels (MIMO-MAC). Network pros use MIMO-MAC as a multiple-access channel in uplink scenarios. In MIMO-MAC, the receiver performs most of the processing, and it requires large levels of uplink capacities.
• MIMO broadcast channels (MIMO-BC). MIMO-BC enables more throughput.
• Cross-layer MIMO. Cross-layer MIMO improves the performance of MIMO links by solving problems that might happen when employing MIMO configurations.
• Dirty paper coding. Dirty paper coding is a technique that enables data to move through channels with interference more efficiently.
• Cooperative MIMO. Cooperative MIMO uses distributed antennas that belong to other users instead of ones that belong to a logical terminal.

Benefits of MU-MIMO

MU-MIMO benefits from its construction and operations in multiple ways, including the following:

• MU-MIMO's use of beamforming to direct signals toward a wireless device.
• A general decrease in the time each device has to wait for signals.
• A general increase in the capacity and efficiency of a user's router.
• MU-MIMOs are affected less by antenna correlation and channel rank loss.
• APs do most of the involved processing.
• A user's devices do not have to use multiple antennas.
• Devices that do not support the technology will still run faster on a MIMO network because devices connected to an MU-MIMO network do not have to wait as long for signals from the Wi-Fi network.
• MU-MIMO can improve video playback streams and eliminate some buffering or lower video quality.

Editor's note: This article was updated in February 2023 to improve the reader experience.