What is MU-MIMO? Why is it essential for your next wireless router?

When examining the specifications of wireless routers available for consumers and businesses, you may notice that many advertise a technology called MU-MIMO. It stands for Multi-User MIMO, and most consumer Wi-Fi routers feature 2x2 MU-MIMO, while higher-end models may offer 4x4 or even 8x8 MU-MIMO capabilities. What exactly does MU-MIMO mean, though? What does it do for your wireless router, and why is it a must-have for fast internet? Additionally, what type of MU-MIMO implementation should you look for in a router? This guide will provide you with all the information you need to understand MU-MIMO and its relevance:

NOTE: Some links in this article direct to Amazon. These are affiliate links, allowing us to earn a small commission from your Amazon purchases to fund some of the work we do at Digital Citizen. To ensure this article is as accurate as possible, I read lots of technical documentation from Cisco, Qualcomm, TP-Link, Arista, and other vendors.

What does MU-MIMO stand for?

MU-MIMO stands for Multi-User MIMO or Multi-User Multiple Input Multiple Output. It’s a wireless technology that enables routers and access points to use their antennas to transmit data to multiple network clients simultaneously, rather than just one at a time. It can also transfer data to a single network client using several data streams simultaneously, increasing the transfer speed. With MU-MIMO, a wireless router can “talk” to more than one device at a time, on a single wireless radio channel, or to one device using multiple data streams on the same channel. However, when “talking” to a router or access point, a network client can only receive or send data at a time, not both simultaneously.

When was MU-MIMO released?

MU-MIMO was introduced by the 802.11ac Wave 2 standard, which is the second iteration of Wi-Fi 5, in June 2016. In its original form, MU-MIMO was used by network clients only to download data from the router or access point they were connected to. They couldn’t use MU-MIMO to upload data. Luckily, this technology has seen continuous improvements, and today it is a core component of wireless networking standards like Wi-Fi 6, Wi-Fi 6E, and Wi-Fi 7. Wi-Fi 6 made the use of MU-MIMO mandatory and improved this technology to work for both downloading and uploading data.

How devices connect to Wi-Fi when using older standards (through SU-MIMO or 1x1 MIMO)

Older wireless routers that do not offer support for MU-MIMO use the so-called SU-MIMO method for transmitting data over a wireless radio channel. SU-MIMO stands for Single-User Multiple Input Multiple Output, meaning that one wireless channel can send and receive data to and from a network client at a time. SU-MIMO is part of the 802.11n (Wi-Fi 4) standard that was finalized and published in October 2009.

All Wi-Fi 4 routers and access points can use SU-MIMO for transmitting data to network clients and back. When using this approach, routers are good at sending and receiving data, but only in one direction, to one client at a time. If you have a wireless router with one antenna for receiving and sending data, it could connect only to one client device at a time.

For instance, let’s assume that you have three users, each with their device connected to the WiFi broadcast by the router. The router can send and receive data only to the first user. When done with the first user, it goes to the second, and then the third, and then goes back to the first, and so on.

SU-MIMO wireless transfers are made to one network client at a time

When using SU-MIMO, the number of simultaneous data streams is limited by the minimum number of antennas in use. If your router has one antenna, it can send one data stream. If the router has four antennas, it can send four data streams simultaneously, for up to four clients. The wireless router or access point acts like a machine gun mounted to a merry-go-round when using SU-MIMO. It rattles off bits of data very quickly to multiple devices, one after the other. Each device waits its turn to send and receive data, so when a new device connects, the line and the wait become longer. Therefore, the more devices you connect to a wireless router using SU-MIMO, the bigger the latency and the less speed you get for each device.

Keep these notations in mind

In some technical documentation, SU-MIMO is referred to as 1x1 MIMO. Keep this in mind when you encounter 1x1 MIMO later in this article and when reviewing technical specifications of wireless routers and access points. Many vendors of networking products also shorten MU-MIMO to MIMO for easier reading. Thus, when you see 2x2 MIMO, it refers to 2x2 MU-MIMO. More on that in the next section of this article.

This is what MU-MIMO does:

As I said earlier, MU-MIMO is the ability to transmit to several clients simultaneously, instead of just one, or to transfer data to a network client using multiple data streams simultaneously, thus increasing the transfer speed. Devices can use many different types of MU-MIMO implementations:

• 2x2 MIMO - has two spatial streams for wirelessly transmitting and receiving data on the same channel or frequency. For this implementation, you need only two antennas, and you can simultaneously connect a maximum of two clients, one on each stream.
• 3x3 MIMO - uses three antennas and offers three spatial streams for transmitting data wirelessly. You can simultaneously connect a maximum of three clients.
• 4x4 MIMO - refers to four spatial streams, requiring four antennas and allowing simultaneous connections to up to four clients. This implementation is less common in consumer Wi-Fi products. However, with the advent of the Wi-Fi 7 standard, it has gained traction, and it’s now available on routers like the TP-Link Archer BE800 and the Netgear Nighthawk RS600.
• 6x6 MIMO - a less common implementation that offers six spatial streams and requires six antennas. In my many years of testing wireless networking devices, I didn’t find this implementation on consumer products. I’ve only seen it in a few products designed for business outdoor use.
• 8x8 MIMO - offers eight spatial streams on the same wireless channel or frequency and can support a maximum of eight clients connected simultaneously. However, this implementation has significant energy requirements and is not found in battery-powered devices like smartphones and laptops. Consequently, in real-life situations, you typically connect a maximum of four devices, each receiving two independent data streams. For 8x8 MIMO, you need eight antennas, and this implementation is seldom seen in consumer wireless routers and mesh Wi-Fi systems. You can find it only on very expensive routers like the ASUS RT-AX89X.
• 16x16 MIMO - was introduced by the Wi-Fi 7 standard, requiring sixteen antennas and offering sixteen spatial streams. It can theoretically allow communication with up to sixteen devices simultaneously. However, I have yet to see it implemented on consumer routers or other networking devices.

To help you better understand how MU-MIMO works, here’s an illustration of a router supporting 3x3 MU-MIMO, communicating simultaneously with three devices. As you can see, three client devices receive data at the same time (the Smart TV, tablet, and gaming console), while only one device waits for its turn. Compare this with the previous illustration I created for SU-MIMO to better grasp how much more efficiently MU-MIMO operates.

How 3x3 MIMO works

Image source: TP-Link

IMPORTANT: When reading the specifications of the wireless router (or mesh Wi-Fi system) you plan to buy, always look for information about the type of MIMO implementation available on that specific model. If the manufacturer doesn’t advertise the MIMO implementation, it’s likely a 2x2 MU-MIMO implementation. If a router offers 3x3 MU-MIMO or more, it will deliver faster wireless transfers and be able to manage a network with greater capacity. This is something to brag about, and manufacturers will highlight their MIMO numbers when offering 3x3 MU-MIMO or more. This is especially true for the more expensive models that provide 4x4 MU-MIMO or greater.

MU-MIMO requires compatible devices

For MU-MIMO to achieve its maximum potential, it’s essential to have connected devices that support this technology. Most modern smartphones and tablets typically utilize a 2x2 MIMO configuration, which demands significantly less energy than other implementations. This is similarly true for laptops and the majority of PCI-Express wireless adapters. In contrast, IoT devices, which generally connect exclusively on the 2.4 GHz band, are equipped with only one physical antenna and operate with 1x1 MIMO.

In a typical wireless network, you use different types of devices that offer different MIMO implementations. Let’s assume that you have a wireless router with 4x4 MIMO. This router provides four data streams. Therefore, you can connect and simultaneously transfer data to two devices using 2x2 MIMO streams or four devices using 1x1 MIMO. You can also have three connected devices, one using 2x2 MIMO and two using 1x1 MIMO.

What are the advantages of MU-MIMO?

If you buy a wireless router or mesh WiFi system with MU-MIMO, you get the following benefits:

• Improved data transmission rates, multiplied by the number of available streams: 2x2, 3x3, 4x4, 6x6, 8x8, 16x16. The higher the number of streams, the higher the data transmission rates.
• Improved Wi-Fi range and reliability.
• Improved power consumption for connected devices.
• Improved latency for client devices translates to less time spent waiting to receive data from the router or access point.
• Higher network capacity. A MU-MIMO-enabled router or mesh Wi-Fi system can handle many more devices connected simultaneously.

According to Qualcomm, MU-MIMO can deliver significant speed improvements when more than four MU-MIMO-enabled clients are connected at the same time. For instance, a network with fifteen connected clients and a router with 3x3 MU-MIMO could operate with three times more data throughput compared to a network that’s not using MU-MIMO, by sending data to five groups of three MU-MIMO-enabled devices.

The downsides of MU-MIMO

MU-MIMO has evolved a lot since its release in 2016, and some of the early issues limiting its usefulness have been fixed over the years:

• Initially, MU-MIMO was available only on the 5 GHz frequency band. This was a major downside that limited its usefulness. Luckily, this problem was fixed by standards like Wi-Fi 6, Wi-Fi 6E, and Wi-Fi 7, which allow routers and access points to use MU-MIMO on all frequency bands (2.4 GHz, 5 GHz, and 6 GHz).
• One drawback of MU-MIMO was that it was limited to downloading data from the router or access point to the network client. However, the Wi-Fi 6 standard and subsequent versions have enhanced this technology, allowing MU-MIMO to also support uploading data from the network client to the router or access point.
• Another issue with MU-MIMO was its requirement for compatible devices. Such devices were hard to find in 2016, when this technology was introduced. However, this is no longer an issue. If your devices are compatible with Wi-Fi 6, Wi-Fi 6E, or Wi-Fi 7, they automatically support MU-MIMO.

Modern-day networking devices can take full advantage of MU-MIMO in most situations. However, this technology still has a few weaknesses:

• It doesn’t provide any benefit in short ranges, close to the router or access point, because network clients already receive data at the maximum possible data transmission rate.
• At longer ranges, near the edge of a wireless network, MU-MIMO does not provide significant performance gains because of the longer path that needs to be traversed by all the data streams to and back from the network client.

What is your experience with MU-MIMO?

You have reached the end of this article, and I hope I’ve answered your questions about the MU-MIMO technology. As you have seen, MU-MIMO is an essential feature of modern Wi-Fi standards. It enables networking equipment, such as routers and mesh Wi-Fi systems, to provide a significantly improved user experience, enhancing their ability to handle a large number of connected devices. My only concern with this technology is that most consumer devices implement 2x2 MU-MIMO, while 3x3 MU-MIMO options are rare and more expensive. But what are your thoughts on this technology? Feel free to share your opinions or questions about MU-MIMO in the comments below.