10 Must-Know Facts about MU-MIMO Wi-Fi
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10 Must-Know Facts about MU-MIMO Wi-Fi

By Enterprise Networking Mag | Friday, September 27, 2019

MU-MIMO is a big breakthrough in wireless connectivity as it allows multiple Wi-Fi devices to receive data at the same time and is a valuable asset for high-density networks.

FREMONT, CA: MU-MIMO stands for multi-user, multiple input, multiple output, and is a wireless technology supported by routers and endpoint devices. The evolution of single-user MIMO (SU-MIMO) has lead to the next level—MU-MIMO. This technology was created to support accessing of a wireless network by multiple users at the same time. In other words, it was designed to accommodate many antennas on a wireless router used for both receiving and transmitting and thereby improving the capacity of wireless connections. Usually, when multiple users try to access the router at or around the same time, users will be allowed to access based on priority, leading to congestion. It also leads to wastage of time when the remaining users need to wait when a user is already accessing.

To overcome this congestion, MU-MIMO allows multiple users to access the router at the same time. MU-MIMO technology is also referred to as Next-Gen AC or AC Wave 2, the AC part relating to the 802.11ac (Wi-Fi 5) protocol. With the introduction of 802.11ax (Wi-Fi 6) standard, there are more improvements to MU-MIMO. Thus, with the emergence of 802.11ax wireless routers and access points (AP), one must be well educated about MU-MIMO.

Here are ten facts about MU-MIMO Wi-Fi.

MU-MIMO can be one-way or two-way

MU-MIMO with 802.11ac works only with downlink wireless connection. Regardless of the streams of data, only wireless router and APs can simultaneously send data to multiple users. Although the wireless devices such as smartphones, laptops, or tablets can individually send multiple streams of data using SU-MIMO, they still send data to a wireless router or AP by taking turns.

When it comes to Wave 2 of 802.11ax, these wireless devices will be able to send data in simultaneous streams. Also, the wireless devices can get data from a wireless router or AP, while sending back at the same time. Because of the back and forth ability to send and receive data via MU-MIMO, the speed of the communication process is increased.

802.11ax (Wi-Fi 6) supports more simultaneous MU-MIMO streams

Because 11ac standard allows only up to four clients in MU-MIMO group, a wireless router or AP is restricted to simultaneously sending data to four devices at a time. However, 11ax allows up to eight clients to be in a group, thereby helping speed up connections and increasing throughput.

OFDMA technology complements MU-MIMO

OFDMA technology, otherwise known as Orthogonal Frequency-Division Multiple Access, is a part of 11ax. It involves the division of channels into smaller segments that allows multiple devices to talk simultaneously in their own channel segment called resource unit (RU). It does not directly increase the data rates but will enable devices to communicate faster by making use of the channels efficiently.

Although both the technologies, OFDMA and MU-MIMO allow devices to transmit simultaneously, they are incredibly different. While OFDMA can help in high-density environments with low throughput applications like IoT sensors, MU-MIMO can aid in high throughput applications.

MU-MIMO possesses beamforming ability

MU-MIMO has a separate feature with 11ac and 11ax known as beamforming that directs signals towards intended wireless devices rather than in all directions. This capability allows the signals to be used efficiently while increasing Wi-Fi ranges and speeds.

MU-MIMO with 802.11ax (Wi-Fi 6) works in both the 2.4GHz and 5GHz bands

When SU-MIMO works in both the 2.4GHz and 5GHz bands, MU-MIMO with 11ac is supported only in the 5GHz band. But MU-MIMO with 802.11ax works in both the bands. This is one of the most significant improvements to 2.4GHz, which was initially a congested band that can only support up to three non-overlapping channels at a time. MU-MIMO with 11ax helps save the 2.4GHz band by speeding it up and making it more usable in dense environments.

MU-MIMO supports legacy devices

Although there are no direct benefits for legacy 11n and 11ac Wi-Fi devices, they see indirect benefits with respect to the range or performance improvement of their connections to 11ax APs or wireless routers. Wi-Fi comprises airtime, that is the time for which if any device is served faster, there will be more time for other devices. The newer technologies like MU-MIMO and OFDMA can help serve supported devices quicker, providing more airtime for other devices, including legacy ones.

Multiple antennas for uplink MU-MIMO

With 11ac, wireless devices do not require multiple antennas to receive MU-MIMO streams from APs and wireless routers. If the wireless device has only one antenna, it can still receive one MU-MIMO data stream from an AP. But with uplink MU-MIMO, wireless devices should have at least two antennas to transmit with MU-MIMO back to the AP or wireless router.

More the number of antennas, higher will be the device ability to support data streams simultaneously as in one stream per antenna, which would be good for the device’s Wi-Fi performance. However, installing multiple antennas in a device accumulates more space and requires more power, leading to additional cost. It requires eight antennas to take full advantage of the 11ax features.

MU-MIMO increases network speed and capacity

When Wi-Fi speed is increased, network capacity is also increased. Thus, the airtime to serve more devices increases with a rise in the number of devices served. MU-MIMO can help alleviate congestion on busy or dense networks, such as Wi-Fi hotspots.

MU-MIMO increases security

The router or AP scrambles data before sending it via airwaves, and the only intended receiving device can unscramble it. MU-MIMO masks the data from eavesdroppers, thereby boosting Wi-Fi security, especially on Wi-Fi networks such as hotspots or those secured with the pre-shared key or personal mode of WPA or WPA2.

With 802.11ac, data scrambling was realized on the downlink, but with 11ax security is bolstered in uplink connections as well.

MU-MIMO supports any channel width

One excellent way to increase throughput on a Wi-Fi channel is via channel bonding involving a combination of two adjacent channels and creating a single channel that is twice as wide, thereby effectively doubling the Wi-Fi speed. When the 11n standard supported 40MHz wide channels, the first wave of 802.11ac supported 80MHz wide channels, the second wave of 802.11ac supported 160MHz wide channels that remained for 11ax.

Even if the network uses narrow channels, which are 20MHz or 40MHz wide, MU-MIMO helps systems to run faster by serving some clients simultaneously. Depending on the number of supported devices on the network, and the number of streams each device supports, the speed of the network varies. But using MU-MIMO, even without implementing wide channels could more than double the downlink of each device.

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