Demystifying MU-MIMO Technology in Wi-Fi 6
Some intimidating and mysterious terminologies like MIMO, spatial streams, and spatial multiplexing may freeze a newbie network manager's brain when deploying wireless networks. A better understanding of these techniques used in Wi-Fi 6 will minimize confusion and lead to wiser decisions in the choice of relevant products or the design of the network deployment.
What is MU-MIMO？
MIMO (multiple-input multiple-output) refers to multiple antennas used simultaneously for the transmission and multiple antennas used simultaneously for the reception all over a radio channel. Specifically speaking, "multiple-input" means multiple transmitter antennas, which input a radio signal into the channel; "multiple-output" means numerous receiver antennas, which take the output from the channel and into the receiver.
MU-MIMO stands for Multi-User Multiple-Input Multiple-Output. It is one of the most important features of the latest Wi-Fi technology standard 802.11ac Wave 2 (i.e. 802.11ac 2.0 standard), which can revolutionize the way Wi-Fi networks operate, significantly increasing the total network throughput and capacity and triple the speed of Internet access.
Depending on the number of antennas, there are SISO, SIMO, MISO, and MIMO systems. The multiple antennas feature allows MIMO systems to produce multiplexing gain and diversity gain. So, is it true that "the more the merrier"? Normally, adding more antennas on the transmitter or receiver can improve link quality and reliability, throughput between the transmitter and receiver, or both.
Multi-user MIMO algorithms are developed to enhance MIMO systems when the number of users or connections is greater than one. MU-MIMO is the next evolution from single-user MIMO (SU-MIMO). In MU-MIMO, the router divides the available bandwidth into individual streams that share the connection equally. MU-MIMO routers are available in 2x2, 3x3, or 4x4 variations, which refer to the number of streams (two, three, or four) that are created by the router. Every access point (AP) or router has a certain fixed number of streams it supports.
MU-MIMO technology utilizes the multiplexing gain of multiple antennas to expand the system throughput. The throughput of wireless networks using MU-MIMO is typically 2-3 times higher than SU-MIMO. The more antennas an AP has, the more space resources it has, and the more throughput it can improve.
MU-MIMO technology utilizes the diversity gain of multiple antennas to improve system performance. MU-MIMO allows multiple terminals to transmit data concurrently, making data transmission in wireless networks more efficient and reducing terminal wait time in timing, thus better meeting the needs of video, audio and other high-traffic, low-latency applications.
MU-MIMO helps to maximize the value of Wi-Fi devices. The signal of MU-MIMO routing is divided into multiple parts in three dimensions: time domain, frequency domain, and air domain, as if multiple different signals are emitted at the same time. MU-MIMO-enabled routers are able to work with multiple devices simultaneously. Especially worth mentioning is that multiple terminals interfere with each other minimally and resources are maximized. So MU-MIMO technology increases the capacity and efficiency of the router, enabling it to handle more WiFi-intensive activities.
How Does MU-MIMO Work?
MU-MIMO is coupled with a beamforming technique to enable simultaneous communication across multiple terminals. Unlike MIMO, which sends a different spatial stream on each antenna, transmit beamforming sends the same stream on multiple antennas with deliberate timing offsets to increase range.
The phase of each stream of data is transmitted by all antennas at different times, so these different signals interfere constructively at one point in space (i.e., the location of the receiver), thereby enhancing the signal strength at that location. When using omnidirectional antennas, the pattern created becomes effectively directional. Transmit Beamforming can therefore only work if the transmitter can derive the location of the Receiver via the use of sounding frames.
MU-MIMO brings this process one step further. By adding more radio chains/antennas, an AP can control the phased antenna pattern to control where the signal is the strongest and where the signal is the weakest. With enough antennas and knowledge about the relative positions of all associated client devices, an AP can create a phased pattern to talk to multiple clients both independently and simultaneously. Therefore, for the very first time, by using multi-user multiple-input, multiple-output (MU-MIMO) technology, a wireless Access Point can transmit to multiple Wi-Fi client devices at the same time.
Wi-Fi 6 Applying MU-MIMO Technologies With Diversities
Based on what we've discussed before, more spatial streams will bring higher throughput, but with higher hardware costs as well. A single radio of an enterprise-class Wi-Fi 6 AP supports up to eight spatial streams, delivering a throughput of up to 9.6 Gbit/s. Wi-Fi 6 which holds enormous capacity potential will provide spatial diversity for MU-MIMO applications. Enterprises must choose APs based on their service requirements for the most cost-effective solution. Furthermore, ever-changing service models drive enterprises to select APs with more spatial streams for Wi-Fi 6 network deployment.
|Service Bandwidth (Mbps)
|Video Streaming (1080p)
|Video Streaming (4K/VR)
For the majority of the enterprises in networking construction, a minimum of 30 to 40 concurrent Stations (STAs) connected to each AP are required to meet the demands for daily production or operation. If services are initiated on 20 STAs concurrently, the provided bandwidth of an enterprise-class 2x2 MU-MIMO Wi-Fi 6 AP only meets the service requirements of 1080p video streaming. For this kind of situation, Wi-Fi 6 APs working in 4x4 MU-MIMO mode or higher are more suitable. Diversified STA types drive enterprises to select APs with more spatial streams on Wi-Fi 6 networks. Wi-Fi 6 AP with 2x2 MIMO configuration and Wi-Fi 6 AP with 4x4 MIMO configuration are the two most common types on the market now.
As one of the key technologies, MIMO technology has been applied widely in the field of wireless communication with continuous development in recent years. As the enhanced version of MIMO technology, MU-MIMO technology is becoming the impetus of the trending Wi-Fi 6. With the number of Wi-Fi 6-capable STAs continues to increase, wireless networks using enterprise-class Wi-Fi 6 APs are becoming more popular than ever before. When upgrading legacy Wi-Fi networks or deploying new Wi-Fi networks, Wi-Fi 6 is the obvious choice for enterprises. And with the development of all-wireless networks, the enterprise digital transformation will be accelerated accordingly.