How will MU-MIMO improve 802.11ac Wi-Fi?

Multi-user multiple input, multiple output, or MU-MIMO, is an advanced features for 802.11ac Wi-Fi, part of Wave 2 features that are in some cases, already on the market and will start being certified for interoperability by Wi-Fi Alliance soon.
The technology enables multiple devices to be served with simultaneous data streams, rather than juggling each device’s access on time-based slices of the available network capacity. Basically, it functions so that it’s as if each device has its own router — up to four devices, and then devices have to start sharing data streams. (Ruckus Wireless has a good primer on how the technology works here.)
Signals Research Group recently conducted independent testing of MU-MIMO for Qualcomm, utilizing Wi-Fi access points that have Qualcomm’s QCA9980 chipset and a mix of consumer electronics devices (smartphones, tablets, and laptops) with Qualcomm system-on-chips that support MU-MIMO. SRG concluded (white paper pdf) that MU-MIMO provides significant improvements to Wi-Fi, and that 802.11ac’s “real potential reveals itself with the inclusion of more advanced features that deliver even higher individual data rates under a wide range of network conditions, not to mention increased network capacity. From a consumer’s perspective, these benefits are obvious when it comes to typical applications such as video streaming.”
SRG categorized MU-MIMO’s benefits in two specific areas: capacity and data rates, ultimately leading to a better user experience because the available Wi-Fi resources are used more efficiently.
A 2×2 antenna configuration for Wi-Fi “nearly doubles the data rate at all levels of signal strength and it can dramatically improve the user experience by reducing video freezes and frame impairments,” SRG reported.
SRG tested devices with 2×2 antenna configuration and 1×1 antenna configuration and said that the former achieved 89% higher throughput over a range of tests — and was also more robust, maintaining a data connection despite an extra 6 dB of pathloss. In a congested network scenario, the 2×2 configuration was still able to stream video with little impairment compared to the 1×1 configuration.
SRG also concluded that “a Wi-Fi AP with MU-MIMO capabilities delivers significantly more network capacity, which benefits all users, including those users with a device that does not support MU-MIMO.” SRG tested capacity with a Wi-Fi AP configured to support either MU-MIMO or single-user MIMO and said that with MU-MIMO, total capacity increased by as much as 112%.
“The additional network capacity should be obvious to any user in the network,” SRG said. “Besides higher data rates, the consumer would easily notice that streamed videos would play nearly flawlessly while with SU-MIMO there would be frequent stalls while viewing the video. Interestingly, STAs without support for MU-MIMO also benefited indirectly from the additional capacity that MU-MIMO delivered.”
One of the drawbacks that MU-MIMO faces, however, is device support. Although there has been notable progress on MU-MIMO chipset support and in router deployments over the past 12-18 months, SRG noted that “we’ve noticed that a rather large percentage of smartphones do not have a 2×2 Wi-Fi antenna configuration” — that while MIMO’s use in HSPA+ and LTE cellular phones is nearly ubiquitous, the same is not true for Wi-Fi. However, newer phones do indeed support MIMO for Wi-Fi, including the Samsung Galaxy S7 and S7 Edge  and Google’s Nexus 5x supporting MU-MIMO — and the number of devices and Wi-Fi clients that support the technology will likely increase as Wi-Fi Alliance certification for Wave 2 features gets underway.
 
Looking for more information on the future of Wi-Fi? Check out RCR Wireless’ new special report.
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