Test: Can Mu-Mimo really boost Wi-Fi capacity?

MU-MIMO is a feature of the 802.11ac Wave 2 standard that can boost Wi-Fi capacity, this test finds.

MU-MIMO enables multiple client stations to receive unique but simultaneous transmissions from a single access point (AP).

Until this advance, each associated station had to wait its turn via the normal contention process and subject to whatever vendor class/quality-of-service mechanisms might be implemented, available, and applied in a given installation.

[ Check out The future of Wi-Fi: The best is yet to come. ]

Importantly, most clients, and especially highly mobile clients like handsets and tablets, are typically limited to only one or two MIMO streams. Consequently, clients typically have demands for throughput well below what can be provisioned in a single transmit cycle from a given AP. Given that Wave 2 enterprise-class 802.11ac APs usually implement three and increasingly four MIMO streams, significant additional network bandwidth and overall system capacity could thus be made available via MU-MIMO.

How to boost Wi-Fi capcity

The question, of course, is how much of a gain can be expected. Most Wi-Fi implementations today enable literally dozens of tweaks to system settings, each with the potential to improve overall throughput and/or capacity, spread across APs, clients, drivers and management consoles, and must also deal with the fundamental vagaries and uncertainty inherent in wireless communications of any form. It can therefore be difficult to evaluate the potential of any given enhancement, like MU-MIMO, under typical operating conditions. A more specialized testing environment is thus required.

So, for this test the objective was to determine what, if any, benefits might accrue from the application of MU-MIMO and to quantify these in an RF-isolated, repeatable test environment thus realizing the long-sought-after level-playing-field, apples-to-apples setting.

Recent advances in the state of the art of wireless testing and performance evaluation allowed us to configure exactly such a platform, and to perform the required testing and evaluation of the results quickly, repeatably, and efficiently – and with a high degree of confidence that our results do, in fact, provide guidance for the setting of both Wi-Fi customer and end-user expectations for MU-MIMO in production environments.

Blocking radio-frequency interference

Farpoint Group has been testing wireless products for more than a quarter of a century, with almost all of these tests performed in freespace – the open air in a given location and physical environment. Because the nature of RF propagation is non-deterministic, given such artifacts as multipath, building construction, and a number of forms of signal fading, we’ve always attempted to average-out externalities via a variety of procedural measures.

Among these are monitoring tests using a spectrum analyzer (after an initial assessment of the state of the spectrum required using this equipment, of course), the use of turntables to eliminate antenna orientation at least on the battery-powered client end, and the averaging of multiple, relatively lengthy (1.5-3 minutes each) test runs, along with the rejection of any clearly anomalous results via substituting the results of yet another test run. While we believe such was indeed the best that could be done at the time and did in fact create a mostly level playing field, it was impossible to guarantee that such results would be repeatable in another physical environment, or even at another time, and consequently a degree of uncertainty existed no matter what steps were taken.

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