Ruckus WiFi Evaluation
23rd April 2006 - Stuart Cheshire, B.A., M.A., M.Sc., Ph.D.
Introduction
According to Ruckus Wireless, by intelligent use of a six-element antenna array, their MF2900 (base station) and MF2501 (client) 802.11g wireless devices achieve superior performance compared to existing 802.11g products. By individually enabling or disabling each element independently, the device has 63 different software-controllable antenna configurations, any one of which may be the best under a given set of circumstances. For example, powering two adjacent elements simultaneously has the effect of forming a directional beam, giving increased range in that direction, and increased noise rejection of signals from other directions.
I discovered that the Ruckus devices do indeed achieve superior performance in three areas:
- Increased range.
- Increased throughput at any given range.
- More consistent throughput.
In my mind it is the third aspect, more consistent throughput, that is the most significant benefit for audio, video, and other modern applications. Most of today’s WiFi devices exhibit pretty variable throughput. Over the course of a minute their throughput can fluctuate fairly dramatically as environmental conditions change, such as people and pets moving around, or interference from cordless telephones and microwave ovens. This variability can be problematic for playback of time-based media such as audio and video. While lulls in network throughput can be survived by the use of sufficient buffering at the playback end, large buffers are undesirable both because they increase hardware cost and because they result in less responsive user interaction.
By switching antenna configuration several times per second, in conjunction with techniques to monitor how well the wireless link is performing from moment to moment in terms of application-layer traffic, Ruckus devices are able to avoid getting stuck in a low-throughput rut for extended periods of time. All WiFi networking is inherently variable, meaning that instantaneous throughput of any given link forms a probability distribution. Considering only the average of that distribution is a gross simplification. By focusing not only on improving the mean, but also on improving the low end of the distribution, Ruckus devices improve the worst-case scenario that audio and video devices have to be engineered to cope with. For example, for a video playback device playing a 10Mb/s data stream over WiFi, knowing that it can rely on getting 10Mb/s 99.99% of the time is a lot more useful than knowing it can get 20Mb/s 50% of the time (but maybe only 1Mb/s 5% of the time).
About the Author
I’m knowledgeable about networking from the Ethernet layer up, but I’m not an expert on analog radio-frequency electronics. Accordingly, I treated the Ruckus devices as “black boxes”. I’m not concerned so much with what they do at the radio-frequency level or how they do it; I’m interested in measuring the end results of whatever they do, to see if it yields tangible benefits at the IP-layer and above. As such, I may have garbled some of the explanations of how they work. For Ruckus’s own explanations of how their BeamFlex [BeamFlex] and SmartCast [SmartCast] technologies work, please consult the Ruckus web site.
I’m not affiliated in any way with Ruckus Wireless, nor have I received any payment for these experiments. My scientific curiosity was caught by their claims, and I was interested to investigate for myself. Here I present the results of my own experiments with the Ruckus MF2900 (base station) and MF2501 (client).
