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Beating WLANs into submission, Part 2: Beamforming

Maximizing throughput, reducing interference

Wireless Alert By Joanie Wexler, Network World
February 18, 2009 12:01 AM ET
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Industry analysis by expert Joanie Wexler, plus links to the day's wireless news headlines

Network World - You've probably heard mentions of a nascent RF capability called transmit beamforming. A couple things to keep in mind: 1) There are various types and implementations of beamforming, so not all beamforming is created equal (or standard); and 2) in large, all-wireless environments, some flavor of beamforming will eventually be needed to allow all types of client devices to run at an optimal, predictable rate and to alleviate unnecessary and troublesome interference.

That said, what the heck is beamforming? Well, it involves a wireless LAN access point (AP) concentrating and focusing energy directly at a receiving Wi-Fi client device. One goal is to improve signal reception at the client and, as a result, deliver improved and consistent throughput. Another is to avoid the unnecessary interference often caused by today’s omnidirectional antennas, which assume a client is every bit as likely to be in one place as another. They thus blast energy in all directions, wasting a good amount of energy that also creates undesirable interference.

There are two primary implementation approaches to beamforming today: chip-level beamforming (and within this category, there are several implementation types to be discussed at a later time) and antenna-based beamforming. Here are the basics.

* Chip-based beamforming
Cisco’s new 1140 Draft N AP contains a proprietary type of chip-level beamforming called ClientLink. It is aimed particularly at protecting investments in 802.11a and 11g technology in a mixed-mode 802.11a/g/n Wi-Fi environment by improving signal gain in the legacy client devices. It does this without requiring client feedback—a key difference in the Cisco implementation compared with the emerging 802.11n optional standard for beamforming. In the draft 802.11n standards, both AP and client must have the beamforming capabilities.

* Antenna-based beamforming
Startup Ruckus Wireless built its business on this type of dynamic beamforming, which is not confined to its 802.11n products. Sometimes also known as smart antenna technology, this approach requires beamforming on the AP side only. Antenna firmware continually gathers information about the client environment and adjusts transmissions accordingly to keep them optimally focused at all times. They do this by maintaining thousands of possible connection paths to a given client and dynamically selecting, on a per-packet basis, the best path to a particular client. The “best path,” in technical terms, is the one in which the amplitude of the signals emitted from both communicating devices match up, or are in phase.

More on the various facets of beamforming in a future newsletter.

Read more about wireless & mobile in Network World's Wireless & Mobile section.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.

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