How are large-scale, dense Wi-Fi networks affecting radio management issues?

Wi-Fi coverage management increasingly moving from manual to automated


One emerging issue for some enterprise Wi-Fi networks is radio management challenges as the number of access points and wireless clients grow.

Wireless LAN vendors have been adding an array of innovative features to address the issues, and to automate the network's response. But large-scale WLANs continually stretch those innovations.

Brandeis University, in Massachusetts, has a campus-wide WLAN, with Aruba Networks as the vendor. The university's IT group relies in part on Aruba's Adaptive Radio Management software, the 2.0 version of which added features to automatically shift Wi-Fi clients to different channels or frequencies for better performance, to schedule equal client access, and reduce co-channel interference among groups of access points.

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"But even with them on, we have to set some of these radios manually, particularly in the 802.11n 5GHz band," says John Turner, the university's director of networks and systems. "As we increase our density, to provide higher quality, resilient wireless access, this problem is going to get worse."

In the past, Turner says, wireless clients typically "heard" only one or two nearby access points. But in today's much denser deployments, they might hear five or six.

"Turning the power down in these situations [a common technique to reduce the size of each access point's coverage area] isn't always the best answer, because optimal coverage will be reduced," Turner says.

Brandeis has specific targets for radio gain on campus. "Our goal is to have every client at a -62dBi or better," he says. "That means in most cases they can hear two other access points in the -70's. That kind of deployment confuses clients with too many 'good' signals. We need a system that can adapt quickly to a client's needs, and adjust power and channel as the AP is loaded up."

"The key is to increase [access point] density, auto-adjust to interferences, and increase radio transmission concurrency," says Paul DeBeasi, Gartner's research vice president for network and telecom.

These kinds of functions -- radio resource management and RF spectrum management -- slowly are moving from manual adjustments to the wireless network infrastructure, says mobile consultant Craig Mathias of Farpoint Group.

Mathias uses the term "spectral assurance" to describe this group of emerging, interrelated capabilities. Aruba Networks and Meru Networks earlier this year introduced features related to this. Separately, Ruckus Wireless has promoted the interference avoidance capabilities of its patented antenna technology.

The University of South Florida and Purdue University were beta test sites for Cisco's recently introduced interference mitigation technology, CleanAir

"Within 30 seconds, the access points picked [the interference source] up, and identified the source as a microwave oven, and showed which channels were being zapped," recalls Joe Rogers, a network administrator for the university. "We could always [in the past] pull data from the access point about the level of channel noise [interference]. But now, the software tells us 'this is what's causing it, here are the channels it's killing, here's the impact on the users, and here's its location.'"

John Cox covers wireless networking and mobile computing for "Network World."



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