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Purdue, USF test-drive Cisco CleanAir, uncover RF interference

New 802.11n radio chip monitors RF to show hidden interference

By , Network World
April 28, 2010 11:10 AM ET

Network World - Asked if he was interested in being a beta test site for Cisco's newest Wi-Fi controller software and access points, Purdue's Scott Ksander clearly remembers his reaction. "Beta tests come and go, so there's a natural skepticism," he says. "I thought 'it might be interesting.' Then, when we got it, it really was interesting. We sat there saying, 'Good Lord, look at that.'"

"That" is what Cisco calls its CleanAir technology for mitigating interference. Essentially, Cisco migrated a chunk of the radio spectrum analysis code, Spectrum Expert, from its Cognio acquisition into a Cisco-designed radio chip for a new line of 802.11n access points, the Aironet 3500 series. The algorithms capture RF data, process it and pass it upstream to a Cisco wireless LAN controller and the Cisco Wireless Control System (WCS) for analysis and display.

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With this combination of silicon and software, network administrators can see a live view of the radio frequency noise on their network, identify specific interferers and, with other Cisco products, locate the source and automatically change channels to improve performance for end users linked to that access point.

Among Cisco's rivals, Ruckus Wireless promotes interference avoidance and mitigation based on its patented antenna design, which is made up of different components that can be reconfigured on the fly to "shape" an optimal RF signal for each wireless client, in response to inference.

Cisco's new chip lets the access point radio handle data traffic as usual, but also lets it monitor its assigned radio channel for other RF activity. Alternatively, the access point can be changed into a RF scanner only, able to monitor all channels on all its frequencies. Based in silicon, CleanAir provides very fast response without affecting the access point's radio performance or CPU cycles.

The combination gives Cisco WLAN administrators something they never had before: a real-time remote view of the RF interference anywhere in the network. Cisco integrated CleanAir technology with its existing Radio Resource Manager (RRM) application, so that once an interferer is found, the access point can reset automatically to a different, cleaner channel or change its radio power level. CleanAir data can also be processed by Cisco's Mobility Services Engine (MSE), which can pinpoint where the interfering radio can be found.

In the case of Purdue, the university got the beta code and a handful of the new 3500 series access points. It deployed some of them at the Union, a major congregating point for students and staff, where there's a diverse radio environment. To the astonishment of Ksander's team, CleanAir identified a previously unknown radio interferer: a Motorola Canopy radio, used for high-throughput wireless backhaul or similar applications.

"We really didn't expect that," says Ksander, who is the university's executive director of networks and security. "We're still looking for it." Without more access points and the other tools in the beta code, they haven't been able to track down the Canopy transmissions, which could be on campus near the Union or in a building off-campus.

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