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All of the content in this wireless series is just a teaser for the book I’ve been working on along with some great writers and developers. The book is titled “SonicWALL Secure Wireless Networking: Integrated Solutions Guide”, link coming as soon as it’s up. The book should show up in stores later this summer.

I told ya I’d get more of these out. This article continues the series on wireless networking. Today we’ll take a look at some common 802.11 interference issues. Although the content here applies to a large commercial deployment, these techniques can also be used in home or home office setups.

These days, finding an environment with no Radio Frequency (RF) interference or noise is fairly implausible. Only if you are setting up an office in a secluded redwood grove you can count on RF interference to be a non-issue. Well… even then, the redwood trees might just be among those fitted with high-gain cellular antennas, an all-too-common occurrence today. Regardless, you should expect to deal with some level of signal interference in your deployment.
The illustration in this article shows three common RF interference types. Let’s discuss what they are and how all three can be addressed.

Radio Frequency Interference

Location A – Rogue access points or wireless test lab:
Problem – Wireless product test labs and other (valid) rogue access points are problems in many WiFi deployments. Even if the access points in question are using different SSID nomenclature, channel overlapping is almost sure to be a bandwidth buster for legitimate wireless users.
Solution – Either eliminate all rogue access points, or force their owners to use a set channel that does not overlap with your distributed wireless solution. For dedicated wireless test labs, or areas that must be secluded from RF noise, convert that specific area into a Faraday cage, blocking a significant amount of wireless signals from entering or leaving the room.

The Faraday Cage was developed by 19th century inventor Michael Faraday. It demonstrates that a room built of a conductive material will shield its contents from electric or static electric currents. This effect also exists for wireless radio transmissions, although to a lesser extent.

Location B – Spectrum noise for 2.4 GHz and 5 GHz
Problem – Your phone system is partially wireless and uses the 2.4GHz spectrum. Whenever someone in the office takes a call on this phone, wireless connection speed is reduced in the surrounding area, and to top it off, callers often complain of white noise during their conversation.
Solution – Give VoIP a try. VoIP will work in tandem with your wireless network, instead of against it. Another option is to try a phone that uses a different spectrum, or to go completely wired for your phone service. For more on SonicWALL VoIP implementation and capabilities, refer to the Configuring VoIP SonicOS feature module available at: http://www.sonicwall.com/us/support

Location C – Off-network access points
Problem – Your neighbors need wireless, too! Unfortunately, the walls that separate you are made of drywall (refer to Table 2 on page 29 for more information on physical barriers). The result is that their wireless signals plus your wireless signals equals client confusion and RF noise. Wireless clients in this area may have trouble connecting or keeping a connection if your channels overlap with those of your neighbors.
Solution – Overpowering your neighbors with high-gain antennas is an option, but not a particularly neighborly one. Instead, you could simply use a different channel for wireless access points bordering this wall and ensure that your neighbors do the same. Performance in some dual-channel wireless devices may take a hit, but it is better than dropped connections—or unhappy neighbors.

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