Connect802 is a nationwide wireless data equipment reseller providing system design consulting, equipment configuration, and installation services.


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April 1, 2005

Essential Wi-Fi:
For those who are new to Wi-Fi networking...
 
Technology and Engineering:
For the engineer and Wi-Fi network administrator...
 
To Infinity... and Beyond!
News from the wireless marketplace...
 

Essential Wi-Fi

We regularly read in literature about 802.11 that 802.11b and 802.11g support 11 channels (14 total, of which only 11 are usable in the U.S., per FCC regulations) of 22 MHz each.  This statement is usually followed by the assertion that this is why only channels 1, 6, and 11 are "non-overlapping."  Until recently, we at Connect802 would have agreed with this statement, but a recent close analysis of the 802.11 standard reveals that this language is imprecise.  This month, we'll examine 802.11b and 802.11g's "channels" more closely and reveal what 802.11 really says about channels.

The definition of an 802.11b/g "channel" starts with a center frequency.  Transmissions on a channel will be most powerful close to the channel's center frequency, and will generally get weaker further from the center frequency.  Technically speaking, the signal power gets alternately weaker and stronger as you move away from the center frequency, but each "peak" gets somewhat lower the further you get from the center frequency.  A picture of the approximate power distribution of an 802.11b channel is pictured below.

What this means for the system designer is that although a standard may imply "non-overlapping" channels there is still signal energy present throughout the entire frequency band. As a result, installation of two (or more) transmitters in close proximity may result in interference even though they are on what would otherwise be considered "non-overlapping" channels. Without a doubt, installing two transmitters so that their antennas were within a foot or so of each other would probably result in co-channel interference without regard for the configuration of the two transmitters. Several feet of separation would probably minimize or eliminate this concern.


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Connectivity was required between the two hangar buildings, but consideration had to be made for the possibility that an airplane's vertical stabilizer might create an obstruction on the ramp area between the buildings.