March 2004 — Features
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Finding Waves
Channel Allocation
The final step in any site survey is to configure the access points to broadcast on nonoverlapping channels. Every access point allows configuration of a channel to broadcast on. If your campus is using the 802.11b wireless networking standard, then there are 11 different channels to choose from. However, it is vital to understand that some of these channels overlap with each other. For example, Channel 1 and Channel 2 are very close to each other in the radio frequency band; therefore, wireless network cards have a difficult time differentiating between the two channels, which results in a slower wireless network.
It is possible to overcome this channel-overlapping problem by using proper channel allocation. In the 802.11b standard, Channels 1, 6 and 11 are referred to as "clear" channels. These channels have very few interfering frequencies and therefore can exist together without network degradation. When configuring a WLAN, be sure to place access points running on identical channels as far away from each other as possible.
CERMUSA found that using the three channels was sufficient for wiring its academic buildings. However, extending the WLAN into the "green spaces" between buildings without overlapping channels was not possible. CERMUSA is currently researching additional wireless standards such as 802.11a to overcome the challenge of these green areas.
Which Method Is Best?
Each of the methods has its strengths and weaknesses. The one that will work best for your facility depends on your budget, time and documentation needs. If you are simply trying to create wireless access in a single classroom or laboratory, then the e-witching method is best. However, if you are trying to create a wireless campus consisting of several buildings and you require extensive documentation, then computer modeling is the way to go. For site surveys that fall somewhere in between, the scientific divining method will provide a sufficient balance between documentation and cost to be effective.
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