Crash Course: Wireless Site Surveys
Posted by
Cornell W. Robinson III
May 31, 2006
AirMagnet and Ekahau, for instance, offer laptop-based tools for a walk-through site survey. AirMagnet's Survey PRO and Ekahau's Site Survey let you "visualize" your WLAN against your floor plan: You place an AP that's part of the site-survey kit in a desired location and then walk through the site with the tool. The tool records the path traversed, giving the software numerous points of reference so it can understand the propagation of the site-survey AP. The data is then used to develop an accurate visualization.
You can use these tools for outdoor WLANs as well. They integrate with a GPS receiver and use GPS coordinates as points of reference you can plot on the site map. These tools provide real signal-strength readings taken at specific locations rather than estimations based on statistical models.
They also collect data points such as nearby access points, received signal strength, AP performance, interference sources and spectrum analysis. And they use your existing Wi-Fi laptop card software and modify it for rapid channel scanning, so you're using the same WLAN NICs that provide your users access to the WLAN.
Once the walk-through is complete with the site survey AP at one location, the survey results are saved, and the AP is moved to a new location. Then, the walk-through process is repeated. These tools let you use a single site survey AP multiple times (it's configured to emulate multiple APs). Once you've gathered all measurements, you can use the tool in simulation mode and move APs around on the floor plan virtually. These simulations are helpful, but sometimes less accurate than those provided by RF modeling tools.
Note that estimation and prediction tools don't provide insight on how interference impacts WLAN performance, though they typically provide spectrum analysis, so you can sweep the site for interference. Spectrum analysis is a must for conducting a site survey for WLANs that require high availability or for congested, unlicensed Wi-Fi bands.
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