March 2004 — Features
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Finding Waves
The steps involved in the site survey using scientific divining are identical to the steps used in e-witching with one exception: The surveyors are now responsible for writing the signal strength for a zone on the spreadsheet. Several access point locations should be surveyed when using this method. If time allows, every location that is a candidate for placement of an access point should be evaluated. For each access point location, the surveyor must use a new printout of the spreadsheet and note the location of the access point during the survey.
Once all access point locations have been surveyed, it is time to determine the most efficient placement. Use the data collected on the spreadsheet in combination with the map(s) to determine which combination of locations provides the best coverage for your needs. The goal is to cover the area with the fewest number of access points. With the data from every survey, a composite of the most suitable locations can be created to visually show which areas will be covered by which access point.
The advantage of scientific divining over e-witching is that documentation is created which shows coverage is complete. In addition, it may be determined that fewer access points were needed than originally thought. The disadvantage of this method is that it requires notably more manpower and time to complete than e-witching.
Computer Modeling
The e-witching and scientific divining methods of performing a site survey are ideal for small, contained environments that have the necessary resources to perform complete surveys. However, when dealing with larger campuses with several buildings, computer modeling may be the most efficient method of performing a site survey. Computer modeling involves creating virtual representations of buildings within a software package and using this model to determine the best locations for the access points. The software package chosen by CERMUSA for computer modeling was SitePlanner from Wireless Valley Inc. (www.wirelessvalley.com).
The first step in computer modeling is to draw the building(s) within the software. SitePlanner allows existing CAD drawings to be imported into the software. If CAD drawings do not exist, then it is necessary to draw the buildings using the drawing tools included in the software. When a building is imported or drawn in the software, each type of building material is given a different signal-attenuation value because some building materials obstruct radio signals more than others.
Once all the floors of a building have been modeled in the software, it is time to begin virtually placing access points. The user tells the software where he or she thinks would be the best places for access points. Once all access point locations are entered, the software will run a prediction and create predicated coverage maps. The coverage maps show the predicted signal strength throughout the building using various colors to represent different signal strengths. If there are spots that need coverage where the software shows there is little or no coverage, then it is necessary to rethink the access point placement and run the prediction again.
