Despite all the advances in Wi-Fi, it is surprising how often the stumbling block for successful wireless deployment is the site survey.
The goal of the site survey is to determine the number and location of access points (APs) required to meet the Wi-Fi project’s design goals, such as coverage, performance and user capacity.
An accurate site survey is just as important as selecting the proper hardware. If the site survey is too optimistic and calls for too few APs, the final installation will yield poor coverage, poor performance, or both. This in turn will require a follow-up survey to determine what changes may be required to the number or location of deployed APs.
The end result is increased costs for additional APs and costs for more cable, equipment, contractors and installation effort. If the survey is too conservative, more APs than needed will be specified and money is wasted on unneeded equipment and labor costs.
Site surveys can be performed by a number of methods but in general fall into two groups: active and predictive. An active survey (sometimes called a live survey) uses an actively transmitting AP and a Wi-Fi-enabled laptop to measure Wi-Fi signal strength from the AP in the actual environment to determine coverage, performance, how many APs are required, and where they will be installed.
| The pros and cons Which wireless LAN site survey method you use depends on the type of project your company is working on. Some of the key considerations between active and predictive surveys include: |
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A predictive site survey uses a software package to simulate the construction of the building. Floor plans of the site are imported into the tool and allow the user to assign attenuation values (how much RF energy is absorbed) for walls, floors, cubicles, windows and other objects in the building (most tools typically have a database of materials to choose from). The application will then predict the number and location of APs required to meet the desired coverage and performance goals.
Each method has advantages and disadvantages: Active site surveys measure the real radio-frequency performance of each AP location and, because they measure real signal propagation, they innately take into account all physical characteristics and contents of the building. There is no need to estimate the thickness or density of walls or floors and provide for things like books on bookshelves, file cabinets, mirrors in the bathroom, contents of closets, insulation in walls, and ducts and piping between floors.
