12.2.3 Wireless Surveys and Heat Maps

12.2.3 Wireless Surveys and Heat Maps Range, interference, and signal strength constitutea complex set of factors that must be considered when designing a wireless network. Additionally, the designer must account for the number of devices in close proximity(device density), how much they move around the site, and special traffic requirements, such as voice or video conferencing. Awireless surveyis a critical planning tool to ensure that the WLANdelivers acceptable data rates to the supported number of devices in all the physical locations expected.The area served by a single AP is referred to as abasic service area(BSA). The area where stations can roam between access points to stay connected to the same ESSID is anextended service area(ESA). A wireless site survey ensures that these areas are properly sized.A wireless survey is performed first by examining the blueprintsor floor plans of the premises to understand the layout and to identify features that might produce radio frequency interference(RFI). This can be backed up by a visual inspection that may reveal things that are not shown on the blueprints, such as thick metal shelving surrounding a room that needs to have WLAN access. Each AP mountingpoint needs a network port and power jack, so it will help to obtain plans that show the locations of available ports.The next step is to create a new plan on which you will mark the basic service areas and associated APs and booster antennae. The idea here is to place APs close enough together to avoid "dead zones"—areas where connectivity is difficult or data transfer rates are below an acceptable tolerance level—but far enough apart that one AP does not interfere with another or that one AP is overutilized and a nearby one underutilized.Position an AP in the first planned location, then use a laptop with a wireless adapter and a wireless survey tool to record signal strength and supported data rate at various points in the intended BSA. Many tools can show the signal strength within a particular channel obtained in different locations as a graphical heat map. The heat map would show areas with a strong signal in greens and yellows with warning oranges and reds where signal strength drops off. This step is then repeated for each planned location. Neighboring APs should be configured with non-overlapping channels to avoid interfering with one another. It may also be necessary to adjust the transmit power of an AP to size its BSA appropriately. Transmit power is a setting that configures the device to use less than its maximum output.