![]() ![]() ![]() The RF doesn’t “stop” at the -65dBm Primary coverage boundary (represented by the black circles around each color), but instead dissipates (diffuses) as it moves away from the antenna. Notice how, in the picture above, the APs are simply moved closer to each other. Secondary Coverage Example (click on the graphic) Let’s now move the APs a little closer to each other to see the effect. The real question is whether or not that level of coverage meets the needs of the client devices and applications. Unless there is no overlap, you will always have some level of Secondary coverage. Now, try calculating the overlapping area of two 3D irregular blobs (instead of spheres), and get back with me when you have that figured out. ![]() If that seems a bit confusing, then try this authority instead. If you’d like to better understand the calculations behind sphere/sphere intersection (as if AP coverage patterns are spheres/circles!), please reference this authority on the subject. That “15-20% overlap” guidance you get from manufacturers’ design guides is non-sense. There are only four kinds of channel overlap: None, Some, Less, and More. Primary Coverage Example (click on the graphic) If that AP dies, is disabled, or stops beaconing, then the signal level from the second strongest AP (called “Secondary” coverage) may be weak (or even zero), not providing the level of service that you expect for your client devices. 25dB) to every “square foot” (also, “square meter”) of the facility from one AP. When designing for Primary coverage only (where overlap is incidental), the goal is to provide the desired RSSI (e.g. It is not a separate thing from Primary coverage. “Secondary” coverage is simply a reference to the intensity of coverage you’re providing – a measure of how much signal overlaps, at what RSSI, in a given area. The goal of this blog is to quickly and visually explain the difference between the two. For those of you who have attended an Ekahau ECSE course or my CWNA course, you will remember the discussions of “Primary” and “Secondary” RF coverage when using predictive modeling software to design your Wi-Fi infrastructure. ![]()
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