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Wireless Network Planning Around Interference

You have many factors to consider when planning a wireless network, from external sources of broad-spectrum interference to the characteristics of building materials to channel selection and range. Proper placement of your Access Points (APs) can make your network the talk of the company.

Improper placement can make you the talk of the company in not-such-a-great way, with a lot of grumbling, cursing, gnashing of teeth, and with people calling you constantly to ask why they spent so much money on a product that does not seem to be working.

Many factors influence radio frequency (RF) signals. You may get signal loss from building materials that usually comes from three main sources, which are based on the types of materials used. These three sources are as follows and are illustrated in the following figure:

  • Absorption occurs when RF waves are absorbed by the materials that they are attempting to pass through. Absorption typically occurs when the waves pass through walls or dense materials. Water and concrete have high RF absorption properties. If you need coverage in stairwells, remember that they are mostly concrete tubes with a bunch of diagonal concrete dividers.

  • Reflection occurs when RF waves cannot penetrate a surface and are returned or bounced off the surface. Reflection is common with metal and glass surfaces. Reflection is the principle behind a Faraday cage, where the holes on the cage surface are smaller than the wavelength of the radiation or signal that they are attempting to block, thereby blocking the signal that is striking its surface.

    So even a thin layer of metal containing no holes can effectively block wireless signals from passing through it.

  • Scattering occurs when the reflective surface is uneven, which causes many random bounces. A reflective signal may still have enough of its original properties to be used, but a scattered signal does not.

    In some cases where you cannot get a direct signal through to your location, you may be able to get a strong enough signal from a bounced RF wave, but only if that wave gets bounced off of a smooth surface; if the surface is uneven then the bounced signal will be useless.


The more issues you have with your signal between the client and the AP, the higher the noise level of the signal. Other sources of noise include other devices that operate in the same wireless band as your AP and devices that might cause broad-spectrum interference. Some level of noise always exists, but if the level is too high, the signal-to-noise ratio will be too low to sustain a proper connection.

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