• Andrew Campbell

How do walls affect Wi-Fi signals?

Updated: Jul 30, 2018

Attenuation is an important physical property that all Wi-Fi designers need to be aware of to avoid dead spots, or more common today, using the wall loss as an advantage when design a high density network.

What is Attenuation?

In physics, attenuation is the loss in intensity of any kind of flux through a medium. Sunglasses attenuate sunlight, lead attenuates X-rays, and water attenuates both light and sound. In Radio Frequency (RF) communications, signals are attenuated by various mediums including walls, furniture, even people and air particles.

Attenuation does not include the decrease in intensity due to the inverse-square law, which is when the signal doubles in distance there is four times the signal loss. Therefore, calculation of the total change in intensity involves both the inverse-square law and an estimation of attenuation over the path.

How Do Walls Attenuate Signals?

Walls affect Wi-Fi signals through a combination of absorption, reflection, and in some circumstances other physical reactions such as refraction, diffraction, and scattering to name a few.

The example below shows a signal hitting a wall with some of the signal reflected back, a portion being absorbed, and the resulting signal after passing through the wall reduced in strength.

Source: Wikipedia

The same phenomenon happens with other waves in nature, whether they are radio waves or water. Imagine a wave hitting a water break wall, some of the wall reduces the strength of the incoming wave.

Different Walls = Different Attenuations

Different types of walls and other obstructions effect signal propagation with varying levels of attenuation.

Think of it in terms of sound. Some apartment complexes have little sound buffering between apartments, most likely due to using drywall with minimal sound proofing between units. You can probably even have a conversation with your neighbor between the walls.

Remember the scene from Office Space where Lawrence yells through the wall to Peter...

PETER: Lawrence, can't you just pretend like we can't hear each other through the wall? LAWRENCE: Oh! I'm sorry man, is Anne over there or something?"

*Note: If you haven't seen Office Space do yourself a favor and get on it.*

Well you get the idea... If the walls on the other hand were made out of 1 foot thick concrete, it is unlikely that Peter and Lawrence would be able to hear each other. The same applies for radio signals, concrete attenuates much more than drywall.

Typical Losses

A joint academic and industry study conducted by the University of Southern California (USC) and Magis Networks, Propagation Losses Through Common Building Materials 2.4 GHz vs 5 GHz, determined that the approximate RF signal loss for various materials the propagation losses through most building materials are almost the same for both frequency bands.

Aside from cement and brick walls which showed somewhat more loss at 5 GHz than at 2.4 GHz, the losses for all other materials tested were very close in both frequency bands.

It is important to note that some materials may vary from the typical values, for instance depending on the construction method concrete can vary widely from site to site. For materials that are not listed or that may vary from the typical values it is recommended that you measure the loss.

Keep in mind that a 3 dBm loss is equivalent to a 50% reduction in power!

Instantaneous Loss

Interior Window: 1 dB

Exterior Window: 3 dB

Dry Wall: 3 dB

Thin Door: 2 dB

Interior Door: 4 dB

Solid Wood Door: 6 dB

Steel Fire Door: 13 dB

Steel Rollup Door: 11 dB

Elevator Shaft: 30 dB

Marble: 6 dB

Brick Walls: 10 dB

Concrete: 12 dB

Refrigerator: 19 dB

Across Area Loss

Heavy Construction Building: 10 dB/m

Light Construction Building: 5 dB/m

Foliage: 2 dB/m

Human Crowd: 3 dB/m

Cubicle: 3 dB/m