Make Wi-Fi Visible #2 – Radio Frequency Reflection

October 18, 2014

François Vergès

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As we all know, Wi-Fi is amazing. The only thing is… it’s invisible.

So let’s start by explaining what makes Wi-Fi invisible? Wi-Fi uses radio frequencies electromagnetic waves to transfer information. These waves have wavelengths that are not within the visible space.

Light is also an electromagnetic wave. However, its wavelength is within the visible spectrum (between 330 nm and 700 nm). This is what make the light visible to the human eye. In fact, any electromagntic radiation having a wavelength between 330 nm and 700 nm is called “light” or to be precise “visible light”.

This means that we can explain Wi-Fi concepts using light analogies. In this set of articles, that is what we are going to do using simple drawings.

EPISODE #2 - RADIO FREQUENCY REFLECTION

Radio frequency reflection occurs when the electromagnetic wave encounters a flat surface and is reflected with a loss of energy. Reflection is such that the angle of incident is equal to the angle of reflection:

Reflection can be illustrated as below using a flashlight pointing towards a mirror. The light is not going through but is reflected by the mirror:

As a radio frequency signal is reflected, it also create multiple wavefronts. These new wavefronts will eventually reach the receiver. The receiver will then receive multiple signals at differents times. This is called multipath. Multipath occurs when a signal takes different paths to go from the transmitter to the receiver:

Reflection and multipath can have a bad impact on a Wi-Fi network since several signals, that had taken different paths, will overlap one another and will then interfere when received by the receiver.

To overcome this issue and take advantage of multipath, multiple streams and antennas are now used by the Wi-Fi technology. This has been introduced with MIMO and IEEE 802.11n.

Written by François Vergès

“Episode #1 – Radio Frequency Propagation” is still available!
“Episode #3 – Radio Frequency Refraction” coming next!

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