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Make Wi-Fi Visible #6 - Radio Frequency Absorption

12/27/2014

1 Comment

 
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 #6 - Radio Frequency Absorption

Let’s finish this first series of article with absorption! Absorption is the fact that a radio wave loses some of its energy going through a medium or an obstacle. A radio wave will typically lose some of its energy as it travels trough the air du to absorption.
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Light waves are easily absorbed. Indeed, the simple fact of blocking a flashlight with your hand will block the light. A wall will also totally block light. Some other materials like glass will let the light pass through with less absorption.
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As you probably understood, absorption depend on the material the radio wave goes through. Typically, a Wi-Fi wave will be less absorbed going through a dry wall than going through a brick wall. While deploying Wi-Fi, it is important to keep in mind what objects absorbe Wi-Fi radio wave the most in order to find the best APs locations. Performing on-site site survey will help you determining the absorption of the objects of your environment.


Written by François Vergès
1 Comment

Make Wi-Fi Visible #5 - Radio Frequency Scattering

12/12/2014

0 Comments

 
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 #5 - Radio Frequency Scattering

Radio waves are sometimes scattered. It happens when the diffusion of the signal is reflected in multiples directions when hitting an uneven surface. It could be the sunlight going through a cloud or a radio wave hitting a rain drop.
Scattering is illustrated below:
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If we think of sunlight going through multiple clouds, some clouds will be thicker and some others will be thinner. The light will be scattered since it will be reflected unevenly as illustrated below:
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As a Wi-Fi professional, it important to remember that as the scattering of a signal continues to occur, the signal will lose its integrity and eventually die off. Scattering could happen indoor if you have a lot of inside trees. It could also happen on outdoor Wi-Fi bridges while raining as the signal hits rain drops.


Written by François Vergès

"Episode #1 - Radio Frequency Propagation" is still available!
"Episode #2 - Radio Frequency Reflection" is still available!
"Episode #3 - Radio Frequency Refraction" is still available!
"Episode #4 - Radio Frequency Diffraction" is still available!
"Episode #6 - Radio Frequency Absorption" coming next!
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Make Wi-Fi Visible #4 - Radio Frequency Diffraction

11/3/2014

1 Comment

 
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 #4 - Radio Frequency Diffraction

Radio waves tend to bend around sharp objects creating a new wave front. This phenomena is called diffraction. This allows the waves to go around an object and still reach a receiver. Diffraction is illustrated below:
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Diffraction can be illustrated using sunlight going through a keyhole. A small portion of the sunlight going towards the door will go through the keyhole. At this moment, the shape of the wave is going to change and the light going inside will light up the room as illustrated below:
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Diffraction, in combination with reflexion, allows Wi-Fi to go around objects in a typical indoor environment avoiding it from being totally blocked. This could be very good advantage if you think about it. However, everything has a cost. A diffracted wave is indeed losing power. This is an important fact to keep in mind! Another important fact to know about diffraction: the higher the frequency, the higher the loss. In Wi-Fi deployments, diffraction will, therefore, generate more loss on 5GHz transmissions than 2.4GHz transmissions.


Written by François Vergès

"Episode #1 - Radio Frequency Propagation" is still available!
"Episode #2 - Radio Frequency Reflection" is still available!
"Episode #3 - Radio Frequency Refraction" is still available!
"Episode #5 - Radio Frequency Scattering" coming next!

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Make Wi-Fi Visible #3 - Radio Frequency Refraction

10/26/2014

0 Comments

 
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 #3 - Radio Frequency Refraction

Radio frequency refraction occurs when a radio wave is moving to a medium having a different density. The direction of the radio wave changes as it moves to the new medium as illustrated below:
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The concept of light being refracted is very familiar. It is easy to demonstrated if you light up an aquarium with a flashlight. You will see the light under water going in a different direction. Light refraction is illustrated below:
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Drywalls, wood, metal or plastic might each, in their own way, refract radio frequency since the density of the materials are different. This can have a little impact on indoor Wi-Fi deployment.

However, refraction is most likely to occur in outdoor site-to-site Wi-Fi links since refraction is usually the result of atmospheric conditions changes. Changes in temperature, existence of water vapor or air pressure can cause refraction. And since the outdoor point-to-point link has to be perfectly aligned in order to work properly, a little bit of refraction can have a bad impact on the Wi-Fi connection.

Written by François Vergès

"Episode #1 - Radio Frequency Propagation" is still available!
"Episode #2 - Radio Frequency Reflection" is still available!
"Episode #4 - Radio Frequency Diffraction" coming next!
0 Comments

Make Wi-Fi Visible #2 - Radio Frequency Reflection

10/18/2014

0 Comments

 
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:
Picture
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:
Picture


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:
Picture


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!
0 Comments
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    François Vergès

    François Vergès is the founder of SemFio Networks. As a Network Engineer, he has a real passion for Wi-Fi.

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