Wireless Networking: Signal Behavior

Today I am going to be discussing wireless signals and how the environment interferes with wireless communications. 

The type of reactions that can happen to a wireless RF signal are: 

1. Signal Reflection
2. Signal Scattering
3. Signal Refraction
4. Signal Diffraction
5. Signal Absorption 

Reflection- Signal reflection occurs when an RF strikes a large, dense, smooth or conductive surface and bounces in a predictable direction rather than being absorbed or passing through the material. Common surfaces that cause reflection are metal, mirrors, large bodies of water, and concrete walls. Signal reflection is a major cause of multipath propagation. Multipath propagation is when multiple copies of the same transmitted RF signal (which carry the same information) arrive at a receiver at slightly different times. 

Scattering- Signal scattering is a wireless phenomenon that occurs when an RF signal strikes an extremely rough, irregular object. Unlike reflection, which causes the signal to bounce in a predictable direction from a large, smooth surface, scattering causes the signal to disperse into many smaller, weaker waves that travel simultaneously in multiple, unpredictable directions. Although both scattering and reflection disperse, the key difference is that reflection happens from smooth surfaces while scattering happens from rough surfaces. Reflection causes predictable directions, but scattering causes unpredictable directions. 

Refraction- Signal refraction is a wireless phenomenon in which an RF signal bends as it passes from one medium into another with different density or electromagnetic properties. Refraction occurs because the speed of the signal changes as it transitions between environments such as moving from air through a glass window or between layers of air with different temperatures. 

Diffraction- Signal diffraction is a wireless phenomenon in which an RF signal bends and spreads around  the edges of obstacles and openings in its path. Unlike reflection, where the signal bounces in a different direction, diffraction allows the signal to travel into shadowed areas even when there is no direct line of sight between the transmitter and the receiver. Examples include the bending around the edges of large furniture (bookshelves, cabinets), doorway edges, and building corners.
Definition: A shadowed area is the region behind an object where the direct line of sight is blocked or significantly weakened. Imagine facing a really tall hill that has a decline ahead, when you are facing the hill the area behind the decline is the shadowed area. 

Absorption- Signal absorption is a wireless phenomenon where the RF signal is taken in (absorbed) by a material rather than passing through it, reflecting from it, or scattering around it. As an RF wave strikes an object such as a concrete wall, a wooden door, water, and the human body, some of the electromagnetic waves energy is converted into a small amount of heat within the material. This reduces the overall strength of the signal that will continue after the obstacle. The signal that got absorbed is no longer traveling after it has been converted into heat.