Diffraction is the bending and spreading of wireless waves around the edges of obstacles such as walls. It can allow communication without a clear line of sight between transmitter and receiver. section 18.1.2
In wireless LAN planning, diffraction is one factor shaping coverage and reliability alongside absorption, reflection, refraction, scattering, and free-space path loss. section 18.1.2 section 18.1.1
Urban coverage
Diffraction can help a wireless signal reach street-level or indoor areas that are not directly visible from a cell tower or wireless access point. section 18.1.2
Figure 18.4 Phenomena affecting the behavior of electromagnetic waves include absorption by a medium, reflection off surfaces, refraction (bending) as waves pass through a medium, diffraction around obstacles, and scattering from irregularities.
Compare diffraction with absorption, reflection, refraction, and scattering in the diagram of electromagnetic-wave behavior. section 18.1.2
