RF Propagation

Basic propagation models
Reflection
Diffraction
Scattering

• Reflection

Reflection occurs when a propagating electromagnetic wave is incident upon an object which has very large dimensions when compared to the wavelength of the propagating wave
Reflection occurs from the surface of the earth and from buildings and walls

• Diffraction

Diffraction occurs when the radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities (edges)
Building edges, roof tops

• Scattering

Scattering occurs when the medium through which the wave travels consist of objects with dimensions that are small compared to the wavelength .
Rough surfaces , Sign posts
Essentially, the radio waves interact with the physical environment along each of these paths.
There are typically (unless you are in free-space) many paths from the transmitter to the receiver.
Each path is called a multipath.

• Fading

Fading occurs when there is more than one transmission path to the MS or BTS, and therefore more than one signal is arriving at the receiver.
This may be due to buildings or mountains, either close to or far from the receiving device.

• Rayleigh Fading

This occurs when a signal takes more than one path between the MS and BTS antennas.
In this case, the signal is not received on a line of sight path directly from the Tx antenna.
Rather, it is reflected off buildings, for example, and is received from several different indirect paths.