In addition to path loss, a signal will typically experience random variation due to blockage from objects
in the signal path, giving rise to a random variation about the path loss at a given distance. In addition,
changes in reflecting surfaces and scattering objects can also cause random variation about the path loss.
Thus, a model for the random attenuation due to these effects is also needed. Since the location, size, and
dielectric properties of the blocking objects as well as the changes in reflecting surfaces and scattering
objects that cause the random attenuation are generally unknown, statistical models are widely used
to characterize this attenuation. The most common model for this additional attenuation is log-normal
shadowing. This model has been confirmed empirically to accurately model the variation in path loss or
received power in both outdoor and indoor radio propagation environments