 is caused by scattering, reflection, diffraction, and refraction of the radio waves by static and moving objects, as well as the medium. It is obvious that different propagation mechanisms results in different channel and path loss models. As a result of wave propagation over multipath fading channels, the radio signal is attenuated due to mean path loss, as well as macroscopic and micro- scopic fading. In an ideal free-space propagation model, the attenuation of RF signal energy between the transmitter and receiver follows the inverse-square law. The received power expressed in terms of transmitted power is attenuated proportional to the inverse of Ls(d), which is called free space loss. The received signal power can be expressed as follows: (9-1) Where Pt and Pr denote the transmitted and the received signal power, G and Gr denote the trans- mitting and receiving antenna gains, d is the distance between the transmitter and the receiver, and A is the wavelength of the RF signal. Macroscopic fading is caused by the shadowing effects of buildings and natural obstructions, and is modeled by the local mean of a fast fading signal. The mean path loss Lp(d) as a function of distance d between the transmitter and receiver is proportional to an nth power of d relative to a reference distance do. In logarithmic scale, it can be expressed as: Lp(d)=Ls(do)+10nlog(d/do) (dB) (9-2) The reference distance do corresponds to a point located in the far field of the antenna, typically 1 km for large cells, 100 m for microcells, and 1 m for indoor channels. In the above equation, Lp (d) is the mean path loss which is typically 10n dB per decade attenuation for d>>do. The value of n depends on the frequency, antenna heights, and propagation environment, and is equal to 2 in free space. The studies show that the path loss Lp(d) is a random variable with log-normal distribution about the mean path loss Lp(d). Let X(0, o2 denote a zero-mean Gaussian random variable with standard deviation o when measured in decibels, then: Lp(d)=Ls(d