 waves (such as sound or radio waves) propagating between a transmitter and a receiver, as well as to pre- dict whether obstructions near the line joining the transmitter and receiver will cause significant interference. New Radio Access Physical Layer Aspects (Part 1) 289 It must be noted that all antenna properties and attributes that we consider in this section assumes far-field patterns. The distance from an antenna, where far-field conditions are met, depends on the dimensions of the antenna relative to the wavelength. For smaller antennas, the wave fronts radiated from the antenna become almost parallel at much closer distance compared to electrically large antennas. A good approximation for small antennas is that far-field conditions are reached at r 2 21. For larger antennas, that is, reflector antennas or array antennas where the dimensions of the antenna L are significantly larger compared to the wavelength L, the far-field distance is approximated as r~2L2/A[26,33]. Macroscopic fading is caused by 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 follows: The reference distance do corresponds to a point located in the far-field of the antenna typi- cally 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 environ- ment that 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 ~ N(0, o2) denote a zero-mean Gaussian random variable with standard deviation o when measured in decibels, then The value of X is often derived empirica