The Mobile Wireless Path

A mobile wireless system communicates between a base station and mobile units via the propagation of radio waves over a path. In an ideal world, the path would be free of obstruction, i.e., have a line of sight (LOS) between transmitter and receiver and attenuate the transmitted signal by a fixed amount across the transmitted signal spectrum, resulting in a predictable and undistorted signal level at the receiver input. Such attenuation is referred to as free space loss. In the real mobile world, however, paths are rarely LOS. Rather, they are mainly non-line-of-sight (NLOS), and the intervening topography and atmospheric conditions normally result in a received signal that deviates significantly from ideal. Changes to the received signal over and above free space loss are referred to as fading. In this chapter, we examine propagation in an ideal environment and then study the various types of fading and how such fading impacts path reliability.