O'Reilly logo

Radiowave Propagation: Physics and Applications by Fernando L. Teixeira, Joel T. Johnson, Curt A. Levis

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

8

EMPIRICAL PATH LOSS AND FADING MODELS

8.1 INTRODUCTION

While the physical models studied in Chapter 7 provide insight into reflection, refraction, and diffraction effects that can occur in propagation between two locations near the Earth's surface, the simplified descriptions of the Earth surface (often modeled as a smooth sphere) and diffraction from obstacles that were used result in only moderate accuracy. The site-specific methods considered in Chapter 7 also require knowledge of terrain along the propagation path; such knowledge sometimes may not be available for fixed transmitters and receivers, or for all possible paths in communication systems involving mobile users or broadcast applications. The methods of Chapter 7 are also oriented primarily to situations involving reflection and/or diffraction from a small number of locations along the propagation path. In many propagation environments, particularly those in urban and suburban areas, there are many possible reflection and diffraction points, resulting in a highly complex propagation environment that is not easily treated using purely physical models.

In complex terrestrial point-to-point propagation problems that exceed the limitations of the methods given in Chapter 7, it is common to apply—in lieu of a physical approach—empirical models for predicting propagation losses. This is also true for point-to-area propagation problems as encountered, for example, in predicting cellular communication coverage. As often occurs ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required