Wireless Communications

Four Laws of Nature and Society: The Governing Principles of Digital Wireless Communication Networks

Andrew J. Viterhi

Four laws, two each from the natural sciences and the social sciences, have formed the basis for the development of digital wireless communication networks. This essay describes their interaction, as well as their logical support for spread-spectrum multiple-access techniques.

E.l OverviewThe first two laws are lawrs of nature, while the last two, though often mistakenly thought as such, are in reality laws of behavior. The order is in the sequence of their discovery and their importance; additionally, as the field of wireless communica­tions has matured, the emphasis and immediate relevance has shifted gradually downward in the list. Without an appreciation for Maxwell's and Hertz's theories, there would be no controlled wireless propagation of electromagnetic waves. Without an understanding of Shannon's theories, efficient use of the spectrum through sophisticated signal processing could not be achieved. Without the conse­quences of Moore's law, these signal processing techniques could not be imple­mented in a useful and economic fashion. And finally, Metcalfe's law, which we shall explore last, helps to predict the success or failure of large new network deployments and, consequently, the wisdom of business strategies involving pro­portionally large capital investments.

!.2 Wireless Propagation and Its Anomalies

In a remarkable sequence of achievements in theoretical and experimental physics toward the end of the nineteenth century, the basis for electromagnetic propagation was established and proved both theoretically and experimentally. Though numer­ous academic researchers, residing in the musty lecture halls and laboratories of that period, shared in the success, the two that stand out are James Clerk Maxwell and Heinrich Hertz. Maxwell's equations, learned by every electrical engineering under­graduate as the elegant synthesis of all the fundamental laws of electricity and mag­netism, represents the framework upon which, with the aid of a few unifying steps, the theoretical proof of electromagnetic wave propagation is readily constructed. Hertz was perhaps the first to verify this theory experimentally Thereafter, just after the turn of the century a succession of pioneering "communication engineers" de­fined this new profession with gradually more convincing experimental successes, culminating in commercial deployments for which the name of Guglielmo Marconi stands out for his outstanding blend of experimental and business acumen. Our pur­pose, however, is not to review the scientific and historical record, far better re­counted elsewhere, but to note the particular features that impact modern wireless multiple access communication embodied in digital cellular networks.

Thus, we take for granted electromagnetic propagation but, as discussed in several chapters of this volume, note that the direct path from transmitter to receiver may not be the only path of signal propagation and, in some cases, may be blocked and hence attenuated far more than other indirect paths created by reflec­tions off terrain or buildings. Consequently, for a transmitted signal -
Download this Book to be continued - Read Comments To Download