ree-space loss is the easiest, the inverse-square rule with a frequency compo- nent: = 32.4 + 20 log r + 20 log f (47.5) where r = distance in kilometers f = carrier frequency in megahertz This equation has a physical reality associated with it. The 20 log r term is the inverse square of distance, the 20 log f is an inverse-square rule in terms of frequency, and the 32.4 is the constant term that scales the result. In free space, we already know that twice as far means four times the path loss, and this formula tells us that twice the fre- quency also means four times the path loss. The rooftop-to-street diffraction component Lrts adds the mobile telephone environ- ment to the radio path loss, as shown in Fig. 47.1. Lrts = - 16.9 - log W + 10 log f + 20 log hm + L (47.6) where W = street width in meters Ahm = hr - hm hm = mobile telephone height in meters hr = rooftop height in meters The L term describes the effect of the radio path orientation relative to the street, as shown in Fig. 47.2. 6COST is the European Cooperation in the field of Scientific and Technical Research (COpera- tion europiénne dans le domaine de la recherche Scientifique et Technique), which has several committees. Their Committee 231 finished its work in land mobile radio communications on April 4, 1996. The Walfisch-Ikegami model is the result of one of their studies. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Propagation Models Propagation Models Station Terminal Figure 47.1 Side view of environment for Walfisch-Ikegami model. L = -9.646 0 VI 35 L = 2.5 + 0.0075( - 35) 35 < < 55 (47.7) L = 4 - 0.0014(₫ -55) 55 < 90 where is the incident angle in degrees relative to the street. The multiscreen loss adds the base station and path environments to the total radio path loss, as shown in Fig. 47.1. Building Building Terminal Building Building Station Figure 47.2 Top v