ion in distance models is the Hata-Okumura model, de- rived from measurements in Tokyo. These estimates are a closer fit to measured data than the simpler inverse fourth power rule. The Hata-Okumura model divides the radio environment into "large city," "medium- small city," "suburban," and "open."4 The basic Hata-Okumura formula is Eq. (47.2): L 69.55 + 26.16 log f - 13.82 loghb-a(hm)+ (44.9 - 6.55 log h,) log r (47.2) 3This is good news for cellular radio because the decrease of radio power with distance is what discriminates between the nearby signal cell and the more distant interfering cells. 4It has been pointed out that the building types in Tokyo are different enough from those in the United States that the model is less valid here. Our suburban areas are somewhere between Oku- mura's suburban and open areas, and Okumura's suburbs are like our metropolitan areas with large groups of row houses. 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 where L = path loss in decibels f = carrier frequency in megahertz hb = base station height in meters hm = mobile telephone height in meters r = distance between them in kilometers All the logarithms are base 10. L is the radio path loss in decibels from the base sta- tion to the mobile telephone. In the large-city environment,5 alarge (hm) = 8.29(1og 1.54hm)2. for f < 200 MHz alarge (hm) = 3.2(log 11.75hm) 4.97 for f > 400 MHz and elsewhere a(hm)=(1.1logf-0.7)hm-(1.56 logf-0.8) = - There are also correction terms for suburban and open environments. The Hata- Okumura equations for four environments are shown in Eq. (47.3): Llarge city =Lo Lmedium-small city = L (47.3) Lsuburban = L + 2[log(f/28)]2 - 5.4 Lopen = L + 4.78(log f)2 18.33 log f + 40.94 The frequency range for f is 150 to 1500 MHz. The base station height hb is from 30 to 200 m. The mobile telephon