Street width W, half the base station height Street angle , 90 degrees Roof height hr, 3 m per floor plus 3 m if the roof is pitched The Walfisch-Ikegami model takes rooftop heights, street width, and street orienta- tion into account, factors not included in the Hata-Okumura model. This makes it a more detailed model but not necessarily a better model. If the extra input parameters are available, then the more detailed model should give more precise forecasts and al- low the engineer to see differences that the less detailed model might miss.7 As an example of the modeling differences, consider a fairly spread out suburban neighborhood compared with a concentrated city center. In the suburban neighborhood, with winding streets, low houses, and high base station towers, the Hata-Okumura model might do just fine. In city center, on the other hand, it could become very im- portant which radio paths go right down the road and which ones are at a 45-degree angle to the block pattern. The difference between accuracy and precision becomes important when discussing mathe- matical models. Let us summarize the difference this way: A model is accurate when it gets some- thing close to the right answer, and a model is precise when it shows differences correctly. We are relying on model accuracy when we want absolute radio path gain, and we are relying on preci- sion when we explore the effect of environmental changes on the signal path. 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 The Hata-Okumura model tends to predict lower path losses than the Walfisch- Ikegami model. There are several parameters in Walfisch-Ikegami that are not in Hata-Okumura, and making different assumptions about these parameters affects the relative values of the two models. Comparing two models with such different levels of input-data d