the propagation of the system as a whole, including its terrain environment. Each bin represents a possible place for a user terminal to be on a wireless telephone call. Each of these terrain profiles is constructed using the elevations of the bins between the base station location and the (x,y) bin being studied. An example of a radio path Figure 47.4 Each bin has a radio path to each base station. 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 Elevation Profile Figure 47.5 Radio path over terrain. over a terrain profile is shown in Fig. 47.5. Each bin represents a piece of the service area where a user terminal could be engaged in a wireless telephone call. Thus we have to choose a realistic height for each bin as an end point of a call radio path. Once we form the geometric radio path over hills and through valleys, we need to culate the radio signal path gain between the base station and a user terminal in the bin. We treat the hilltops as knife-edge diffraction points and use rules of propagation to de- termine the signal path gain. The loss at each hilltop is based on radio frequency and the angle of the path change over the hilltop. If we have information about vegetation or den- sity of buildings, then that information also goes into the propagation model. The terrain-based propagation calculation is done for each base station. Sector plans come later because all the antenna faces are within a few meters of each other. If the antennas faces are mounted at different heights for some reason, then their propaga- tion would have to be calculated separately. The result of a terrain-based propagation model is a calculation for each base station for each bin. The full-blown propagation database can be very large if every bin has a path gain value stored for every base station. Storage 