space can be saved by realizing that there is a range beyond which the radio contribution of a base station is insignificant. 47.5 In-Building Models The terrain-based models described earlier work well for open space but are not help- ful when an entire subscriber community is entirely within one building in one (x,y) bin. Adding the third dimension of height to create (x, y, z) bins is not going to address the radio propagation issues of a single, large office building. When considering one or more picocells in a building, we need to model the radio propagation within the build- ing structure. 8 For each area we want to serve, we can do a direct ray calculation from the picocell an- tenna to the user terminal location. We draw the straight-line radio path and calculate the attenuation of whatever walls and floors are between the picocell and user terminal. Normal office building floors start at 10 dB of attenuation for floors of concrete and ceilings of acoustic tile with pipes above. If there are steel panels between the ceiling and the floor, then the attenuation may be much greater. The choice of office furniture makes a difference in the radio path gain between floors of an office building. 8 We are going to give a brief overview of in-building and ray-tracing propagation models. For a much more involved description of these models and other radio propagation issues, we direct the reader to Bertoni (2000). 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 Modeling for CDMA Attenuation of a radio signal through a wall depends on the radio frequency, the ma- terials used in the wall, and the furniture on either side. The signal loss through a fab- ric cubical barrier is small, and even a concrete interior wall only adds about -2 dB in path gain at 900 MHz. These same concrete walls lose 10 to 15 dB at 6 GHz. If the walls