dio propagation models described in Chap. 47. 15 Figure 27.22 shows the contrast between the geometric hexa- gons we draw and the cell shapes that we actually see in the field. The boundaries be- tween cells are fuzzy, actually, because of radio measurement error in call setup and handoff. We have discussed the variation in radio propagation that would deform the even boundaries between cells, but there are other effects as well. The information an AMPS 14 We are taking two liberties here, rounding 2.08 percent to 2 and assuming that blocking on the two attempts is independent in a statistical sense. While neither of these assumptions is ab- solutely true, they are close enough for our example to make sense. 5At this point in the discussion we will point out that one of us (Rosenberg) has been on both sides of the cookie-cutter hexagon fence. He worked with some amazing coworkers to develop soft- ware growth models that took regular geometric reuse as far as anybody has ever taken it (so far as we know). And he worked with many of the same people to develop simulation models and pro- scriptive tools that used radio propagation and measurement models to evaluate the true impact of cellular design proposals. 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. Conventional Reuse Principles Conventional Reuse Principles Coverage Figure 27.22 Cookie-cutter hexagons and more realistic cell shapes. or GSM cellular system has to locate a mobile telephone is the radio signal measure- ments it makes. Initial call setup and cell-to-cell handoffs are all made based on radio power measurements and internally set threshold levels. Creating the threshold levels and handoff neighbor lists to operate an AMPS or GSM system with hundreds of cells is a daunting job. 27.11 Capacity Rules of Thumb There are some simple formulas for capacity of conventional reuse cellu