e at the same base station. The extra server group is a software change only because the extra cell radius is cre- ated by changing access and handoff parameters for some of the radio channels. In Fig. 27.18 we have the same growth cells, but now we have overlaid all the cells that are too close by D/R rules. The large C cell on the right side of Fig. 27.18 cannot share channels with the small C cell a few steps to the left side of it. We have added an overlaid small C cell that can share those channels SO that the capacity of the large C cell is no longer compromised by adding the small C cell. Another way to use overlaid cells is reuse partitioning. Suppose that a reuse ratio of N = 7 is required to serve an entire wireless subscriber community. Then the user ter- minals nearer the base stations have radio path gain high enough that N = 4 reuse will serve them adequately. Because they are closer to the cell center, they can enjoy N = 7 D/R with N = 4 reuse. 13 In Fig. 27.19 we overlay an N = 4 system on top of an N = 7 system. Reuse partitioning has two advantages. First, it increases capacity SO that it can de- lay initial cell splitting of an existing large-cell grid and make a small-cell grid more ef- ficient. Second, it gives the cellular carrier flexibility in tuning the reuse ratio of the 13 While we refer to close and far as geometric terms and draw the figures that way, the actual discrimination in a reuse-partitioned system, or any overlaid cell with more than one server group, is based on radio signal path. Downloaded from Digital Engineering Library @ McGraw-Hil (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 Figure 27.18 A growing N = 7 system with overlaid cells. Figure 27.19 Reuse-partitioning N = 7 and N = 4. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) reserved. Copyright ©