some power control. 27.7 Growing for Increasing Demand The cellular system is designed to grow. A successful wireless telephone service attracts more subscriber demand, and the tools for serving that increased demand are built into the conventional reuse cellular technology. Serving more subscribers almost always in- volves adding new base stations, and that can be costly. Received Power dBm Figure 27.13 Signal and interference with more power control. 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 27.7.1 Smaller cell grid If we have an N = 7 system serving its customers and we wake up one morning to find four users for every one we had before, then we can make a grid four time denser with cells half the size and one-quarter the area. Figure 27.14 shows the four-to-one cell left splitting that has been used in many AMPS systems. The larger N = 7 grid on the continues onto the smaller right-side grid. The shading of the cells on the right shows the original, larger N = 7 grid. Please note that the smaller grid is a full N = 7 grid with no obvious indication that it was split from a larger grid. Similarly, should we wake up to find that our demand has tripled instead of quadru- pled, we can make a grid three times denser with cells V 3/3 the size and one-third used the area. Figure 27.15 shows the three-to-one cell splitting that also has been in AMPS and GSM systems. Again, the larger N = 7 grid on the left continues onto many the smaller right-side grid with the shading to show the original, larger grid. Again, the smaller grid is a full N = 7 grid on its own. While an N = 7 layout can split GDAEBF AEBCG cGDAEB DAEBFC EBFCGD FCGDAE EBFCG Figure 27.14 Four-to-one cell splitting. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) reserved. C