opyright © 2004 The McGraw-Hill Companies. All rights Any use is subject to the Terms of Use as given at the website. Conventional Reuse Principles Capacity and Quality Principles Figure 27.15 Three-to-one cell splitting. either four-to-one or three-to-one, an N = 4 grid can only split three-to-one and still have the old cells retain their channel sets. At the time we were designing the first AMPS systems, retuning a radio transmitter was a big deal, and retaining channel sets was a serious issue. 27.7.2 Cell splitting In real life, the growth in a cellular system usually is concentrated in some area or in a small collection of areas. As the demand for cellular service grows in the center of town near the river, 12 we split a few cells to meet the demand, and the new cells follow the new, smaller grid. More growth begets more small-grid cells to relieve the cellular congestion. In Fig. 27.16 we see an N = 7 system using three-for-one cell splitting 12 There is almost always a river in the busy part of town. Denver, Colorado, is the only excep- tion that comes to mind. 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 Figure 27.16 A growing N = 7 system with three-for-one cell splitting. to serve its growing demand. The smaller grid is starting to become a cellular grid in itself with a full seven-cell cluster and three channel sets (D, E, and G) already show- ing reuse. The A cell in the center of the small-cell cluster is a large cell that became a small cell as it was relieved of excess traffic six times with six new small-cell neighbors. In its metamorphosis from large to small, this cell retained its A channel set. Why did we add these new cells? The simplest reason is a measured increase in cel- lular congestion resulting in too many ineffective call attempts on that cell. A slig