parate early coverage phase before the long-term growth phase. Again, in the early days of AMPS, there was contention between N = 7 with three-sector cells and N = 4 with six-sector cells. Going to six sectors gains 3 dB, whereas going to N = 4 loses 5 dB for a net performance loss of 2 dB. Cellular service providers had to decide whether the higher ra- dio performance of N = 7 and three sectors was worth the higher cost. 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 27.11.4 Overlaid cells Overlaid cells are worth another 30 percent, 2 dB. This is the incremental capacity of being able to use a second cell radius at one base station. This advantage comes from being able to reuse channels from large to small cells at closer range, and it seems to be a consistent advantage over a wide range of traffic demand density distributions and values of N. The same advantage of overlaid cells can be realized by using reuse parti- tioning in the early stages of cellular system growth. Allowing more than two cell sizes, multiplying overlaid cells, is worth another 15 per- cent, 1 dB. A growing reuse-partitioned cellular system would have as many as six cell sizes, six server groups, served by the same base station. The engineering would quite complicated, but the result would be that the cells could handle more traffic. 27.11.5 Nonregular channel reuse Finally, we can leave geometric reuse altogether. Once the traffic and terrain are non- regular, the geometric regularity that inspired cellular thinking in 1966 can give way to a nonregular assignment that takes full advantage of every reuse opportunity. Analysis and simulation studies have showed this was worth another factor of 2 in ca- pacity, 6 dB. Getting the benefit of this requires solving some terribly difficult mathe- matical optimizati