 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 system. There is no N = 5 regular reuse ratio, but a reuse-partitioned system with N = 7 and N = 4 can have more or less of the traffic on each value of N for an equiva- lent of N = 5 or N = 6 or even N = 5.5. The outer thresholds for the N = 4 part of the system determine the equivalent value of N. The bad side of reuse partitioning is that it is a major engineering challenge to keep track of all the channel sets. The system shown in the figure, for example, has N = 7 and N = 4 for a total of 11 channel sets. 27.7.4 Economics of growth Mixing cell sizes extracts a price in capacity. Maintaining D/R ratios with different D and R values partitions channel sets into large-cell channels and small-cell channels. Adding a third tier of even smaller cells only aggravates the channel-assignment prob- lem. An aggressive AMPS or GSM cellular engineer can maintain about two-thirds of the channel set at each cell in a growing system. Thus our N = 4 system averages 80 channels per cell instead of 125. Using traffic engineering analysis in Chap. 23, such cells might average 70 percent occupancy, 40 erlangs during the busy hour. The cellular provider gasps at this point, spending as much as a million U.S. dollars per cell site for just 40 average simultaneous busy-hour calls. The economics of a grow- ing system only get worse as the system keeps growing, and no providers are anxious to tell their stockholders that they have decided to stop growing their cellular systems just so the company can make some money. The early days of cellular ran rivers of red ink companies found themselves investing and investing in a future that stayed years away. 27.8 Power Balancing As a conventional reuse wireless telephone system grows by splitting cells, the channel sets become complicated. Often a single radio channel is used for cells of different sizes. Consider a channel 