r a given blocking rate goes down, so smaller quantities of call demand use voice links less efficiently. At the 2 to 10 percent blocking levels typically desired in cellular systems and at the num- bers of radios in cellular systems, the busy-hour occupancy ranges from 50 to 80 percent. Offering reasonably low blocking rates, under the best of circumstances, requires at least one-fifth of the voice links to be idle even during the peak-usage period. Within a cellular service provider, there is a danger that financial planners working on a cellular growth plan will set budgets based on an oversimplified model of demand and capacity. It is essential that cellular engineers communicate the complexity of these issues early and often and that they explain the results of their statistical mod- eling in a way that the financial executives can understand. It is also essential that organization foster good communication and mutual respect between these groups that the financial plan is sufficient to support a realistic engineering growth plan. 12.5.7 Changing channel conditions A single CDMA carrier varies in capacity over time. The notion of a carrier or set of car- riers with varying capacity is a new concept to most telephone engineers. Even those of us familiar with conventional reuse (FDMA and TDMA) are not used to a carrier set 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. Telephony Engineering Concepts Key Telephony Concepts whose capacity changes over time. In CDMA, calls with poorer radio links (coming from inside buildings, for example) use a larger slice of the CDMA pie than other calls, add more interference to the other calls, and reduce the carrier's total capacity. The num- ber of calls that can be served by a single carrier depends on the local conditions where the calls are calling from. Cell capacity also depends on the quality o