 sector can share an antenna and power amplifier, then the per-carrier cost includes one-quarter of the antenna and power amplifier cost. Each layer in the equipment hierarchy inherits the proportional cost of shared equip- ment at higher levels. Since a base station supports three sectors and a sector supports 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. Business-Case Models Modeling for CDMA an average of four carriers, we can assign each carrier one-third of the per-sector cost and one-twelfth of the per-cell cost because each cell in this example has 12 carriers. We can extend this further up the equipment hierarchy to include the MSC cost as well. If each MSC can serve 200 cells, then the per-cell cost includes 1/200 of the cost of an MSC. If we carry this down to the sector level, then the per-cell cost of an MSC 1/600 of the cost of the MSC. And we can extend this further down the equipment hierarchy to the individual channel level. If each cdmaOne carrier has 24 channel cards installed, then each of these cards inherits 1/24 of the per-carrier cost, which includes a share of the per-sector, per-cell, and per-MSC costs. This is a good method for calculating average costs as long as the decision we are making with it does not involve changing the ratios. If we are considering adding three- sector cells to a system, then dividing the per-cell cost by three for each sector makes sense. If, however, we are considering going from three to six sectors for some of the cells, then we have to separate the per-cell and per-sector costs. 46.1.4 The postage-stamp model Sometimes the proportional-cost model does not have enough detail. A base station re- quires an MSC so that it can operate, but up to 200 base stations can share the same MSC. If we deploy base station number 201 in our example, then we are going to buy another MSC for the syste