y not be a bargain if the smaller unit already meets our needs. 1 A wireless telephone system 1 In the consumer arena, a shameful example of this kind of marketing is the selling of a 20- minute long distance call for one dollar with no discount for shorter duration. Since most calls are much shorter than 20 minutes, most calls have a far higher unit price per minute than the ad- vertised 5 cents. 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 Business-Case Models with hundreds of base stations may not offer the option of concentrating its equipment into larger and more economical units. Buying equipment often has a fixed cost as well. If we are buying amplifiers from one vendor and decide to buy amplifiers from another vendor, then we may have to buy a whole new suite of test equipment and train our repair staff on new procedures. These costs are fixed costs of owning any amount of a product, no matter how little. To make purchase decisions more complicated, the fixed cost of owning a line of equipment of- ten depends on whether or not we already own equipment from a particular vendor. We do not have to count every piece of equipment separately in a cost model. If every antenna requires a cable and mounting equipment, then all of these can be lumped to- gether in estimating cost. Whatever need made us buy an antenna is going to make us buy all the associated equipment as well. Another issue in evaluating equipment cost is the cost of multiple subcomponents. A base stations is divided into sectors, and a sector may have several code division mul- tiple access (CDMA) carriers. Depending on the level of detail we need, we can aggre- gate some of the subcomponents For example, an MSC handles 200 base stations, each base stations has three sec- tors, and each sector has up to five carriers. When we are estimating the cost o