We should compare the ROI of our system with other financial opportunities because we can be sure that our investors will be making such comparisons. Once the initial capital outlay has been made, there is typically a period of time where equipment is new and requires less repair and replacement than it does in the 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 long term. Initial low repair costs make the payback period shorter, a good thing for in- vestor confidence. As demand for wireless service grows, we want to grow our system to serve the de- mand. This is good for business in the future because we are configuring the wireless telephone system to earn the most revenue from the subscriber demand opportunity. Paying for a growing system, however, makes the paypack period longer and makes the ROI figures less favorable for short-term gain. If we continue to grow our system, then we continue to spend money on new equipment. The new equipment eventually will earn revenue, but that revenue is used to pay for even more new equipment as growth continues. In the early days of Advanced Mobile Phone System (AMPS) cellular, service providers were caught by surprise by the astonishing growth rate of cellular and had growing concerns about the continuously increasing costs, whose revenue was contin- uously being consumed to provide for yet more growth. Wireless service providers faced with growth in subscriber demand have to make a decision about how to manage their costs and revenues. Paying for growth without re- alizing a profit is tough on investors. On the other hand, making a profit-taking deci- sion to spend less on equipment and not to satisfy all the demand rubs engineers the wrong way. However, deciding how to manage costs during extended periods of rapid growth is a good problem to have. 46.4 Conclu