he first mission of a wireless telephone system is to reach its subscribers, providing radio coverage. Subscribers in areas not covered well will find wireless telephone ser- vice from someone else, someone who does cover those areas well. Even subscribers who spend most of their time in good coverage areas will find occasional poor coverage a good reason to switch from one wireless service provider to another. In a CDMA environment, poor coverage means lower signal levels competing with thermal noise in the receiver. As long as the CDMA signal is strong, we can ignore ther- mal noise as a factor in capacity planning because CDMA power control can turn down the power levels. When the CDMA signal is weak due to poor radio coverage, the power levels are turned up as far as they can go, but fewer channels can be served when the transmitters run out of power. In the older technologies, FDMA and TDMA, coverage and capacity are distinct is- sues. Once the radio signal gets from transmitter to receiver, better radio conditions do not increase system capacity. FDMA and TDMA wireless planning methods have dis- tinct phases for coverage and capacity. The capacity of CDMA is based on its ability to operate with less signal than noise, so a relative weakening of its signal is going to re- duce its capacity. The result is a continuous tradeoff between coverage and capacity. As a result, a larger cell can support fewer CDMA channels. For a particular environment, when we know the transmitting and receiving equip- ment, antenna gains, and radio signal paths, we can do a link-budget analysis that shows the relationship between cell size and CDMA capacity. The maximum cell size 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. Base Station Planning Planning for CDMA Capacity for coverage is highly dependent on these factors, so there is no global rule of thumb