 is green-area demand that already has high radio signal path gain between the user terminals and the antenna face. When the forward transmit amplifier is spending significant time in the 20 to 40 cent power range, then we conclude that there is significant subscriber traffic in yellow areas, where increasing radio power will directly increase CDMA capacity. These are the sectors where we want to consider adding power. 41.3 Adding Carriers When we put a cell in a CDMA system, we do not automatically install every CDMA carrier on every antenna face. The reason is simply a matter of equipment cost. Adding carriers is expensive. Even if multiple carriers can share transmit amplifiers, there is other base station equipment that has to be present for each CDMA carrier. We should only consider adding a CDMA carrier to a cell next to another cell that ready uses the same carrier. Having a gap in a CDMA carrier does not reduce the in- terference by keeping the reuse further away because calls using that carrier will ex- tend into the middle area and create either a coverage problem or a pilot-pollution problem. Each carrier is a separate CDMA planning problem, and each carrier has to maintain a solid grid that avoids pilot pollution. We want to avoid multiple small is- lands of carrier coverage, and we want to maintain a convex coverage area, as de- scribed in Sec. 32.3. By keeping a tight grid of cells in a convex shape, we can avoid four- and five-way zones, as described in Sec. 32.1. There are two circumstances where we are comfortable having a new area of a CDMA carrier. The first is when we expand the radio spectrum to include a new car- rier. If we are going to introduce a new carrier to a wireless system, then we have to 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. Increasing Capacity of a Base Station Increasing Capacity start somewhere. 