tain the grid in the low-density areas because they may grow into higher-density areas over time. Putting radio equipment in a base station for all the carriers costs a lot more money than just installing the carriers needed to serve the traffic. In any case, there typically a community of base stations that are not using all the CDMA carriers. We could economize on equipment by using fewer antenna faces, perhaps even using omnidirectional cells. We recommend against this for two reasons. First, when the wireless demand does grow, adding sectors means reconfiguring many antennas on top of a high tower. Second, cells that are coverage-limited need higher antenna gain to reach their tough areas. Sector antennas have higher gain because they cover a narrow arc. Thus, when we do not need sectors for their narrow-beam capacity, we need them for their high-gain coverage. The fringe of the wireless telephone system will have cells with just a single carrier. These cells with just one carrier frequency are called F1 cells. As we progress toward the busy region, we run into F2 cells with two carrier frequencies. These increase as we work our way to the denser demand areas. Even if F1 cells cost a lot of money and do 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 Base Station Planning not earn enough revenue to pay their way in the early system stages, we expect our wireless system to grow, and we expect these outer cells to become F2 and F3 cells over time. Even if they never grow, they can add value by providing seamless service SO that high-density-area subscribers see no gaps in their service when they travel further out or because they help the cellular carrier remain in compliance with government re- quirements to provide coverage. We call the carrier used in F1 cells the first carrier and the carriers added to cells af- t