.8. No- tice that the rectangle does not have the four-way zones at its corners that we saw in Fig. 32.6. Not only is the eventual four-to-one splitting grid reasonably free of pilot- polluting four-way zones, but the transition and boundary areas of the four-to-one grid are also low in pilot pollution. We have to remember to keep the new grid of small cells in a convex shape, as de- scribed in Sec. 32.3. Any U-shaped regions in the boundary will be four-way zones with some pilot pollution. Sometimes we need to add transition cells, as described in Sec. 33.4, to keep the region convex. 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. Adding Cells to a CDMA System Increasing Capacity Getting base stations in the right places is an ongoing tough battle. We should not allow difficulties in site acquisition to thwart our growth plans. If a site is hard to get, then we should consider sites nearby. 1 If a base station for a transition cell is taking longer to build, then we probably should deploy the other growth cells and live with some pilot pollution for a while. Many factors make site acquisition a challenge. It is hard enough to engineer a CDMA system with hundreds of cells without the extra challenge of not being able to put base stations where we want them, but this is part of the real engineering world. We can put an X on the map where the base station should be, and then there is the challenge of putting the base station close to that X. Here in the United States, local zoning boards often prohibit towers in some areas, usually areas where a lot of rich people live, areas where we want good cellular coverage. Getting the land for a base station can be hard as well. A tower that is already built and is not too far away may be a far better choice than starting from scratch. Or a location closer to a transport node, a point of presence (POP)