Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com reserved. Copyright © 2004 The McGraw-Hill Companies. All rights website. Any use is subject to the Terms of Use as given at the Planning Locations for Base Stations Planning for CDMA Capacity Figure 32.4 A cell layout that follows a warped grid. so the initial cell layout has to be ready for large volumes of calls in the densest areas. The goal of efficient cell placement is to put cells where the demand is going to be. We have forecasts and maps, and we want to add enough cells to meet the demand. We also want to have each cell pulling its own weight, each cell carrying its share of the revenue-producing subscriber demand. The result of good planning is that the number of cells in a neighborhood follows the subscriber demand for service. This may sound obvious, but cellular engineers experienced in FDMA and TDMA may remember when cell splitting was dictated by channel sets as much as by local demand. The CDMA air interface allows us to follow subscriber demand much more closely in deploying base stations. Pilot pollution is a concern for cell splitting. The same issues that apply when laying out coverage cells also apply when adding cells for expected demand. The growing grid maintains low pilot pollution and simpler handoff lists. It is not as nice as the perfect honeycomb pattern without any growth cells, but a growing grid is going to be easier and better than adding cells without the grid structure. 20 North America, the Federal Communications Commission (FCC) required that winners of grants or auctions for broadcast licenses in the cellular band guarantee service to a certain per- centage of the population in the area covered by the license. To meet this requirement, first- and second-generation cellular providers built very large coverage cells in areas of low demand. If such a regulatory requirement is not present in current plans, cellular engineers are free to develop plans based primarily or exclusively on mar