The cell layout with coverage cells and growth cells should avoid valleys, that is, four-way zones of CDMA coverage. The lack of valleys will be visually apparent in good layout and can be confirmed with planning tools that look for small fourth-pilot delta values. This procedure gives us a good layout for macrocells, the regular big-tower 4The term convex area is mathematically defined as an area where line segments between any two points in the area are entirely contained in the area. This describes a region with no holes and no U shapes in its boundary. Small Cell Figure 32.8 Four-to-one split creates a rectangular cell. 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. Planning Locations for Base Stations Planning for CDMA Capacity Figure 32.9 Four-to-one cell splitting with a four-cell zone. cells that cover large geographic areas. We now turn our attention to spot engineering with microcells, picocells, and repeaters. 32.4 Microcells for Highly Concentrated Demand Once we have covered the geographic service area of a wireless telephone system, we look at local hot spots. We can use the high-reuse capability of CDMA to treat local high-density areas with local equipment, including microcells, picocells, and repeaters. The estimation process that gave us the geographic distribution of wireless demand also should identify local areas of high density. The high density could be a large com- munity of voice calls, or it could be a community of very active data subscribers. It takes only a few high-rate data users to use a lot of CDMA capacity, especially if they require low delay and high accuracy. Once we identify these subscriber communities, we can use local equipment to meet their needs. If a high-demand area is a few hundred meters in radius, then we can use a micro- cell to serve it. Microcells typically are mounted low to limit their ra