ctive as long as new sectors serve new traffic more cheaply than a new cell. Each antenna face at a base station adds less capacity than the one before. There is a decreasing capacity gain as a cell has more sectors. This happens because the same amount of sector-to-sector radio interference is a greater proportion of a smaller sector angle. The result of this sector interference is that a three-sector cell generally serves 2.5 times the traffic that an omnidirectional cell would serve, and a six-sector cell serves about 4 times the omnidirectional traffic. This means that twice the equipment generates 1.5 times the revenue, but we save the cost of an extra building and tower going from three to six sectors. We want to keep sector boundaries away from cell boundaries, especially three- and four-cell zones. A sector boundary produces just as much pilot pollution as a cell bound- ary. While cell boundaries depend on terrain, buildings, and even vegetation, sector boundaries are clean, straight lines from the base station. We have to be careful about relying on cookie-cutter hexagons while splitting cells as described in Sec. 32.3. How- ever, we can rely on cookie-cutter lines on a map for sector boundaries that depend on the antenna radiation patterns and their orientation and not on the terrain between the base station and the user terminal. Sectors can be whatever shape satisfies the subscriber demand. We do not have to have three or six sectors. We do not have to have evenly spaced sectors. If a 30-degree wedge sector with a super-high-gain antenna is the best solution to serve a particular 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 of a Base Station region, then we do not need 11 other sectors in that cell. The rest of the cell can be three 110-degree sectors so that it otherwi