the vertical-beam radiation pattern of the sec- tor antennas. The result of a downtilting study is a plan that coordinates splitting cells for CDMA growth and downtilting antennas to get the most capacity from both the old cells and the new cells. We can lower antennas on the tower to reduce the effective cell size. This is an alternative to downtilting, but it is usually more expensive and less effective. The path-gain reduction from a lower antenna is greater at longer distances, so lowering the antennas gives a relative advantage for calls close to the base station. 42.5 Microcells for High Traffic Density Sometimes system growth is concentrated in a small area so that a full-sized macrocell would spread the CDMA interference over a larger area than the concentrated traffic. And sometimes the concentration is so great that there is enough wireless traffic in a small area to keep one or more CDMA carriers busy. In the case of concentrated demand, a microcell may be a better solution than a macrocell. A microcell is a smaller base station designed for short radio range of a few hundred meters. A microcell has a low antenna height and a lower-power amplifier than a macrocell. Since its coverage area is deliberately small, a microcell may be placed off the grid pattern without producing the interference and pilot pollution of a regular macrocell in that same off-grid location. We can put microcells on the grid positions for cell splitting as well. If the traffic con- tinues to grow, then we can continue to split cells in the grid so that the microcell grows in function to be a regular cell. We may need to raise the antennas higher and down- tilt them to get the local coverage needed for macrocell function. The plan for microcells is to identify concentrated areas of growth in small geographic areas that are easily reached with a shorter-range radio system. 2Obviously, downtilting only works at a base station with multiple antenna faces. But any cell with only a single omnidirectional sector is almost certainly goi