Small Cell

A small cell is a low-power base station that serves a small area on purpose. Where a macro cell on a tower covers a wide region and gets shared by everyone in it, a small cell drops capacity exactly where it's concentrated — a busy plaza, a transit station, a dense city block, an indoor space the macro can't reach well. Coverage area scales roughly with power, so the rough hierarchy runs microcell (largest of the small cells, often outdoor street-level) down through picocell (indoor/enterprise) to femtocell (home/small office, lowest power).

The strategic point is densification. Once a macro cell is congested, you can't conjure more spectrum, so the practical way to add capacity is to add cells and reuse the spectrum more times over a given area — and small cells are how you do that without erecting more towers. The catches are operational rather than technical: you need power and (good) backhaul at every site, the sites are numerous so acquisition and maintenance add up, and dense small cells need careful interference coordination with the macro layer above them (the heterogeneous-network, or HetNet, problem). They complement macros; they don't replace them.