A small cell is just a cellular radio access point with lower RF power output, range, footprint, and size than the typical homogenous macrocell. Small cell is also a blanket term for a wide range of cell types that are smaller than traditional macrocells.
Given their small size, some small cells can be installed in places where radio access hardware from macrocells would not be able to be installed due to their size, cost, or performance. Small cells can be designed to provide improved capacity and coverage in targeted areas, often at less cost, infrastructure, or licensing requirements compared to macrocell radio access hardware.
With the addition of small cells, many mobile networks can evolve from homogenous networks to heterogeneous networks with macrocells installed on tall cell towers providing wide coverage range and high power communication at nominal bandwidths, and small cells providing different services, features, and enhanced throughput for users in a smaller area. The smallest small cell devices are being designed for indoor residential use with larger small cells providing moderate range, and possibly filling blind spots or areas of poor coverage from nearby macrocells.
With the ongoing deployments of 5G networks, including millimeter-wave 5G, small cells are commonly being employed by mobile network operators, as the higher frequency band of 5G services suffer from greater atmospheric attenuation and much narrower beamwidths. Hence, millimeter-wave (high-band) 5G deployments are better served with more numerous small cells, rather than much higher power and less efficient macrocells. Some small cells are small enough, and are being designed, to readily operate in dense urban areas, as well as more spacious suburban areas.
Small cells are sometimes broken down into three main categories, based on their use cases and size, microcells, picocells, and femtocells. Typically, all small cells require base station hardware, though this can be somewhat compact, and a fiber optic connection to the mobile network.
Microcells
Microcells are small cells designed to be deployed outdoors in moderately populated areas. Typically, a microcell will have a maximum range around 1 kilometer, and services hundreds of users simultaneously.
Picocells
A picocell can be installed indoors or outdoors but is generally designed to be deployed in large public spaces with a range of a couple hundred meters. Picocells may be commonly installed in hospitals, public transportation hubs (airports, translations, bus stations), stadiums, open air markets, and etc.
Femtocells
Femtocells are currently considered the smallest small cells and may be small enough and low enough cost to be purchased by consumers for home or small business use. Customer Premise Equipment (CPE) that uses cellular connectivity to provide internet services is an example of a femtocell use case.
