Small cell
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Introduction
Small cells are low-powered radio access nodes that operate in licensed and unlicensed spectrum that have a range of 10 meter to 200 meters, compared to a mobile macrocell which might have a range of a few kilometres.
Types of small cells
Small cells encompass femtocells, beam-forming (focusing a radio signal on a very specific area), picocells/microcells and distributed radio technologies that comprise a centralised baseband with remote radio heads (such as the Alcatel-Lucent Light Radio and Nokia Siemens Networks Liquid Radio ). A common factor in all these approaches to small cells is that they are mobile network operator managed.
Smalls cell provide a small radio footprint, which can range from 10 meters within urban and in-building locations to 2km for a rural location. Picocells and microcells can also have a range of a few hundred meters to a few kilometers, but they differ from femtocells in that they do not have self-organising and self-management capabilities .
Compatible technology
Small cells are available for a wide range of air interfaces including GSM, CDMA2000, TD-SCDMA, W-CDMA, LTE and WiMax. In 3GPP terminology, a Home NodeB (HNB) is a 3G femtocell. A Home eNodeB (HeNB) is an LTE femtocell. Wi-Fi is a small cell but does not operate in licensed spectrum therefore cannot be managed as effectively as small cells utilising licensed spectrum.
Purpose
Small cells can be used to provide in-building and outdoor wireless service. Mobile operators use small cells to extend their service coverage and/or increase network capacity. With small cells, mobile operators can offload traffic as much as 80% during peak times. ABI Research estimates that by 2015, 48% of mobile data traffic will be offloaded from the macro network. No individual technology will dominate offloading.
ABI Research also believes that small cells also help service providers discover new revenue opportunities through their location and presence information, argues ABI Research. If a registered user enters a femtozone, the network is notified of their location. The service provider, with the user's permission, could share this location information to update user's social media status, for instance. Opening up small cells APIs to the wider mobile ecosystem could enable a Long Tail effect.
Umbrella term
The most common form of small cells are femtocells. Femtocells were initially designed for residential and small business use , with a short range and a limited number of channels. Femtocells with increased range and capacity spawned a proliferation of terms: metrocells, metro femtocells, public access femtocells, enterprise femtocells, super femtos, Class 3 femto, greater femtos and microcells. The term smalls cells is frequently used by analysts and the industry as an umbrella to describe the different implementations of femtocells , and to clear up any confusion that femtocells are limited to residential uses. Small cells are sometimes, incorrectly, also used to describe DAS which are not low-powered access nodes.
Future mobile networks
Small cells are an integral part of future LTE networks. In 3G networks, small cells are viewed as an offload technique. In 4G networks, the principal of heterogeneous network (HetNet) is introduced where the mobile network is constructed with layers of small and large cells. In LTE, all cells will be self-organizing, drawing upon the principles laid down in current Home NodeB (HNB), the 3GPP term for residential femtocells.
Future innovations in radio access design, such as Alcatel-Lucent's Light Radio Cube introduce the idea of an almost flat architecture where the difference between a small cell and a macrocell depends on how may cubes are stacked together. With software-defined radio, a base station could be 2G, 3G or 4G at the flick of a switch, and the antennae range can be easily tuned.