Not all small cells are created equal, so let's look at the key differences between the various small basestations that share the "small cell" moniker.
The central concept of a small cell is basically the same: A small cell is a diminutive, self-contained basestation that extends coverage at the edge of the macro network. In theory, such a unit can help fix voice and data coverage holes, add capacity where needed, and increase data connection speed. The crux of the idea being that the closer a user is to a cellular radio, the better the network performance will be.
Small cells, however, diverge into three distinct flavors from that point on. Here's how we categorize them:
Femtocells Femtocells -- otherwise known as home basestations -- are the most mass-market member of the small cell clan right now. AT&T Inc. (NYSE: T) and Sprint Corp. (NYSE: S) have sent out more than a million of these units each. Femtocells are backhauled over a user's cable broadband or DSL connection and can be used to conquer deadspots in the home, improve call quality, and improve mobile data speeds. The units can typically be deployed by the user themselves. (See Top 6 Small Cells Movers & Shakers.)
Enterprise Small Cells Enterprise small cells are intended to provide coverage to all or part of a floor of an office building or other indoor space (and sometimes even an outdoor space) and are most often deployed en masse within buildings to provide blanket coverage. With the bring-your-own-device (BYOD) trend, providing cellular coverage throughout offices is becoming crucial for many businesses. The basestations are typically backhauled over the enterprise Ethernet network. Enterprise small cells are often promoted as a less expensive alternative to distributed antenna systems (DAS) for providing cell coverage. This sector is starting to climb out of its hype-cycle with some deployments now underway. (See SpiderCloud Eyes LTE Enterprise Small Cells in 2014, Joint Qualcomm & AlcaLu Small Cells Due Mid-Year, Ericsson Expects Smooth Sailing for Radio Dot and Slide Show: Cisco's Small Cell Bureau.)
Public Access Small Cells Public access small cells are basestations intended to improve voice and data coverage in large malls, stadiums, and outdoor public spaces. They can be mounted in buildings, on outer walls, or on lamp posts and other utility poles. These are the units that are proving most difficult to bring to commercial service, with many tests and trials still ongoing. In addition to the problems associated with site acquisition, this type of small cell is arguably the most difficult to deploy, often requiring new backhaul connections, and posing power supply challenges, especially when the units are located that might be mounted up a pole or high on a building. They also tend to produce more transmit power, so can pose more potential interference problems with the macro cellular network. (See Fibertech Claims US Small-Cell First, 3G, 4G & Wi-Fi: AT&T Plans Small-Cell Threesome and Small Cells: The Battle for the Lamp Post.)
Heavy Reading is predicting that there will be 700,000 public access small cells in service worldwide requiring new backhaul connections by the end of 2017. The wireless CTO of Taqua LLC , John Hoadley, recently told Light Reading that he expects up to 50% of all the public access small cells will require new backhaul connections. (See How Heavy Reading Called Small Cells Right.)
Here's some of the basic requirements for the different types of small cells.
Table 1: Small Cell Types & Requirements
|Type||Typical applications||Radio connections||Backhaul connections||Number of simultaneous calls supported||RF power output||Coverage Range|
|Femtocell||Indoor residential||2G/3G||Home DSL/Cable||Up to 8||Up to 20mW||5 to 20 meters|
|Enterprise Small Cell||Indoor private & open access, outdoor private access||3G/WiFi (integrated multimode systems supporting 3G, WiFi and LTE arriving soon)||Ethernet||Up to 32 on 3G||Up to 250mW||5 to 200 meters|
|Public Access Small Cell||Outdoor & large in-building coverage (airports/ stadiums)||3G/WiFi (integrated multimode systems supporting 3G, WiFi and LTE in tests)||Fiber/ Microwave/ Copper-over-Ethernet||Up to 64 on higher-power units||250mW to 5 Watts||10 to 2,000 meters (rural sites will get better range)|
|Sources: Heavy Reading, vendor data|
A note on terminology I've stuck to femtocells, enterprise small cells, and public access as the terminology for this little primer. Others have used picocell and nanocell to describe the smaller variants of home and enterprise small cells. Metrocell, meanwhile, is the term often used to describe larger public access small cells. Given the profusion of differing terminology used in this industry it seems more helpful -- to me, at least -- to describe the small cell by the application for which it will be used.
If you agree, disagree, or have more to add on the definitions of small cells, please chime in on the message board below.
— Dan Jones, Mobile Editor, Light Reading