Small cells are low-powered radio access nodes that operate in licensed and
unlicensed spectrum that have a range of 10 meters to 1 or 2 kilometers. They are
"small" compared to a mobile macrocell, which may have a range of a few tens of
kilometers. With mobile operators struggling to support the growth in
mobile data traffic, many are using Mobile data offloading as a more
efficient use of radio spectrum. Small cells are a vital element to 3G data
offloading, and many mobile network operators see small cells as vital to
managing LTE Advanced spectrum more efficiently compared to using just
macrocells. ARCchart estimates that by 2017 a total of 5 million small cells
will ship annually. Types of small cells
Small cells may encompass femtocells, picocells, and microcells. Small-cell
networks can also be realized by means of distributed radio technology using
centralized baseband units and remote radio heads. Beamforming technology can
further enhance or focus small cell coverage. These approaches to small
cells all feature central management by mobile network operators.
Small cells provide a small radio footprint, which can range from 10
meters within urban and in-building locations to 2 km 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 always
have self-organising and self-management capabilities.
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 Node
B is a 3G femtocell. A Home eNode B 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. The detail and best
practice associated with the deployment of small cells varies according to use
case and radio technology employed. Purpose
Small cells can be used to provide in-building and outdoor wireless
service. Mobile operators use them 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.
ABI Research also argues that small cells also help service providers
discover new revenue opportunities through their location and presence
information. 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-cell APIs to the wider mobile ecosystem could enable
a long-tail effect. Rural coverage is also a key market that
has developed as mobile operators have started to install public access
metrocells in remote and rural areas that either have only 2G coverage or no
coverage at all. The cost advantages of small cells compared with macro cells
make it economically feasible to provide coverage of much smaller communities -
from a few tens to a few hundreds. The Small Cell Forum have published a white
paper outlining the technology and business case aspects. Mobile operators
in both developing and developed world countries are either trialing or
installing such systems. The pioneer in providing rural coverage using small
cells was SoftBank Mobile - the Japanese mobile operator - who have installed
more than 3000 public access small cells on post offices throughout rural Japan.
To overcome the backhaul challenge in remote locations they have used VSAT
satellite backhaul to link sites to their core network. The Informa Telecoms
and Media consultancy also have a paper covering this use of small cells.
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
"small 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 distributed-antenna
systems 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 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, the 3GPP term for residential femtocells.
Future innovations in radio access design introduce the idea of an almost
flat architecture where the difference between a small cell and a macrocell
depends on how many 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 antenna
range can easily be tuned. = Deployment =
9.6 million residential femtocells have been deployed, representing 56% of all
base stations globally, as of February 2013. In total, almost 11 million small
cells encompassing public, enterprise and residential have been deployed by 47
operators worldwide. Small cell backhaul
Backhaul is needed to connect the small cells to the core network, internet and
other services. Mobile operators consider this more challenging than
macrocell backhaul because a) small cells are typically in hard-to-reach,
near-street-level locations rather than in more open, above-rooftop locations
and b) carrier grade connectivity must be provided at much lower cost per bit.
In one survey, 55% operators listed backhaul as one of their biggest
challenge for small cell rollout. Many different wireless and wired
technologies have been proposed as solutions, and it is agreed that a
‘toolbox’ of these will be needed to address a range of deployment scenarios.
An industry consensus view of how the different solution characteristics match
with requirements is published by the Small Cell Forum . The backhaul
solution is influenced by a number of factors, including the operator’s
original motivation to deploy small cells, which could be for targeted
capacity, indoor or outdoor coverage . In August 2013 the US Federal
Communications Commission announced a change in its rules governing the 60 GHz
band, making it one of the key technologies for LTE backhaul. The
regulator states in its press announcement that this move will
"facilitate the use of this unlicensed spectrum as a backhaul alternative in
densely populated areas where 4G and other wireless services are experiencing
an ever-increasing need for additional spectrum."
References External links
Small Cell Forum Small Cell Forum Release program
Small Cell Hub News ThinkSmallCell
Introduction of Small Cells Youtube video interview between RCR
Wireless News and Senza Fili Consulting president Monica Paolini