Scott Reeves takes a look some of the advantages and disadvantages of femtocells.
What
exactly is a femtocell? The short answer is that a femtocell is a very
low-range, low-power base station, able to be deployed in a home, home
office or office. It is usually provided by a mobile network operator,
and operates in licensed frequency bands.
A small amount of
terminology may be of use before we proceed further into the world of
femtocells. A macrocell defines the cell controlled by the base station
of a mobile network operator. A femtocell is the cell controlled by the
femto base station. The main difference between a femtocell and a base
station is the range. A base station might have a radius of 20-30 km,
whereas a femtocell has a radius up to10 metres. However, a femtocell
uses the same licensed frequency band as the macrocell. Femtocells can
operate with various types of mobile systems such as UMTS and CDMA2000.
In future, LTE and WiMax capable femtocells are expected to be deployed.
For
backhaul, the femtocell requires a connection to the mobile network
operator. This is typically via a fixed line, be it cable, fibre-optic
or a twisted pair telephone line. This connection enables the femtocell
to interface with the operator’s base station, and provides a way for
the two to coordinate when (for example) to handover your mobile device
to the femtocell or back to the main base station.
The
femtocell needs to co-exist peacefully with neighbouring users and
possibly neighbouring femtocells. This is not too difficult; a femtocell
can sniff the spectrum and detect other femtocells. A femtocell will
only use the frequency bands it has been allotted. Its short range and
inbuilt intelligence means that it can adjust transmission power up or
down, according to where its users are and whether neighbouring users
are using the spectrum.
Advantages and disadvantages
There
are a few controversies around the deployment of femtocells. One of
them was pointed out by an erstwhile colleague when he was trying to
sort out his home phone issues. He got somewhat irate when the company
suggested a femtocell. His gripe was that the Telco company was making
him fix their black spots.
Of course, there are advantages to
having a femtocell. One of these is that the coverage is likely to
remain consistent wherever you are located in the office/home, due to
the femtocell. This has the flow-on effect that your mobile
terminal/phone won’t use as much power, hence giving more battery time. A
further advantage is that a mobile phone can be used as the main
phone(s). Femtocells have the capacity to limit how many people are
permitted to log on. This is a mechanism to restrict coverage. It makes
using a femtocell in a small office attractive.
There are
drawbacks. Femtocells utilise the broadband connection, which may also
be used for other applications such as video streaming. There can be
problems when the provider of the broadband service differs from the
mobile network provider. These relate to Quality of Service guarantees. A
further issue relates to interference. Although the deployment of
femtocells suggests that interference with other femtocells is not a
huge issue, there is still some controversy over whether this will
continue to be the case.
The use of femtocells is part of a more
general trend in mobile communications toward smaller cell sizes. Whilst
there are some drawbacks to femtocells, the advantages of using them
could be seen in homes and in small offices or home offices.
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