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This
page considers use of domestic and other power lines for
internet traffic.
It covers -
introduction
As the name suggests, digital powerline communication
(PLC) - or broadband over power lines (BPL) - uses existing
electrical power grids rather than dedicated telephone
wiring and television cable to provide access to the net.
Digital content - which might be a sound recording, a
web page, email or a telephone call - is converted to
a radio frequency signal that shares the same copper wire
used to deliver electricity to commercial/residential
buildings and to points within those buildings. Accessing
the content involves converting the PLC signal, whether
on a 'whole of building' or 'socket by socket' basis .
PLC essentially takes two forms - to the household (sometimes
labelled as 'longline PLC' and within the household.
The first - sometimes mooted as an answer to the 'last
mile' problem - involves existing grids used by power
utilities to deliver electricity from generators to consumers.
Typically digital content is converted to radio frequency
transmissions at gateways located at major nodes of the
power grid, for example at a power station or a distribution
substation. The gateways link the PLC network to conventional
high-speed communication links - usually optical fibre
- with the internet and public subscriber telephone network.
At the edge of the power network (eg individual houses,
schools, commercial buildings or office suites) the radio
transmissions are filtered by a device for delivery through
an conventional local area network (eg the "blue
cable" found in many buildings) that does not reticulate
power for airconditioning, toasters, personal computers
or other devices.
The second form - sometimes characterised as powerplug
communication - uses the same principles to deliver content
via existing electrical wiring within a building. Proponents
argue that the technology means that "every power
plug can be an internet access point". A gateway
device at a house's perimeter might, for example serve
as a bridge between the phone network and the building's
internal grid - the fuses, wires and sockets that are
used to run the lights, heating and domestic appliances.
One or more devices - ideally small, resilient and cheap
- could be plugged into that grid, converting the signal
back into the form expected by a conventional phone, a
personal computer or a wifi station.
Proponents argue that digital powerline technology has
a range of benefits including
- the
theoretical potential to "provide every home with
a fast internet connection, given that almost all homes
are on an electricity supply grid"
- use
of wiring within buildings means that every power socket
is an internet access point.
- provision
of an always-on service with the same characteristics
as DSL and cable modem connectivity
-
improved "safety and efficiency of the power network",
with remote control and monitoring of appliances via
power lines.
In
practice those claims have not been tested on a large
scale in a commercial environment. There has probably
been more writing about PLC than implementation, particularly
because PLC has been seen as hyped as revolutionary, freedom
from telecommunication providers or as a low-cost mechanism
for bridging digital divides
in environments with inadequate phone/cable infrastructure
("broadband for everyone").
Tests suggest that data transmission rates with powerline
technology might be above most ISDN connections, with
for example claims of 6Mbit/s in both directions.
status
PLC technology has attracted some industry and government
attention, in some instances with tangible funding, but
essentially has not moved from pilot installations to
'real world' use across a range of households and organisations
and with a range of equipment.
Major telecommunication and consumer product manufacturers
have been reluctant to make a commitment to production
of powerline gear and certification by standard-setting
bodies has been exploratory rather than concerned with
day to day implementation. In the marketplace PLC appears
to be less competitive than wifi and wimax and thus is
attracting less support than those technologies.
Overall, like some other technologies, PLC appears likely
to be "the technology of the next generation ...
and always going to be". Critics have argued that
PLC faces substantial consumer (and regulatory) resistance,
is over-sold and under-supported or is a solution looking
for a problem.
That is consistent with the basket of potential uses identified
on the Powerline Communications Association site
- including home automation, surveillance and of course
gaming - and problematical claims that internet/phone
access will be free because electricity providers will
not need to charge.
Projects include the EU Opera
(Open PLC European Research Alliance) initiative and small-scale
trials in Australia (eg in Queanbeyan)
and overseas.
issues
PLC advocates face at least three issues.
The first, and arguably most critical, is competition
from existing and emerging network technologies. PLC may
be feasible but is being beaten by wireless alternatives
and old-fashioned twisted-pair. There is little sign of
strong consumer demand. It is unlikely that there will
be substantial consumer demand in the absence of perceived
major advantages, industry support and greater comfort
with 'hot wires'.
From a technical perspective radio frequency signals over
power grids
- are
affected by interference from non-communication devices
that are on the same network, eg domestic blenders,
sanders, milling equipment
- encounter
problems with bandwidth when there are major demands
for access at peak periods in a local loop
Those
performance problems are similar to difficulties explored
in our discussion of wireless networking. They are significant
because, despite some visions of "plug & play"
at any power point (contrasted with "plug & pray"
with modems), the technology has definite limitations.
Critics note that domestic filters are vulnerable to lightning
strikes or other power surges and that the environment
in utility substations is unfriendly (eg high temperatures,
dust, substantial electromagnetic noise).
A third issue is indifferent industry support and the
absence of major commercial and regulatory champions.
Powerline communication is often seen as "out there"
or a curiosity, rather than a commercially credible product
that is likely to gain the traction of wifi and wimax.
There is no consensus about standards; there is disagreement
about both technical and commercial feasibility.
Figures about the cost of infrastructure for 'to the household'
delivery in Australia, North America and Europe are contentious,
although it has been claimed the configuration of power
grids in much of Europe means that costs would be somewhat
lower than in the US. Benefits for utility operators -
notably remote telemetry of consumer power usage - might
be more cost-effectively achieved through wireless-enabled
meters.
In Europe there has been increasing concern over interference,
with comments that PLC is inconsistent with the Digital
Radio Mondiale (DRM)
standard, which uses compression to deliver near-FM quality
digital sound over existing AM broadcast frequences. Studies
in the UK during 2004 suggest that there is significant
degradation of DRM signals through interference from internet
powerline systems. DRM has been recognised by the European
Telecommunications Standards Institute (ETSI), the International
Electrotechnical Committee (IEC) and International Telecommunications
Union (ITU) Radio Regulations
Board.
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