PLC modems transmit in medium and high
frequency (1.6 to 30 MHz electric carrier). The asymmetric speed in the
modem is generally from 256 kbit/s to 2.7 Mbit/s. In the repeater situated
in the meter room the speed is up to 45 Mbit/s and can be connected to 256
PLC modems. In the medium voltage stations, the speed from the head ends to
the Internet is up to 135 Mbit/s. To connect to the Internet, utilities can
use optical fiber backbone or wireless link.
Much higher speed transmissions using microwave frequencies transmitted via
a newly discovered surface wave propagation mechanism have been demonstrated
using only a single power line conductor. These systems have shown the
potential for symmetric and full duplex communication well in excess of 1
Gbit/s in each direction. Multiple WiFi channels as well as simultaneous
analog television in the 2.4 and 5.3 GHz unlicensed bands have been
demonstrated operating over medium voltage lines. Furthermore, because it
can operate anywhere in the 100 MHz - 10 GHz region, this technology can
completely avoid the interference issues associated with utilizing spectrum
shared with other services.
Differences in the electrical distribution systems in North America and
Europe affect the implementation of BPL. In North America relatively few
homes are connected to each distribution transformer, whereas European
practice may have hundreds of homes connected to each substation. Since the
BPL signals do not propagate through the distribution transformers, extra
equipment is needed in the North American case. However, since bandwidth is
limited this can increase the speed each household can connect at, due to
fewer people sharing the same line.
The system has a number of complex issues, the primary one being that power
lines are inherently a very noisy environment. Every time a device turns on
or off, it introduces a pop or click into the line. Energy-saving devices
often introduce noisy harmonics into the line. The system must be designed
to deal with these natural signaling disruptions and work around them.
Broadband over powerlines has developed faster in Europe than in the US due
to a historical difference in power system design philosophies. Nearly all
large power grids transmit power at high voltages in order to reduce
transmission losses, then near the customer use step-down transformers to
reduce the voltage. Since BPL signals cannot readily pass through
transformers — their high inductance makes them act as low-pass filters,
blocking high-frequency signals — repeaters must be attached to the
transformers. In the US, it is common for a small transformer hung from a
utility pole to service a single house. In Europe, it is more common for a
somewhat larger transformer to service 10 or 100 houses. For delivering
power to customers, this difference in design makes little difference, but
it means delivering BPL over the power grid of a typical US city will
require an order of magnitude more repeaters than would be required in a
comparable European city. One possible alternative is to use BPL as the
backhaul for wireless communications, by for instance hanging Wi-Fi access
points or cellphone base stations on utility poles, thus allowing end-users
within a certain range to connect with equipment they already have. In the
near future, BPL might also be used as a backhaul for WiMAX networks.
The second major issue is signal strength and operating frequency. The
system is expected to use frequencies in the 10 to 30 MHz range, which has
been used for decades by amateur radio operators, as well as international
shortwave broadcasters and a variety of communications systems (military,
aeronautical, etc.). Power lines are unshielded and will act as transmitters
for the signals they carry, and have the potential to completely wipe out
the usefulness of the 10 to 30 MHz range for shortwave communications
purposes.
Modern BPL systems use OFDM modulation which allows the mitigation of
interference with radio services by removing specific frequencies used. A
2001 joint study by the ARRL and HomePlug powerline alliance showed that
modems using this technique "in general that with moderate separation of the
antenna from the structure containing the HomePlug signal that interference
was barely perceptible" and interference only happened when the "antenna was
physically close to the power lines".
Technology
Technology will deliver speeds of up to 200 Mbit/s at the physical layer and
130 Mbit/s at the application layer using HomePlug AV standard
(interoperable with HomePlug 1.0 or Intellon proprietary 85 Mbit/s Turbo
mode, already available) or proprietary DS2 technology which is based on
OFDM modulation with 1536 carriers and TDD or FDD channel access method. DS2
technology may operate between 1 and 34MHz. It provides a high dynamic range
(90 dB) and offers frequency division and time division repeating
capabilities. These characteristics allow the implementation of quality of
service (QoS) and class of service (CoS) capabilities.
Standards
Several competing standards are evolving including the HomePlug powerline
alliance, Universal Powerline Association, and the IEEE. It is unclear which
standard will come out ahead. X10 is a de facto standard also used by
RadioShack's Plug'n'Power system.
HomePlug Powerline Alliance
The HomePlug powerline alliance has defined a number of standards:
HomePlug 1.0 — specification for connecting devices via power lines in the
home
HomePlug AV — designed for transmitting HDTV and VoIP around the home
HomePlug BPL — a working group to develop a specification for to-the-home
connection
IEEE
IEEE P1901 is a working group for delivering broadband over power lines. The
aim is to define medium access control and physical layer specifications
that can be all classes of BPL devices - from the long distance connections
to those within the home. [1]
Other related IEEE groups:
IEEE BPL — Standardization of Broadband Over Power Line Technologies [2]
IEEE P1675 — Standard for Broadband over Power Line Hardware [3]
IEEE P1775 — Another project approved by NesCom (IEEE Communications
Society) on 12 May 2005 focuses on PLC equipment, electromagnetic
compatibility requirements, and testing and measurement methods.
OPERA
OPERA (Open PLC European Research Alliance) is a R&D Project with funding
from the European Commission. It aims to improve the existing systems,
develop PLC service, and standardise systems.
Universal Powerline Association (UPA)
The Universal Powerline Association (UPA) aligns industry leaders in the
global Powerline Communications (PLC) market and covers all markets and both
access and an in-home PLC technology to ensure a level playing field for the
deployment of interoperable and coexisting PLC products to the benefit of
consumer’s worldwide.
In May 2004, the UPA interest group was established by founding members.
These founding members signed a Memorandum of Understanding in September
2004, and the UPA was officially announced in December 2004. The UPA members
share a vision of openness and a federated PLC world to harmonize and share
standards and regulations globally.
Members of the UPA are: Ambient Corporation, Ascom Powerline Communications,
Corinex Communications, DS2, EDF (Electricite de France), Ilevo - Schneider
Electric Powerline Communications AB (SEPC), Itochu, Sumitomo Electric
Industries, Ltd. (SEI), and TOYOCOM.
Potential for Interference
Some groups oppose the proliferation of this technology, mostly due to its
potential to interfere with radio transmissions. As power lines are
typically untwisted and unshielded, they are essentially large antennas, and
will broadcast large amounts of radio energy (see the American Radio Relay
League's article). Because of their lack of shielding, the BPL systems are
also at risk of being interfered with by outside radio signals.
Recently, power and telecommunications companies have started tests of the
BPL technology, over the protests of the radio groups. After claims of
interference by these groups, many of the trials were ended early and
proclaimed successes, though the ARRL and other groups claimed otherwise.
Some of the providers conducting those trials have now begun commercial
roll-outs in limited neighborhoods in selected cities, with some level of
user acceptance. There have been many documented cases of interference
reported to the FCC by Amateur Radio users. A video clearly showing the
interference at a site at Briarcliff Manor, NY is available on the ARRL
website. Because of these continued problems, Amateur Radio operators and
others filed a petition for reconsideration with the FCC in February 2005.
Austria, Australia, New Zealand and other locations have also experienced
BPL's spectrum pollution and raised concerns within their governing bodies.
In the UK, the BBC has published the results of a number of tests to detect
interference from BPL installations. They have also made a video (Real Media
format), showing broadcast of data and interference from in-home BPL
devices.
New FCC rules require BPL systems to be capable of remotely notching out
frequencies on which interference occurs, and of shutting down remotely if
necessary to resolve the interference. BPL systems operating within FCC Part
15 emissions limits may still interfere with wireless radio communications
and are required to resolve interference problems. A few early trials have
been shut down, though whether it was in response to complaints is
debatable.
Recently, Motorola has announced a new Low Voltage Access BPL system that
has a reduced potential for interference over the Amperion Inc. and Current
Technologies LLC systems. The American Radio Relay League was invited by
Motorola to participate with these tests, and even installed the Motorola
system at their headquarters. Preliminary results were very positive with
regard to interference.
FCC
On October 14, 2004, the U.S. Federal Communications Commission adopted
rules to facilitate the deployment of "Access BPL" -- i.e., use of BPL to
deliver broadband service to homes and businesses. The technical rules are
more liberal than those advanced by ARRL and other spectrum users, but
include provisions that require BPL providers to investigate and correct any
interference they cause. These rules may be subject to future litigation.
Deployment
Australia, Tasmania: In September 2005 electricity retailer Aurora Energy
began a commerical trial of the technology, offering BPL services to 500
homes in the suburb of Tolmans Hill near Hobart . This followed a successful
technological trial earlier that year. [4]
United States, Virginia: In October 2005 the city of Manassas began the
first wide-scale deployment of BPL service in the nation, offering 10 Mbit/s
service for under $30 USD per month to its 35,000 city residents.
BPL vendors such as Amperion Inc., Current Technologies LLC, Corinex and
InovaTech have deployed BPL systems in limited areas.
InovaTech has been particularly active throughout Asia Pacific and Oceania
regions with many successful trials in Australia, China, Indonesia, Hong
Kong, Malaysia, Philippines and Taiwan. InovaTech has recently increased its
focus to include Europe, the Middle East and Africa where it has undertaken
several successful field trials and is believed to readying commercial
operations in several locations. InovaTech is also understood to have a long
term trial running in Russia. One of the most active solution providers,
InovaTech is the first vendor to develop an integrated offering which
integrates telecommunications and energy management capabilities.
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