Jump to content

Power-line communication: Difference between revisions

From Wikipedia, the free encyclopedia
Content deleted Content added
 
Line 1: Line 1:
{{Short description|Data network that uses electrical wiring}}
{{cleanup}}
{{for|other schemes to deliver data and power over one cable|Power over}}
{{Use dmy dates|date=June 2020}}
{{Use American English|date=October 2024}}
[[File:PLC使用風景.jpg|thumb|Power line adapter]]


'''Power-line communication''' ('''PLC''') is the carrying of data on a conductor that is also used simultaneously for AC [[electric power transmission]] or [[electric power distribution]] to consumers. The line that does so is known as a '''power-line carrier'''.
'''Power line communication''' ('''PLC'''), also called '''Broadband over Power Lines''' ('''BPL''') or '''Power Line Telecoms''' ('''PLT'''), is a [[wire]]line method of [[communication]] that uses the existing [[electric power transmission]] and [[electricity distribution]] lines. The carrier can communicate voice and data by superimposing an [[analog signal]] over the standard 50 or 60 [[Hertz|Hz]] [[alternating current]] (AC). Traditionally electrical [[utilities]] used low-speed power-line carrier circuits for control of substations, voice communication, and protection of high-voltage transmission lines. More recently, high-speed data transmission has been developed using the lower voltage transmission lines used for power distribution. A short-range form of power-line carrier is used for home automation and intercoms.


In the past, [[power line]]s were solely used for transmitting electricity. However, with the introduction of advanced networking technologies, there has been a push for utility and service providers to find cost-effective and high-performance solutions. The possibility of using powerlines as a universal medium to transmit not just electricity or control signals, but also high-speed data and multimedia, is now under investigation.{{by whom|date=March 2024}}<ref>{{Cite thesis |last=Sagar |first=Nishant |title=Powerline Communications Systems: Overview and Analysis |url=https://rucore.libraries.rutgers.edu/rutgers-lib/34055/ |journal=Rutgers University Libraries |date=2011 |doi=10.7282/T3RR1XJ7 |url-status=live |archive-url= https://web.archive.org/web/20240416103925/https://rucore.libraries.rutgers.edu/rutgers-lib/34055/ |archive-date= Apr 16, 2024 }}</ref>
== Types of PLC technology ==


A wide range of power-line communication technologies are needed for different applications, ranging from [[home automation]] to [[Internet access]], which is often called [[broadband over power lines]] (BPL). Most PLC technologies limit themselves to one type of wires (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations.
===Indoors/Short Range===
Indoors, the PLC equipment can use the household electrical power wiring as a transmission medium. This is a technique used in [[domotics|home automation]] for remote control of lighting and appliances without installation of additional control wiring. The [[Homeplug]] system is an example of this technology. The [[X10]] [[home automation]] system uses power line communication at the [[zero crossing]] voltage point in the AC wave.


A number of difficult technical problems are common between [[wireless]] and power-line communication, notably those of [[spread spectrum]] radio signals operating in a crowded environment. Radio interference, for example, has long been a concern of [[amateur radio]] groups.<ref name="notch">{{Cite news |title= ARRL Strengthens the Case for Mandatory BPL Notching |url= http://www.arrl.org/news/arrl-strengthens-the-case-for-mandatory-bpl-notching |date= 2 December 2010 |work= News release |publisher= [[American Amateur Radio League]] |access-date= 24 November 2011 }}</ref>
Typically these devices operate by injecting a [[carrier]] wave of between 20 and 200 [[kHz]] into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver. These devices may either be plugged into regular power outlets or else permanently wired in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same distribution system, these control schemes have a "house address" that designates the owner.


== Basics ==
There are also some very low-bit rate power line communication systems used for [[meter reading]].
Power-line [[communications system]]s operate by adding a modulated carrier signal to the wiring system. Different types of power-line communications use different frequency bands. Since the power distribution system was originally intended for transmission of [[AC power]] at typical frequencies of 50 or 60 [[Hertz|Hz]], power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power-line communications.


The main issue determining the frequencies of power-line communication is laws to limit interference with radio services. Many nations regulate unshielded wired emissions as if they were radio transmitters. These jurisdictions usually require unlicensed uses to be below 500&nbsp;kHz or in unlicensed radio bands. Some jurisdictions (such as the EU), regulate wire-line transmissions further. The U.S. is a notable exception, permitting limited-power wide-band signals to be injected into unshielded wiring, as long as the wiring is not designed to propagate radio waves in free space.
===Outdoors/Long Haul===
Utility companies use special coupling [[capacitor]]s to connect low-frequency radio transmitters to the power-frequency AC conductors. Frequencies used are in the range of 30 to 300 kHz, with transmitter power levels up to hundreds of watts. These signals may be impressed on one conductor, on two conductors or on all three conductors of a high-voltage AC transmission line. Several different PLC channels may be coupled onto one HV line. Filtering devices are applied at substations to prevent the carrier frequency current from bypassed through the station apparatus and to ensure that distant faults do not affect the isolated segments of the PLC system. These circuits are used for control of switchgear, and for protection of transmission lines. For example, a protection relay can use a PLC channel to trip a line if a fault is detected between its two terminals, but to leave the line in operation if the fault is elsewhere on the system.


[[Data signaling rate|Data rates]] and distance limits vary widely over many power-line communication standards. Low-frequency (about 100–200&nbsp;kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a [[local area network]] operating at millions of bits per second may only cover one floor of an office building, but eliminates the need for installation of dedicated network cabling.
While utility companies use microwave and now, increasingly, fiber optic cables for their primary system communication needs, the power-line carrier apparatus may still be useful as a backup channel or for very simple low-cost installations that do not warrant a fibre drop.


==Broadband over power lines==
== Types of PLC ==
Although different protocols and legislation exists throughout the world, there are basically only two types of PLC: the ''indoor'' PLC and the ''outdoor'' PLC.<ref name=":0" />
'''Broadband over Power Lines''' (BPL) is the use of PLC technology to provide broadband [[Internet access]] through ordinary power lines. A computer (or any other device) would need only to plug a BPL "[[modem]]" into any outlet in an equipped building to have high-speed Internet access.


* '''Indoor PLC''': indoor PLC is used for LAN networking and narrowband in-house applications, such as home automation. It uses house power wiring to transmit data, injecting the current directly in the power plugs.
BPL offers obvious benefits over regular [[Cable modem|cable]] or [[DSL]] connections: the intensive infrastructure already available would allow more people in more locations to have access to the Internet. Also, such ubiquitous availability would make it much easier for other electronics, such as [[television]]s or sound systems, to hook up. The amount of bandwidth a BPL system can provide compared to cable and wireless is in question, however.
* '''Outdoor PLC''': applied in the main power line transmissions, such as low-frequency PLC (for telemetry and grid control), and in BPL, for internet transmission via power network. In this type of PLC, the equipment must be robust, to deal with the high voltage levels of the power lines.


== Ripple control ==
High-speed data transmission, or '''Broadband over Power Line {BPL}'''
[[Load management#Ripple control|Ripple control]] adds an audio-frequency tone to an AC line. Typical frequencies are from 100 to 2400 [[Hz]]. Each district usually has its own frequency, so that adjacent areas are unaffected. Codes are sent by slowly turning the tone on and off. Equipment at a customer site receives the codes, and turns customer equipment off and on. Often the decoder is part of a standard [[electricity meter]], and controls relays. There are also utility codes, e.g. to set the clocks of the power meters at midnight.
uses the electric circuit between the electric [[substation]]s and home networks. A standard used for this is ''[[ETSI]] PLT''.


In this way, the utility can avoid up to 20% of capital expenses for generating equipment. This lowers costs for electricity and fuel usage. Brownouts and rolling blackouts are more easily prevented. Grids that use [[Combined cycle|cogeneration]] can enable auxiliary customer equipment when the generators are being run to generate heat rather than electricity.
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 [[Kilobit per second|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 end]]s to the [[Internet]] is up to 135 Mbit/s. To connect to the Internet, [[public utility|utilities]] can use [[optical fiber]] [[backbone]] or [[wireless]] link.


An annoyance for customers is that sometimes the code to turn equipment on is lost, or load shedding is inconvenient or dangerous. For example, during a party, a dangerous heat wave or when life-preserving medical equipment is on-site. To handle these cases, some equipment includes switches to circumvent load shedding. Some meters switch into a higher billing rate when the ''party switch'' is flipped.
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.


== Long haul, low frequency ==
==Technology==
Utility companies use special coupling [[capacitor]]s to connect radio transmitters and receivers to the AC power-carrying conductors. Power meters often use small transformers with linear amplifiers in the range of tens of watts. Most of the expense of any PLC system is the power electronics. By comparison, the electronics to encode and decode is usually small, in a special-purpose integrated circuit. Thus even the complicated OFDM standards can still be economical.
Technology delivers speeds of up to 200 Mbps uising propietary [[DS2]] technology which is based on [[OFDM]] modulation. It provides a high dynamic range (90 dB) and offers [[frequency division]] and [[time division]] repeating capabilities. These characteristics allow the implementation of [[QoS]] and [[CoS]] capabilities.


Frequencies used are in the range of 24 to 500&nbsp;kHz, with transmitter power levels up to hundreds of [[watt]]s. These signals may be impressed on one conductor, on two conductors or on all three conductors of a high-voltage AC transmission line. Several PLC channels may be coupled onto one HV line. Filtering devices are applied at substations to prevent the carrier frequency current from being bypassed through the station apparatus and to ensure that distant faults do not affect the isolated segments of the PLC system. These circuits are used for control of switchgear, and for protection of transmission lines. For example, a [[protective relay]] can use a PLC channel to trip a line if a fault is detected between its two terminals but to leave the line in operation if the fault is elsewhere on the system.
==Standards==
Several competing standards are evolving including the [[HomePlug powerline alliance]] (which has defined the '''HomePlug 1.0''' and is finalizing the '''HomePlug AV''' high-speed networking technology), [http://www.upaplc.org/ Universal Powerline Association], and the [http://grouper.ieee.org/groups/bpl/ 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.


While utility companies use microwave and now, increasingly, [[fiber-optic cable]]s for their primary system communication needs, the power-line carrier apparatus may still be useful as a backup channel or for very simple low-cost installations that do not warrant installing fiber optic lines, or which are inaccessible to radio or other communication.
==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 [[antenna (electronics)|antenna]]s, and will broadcast large amounts of radio energy (see the [[American Radio Relay League]]'s [http://www.arrl.org/tis/info/HTML/plc/ article]).


Power-line carrier communication (PLCC) is mainly used for [[telecommunication]], tele-protection and tele-monitoring between [[electrical substation]]s through [[power line]]s at [[high voltage]]s, such as 110 kV, 220 kV, 400 kV.<ref>{{cite book|author=Stanley H. Horowitz|author2=Arun G. Phadke|title=Power system relaying third edition|publisher=John Wiley and Sons|year=2008|isbn=978-0-470-05712-4|pages=64–65}}</ref>
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.


The modulation generally used in these system is [[amplitude modulation]]. The carrier frequency range is used for audio signals, protection and a pilot frequency. The pilot frequency is a signal in the audio range that is transmitted continuously for failure detection.
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 [[http://www.qrpis.org/~k3ng/bpl.html#56 few]] early trials have been [[http://www.arrl.org/news/stories/2004/06/28/2/?nc=1 shut]], [[http://www.arrl.org/news/stories/2004/07/28/5/?nc=1 down]] though whether it was in response to complaints is debatable.


The voice signal is compressed and filtered into the 300&nbsp;Hz to 4000&nbsp;Hz range, and this audio frequency is mixed with the carrier frequency. The carrier frequency is again filtered, amplified and transmitted. The transmission power of these HF carrier frequencies will be in the range of 0 to +32 [[Decibel|dbW]]. This range is set according to the distance between substations.
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.


PLCC can be used for interconnecting [[private branch exchange]]s (PBXs).
Recently, [[Motorola]] has [[http://www.motorola.com/mediacenter/news/detailpf/0,,5519_5509_23,00.html announced]] a new Low Voltage Access BPL system that has a reduced potential for interference over the [[Amperion Inc.]] and [[Current Technologies LLC]] systems.


To sectionalize the transmission network and protect against failures, a ''wave trap'' is connected in series with the power (transmission) line. They consist of one or more sections of resonant circuits, which block the high-frequency carrier waves (24–500&nbsp;kHz) and let power frequency current (50–60&nbsp;Hz) pass through. Wave traps are used in the switchyards of most power stations to prevent carriers from entering the station equipment. Each wave trap has a lightning arrester to protect it from surge voltages.
==FCC==


A coupling capacitor is used to connect the transmitters and receivers to the high-voltage line. This provides a low-impedance path for carrier energy to HV line but blocks the power frequency circuit by being a high-impedance path. The coupling capacitor may be part of a [[capacitor voltage transformer]] used for voltage measurement.
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.


Power-line carrier systems have long been a favorite at many utilities because it allows them to reliably move data over an infrastructure that they control.
BPL vendors such as [[Amperion Inc.]] and [[Current Technologies LLC]] have begun offering BPL service in limited areas.


A ''PLC carrier repeating station'' is a facility, at which a power-line communication (PLC) signal on a [[Electric power transmission|powerline]] is refreshed. Therefore
==References==
the signal is filtered out from the powerline, [[Demodulation|demodulated]] and [[Modulation|modulated]] on a new [[Carrier wave|carrier frequency]], and then reinjected onto the powerline again. As PLC signals can carry long distances (several hundred kilometers), such facilities only exist on very long power lines using PLC equipment.
J. L. Blackburn (ed),''Applied Protective Relaying'', Westinghouse Electric Corporation (1976)Newark, New Jersey USA, no ISBN, Library of Congress Card No. 76-8060


PLC is one of the technologies used for automatic meter reading. Both one-way and two-way systems have been successfully used for decades. Interest in this application has grown substantially in recent history—not so much because there is an interest in automating a manual process, but because there is an interest in obtaining fresh data from all metered points in order to better control and operate the system. PLC is one of the technologies being used in [[Advanced Metering Infrastructure]] (AMI) systems.
==See also==

[[List of PLC manufacturers]]
In a one-way (inbound only) system, readings bubble up from end devices (such as meters), through the communication infrastructure, to a ''master station'' which publishes the readings. A one-way system might be lower-cost than a two-way system, but also is difficult to reconfigure should the operating environment change.

In a two-way system (supporting both outbound and inbound), commands can be broadcast out from the master station to end devices (meters) – allowing for reconfiguration of the network, or to obtain readings, or to convey messages, etc. The device at the end of the network may then respond (inbound) with a message that carries the desired value. Outbound messages injected at a utility substation will propagate to all points downstream. This type of broadcast allows the communication system to simultaneously reach many thousands of devices—all of which are known to have power, and have been previously identified as candidates for load shed. PLC also may be a component of a [[smart grid]].

== Medium frequency (100&nbsp;kHz) ==
These systems are often used in countries in which it is illegal to transmit signals that interfere with normal radio. The frequencies are so low that they are unable to start radio waves when sent over the utility wiring.

=== Home control (narrowband) ===
Power-line communications technology can use the electrical power wiring within a home for [[home automation]]: for example, remote control of lighting and appliances without installation of additional control wiring.

Typically home-control power-line communication devices operate by modulating in a [[carrier wave]] of between 20 and 200 [[Hertz|kHz]] into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver. These devices may be either plugged into regular power outlets or permanently wired in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same distribution system, these control schemes have a ''house address'' that designates the owner. A popular technology known as [[X10 (industry standard)|X10]] has been used since the 1970s.<ref>{{cite web |title= The history of X10 |author= Edward B.Driscoll Jr. |url= http://home.planet.nl/~lhendrix/x10_history.htm |access-date= 22 July 2011 }}</ref>

The [[universal powerline bus]], introduced in 1999, uses [[pulse-position modulation]] (PPM). The physical layer method is a very different scheme than the X10.<ref>{{cite web |title= What is Univeral (sic) Powerline Bus? |publisher= Powerline Control Systems, Inc |url= http://pulseworx.com/UPB_.htm |access-date= 22 July 2011 |archive-date= 18 July 2011 |archive-url= https://web.archive.org/web/20110718042743/http://www.pulseworx.com/UPB_.htm |url-status= dead }}</ref> [[LonTalk]], part of the [[LonWorks]] home automation product line, was accepted as part of some automation standards.<ref>{{cite news |title= Echelon Announces ISO/IEC Standardization of LonWorks® Control Networks |publisher= Echelon Corporation |work= News release |date= 3 December 2008 |url= http://www.echelon.com/company/press/2008/lonworksISO.htm |access-date= 22 July 2011 |url-status= dead |archive-url= https://web.archive.org/web/20120407150936/http://www.echelon.com/company/news-room/2008/lonworksISO.htm |archive-date= 7 April 2012}}</ref>

=== Low-speed narrow-band ===
Narrowband power-line communications began soon after electrical power supply became widespread. Around the year 1922 the first carrier frequency systems began to operate over high-tension lines with frequencies of 15 to 500&nbsp;kHz for telemetry purposes, and this continues.<ref>{{cite journal|first=K|last=Dostert|year=1997|title=Telecommunications over the Power Distribution Grid- Possibilities and Limitations|journal=Proc 1997 Internat. Symp. On Power Line Comms and Its Applications|pages=1–9|url=http://www.isplc.org/docsearch/Proceedings/1997/pdf/0563_001.pdf}}</ref> Consumer products such as baby alarms have been available at least since 1940.<ref>{{cite conference|first=R.|last=Broadridge|title=Power line modems and networks|conference=Second IEE National Conference on Telecommunications|year=1989|pages=294–296|location=London UK|url=https://ieeexplore.ieee.org/document/20724}}</ref>

In the 1930s, ripple carrier signaling was introduced on the medium (10–20 kV) and low voltage (240/415&nbsp;V) distribution systems.

For many years the search continued for a cheap bi-directional technology suitable for applications such as remote meter reading. French electric power ''[[Électricité de France]]'' (EDF) prototyped and standardized a system called spread frequency shift keying or S-FSK. (See [[IEC 61334]]) It is now a simple, low cost system with a long history, however it has a very slow transmission rate. In the 1970s, the [[Tokyo Electric Power Company]] ran experiments that reported successful bi-directional operation with several hundred units.<ref>{{cite conference|first=M|last=Hosono|title=Improved Automatic meter reading and load control system and its operational achievement|conference=4th International Conference on Metering, Apparatus and Tariffs for Electricity Supply|pages=90–94|date=26–28 October 1982|publisher=IEE}}</ref> {{As of|2012}} the system was widely used in Italy and some other parts of the EU.

S-FSK sends a burst of 2, 4 or 8 tones centered around the time when the AC line passes through zero voltage. In this way, the tones avoid most radio-frequency noise from arcing. (It is common for dirty insulators to arc at the highest point of the voltage, and thus generate a wide-band burst of noise.) To avoid other interference, receivers can improve their signal-to-noise ratio by measuring the power of only the ''1'' tones, only the ''0'' tones or the differential power of both. Different districts use different tone pairs to avoid interference. The bit timing is typically recovered from the boundaries between tones, in a way similar to a [[UART]]. Timing is roughly centered on the zero crossing with a timer from the previous zero crossing. Typical speeds are 200 to 1200 bits per second, with one bit per tone slot. Speeds also depend on the AC line frequency. The speed is limited by noise, and the jitter of the AC line's zero crossing, which is affected by local loads. These systems are usually bidirectional, with both meters and central stations sending data and commands. Higher levels of the protocols can have stations (usually smart meters) retransmit messages. (See [[IEC 61334]])

Since the mid-1980s, there has been a surge of interest in using the potential of digital communications techniques and [[digital signal processing]]. The drive is to produce a reliable system that is cheap enough to be widely installed and able to compete cost effectively with wireless solutions. But the narrowband powerline communications channel presents many technical challenges, a mathematical channel model and a survey of work is available.<ref>{{cite journal|last=Cooper|first=D. |author2= Jeans, T. |title= Narrowband, low data rate communications on the low-voltage mains in the CENELEC frequencies. I. Noise and attenuation|journal=IEEE Transactions on Power Delivery|date=1 July 2002|volume=17|issue=3|pages=718–723|doi=10.1109/TPWRD.2002.1022794}}</ref>

Applications of mains communications vary enormously, as would be expected of such a widely available medium. One natural application of narrow-band power-line communication is the control and [[telemetry]] of electrical equipment such as meters, switches, heaters and domestic appliances. A number of active developments are considering such applications from a systems point of view, such as [[demand side management]].<ref>{{cite journal|last=Newbury|first=J.|title=Communication requirements and standards for low voltage mains signalling|journal=IEEE Transactions on Power Delivery|date=Jan 1998|volume=13|issue=1|pages=46–52|doi=10.1109/61.660847}}</ref> In this, domestic appliances would intelligently co-ordinate their use of resources, for example limiting peak loads.

Control and telemetry applications include both ''utility side'' applications, which involve equipment belonging to the utility company up to the domestic meter, and ''consumer-side'' applications which involve equipment in the consumer's premises. Possible utility-side applications include [[automatic meter reading]] (AMR), dynamic tariff control, load management, load profile recording, credit control, pre-payment, remote connection, fraud detection and network management,<ref>{{cite conference|first=T J|last=Sheppard|title=Mains Communications- a practical metering system|conference=7th International Conference on Metering Applications and Tariffs for Electricity Supply|pages=223–227|date=17–19 November 1992|location=London UK|publisher=IEE}}</ref> and could be extended to include gas and water.

[[Open Smart Grid Protocol]] (OSGP) is one of the most proven narrowband PLC technologies and protocols for smart metering. There are{{as of?|date=August 2021}} more than five million smart meters, based on OSGP and using BPSK PLC, installed and operating around the World. The OSGP Alliance, a non-profit association originally established as ESNA in 2006, led an effort to establish a family of specifications published by the European Telecommunications Standards Institute (ETSI) used in conjunction with the ISO/IEC 14908 control networking standard for smart grid applications. OSGP is optimized to provide reliable and efficient delivery of command and control information for smart meters, direct load control modules, solar panels, gateways, and other smart grid devices. OSGP follows a modern, structured approach based on the OSI protocol model to meet the evolving challenges of the smart grid.

At the physical layer, OSGP currently uses ETSI 103 908 as its technology standard. This uses binary phase shift keying at 3592.98 BAUD, using a carrier tone of 86.232&nbsp;KHz +/- 200ppm.<ref>{{cite web |title=ETSI TS 103 908 V1.1.1 |url=https://www.etsi.org/deliver/etsi_ts/103900_103999/103908/01.01.01_60/ts_103908v010101p.pdf |website=ETSI Delivery |publisher=ETSI |access-date=16 August 2021}}</ref> (Note: The bit clock is almost exactly 1/24 of the carrier.) At the OSGP application layer, ETSI TS 104 001 provides a table-oriented data storage based, in part, on the ANSI C12.19 / MC12.19 / 2012 / IEEE Std 1377 standards for Utility Industry End Device Data Tables and ANSI C12.18 / MC12.18 / IEEE Std 1701, for its services and payload encapsulation. This standard and command system provides not only for smart meters and related data but also for general-purpose extension to other smart grid devices.

A project of EDF, France includes demand management, street lighting control, remote metering and billing, customer-specific tariff optimization, contract management, expense estimation and gas applications safety.<ref>{{cite journal|first=G|title=Applications of power-line carrier at Electricite de France|journal=Proc 1997 Internat. Symp. On Power Line Comms and Its Applications|pages=76–80|last=Duval}}</ref>

There are also many specialized niche applications that use the mains supply within the home as a convenient data link for telemetry. For example, in the UK and Europe a TV audience monitoring system uses powerline communications as a convenient data path between devices that monitor TV viewing activity in different rooms in a home and a data [[concentrator]] which is connected to a telephone modem.

=== Medium-speed narrow-band ===
The Distribution Line Carrier (DLC) System technology used a frequency range of 9 to 500&nbsp;kHz with data rate up to {{nowrap|576 kbit/s}}.<ref>{{cite web |title= Distribution Line Carrier System |publisher= Power-Q Sendirian Bhd |url-status=dead |url= http://www.powerq.com.my/telecommunication/distribution-line-carrier-system |archive-url= https://web.archive.org/web/20090520004013/http://www.powerq.com.my/telecommunication/distribution-line-carrier-system |archive-date= 20 May 2009 |access-date= 22 July 2011 }}</ref>

A project called Real-time Energy Management via Powerlines and Internet (REMPLI) was funded from 2003 to 2006 by the [[European Commission]].<ref>{{cite web |title=Real-time Energy Management via Powerlines and Internet |work=official web site |url-status=dead |url= http://www.rempli.org/ |archive-url= https://web.archive.org/web/20090214043341/http://www.rempli.org/ |archive-date= 14 February 2009 |access-date= 22 July 2011 }}</ref>

More modern systems use [[OFDM]] to send data at faster bit rates without causing radio frequency interference. These utilize hundreds of slowly-sending data channels. Usually, they can adapt to noise by turning off channels with interference. The extra expense of the encoding devices is minor compared to the cost of the electronics to transmit. The transmission electronics is usually a high-power operational amplifier, a coupling transformer and a power supply. Similar transmission electronics is required on older, slower systems, so with improved technology, improved performance can be very affordable.

In 2009, a group of vendors formed the PoweRline Intelligent Metering Evolution (PRIME) alliance.<ref>{{cite web |title= Welcome To PRIME Alliance |work= Official web site |url= http://www.prime-alliance.org/ |access-date= 22 July 2011 }}</ref> As delivered, the physical layer is [[OFDM]], sampled at 250&nbsp;kHz, with 512 [[differential phase shift keying]] channels from 42–89&nbsp;kHz. Its fastest transmission rate is {{nowrap|128.6 kbit/s}}, while its most robust is {{nowrap|21.4 kbit/s}}. It uses a [[convolutional code]] for error detection and correction. The upper layer is usually [[IPv4]].<ref>{{cite book|chapter-url=http://www.lit.lnt.de/papers/isplc_2011_hoch.pdf|last=Hoch|first=Martin|title=2011 IEEE International Symposium on Power Line Communications and Its Applications |chapter=Comparison of PLC G3 and PRIME |doi=10.1109/ISPLC.2011.5764384|pages=165–169|year=2011|isbn=978-1-4244-7751-7|s2cid=13741019|access-date=16 May 2012|archive-date=10 August 2017|archive-url=https://web.archive.org/web/20170810045448/http://www.lit.lnt.de/papers/isplc_2011_hoch.pdf|url-status=dead}}</ref>

In 2011, several companies including distribution network operators ([[Électricité de France#Distribution network (RTE and Enedis)|ERDF]], Enexis), meter vendors ([[Sagemcom]], Landis&Gyr) and chip vendors ([[Maxim Integrated]], [[Texas Instruments]], [[STMicroelectronics]], [[Renesas]]) founded the G3-PLC Alliance<ref>{{cite web |title= G3-PLC Official Web Site |work= Official web site |url= http://www.g3-plc.com/ |access-date= 6 March 2013 }}</ref> to promote G3-PLC technology. G3-PLC is the low-layer protocol to enable large scale infrastructure on the electrical grid. G3-PLC may operate on CENELEC A band (35 to 91&nbsp;kHz) or CENELEC B band (98&nbsp;kHz to 122&nbsp;kHz) in Europe, on ARIB band (155&nbsp;kHz to 403&nbsp;kHz) in Japan and on FCC (155&nbsp;kHz to 487&nbsp;kHz) for the US and the rest of the world. The technology used is [[OFDM]] sampled at 400&nbsp;kHz with adaptative modulation and tone mapping. Error detection and correction is made by both a [[convolutional code]] and [[Reed-Solomon error correction]]. The required [[media access control]] is taken from [[IEEE 802.15.4]], a radio standard. In the protocol, [[6loWPAN]] has been chosen to adapt [[IPv6]] an internet network layer to constrained environments which is Power line communications. [[6loWPAN]] integrates routing, based on the [[mesh network]] LOADng, header compression, fragmentation and security. G3-PLC has been designed for extremely robust communication based on reliable and highly secured connections between devices, including crossing Medium Voltage to Low Voltage transformers. With the use of IPv6, G3-PLC enables communication between meters, grid actuators as well as smart objects. In December 2011, G3 PLC technology was recognized as an international standard at [[ITU]] in Geneva where it is referenced as G.9903,<ref>{{cite web |title= G.9903 ITU-T Web Page |work= Official web site |url= http://www.itu.int/rec/T-REC-G.9903-201210-I/en |access-date= 6 March 2013 }}</ref> Narrowband orthogonal frequency division multiplexing power line communication transceivers for G3-PLC networks.

=== Transmitting radio programs ===
{{main|Carrier current}}
Sometimes PLC was used for transmitting radio programs over powerlines. When operated in the AM radio band, it is known as a [[carrier current]] system.

== High frequency (≥ 1&nbsp;MHz) ==
High-frequency communication may (re)use large portions of the radio spectrum for communication, or may use select (narrow) band(s), depending on the technology.

=== Home networking (LAN) ===
Power line communications can also be used in a home to interconnect home computers and peripherals, and home entertainment devices that have an [[Ethernet]] port. Powerline adapter sets plug into power outlets to establish an Ethernet connection using the existing electrical wiring in the home (power strips with filtering may absorb the power line signal). This allows devices to share data without the inconvenience of running dedicated network cables.

The widely deployed powerline networking standard are from [[Nessum Alliance]] and [[HomePlug Powerline Alliance]]. HomePlug Powerline Alliance announced in October 2016 that it would wind down its activities, and the Alliance website (homeplug.org) has been closed. [[Nessum]] (formerly [[HD-PLC]]), and HomePlug AV which is the most current of the HomePlug specifications were adopted by the [[IEEE 1901]] group as baseline technologies for their standard, published 30 December 2010. HomePlug estimates that over 45 million HomePlug devices have been deployed worldwide. Other companies and organizations back different specifications for power line home networking and these include the [[Universal Powerline Association]], [[SiConnect]], [[Xsilon]], and the [[ITU-T]]'s [[G.hn]] (HomeGrid) specification.

=== Non-home networking (LAN) ===
With the diversification of IoT applications, the demand for high-speed data communication such as transmission of high-definition video data and/or high-frequent sensor data is increasing in the field of smart building, smart factory, smart city, etc. In such use cases, power line communication technologies can also be used and provides the same advantage of reusing existing cables.

Nessum has developed a multi-hop technology that can be used to build large-scale networks. In addition, the latest Nessum technology (4th-generation HD-PLC technology) provides multiple channels, which enables high-speed and long-range communication by selecting the optimal channel.

===Broadband over power line===
{{main|Broadband over power lines|IEEE 1901}}

Broadband over power line (BPL) is a system to transmit two-way data over existing AC MV (medium voltage) electrical distribution wiring, between transformers, and AC LV (low voltage) wiring between transformer and customer outlets (typically 100 to 240 V). This avoids the expense of a dedicated network of wires for data communication, and the expense of maintaining a dedicated network of antennas, radios and routers in a wireless network.

BPL uses some of the same radio frequencies used for over-the-air radio systems. Modern BPL employs Wavelet-OFDM, FFT-OFDM, or [[frequency-hopping spread spectrum]] to avoid using those frequencies actually in use, though early pre-2010 BPL standards did not. The criticisms of BPL from this perspective are of pre-OPERA, pre-1905 standards.

The BPL OPERA standard is used primarily in Europe by ISPs. In North America, it is used in some places (Washington Island, WI, for instance) but is more generally used by electric distribution utilities for [[smart meter]]s and load management.

Since the ratification of the [[IEEE 1901]] (Nessum, HomePlug) LAN standard and its widespread implementation in mainstream router chipsets, the older BPL standards are not competitive for communication between AC outlets within a building, nor between the building and the transformer where MV meets LV lines.

==Ultra-high frequency (≥ 100&nbsp;MHz)==
Even higher information rate transmissions over power line use RF through microwave frequencies transmitted via a [[transverse mode]] surface wave propagation mechanism that requires only a single conductor. An implementation of this technology is marketed as [[E-Line (power line communication)|E-Line]]. These use microwaves instead of the lower frequency bands, up to 2–20&nbsp;GHz. While these may interfere with [[radio astronomy]]<ref>{{Cite web |url=http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group13/index.html#21 |title=Broadband over Power Lines (BPL) |access-date=2 September 2019 |archive-date=12 February 2019 |archive-url=https://web.archive.org/web/20190212081059/http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group13/index.html#21 |url-status=dead }}</ref> when used outdoors, the advantages of speeds competitive with [[fiber optic cable]]s without new wiring are likely to outweigh that.

These systems claim symmetric and full duplex communication in excess of {{nowrap|1 Gbit/s}} in each direction.<ref>{{cite news |title= Understanding the information rate of BPL and other last-mile pipes |author= Glenn Elmore |work= Computing Unplugged magazine |url= http://www.computingunplugged.com/issues/issue200608/00001828001.html |date= August 2006 |access-date= 22 July 2011 |url-status= dead |archive-url= https://web.archive.org/web/20110722055823/http://www.computingunplugged.com/issues/issue200608/00001828001.html |archive-date= 22 July 2011 |df= mdy-all }}</ref> Multiple Wi-Fi channels with simultaneous analog television in the 2.4 and 5.0&nbsp;GHz unlicensed bands have been demonstrated operating over a single medium voltage line conductor. Because the underlying propagation mode is extremely [[broadband]] (in the technical sense), it can operate anywhere in the 20&nbsp;MHz{{snd}}20&nbsp;GHz region. Also since it is not restricted to below 80&nbsp;MHz, as is the case for high-frequency BPL, these systems can avoid the interference issues associated with use of shared spectrum with other licensed or unlicensed services.<ref>{{cite web |title= Introduction to the Propagating TM Wave on a Single Conductor |author= Glenn Elmore |date= 27 July 2009 |url= http://www.corridor.biz/FullArticle.pdf |publisher= Corridor Systems |access-date= 22 July 2011 }}</ref>

== Standards ==
Two distinctly different sets of standards apply to powerline networking as of early 2010.

Within homes, the [[IEEE 1901]] standards specify how, globally, existing AC wires should be employed for data purposes. The IEEE 1901 includes Nessum and HomePlug AV as baseline technologies. Any IEEE 1901 products can coexist and be fully interoperable between products using the same technology. On the other hand, medium-frequency home control devices remain divided, although X10 tends to be dominant. For power grid use, IEEE has approved a low-frequency (≤ 500&nbsp;kHz) standard called IEEE 1901.2 in 2013.<ref name=ieee1901-2>{{cite web |title= IEEE 1901.2-2013 - IEEE Standard for Low-Frequency (less than 500 kHz) Narrowband Power Line Communications for Smart Grid Applications |website=IEEE SA |url=https://standards.ieee.org/standard/1901_2-2013.html |archive-url=https://web.archive.org/web/20181216053334/https://standards.ieee.org/standard/1901_2-2013.html |url-status=dead |archive-date=16 December 2018 |access-date= 23 December 2013 }}</ref>

===Standards organizations===
Several competing organizations have developed specifications, including the [[HomePlug Powerline Alliance]] (defunct), [[Universal Powerline Association]] (defunct), and [[Nessum Alliance]] (active). In October 2009, the ITU-T adopted Recommendation [[G.hn]]/G.9960 as a standard of networks for high-speed powerline, coax, and phoneline communications.<ref>{{cite web |url=http://www.itu.int/ITU-T/newslog/New+Global+Standard+For+Fully+Networked+Home.aspx |title=New Global Standard for Fully Networked Home |publisher= ITU-T Newslog |date=2008-12-12 |access-date=2010-10-11 |url-status=dead |archive-url=https://web.archive.org/web/20090221090736/http://www.itu.int/ITU-T/newslog/New+Global+Standard+For+Fully+Networked+Home.aspx |archive-date=21 February 2009}}</ref> The [[National Energy Marketers Association]] (a US trade body) was also involved in advocating for standards.<ref>{{cite web |title=NEM: National Energy Marketers Association |url=https://www.energymarketers.com |website=www.energymarketers.com|access-date=14 October 2019}}</ref>

In July 2009, the IEEE Power line Communication Standards Committee approved its draft standard for broadband over power lines. The [[IEEE 1901]] final standard was published on 30 December 2010, and included features from HomePlug and Nessum. Power line communication via IEEE 1901 and [[IEEE 1905]] compliant devices is indicated by the [[nVoy]] certification all major vendors of such devices committed to in 2013. &nbsp;[[National Institute of Standards and Technology|NIST]] has included [[IEEE 1901]] (Nessum, [[HomePlug]] AV) and [[ITU-T]] [[G.hn]] as "Additional Standards Identified by NIST Subject to Further Review" for the [[Smart grid in the United States]].<ref>{{cite web|url=http://www.nist.gov/public_affairs/releases/upload/smartgrid_interoperability_final.pdf |title=NIST Framework and Roadmap for Smart Grid Interoperability Standards, Release 1.0 |publisher=Nist.gov |access-date=2012-05-08}}</ref> IEEE also came up with a low-frequency standard for long-distance smart grids called IEEE 1901.2 in 2013.<ref name=ieee1901-2/>


== Applications ==
PLC technology is widely used in the following systems to empower Smart Building, Smart Factory, Smart Grid, and Smart City, etc., as a solution to reduce network construction costs.<ref>{{Cite web |date=2021 |title=What is Power Line Communications |url=https://nessum.org/media/technology-blog/what-is-power-line-communication |website=Nessum}}</ref>

* Advanced Metering Infrastructure (AMI) systems
* Micro-inverters
* HVAC systems
* Elevators
* Storage batteries
* Smart streetlights
* Lighting control systems
* Intercom systems
* Security camera systems

== Challenges for PLC ==
The primary challenge with the PLC to date is the unshielded and untwisted power wiring. This type of wiring releases significant radio energy, potentially disrupting others using the same frequency band. Additionally, the BPL (Broadband over Power Line) systems may experience interference from the radio signals produced by the PLC wiring.<ref name=":0">{{Cite web |last=Pandit |first=Abhimanyu |date=2019 |title=What is Power Line Communication (PLC) and How it works |url=https://circuitdigest.com/article/what-is-power-line-communication-plc-and-how-does-it-work |website=Circuit Digest}}</ref>

For home networks relying on powerline communication technology, how to deal with electrical noise injected into the system from standard household appliances remains the largest challenge. Whenever any appliance is turned on or turned off it creates noise that could possibly disrupt data transfer through the wiring. IEEE products that are certified to be [[HomePlug]] 1.0 compliant have been engineered to no longer interfere with, or receive interference from other devices plugged into the same home's electrical grid.<ref name="plug">“Frequently Asked Questions,” HomePlug Powerline Alliance, http://www.homeplug.org/about/faqs/ {{Webarchive|url=https://web.archive.org/web/20140331191754/http://www.homeplug.org/about/faqs/|date=2014-03-31}} (accessed June 22, 2010).</ref>

== See also ==
* [[HomePNA]]
* [[IEEE 1675-2008]]
* [[KNX (standard)]]
* [[List of broadband over power line deployments]]
* [[Multimedia over Coax Alliance]]
* [[National Emergency Alarm Repeater]]
* [[Residential gateway]]

== References ==
{{reflist}}

==Further reading==
* Powerline Communication: Potential and Critical System, Existing Technologies and Prospects for Future Development http://www.tesionline.it/default/tesi.asp?idt=34078
* {{cite book |title=Applied Protective Relaying|editor1-first= J. L.|editor1-last=Blackburn|year= 1976|publisher= Westinghouse Electric Corp., Relay-Instrument Division|location=Newark, N.J.|isbn= 9781118701515|oclc=2423329 |lccn=76008060}}
* {{cite book |title= Réseaux CPL par la pratique|last= Carcelle|first=Xavier|year= 2006|publisher= Eyrolles|location= Paris|isbn=978-2-212-11930-5|language= fr|oclc=421746698}}


==External links==
==External links==
* {{cite web |title=Nessum |url=https://nessum.org/ |publisher=Nessum Alliance |work=Official web site}}
*[http://library.abb.com/GLOBAL/SCOT/scot221.nsf/VerityDisplay/25E939327490B9E4C1256CF500464EC2/$File/547_PLC_Engineering%20final.pdf ABB description of power line carrier equipment for high-voltage lines]
* [http://www.gobpl.com GoBPL]
*[http://www.osgp.org OSGP Alliance]
*[http://www.etsi.org European Telecommunications Standards Institute]
* Associations or Alliances

** [http://www.plcforum.com PLC Forum]
{{Internet Access}}
** [http://www.upaplc.org Universal Powerline Association]

** [http://www.ist-opera.org/ '''O'''pen '''P'''LC '''R'''esearch '''A'''lliance] (OPERA)
[[Category:Computer networking]]
* [http://www.iqpc.com/NA-2438/ediary BPL 2005, International Powerline Communications Series]
[[Category:Internet access]]
* [http://www.iqpc.com/cgi-bin/templates/genevent.html?event=5359&topic=233 BPL October 2004, International Powerline Communications Series].
[[Category:Electrical grid]]
* [http://www.commercialisingpowerline.com IQPC Leading provider in Powerline Communications Training]
[[Category:Smart grid|*]]
* [http://www.etsi.org/plt/ PLT standard]
* Utilities
** Austria
*** [http://www.linzag.at Linz AG]
*** [http://www.tiwag.at/ TiWag]
** Germany
*** [http://www.drewag.de/ Drewag]
*** [http://www.stadtwerke-hameln.de/ Stadtwerke Hameln]
** Spain
*** [http://www.iberdrola.es Iberdrola]
*** [http://www.unionfenosa.es/ Union Fenosa]
*** [http://www.plcendesa.com/ PLC Endesa], Spanish utility offering commercial PLC to their customers since September 2001
** Switzerland
*** [http://www.eef.ch/ EEF], Swiss utility offering commercial broadband PLC to their customers since September 2001
** USA
*** [http://www.cinergy.com/ Cinergy]
* [http://www.arrl.org/tis/info/HTML/plc/other-articles.html, Broadband Over Power Line (BPL) and Amateur Radio]
* [http://www.qrpis.org/~k3ng/bpl.html BPL FAQ]
* News
** [http://www.computerworld.com/governmenttopics/government/policy/story/0%2C10801%2C90212%2C00.html FCC moves ahead with power-line broadband rules]
** [http://www.ibec.net/ International Broadband Electric Communications - Company providing BPL Internet Access]: BPL vendors such as Amperion Inc. and Current Technologies LLC have begun offering BPL service in limited areas.
* Technologie developers
** [http://www.ds2.es] [[DS2]], Design of Systems on Silicon Spanish chipset developer
* Related technologie
** [http://www.homeplug.org Homeplug]
** [http://www.homeplug.org/news/press102104.html HomePlug Press Release on FCC Rulemaking Affecting BPL]
[[Category:Electrical engineering]]
[[Category:Telecommunications]]
[[Category:Broadband]]
[[Category:Internet]]
[[de:Powerline]] [[es:Power line communication]]
[[fr:Courants porteurs en ligne]]
[[ja:&#38651;&#21147;&#32218;&#25644;&#36865;&#36890;&#20449;]]

Latest revision as of 20:19, 6 December 2024

Power line adapter

Power-line communication (PLC) is the carrying of data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. The line that does so is known as a power-line carrier.

In the past, power lines were solely used for transmitting electricity. However, with the introduction of advanced networking technologies, there has been a push for utility and service providers to find cost-effective and high-performance solutions. The possibility of using powerlines as a universal medium to transmit not just electricity or control signals, but also high-speed data and multimedia, is now under investigation.[by whom?][1]

A wide range of power-line communication technologies are needed for different applications, ranging from home automation to Internet access, which is often called broadband over power lines (BPL). Most PLC technologies limit themselves to one type of wires (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations.

A number of difficult technical problems are common between wireless and power-line communication, notably those of spread spectrum radio signals operating in a crowded environment. Radio interference, for example, has long been a concern of amateur radio groups.[2]

Basics

[edit]

Power-line communications systems operate by adding a modulated carrier signal to the wiring system. Different types of power-line communications use different frequency bands. Since the power distribution system was originally intended for transmission of AC power at typical frequencies of 50 or 60 Hz, power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power-line communications.

The main issue determining the frequencies of power-line communication is laws to limit interference with radio services. Many nations regulate unshielded wired emissions as if they were radio transmitters. These jurisdictions usually require unlicensed uses to be below 500 kHz or in unlicensed radio bands. Some jurisdictions (such as the EU), regulate wire-line transmissions further. The U.S. is a notable exception, permitting limited-power wide-band signals to be injected into unshielded wiring, as long as the wiring is not designed to propagate radio waves in free space.

Data rates and distance limits vary widely over many power-line communication standards. Low-frequency (about 100–200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates the need for installation of dedicated network cabling.

Types of PLC

[edit]

Although different protocols and legislation exists throughout the world, there are basically only two types of PLC: the indoor PLC and the outdoor PLC.[3]

  • Indoor PLC: indoor PLC is used for LAN networking and narrowband in-house applications, such as home automation. It uses house power wiring to transmit data, injecting the current directly in the power plugs.
  • Outdoor PLC: applied in the main power line transmissions, such as low-frequency PLC (for telemetry and grid control), and in BPL, for internet transmission via power network. In this type of PLC, the equipment must be robust, to deal with the high voltage levels of the power lines.

Ripple control

[edit]

Ripple control adds an audio-frequency tone to an AC line. Typical frequencies are from 100 to 2400 Hz. Each district usually has its own frequency, so that adjacent areas are unaffected. Codes are sent by slowly turning the tone on and off. Equipment at a customer site receives the codes, and turns customer equipment off and on. Often the decoder is part of a standard electricity meter, and controls relays. There are also utility codes, e.g. to set the clocks of the power meters at midnight.

In this way, the utility can avoid up to 20% of capital expenses for generating equipment. This lowers costs for electricity and fuel usage. Brownouts and rolling blackouts are more easily prevented. Grids that use cogeneration can enable auxiliary customer equipment when the generators are being run to generate heat rather than electricity.

An annoyance for customers is that sometimes the code to turn equipment on is lost, or load shedding is inconvenient or dangerous. For example, during a party, a dangerous heat wave or when life-preserving medical equipment is on-site. To handle these cases, some equipment includes switches to circumvent load shedding. Some meters switch into a higher billing rate when the party switch is flipped.

Long haul, low frequency

[edit]

Utility companies use special coupling capacitors to connect radio transmitters and receivers to the AC power-carrying conductors. Power meters often use small transformers with linear amplifiers in the range of tens of watts. Most of the expense of any PLC system is the power electronics. By comparison, the electronics to encode and decode is usually small, in a special-purpose integrated circuit. Thus even the complicated OFDM standards can still be economical.

Frequencies used are in the range of 24 to 500 kHz, with transmitter power levels up to hundreds of watts. These signals may be impressed on one conductor, on two conductors or on all three conductors of a high-voltage AC transmission line. Several PLC channels may be coupled onto one HV line. Filtering devices are applied at substations to prevent the carrier frequency current from being bypassed through the station apparatus and to ensure that distant faults do not affect the isolated segments of the PLC system. These circuits are used for control of switchgear, and for protection of transmission lines. For example, a protective relay can use a PLC channel to trip a line if a fault is detected between its two terminals but to leave the line in operation if the fault is elsewhere on the system.

While utility companies use microwave and now, increasingly, fiber-optic cables for their primary system communication needs, the power-line carrier apparatus may still be useful as a backup channel or for very simple low-cost installations that do not warrant installing fiber optic lines, or which are inaccessible to radio or other communication.

Power-line carrier communication (PLCC) is mainly used for telecommunication, tele-protection and tele-monitoring between electrical substations through power lines at high voltages, such as 110 kV, 220 kV, 400 kV.[4]

The modulation generally used in these system is amplitude modulation. The carrier frequency range is used for audio signals, protection and a pilot frequency. The pilot frequency is a signal in the audio range that is transmitted continuously for failure detection.

The voice signal is compressed and filtered into the 300 Hz to 4000 Hz range, and this audio frequency is mixed with the carrier frequency. The carrier frequency is again filtered, amplified and transmitted. The transmission power of these HF carrier frequencies will be in the range of 0 to +32 dbW. This range is set according to the distance between substations.

PLCC can be used for interconnecting private branch exchanges (PBXs).

To sectionalize the transmission network and protect against failures, a wave trap is connected in series with the power (transmission) line. They consist of one or more sections of resonant circuits, which block the high-frequency carrier waves (24–500 kHz) and let power frequency current (50–60 Hz) pass through. Wave traps are used in the switchyards of most power stations to prevent carriers from entering the station equipment. Each wave trap has a lightning arrester to protect it from surge voltages.

A coupling capacitor is used to connect the transmitters and receivers to the high-voltage line. This provides a low-impedance path for carrier energy to HV line but blocks the power frequency circuit by being a high-impedance path. The coupling capacitor may be part of a capacitor voltage transformer used for voltage measurement.

Power-line carrier systems have long been a favorite at many utilities because it allows them to reliably move data over an infrastructure that they control.

A PLC carrier repeating station is a facility, at which a power-line communication (PLC) signal on a powerline is refreshed. Therefore the signal is filtered out from the powerline, demodulated and modulated on a new carrier frequency, and then reinjected onto the powerline again. As PLC signals can carry long distances (several hundred kilometers), such facilities only exist on very long power lines using PLC equipment.

PLC is one of the technologies used for automatic meter reading. Both one-way and two-way systems have been successfully used for decades. Interest in this application has grown substantially in recent history—not so much because there is an interest in automating a manual process, but because there is an interest in obtaining fresh data from all metered points in order to better control and operate the system. PLC is one of the technologies being used in Advanced Metering Infrastructure (AMI) systems.

In a one-way (inbound only) system, readings bubble up from end devices (such as meters), through the communication infrastructure, to a master station which publishes the readings. A one-way system might be lower-cost than a two-way system, but also is difficult to reconfigure should the operating environment change.

In a two-way system (supporting both outbound and inbound), commands can be broadcast out from the master station to end devices (meters) – allowing for reconfiguration of the network, or to obtain readings, or to convey messages, etc. The device at the end of the network may then respond (inbound) with a message that carries the desired value. Outbound messages injected at a utility substation will propagate to all points downstream. This type of broadcast allows the communication system to simultaneously reach many thousands of devices—all of which are known to have power, and have been previously identified as candidates for load shed. PLC also may be a component of a smart grid.

Medium frequency (100 kHz)

[edit]

These systems are often used in countries in which it is illegal to transmit signals that interfere with normal radio. The frequencies are so low that they are unable to start radio waves when sent over the utility wiring.

Home control (narrowband)

[edit]

Power-line communications technology can use the electrical power wiring within a home for home automation: for example, remote control of lighting and appliances without installation of additional control wiring.

Typically home-control power-line communication devices operate by modulating in a carrier wave of between 20 and 200 kHz into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver. These devices may be either plugged into regular power outlets or permanently wired in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same distribution system, these control schemes have a house address that designates the owner. A popular technology known as X10 has been used since the 1970s.[5]

The universal powerline bus, introduced in 1999, uses pulse-position modulation (PPM). The physical layer method is a very different scheme than the X10.[6] LonTalk, part of the LonWorks home automation product line, was accepted as part of some automation standards.[7]

Low-speed narrow-band

[edit]

Narrowband power-line communications began soon after electrical power supply became widespread. Around the year 1922 the first carrier frequency systems began to operate over high-tension lines with frequencies of 15 to 500 kHz for telemetry purposes, and this continues.[8] Consumer products such as baby alarms have been available at least since 1940.[9]

In the 1930s, ripple carrier signaling was introduced on the medium (10–20 kV) and low voltage (240/415 V) distribution systems.

For many years the search continued for a cheap bi-directional technology suitable for applications such as remote meter reading. French electric power Électricité de France (EDF) prototyped and standardized a system called spread frequency shift keying or S-FSK. (See IEC 61334) It is now a simple, low cost system with a long history, however it has a very slow transmission rate. In the 1970s, the Tokyo Electric Power Company ran experiments that reported successful bi-directional operation with several hundred units.[10] As of 2012 the system was widely used in Italy and some other parts of the EU.

S-FSK sends a burst of 2, 4 or 8 tones centered around the time when the AC line passes through zero voltage. In this way, the tones avoid most radio-frequency noise from arcing. (It is common for dirty insulators to arc at the highest point of the voltage, and thus generate a wide-band burst of noise.) To avoid other interference, receivers can improve their signal-to-noise ratio by measuring the power of only the 1 tones, only the 0 tones or the differential power of both. Different districts use different tone pairs to avoid interference. The bit timing is typically recovered from the boundaries between tones, in a way similar to a UART. Timing is roughly centered on the zero crossing with a timer from the previous zero crossing. Typical speeds are 200 to 1200 bits per second, with one bit per tone slot. Speeds also depend on the AC line frequency. The speed is limited by noise, and the jitter of the AC line's zero crossing, which is affected by local loads. These systems are usually bidirectional, with both meters and central stations sending data and commands. Higher levels of the protocols can have stations (usually smart meters) retransmit messages. (See IEC 61334)

Since the mid-1980s, there has been a surge of interest in using the potential of digital communications techniques and digital signal processing. The drive is to produce a reliable system that is cheap enough to be widely installed and able to compete cost effectively with wireless solutions. But the narrowband powerline communications channel presents many technical challenges, a mathematical channel model and a survey of work is available.[11]

Applications of mains communications vary enormously, as would be expected of such a widely available medium. One natural application of narrow-band power-line communication is the control and telemetry of electrical equipment such as meters, switches, heaters and domestic appliances. A number of active developments are considering such applications from a systems point of view, such as demand side management.[12] In this, domestic appliances would intelligently co-ordinate their use of resources, for example limiting peak loads.

Control and telemetry applications include both utility side applications, which involve equipment belonging to the utility company up to the domestic meter, and consumer-side applications which involve equipment in the consumer's premises. Possible utility-side applications include automatic meter reading (AMR), dynamic tariff control, load management, load profile recording, credit control, pre-payment, remote connection, fraud detection and network management,[13] and could be extended to include gas and water.

Open Smart Grid Protocol (OSGP) is one of the most proven narrowband PLC technologies and protocols for smart metering. There are[as of?] more than five million smart meters, based on OSGP and using BPSK PLC, installed and operating around the World. The OSGP Alliance, a non-profit association originally established as ESNA in 2006, led an effort to establish a family of specifications published by the European Telecommunications Standards Institute (ETSI) used in conjunction with the ISO/IEC 14908 control networking standard for smart grid applications. OSGP is optimized to provide reliable and efficient delivery of command and control information for smart meters, direct load control modules, solar panels, gateways, and other smart grid devices. OSGP follows a modern, structured approach based on the OSI protocol model to meet the evolving challenges of the smart grid.

At the physical layer, OSGP currently uses ETSI 103 908 as its technology standard. This uses binary phase shift keying at 3592.98 BAUD, using a carrier tone of 86.232 KHz +/- 200ppm.[14] (Note: The bit clock is almost exactly 1/24 of the carrier.) At the OSGP application layer, ETSI TS 104 001 provides a table-oriented data storage based, in part, on the ANSI C12.19 / MC12.19 / 2012 / IEEE Std 1377 standards for Utility Industry End Device Data Tables and ANSI C12.18 / MC12.18 / IEEE Std 1701, for its services and payload encapsulation. This standard and command system provides not only for smart meters and related data but also for general-purpose extension to other smart grid devices.

A project of EDF, France includes demand management, street lighting control, remote metering and billing, customer-specific tariff optimization, contract management, expense estimation and gas applications safety.[15]

There are also many specialized niche applications that use the mains supply within the home as a convenient data link for telemetry. For example, in the UK and Europe a TV audience monitoring system uses powerline communications as a convenient data path between devices that monitor TV viewing activity in different rooms in a home and a data concentrator which is connected to a telephone modem.

Medium-speed narrow-band

[edit]

The Distribution Line Carrier (DLC) System technology used a frequency range of 9 to 500 kHz with data rate up to 576 kbit/s.[16]

A project called Real-time Energy Management via Powerlines and Internet (REMPLI) was funded from 2003 to 2006 by the European Commission.[17]

More modern systems use OFDM to send data at faster bit rates without causing radio frequency interference. These utilize hundreds of slowly-sending data channels. Usually, they can adapt to noise by turning off channels with interference. The extra expense of the encoding devices is minor compared to the cost of the electronics to transmit. The transmission electronics is usually a high-power operational amplifier, a coupling transformer and a power supply. Similar transmission electronics is required on older, slower systems, so with improved technology, improved performance can be very affordable.

In 2009, a group of vendors formed the PoweRline Intelligent Metering Evolution (PRIME) alliance.[18] As delivered, the physical layer is OFDM, sampled at 250 kHz, with 512 differential phase shift keying channels from 42–89 kHz. Its fastest transmission rate is 128.6 kbit/s, while its most robust is 21.4 kbit/s. It uses a convolutional code for error detection and correction. The upper layer is usually IPv4.[19]

In 2011, several companies including distribution network operators (ERDF, Enexis), meter vendors (Sagemcom, Landis&Gyr) and chip vendors (Maxim Integrated, Texas Instruments, STMicroelectronics, Renesas) founded the G3-PLC Alliance[20] to promote G3-PLC technology. G3-PLC is the low-layer protocol to enable large scale infrastructure on the electrical grid. G3-PLC may operate on CENELEC A band (35 to 91 kHz) or CENELEC B band (98 kHz to 122 kHz) in Europe, on ARIB band (155 kHz to 403 kHz) in Japan and on FCC (155 kHz to 487 kHz) for the US and the rest of the world. The technology used is OFDM sampled at 400 kHz with adaptative modulation and tone mapping. Error detection and correction is made by both a convolutional code and Reed-Solomon error correction. The required media access control is taken from IEEE 802.15.4, a radio standard. In the protocol, 6loWPAN has been chosen to adapt IPv6 an internet network layer to constrained environments which is Power line communications. 6loWPAN integrates routing, based on the mesh network LOADng, header compression, fragmentation and security. G3-PLC has been designed for extremely robust communication based on reliable and highly secured connections between devices, including crossing Medium Voltage to Low Voltage transformers. With the use of IPv6, G3-PLC enables communication between meters, grid actuators as well as smart objects. In December 2011, G3 PLC technology was recognized as an international standard at ITU in Geneva where it is referenced as G.9903,[21] Narrowband orthogonal frequency division multiplexing power line communication transceivers for G3-PLC networks.

Transmitting radio programs

[edit]

Sometimes PLC was used for transmitting radio programs over powerlines. When operated in the AM radio band, it is known as a carrier current system.

High frequency (≥ 1 MHz)

[edit]

High-frequency communication may (re)use large portions of the radio spectrum for communication, or may use select (narrow) band(s), depending on the technology.

Home networking (LAN)

[edit]

Power line communications can also be used in a home to interconnect home computers and peripherals, and home entertainment devices that have an Ethernet port. Powerline adapter sets plug into power outlets to establish an Ethernet connection using the existing electrical wiring in the home (power strips with filtering may absorb the power line signal). This allows devices to share data without the inconvenience of running dedicated network cables.

The widely deployed powerline networking standard are from Nessum Alliance and HomePlug Powerline Alliance. HomePlug Powerline Alliance announced in October 2016 that it would wind down its activities, and the Alliance website (homeplug.org) has been closed. Nessum (formerly HD-PLC), and HomePlug AV which is the most current of the HomePlug specifications were adopted by the IEEE 1901 group as baseline technologies for their standard, published 30 December 2010. HomePlug estimates that over 45 million HomePlug devices have been deployed worldwide. Other companies and organizations back different specifications for power line home networking and these include the Universal Powerline Association, SiConnect, Xsilon, and the ITU-T's G.hn (HomeGrid) specification.

Non-home networking (LAN)

[edit]

With the diversification of IoT applications, the demand for high-speed data communication such as transmission of high-definition video data and/or high-frequent sensor data is increasing in the field of smart building, smart factory, smart city, etc. In such use cases, power line communication technologies can also be used and provides the same advantage of reusing existing cables.

Nessum has developed a multi-hop technology that can be used to build large-scale networks. In addition, the latest Nessum technology (4th-generation HD-PLC technology) provides multiple channels, which enables high-speed and long-range communication by selecting the optimal channel.

Broadband over power line

[edit]

Broadband over power line (BPL) is a system to transmit two-way data over existing AC MV (medium voltage) electrical distribution wiring, between transformers, and AC LV (low voltage) wiring between transformer and customer outlets (typically 100 to 240 V). This avoids the expense of a dedicated network of wires for data communication, and the expense of maintaining a dedicated network of antennas, radios and routers in a wireless network.

BPL uses some of the same radio frequencies used for over-the-air radio systems. Modern BPL employs Wavelet-OFDM, FFT-OFDM, or frequency-hopping spread spectrum to avoid using those frequencies actually in use, though early pre-2010 BPL standards did not. The criticisms of BPL from this perspective are of pre-OPERA, pre-1905 standards.

The BPL OPERA standard is used primarily in Europe by ISPs. In North America, it is used in some places (Washington Island, WI, for instance) but is more generally used by electric distribution utilities for smart meters and load management.

Since the ratification of the IEEE 1901 (Nessum, HomePlug) LAN standard and its widespread implementation in mainstream router chipsets, the older BPL standards are not competitive for communication between AC outlets within a building, nor between the building and the transformer where MV meets LV lines.

Ultra-high frequency (≥ 100 MHz)

[edit]

Even higher information rate transmissions over power line use RF through microwave frequencies transmitted via a transverse mode surface wave propagation mechanism that requires only a single conductor. An implementation of this technology is marketed as E-Line. These use microwaves instead of the lower frequency bands, up to 2–20 GHz. While these may interfere with radio astronomy[22] when used outdoors, the advantages of speeds competitive with fiber optic cables without new wiring are likely to outweigh that.

These systems claim symmetric and full duplex communication in excess of 1 Gbit/s in each direction.[23] Multiple Wi-Fi channels with simultaneous analog television in the 2.4 and 5.0 GHz unlicensed bands have been demonstrated operating over a single medium voltage line conductor. Because the underlying propagation mode is extremely broadband (in the technical sense), it can operate anywhere in the 20 MHz – 20 GHz region. Also since it is not restricted to below 80 MHz, as is the case for high-frequency BPL, these systems can avoid the interference issues associated with use of shared spectrum with other licensed or unlicensed services.[24]

Standards

[edit]

Two distinctly different sets of standards apply to powerline networking as of early 2010.

Within homes, the IEEE 1901 standards specify how, globally, existing AC wires should be employed for data purposes. The IEEE 1901 includes Nessum and HomePlug AV as baseline technologies. Any IEEE 1901 products can coexist and be fully interoperable between products using the same technology. On the other hand, medium-frequency home control devices remain divided, although X10 tends to be dominant. For power grid use, IEEE has approved a low-frequency (≤ 500 kHz) standard called IEEE 1901.2 in 2013.[25]

Standards organizations

[edit]

Several competing organizations have developed specifications, including the HomePlug Powerline Alliance (defunct), Universal Powerline Association (defunct), and Nessum Alliance (active). In October 2009, the ITU-T adopted Recommendation G.hn/G.9960 as a standard of networks for high-speed powerline, coax, and phoneline communications.[26] The National Energy Marketers Association (a US trade body) was also involved in advocating for standards.[27]

In July 2009, the IEEE Power line Communication Standards Committee approved its draft standard for broadband over power lines. The IEEE 1901 final standard was published on 30 December 2010, and included features from HomePlug and Nessum. Power line communication via IEEE 1901 and IEEE 1905 compliant devices is indicated by the nVoy certification all major vendors of such devices committed to in 2013.  NIST has included IEEE 1901 (Nessum, HomePlug AV) and ITU-T G.hn as "Additional Standards Identified by NIST Subject to Further Review" for the Smart grid in the United States.[28] IEEE also came up with a low-frequency standard for long-distance smart grids called IEEE 1901.2 in 2013.[25]


Applications

[edit]

PLC technology is widely used in the following systems to empower Smart Building, Smart Factory, Smart Grid, and Smart City, etc., as a solution to reduce network construction costs.[29]

  • Advanced Metering Infrastructure (AMI) systems
  • Micro-inverters
  • HVAC systems
  • Elevators
  • Storage batteries
  • Smart streetlights
  • Lighting control systems
  • Intercom systems
  • Security camera systems

Challenges for PLC

[edit]

The primary challenge with the PLC to date is the unshielded and untwisted power wiring. This type of wiring releases significant radio energy, potentially disrupting others using the same frequency band. Additionally, the BPL (Broadband over Power Line) systems may experience interference from the radio signals produced by the PLC wiring.[3]

For home networks relying on powerline communication technology, how to deal with electrical noise injected into the system from standard household appliances remains the largest challenge. Whenever any appliance is turned on or turned off it creates noise that could possibly disrupt data transfer through the wiring. IEEE products that are certified to be HomePlug 1.0 compliant have been engineered to no longer interfere with, or receive interference from other devices plugged into the same home's electrical grid.[30]

See also

[edit]

References

[edit]
  1. ^ Sagar, Nishant (2011). Powerline Communications Systems: Overview and Analysis. Rutgers University Libraries (Thesis). doi:10.7282/T3RR1XJ7. Archived from the original on 16 April 2024.
  2. ^ "ARRL Strengthens the Case for Mandatory BPL Notching". News release. American Amateur Radio League. 2 December 2010. Retrieved 24 November 2011.
  3. ^ a b Pandit, Abhimanyu (2019). "What is Power Line Communication (PLC) and How it works". Circuit Digest.
  4. ^ Stanley H. Horowitz; Arun G. Phadke (2008). Power system relaying third edition. John Wiley and Sons. pp. 64–65. ISBN 978-0-470-05712-4.
  5. ^ Edward B.Driscoll Jr. "The history of X10". Retrieved 22 July 2011.
  6. ^ "What is Univeral (sic) Powerline Bus?". Powerline Control Systems, Inc. Archived from the original on 18 July 2011. Retrieved 22 July 2011.
  7. ^ "Echelon Announces ISO/IEC Standardization of LonWorks® Control Networks". News release. Echelon Corporation. 3 December 2008. Archived from the original on 7 April 2012. Retrieved 22 July 2011.
  8. ^ Dostert, K (1997). "Telecommunications over the Power Distribution Grid- Possibilities and Limitations" (PDF). Proc 1997 Internat. Symp. On Power Line Comms and Its Applications: 1–9.
  9. ^ Broadridge, R. (1989). Power line modems and networks. Second IEE National Conference on Telecommunications. London UK. pp. 294–296.
  10. ^ Hosono, M (26–28 October 1982). Improved Automatic meter reading and load control system and its operational achievement. 4th International Conference on Metering, Apparatus and Tariffs for Electricity Supply. IEE. pp. 90–94.
  11. ^ Cooper, D.; Jeans, T. (1 July 2002). "Narrowband, low data rate communications on the low-voltage mains in the CENELEC frequencies. I. Noise and attenuation". IEEE Transactions on Power Delivery. 17 (3): 718–723. doi:10.1109/TPWRD.2002.1022794.
  12. ^ Newbury, J. (January 1998). "Communication requirements and standards for low voltage mains signalling". IEEE Transactions on Power Delivery. 13 (1): 46–52. doi:10.1109/61.660847.
  13. ^ Sheppard, T J (17–19 November 1992). Mains Communications- a practical metering system. 7th International Conference on Metering Applications and Tariffs for Electricity Supply. London UK: IEE. pp. 223–227.
  14. ^ "ETSI TS 103 908 V1.1.1" (PDF). ETSI Delivery. ETSI. Retrieved 16 August 2021.
  15. ^ Duval, G. "Applications of power-line carrier at Electricite de France". Proc 1997 Internat. Symp. On Power Line Comms and Its Applications: 76–80.
  16. ^ "Distribution Line Carrier System". Power-Q Sendirian Bhd. Archived from the original on 20 May 2009. Retrieved 22 July 2011.
  17. ^ "Real-time Energy Management via Powerlines and Internet". official web site. Archived from the original on 14 February 2009. Retrieved 22 July 2011.
  18. ^ "Welcome To PRIME Alliance". Official web site. Retrieved 22 July 2011.
  19. ^ Hoch, Martin (2011). "Comparison of PLC G3 and PRIME" (PDF). 2011 IEEE International Symposium on Power Line Communications and Its Applications. pp. 165–169. doi:10.1109/ISPLC.2011.5764384. ISBN 978-1-4244-7751-7. S2CID 13741019. Archived from the original (PDF) on 10 August 2017. Retrieved 16 May 2012.
  20. ^ "G3-PLC Official Web Site". Official web site. Retrieved 6 March 2013.
  21. ^ "G.9903 ITU-T Web Page". Official web site. Retrieved 6 March 2013.
  22. ^ "Broadband over Power Lines (BPL)". Archived from the original on 12 February 2019. Retrieved 2 September 2019.
  23. ^ Glenn Elmore (August 2006). "Understanding the information rate of BPL and other last-mile pipes". Computing Unplugged magazine. Archived from the original on July 22, 2011. Retrieved July 22, 2011.
  24. ^ Glenn Elmore (27 July 2009). "Introduction to the Propagating TM Wave on a Single Conductor" (PDF). Corridor Systems. Retrieved 22 July 2011.
  25. ^ a b "IEEE 1901.2-2013 - IEEE Standard for Low-Frequency (less than 500 kHz) Narrowband Power Line Communications for Smart Grid Applications". IEEE SA. Archived from the original on 16 December 2018. Retrieved 23 December 2013.
  26. ^ "New Global Standard for Fully Networked Home". ITU-T Newslog. 12 December 2008. Archived from the original on 21 February 2009. Retrieved 11 October 2010.
  27. ^ "NEM: National Energy Marketers Association". www.energymarketers.com. Retrieved 14 October 2019.
  28. ^ "NIST Framework and Roadmap for Smart Grid Interoperability Standards, Release 1.0" (PDF). Nist.gov. Retrieved 8 May 2012.
  29. ^ "What is Power Line Communications". Nessum. 2021.
  30. ^ “Frequently Asked Questions,” HomePlug Powerline Alliance, http://www.homeplug.org/about/faqs/ Archived 2014-03-31 at the Wayback Machine (accessed June 22, 2010).

Further reading

[edit]
[edit]