Power line communication
Encyclopedia
Power line communication or power line carrier (PLC), also known as power line digital subscriber line (PDSL), mains communication, power line telecom (PLT), power line networking (PLN), or broadband over power lines (BPL) are systems for carrying data on a conductor also used for electric power transmission
.
A wide range of power line communication technologies are needed for different apllications, ranging from home automation
to Internet access
.
Electrical power is transmitted over long distances using high voltage transmission lines, distributed over medium voltages, and used inside buildings at lower voltages. Most PLC technologies limit themselves to one set 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.
Potential interference, for example, has been a long concern of amateur radio
groups.
s operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. 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.
Data rate
s 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.
s to connect radio transmitters to the power-frequency AC conductors. Frequencies used are in the range of 24 to 500 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.
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.
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. The major benefit is the union of two applications in a single system, which is particularly useful for monitoring electric equipment and advanced energy management
techniques (such asOpenADR and OpenHAN
).
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 KHz to 500 KHz) and let power frequency current (50 Hz - 60 Hz) pass through. Wave traps are used in switchyard of most power stations to prevent carrier 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 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 carriers may change its transmission system from analog to digital to enable Internet Protocol
devices. Digital power line carrier (DPLC) was developed for digital transmission via power lines. DPLC has the required quality of bit error rate characteristics and transmission ability such as transmitting information from monitored electric-supply stations and images.
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. Many technologies are capable of performing multiple applications. For example, a communication system bought initially for automatic meter reading
can sometimes also be used for load control or for demand response
applications.
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.
: 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.
The "universal powerline bus
", introduced in 1999, uses pulse-position modulation
(PPM). The physical layer method is a very different scheme than the X10. LonTalk
, part of the LonWorks
home automation product line, was accepted as part of some automation standards.
In the 1930s, ripple carrier signalling 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. For example, the Tokyo Electric Power Co ran experiments in the 1970s which reported successful bi-directional operation with several hundred units. 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 which 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.
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. 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 involves equipment belonging to the utility company (i.e. between the supply transformer substation up to the domestic meter), and 'consumer-side' applications which involves 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, and could be extended to include gas and water.
A project of EDF, France includes demand management, street lighting control, remote metering and billing, customer specific tariff optimisation, contract management, expense estimation and gas applications safety.
There are also many specialised niche applications which 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.
A project called Real-time Energy Management via Powerlines and Internet (REMPLI) was funded from 2003 to 2006 by the European Commission
.
In 2009, a group of vendors formed the PoweRline Intelligent Metering Evolution (PRIME) alliance.
system. Such devices were in use in Germany, where it was called Drahtfunk, and in Switzerland, where it was called Telefonrundspruch, and used telephone lines. In the Soviet Union
, PLC was very common for broadcasting since the 1930s because of its low cost and accessibility. In Norway the radiation of PLC systems from powerlines was sometimes used for radio supply. These facilities were called Linjesender
. In all cases the radio programme was fed by special transformers into the lines. To prevent uncontrolled propagation, filters for the carrier frequencies of the PLC systems were installed in substations and at line branches.
An example of the programs carried by "wire broadcasting" in Switzerland:
port. Powerline adapter sets plug into power outlets and 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 video and data without the inconvenience of running dedicated network cables.
The most widely deployed powerline networking standard is from the HomePlug Powerline Alliance
. HomePlug AV is the most current of the HomePlug specifications and was adopted by the IEEE P1901
group as a baseline technology 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
, the HD-PLC Alliance and the ITU-T
’s G.hn
specification.
(DC) battery power-line. Advanced digital communication techniques tailored to overcome hostile and noisy environment are implemented in a small size silicon device. One power line can be used for multiple independent networks. The benefits would be lower cost and weight (compared to separate power and control wiring), flexible modification, and ease of installation. Potential problems in vehicle applications would include the higher cost of end devices, which must be equipped with active controls and communication, and the possibility of intereference with other radio frequency devices in the vehicle or other places.
Prototypes are successfully operational in vehicles, using automotive compatible protocols such as CAN-bus, LIN-bus
over power line (DC-LIN) and [DC-bus].
LonWorks power line based control has been used for an HVAC system in a production model bus.
The SAE J1772
committee developing standard connectors for plug-in electric vehicle
s proposes to use power line communication between the vehicle, off-board charging station
, and the smart grid, without requiring an additional pin; SAE
and the IEEE Standards Association
are sharing their draft standards related to the smart grid and vehicle electrification.
While some have been in widespread use for a decade,
integrated circuits implementing one standard were introduced in May 2011.
service through existing power lines is often marketed as broadband over power lines (BPL), also known as power-line Internet or powerband. 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. International Broadband Electric Communications or IBEC and other companies currently offer BPL service to several electric cooperatives.
BPL may offer benefits over regular cable modem
or digital subscriber line
(DSL) connections: the extensive infrastructure already available appears to allow people in remote locations to access the Internet with relatively little equipment investment by the utility. Cost of running wires such as Ethernet in many buildings can be prohibitive; Relying on wireless has a number of predictable problems including security, limited maximum throughput and inability to power devices efficiently.
But variations in the physical characteristics of the electricity network and the lack of standards mean that provisioning of the service is far from being a standard, repeatable process. And, the bit rate
a power line system can provide compared to cable and wireless is in question. The prospect of BPL was predicted to possibly motivate DSL and cable operators to more quickly serve rural communities.
PLC modems transmit in medium and high frequency (1.6 to 80 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 end
s to the Internet
is up to 135 Mbit/s. To connect to the Internet, utilities
can use optical fiber
backbone
or wireless
link
.
Deployment of BPL has illustrated a number of fundamental challenges, 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. Switching power supplies
often introduce noisy harmonic
s into the line. And unlike coaxial cable
or twisted-pair, the wiring has no inherent noise rejection. The system must be designed to deal with these natural signaling disruptions and work around them. For these reasons BPL can be thought of as a compromise between wireless transmission (where likewise there is little control of the medium through which signals propagate) and wired transmission (but not requiring any new cables).
Broadband over power lines has developed faster in Europe than in the United States due to a historical difference in power system design philosophies. Power distribution uses step-down transformer
s to reduce the voltage for use by customers. BPL signals cannot readily pass through transformers, as their high inductance
makes them act as low-pass filter
s, blocking high-frequency signals. So, repeaters must be attached to the transformers. In the U.S., it is common for a small transformer hung from a utility pole to service a single house or a small number of houses. In Europe, it is more common for a somewhat larger transformer to service 10 or 100 houses. This makes little difference for power distribution. But delivering BPL in a typical U.S. city requires an order of magnitude more repeaters than in a comparable European city. On the other hand, since bandwidth to the transformer is limited, this can increase the speed at which each household can connect, due to fewer people sharing the same line. One possible solution is to use BPL as the backhaul
for wireless communications, for instance by 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.
The second major issue is signal strength
and operating frequency
. The system was expected to use frequencies of 10 to 30 MHz, which has been used for many decades by amateur radio operator
s, as well as international shortwave
broadcasters and a variety of communications systems (military, aeronautical, etc.). Power lines are unshielded and will act as antenna
s for the signals they carry, and they will interfere with shortwave
radio communications. Modern BPL systems use orthogonal frequency-division multiplexing
(|OFDM), which allows them to mitigate interference with radio services by removing specific frequencies used. A 2001 joint study by the American Radio Relay League
(ARRL) and HomePlug Powerline Alliance
showed that for 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 at the notched frequencies" and interference only happened when the "antenna was physically close to the power lines" (however other frequencies still suffer from interference).
What the effects of large scale deployment on PLT modems in house will do to the notching has still to be defined, however in lab tests the notches appear to fill in due to intermodulation between modems.
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
http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group13/index.html#21 when used outdoors, the advantages of speeds competitive with fibre 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. Multiple Wi-Fi channels with simultaneous analog television in the 2.4 and 5.3 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.
adopted rules to facilitate the deployment of "Access BPL", the marketing term for Internet access
service over power lines. The technical rules are more liberal than those advanced by the US national amateur radio
organization, the American Radio Relay League
(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.
One service was announced in 2004 for Ohio
, Kentucky
, and Indiana
.
On 3 August 2006 FCC adopted a memorandum opinion
and an order on broadband over power lines, giving the go-ahead to promote broadband service to all Americans. The order rejected calls from aviation, business, commercial, amateur radio and other sectors of spectrum users to limit or prohibit deployment until further study was completed. FCC chief Kevin Martin said that BPL "holds great promise as a ubiquitous broadband solution that would offer a viable alternative to cable, digital subscriber line, fiber, and wireless broadband solutions".
In the US, simply ignoring wireless users was apparently not legal. The ARRL sued the FCC, claiming that the FCC violated the Administrative Procedure Act
in creating its rules. On 25 April 2008, a US Court of Appeals
agreed with the ARRL that the FCC violated the APA, especially by redacting data from the public that could have shed doubt on the FCC's decision.
US power and telecommunications companies had meanwhile 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 same providers conducting those trials later began commercial roll-outs in limited neighborhoods in selected cities, with some level of user acceptance but also many documented cases of interference reported to the FCC by amateur radio users. Some wireless users filed a petition for reconsideration with the FCC in February 2005.
In 2010, the AARL posposed a required 35 dB "notch depth".
and many other countries, high-voltage power lines are called "the mains" and power line communication is often called power line telecommunication (PLT).
Concern of radio users about the proliferation of PLT technology was acknowledged by the European Commission
who, in August 2001 issued a Harmonised Standard. A Harmonised Standard can be used by manufacturers to demonstrate compliance with the Electromagnetic Compatibility (EMC) Directive (but is not mandatory) and will act as a benchmark for enforcement authorities across Europe.
The UK communications regulator Office of Communication
commissioned a study into PL, published in June 2010.
Ofcom also investigated alleged complaints of interference attributed to PLT apparatus. Complaints are from radio amateurs
, CB radio users and shortwave listeners
and are normally httpresolved. No other radio service has been affected.
The independent study said it was "important that mitigating features are implemented in future
PLT devices." Newer PLT products adopted interference mitigation in their design.
An ‘adjournment debate’ on PLT took place on 18 May 2011, Mark Prisk (Minister for Business and Enterprise) responded on behalf of the government to a question tabled by Mark Lancaster) the adjournment debate can be viewed here, the transcript is here.
A draft European Standard (FprEN 50561-1) for PLT has been developed by CENELEC.
The Electromagnetic Compatibility Industry Association (EMCIA), formed in March 2002 for the benefit of companies involved in the supply, design, test or manufacture of EMC products, or the provision of EMC Services and is a UKTI Accredited Trade Organisation, submitted a stern report to the Parliamentary Committee overseeing broadband, stating that they "..very strongly recommend that the Committee specifically excludes the use of PowerLine Telecommunication (PLT*)..."
The Radio Society of Great Britain is extremely concerned over PLT and has established a Spectrum Defence Fund.
has published the results of a number of tests (The effects of PLT on broadcast reception,PLT and Broadcasting, Co-existence of PLT and Radio Services) to detect interference from BPL installations. It has also made a video (Real Media format), showing broadcast of data and interference from in-home BPL devices.
In April 2009 the Wireless Institute of Australia reported that radio amateurs in Australia appear to be safe from the rollout of a nationwide Broadband over Powerline or BPL system. Australia's government announced that it will be building a system based on fibre optic technology for its backbone - though it would likely still rely on BPL on high-voltage lines in remote areas. This decision would appear to remove the possibility of widespread interference to radio communications from any network-wide adoption of BPL technology, but still leaves as a concern the possibility of interference from in-home use of G.hn over AC.
In June 2007, NATO Research and Technology Organisation
released a report titled HF Interference, Procedures and Tools (RTO-TR-IST-050) which concluded that widespread deployment of BPL may have a "possible detrimental effect upon military HF radio communications and COMINT systems."
Within homes, the HomePlug AV and IEEE 1901 standards specify how, globally, existing AC wires should be employed for data purposes. The IEEE 1901 includes HomePlug AV as a baseline technology, so any IEEE 1901 products are fully interoperable with HomePlug AV, HomePlug Green PHY or the forthcoming HomePlug AV2 specification (under development now and expected to be approved in Q1 2011).
Unlike home users, power providers are more able to consider widespread deployment of fiber optic cables immune to electromagnetic interference (and which do not generate any) and for which mature devices (switches, repeaters) are available. Accordingly there is no one single compelling reason to carry data on the existing power lines themselves as there is in homes, except in remote regions where fibre optic networks would not normally be deployed at all. Power network architectures with many transformers are more likely to be served using fibre.
Even if a home is using BPL it may not necessarily connect to the Internet using a BPL-based gateway (typically a smart meter
), although this would have major advantages to both the consumer and provider. NIST and IEEE have considered whether requiring smart meters to all be fully functioning BPL gateways would not accelerate demand side management and create a uniform market into which security, home control and other providers can sell.
, Universal Powerline Association
and HD-PLC Alliance. On December 2008, the ITU-T adopted Recommendation G.hn
/G.9960 as a standard for high-speed powerline, coax and phoneline communications. The National Energy Marketers Association
was also involved in advocating for standards. IEEE P1901
is an IEEE working group developing the global standard for high speed powerline communications. In July 2009, the working group approved its "IEEE 1901 Draft Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications" as an IEEE draft standard for broadband over power lines defining medium access control
and physical layer
specifications. The IEEE 1901 Draft Standard was published by the IEEE in January 2010, the final standard approved on 30 September 2010 and published on 1 February 2011.
NIST
has included IEEE 1901, 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
.
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
.
A wide range of power line communication technologies are needed for different apllications, ranging from home automation
Home automation
Home automation is the residential extension of "building automation". It is automation of the home, housework or household activity. Home automation may include centralized control of lighting, HVAC , appliances, and other systems, to provide improved convenience, comfort, energy efficiency and...
to Internet access
Internet access
Many technologies and service plans for Internet access allow customers to connect to the Internet.Consumer use first became popular through dial-up connections in the 20th century....
.
Electrical power is transmitted over long distances using high voltage transmission lines, distributed over medium voltages, and used inside buildings at lower voltages. Most PLC technologies limit themselves to one set 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
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
and power line communication, notably those of spread spectrum
Spread spectrum
Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth...
radio signals operating in a crowded environment.
Potential interference, for example, has been a long concern of amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
groups.
Basics
Power line communications systemCommunications system
In telecommunication, a communications system is a collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment usually capable of interconnection and interoperation to form an integrated whole...
s operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power distribution system was originally intended for transmission of AC power
AC power
Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow...
at typical frequencies of 50 or 60 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, 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.
Data rate
Data rate
Data rate can refer to:* Bit rate, or data transfer rate* Data signaling rate* Data rate units-See also:* Baud rate* Channel capacity* Throughput* Bandwidth everything in this page is falsified...
s 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
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
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.
Long haul, low frequency
Utility companies use special coupling capacitorCapacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s to connect radio transmitters to the power-frequency AC conductors. Frequencies used are in the range of 24 to 500 kHz, with transmitter power levels up to hundreds of watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
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
Protective relay
In electrical engineering, a protective relay is a complex electromechanical apparatus, often with more than one coil, designed to calculate operating conditions on an electrical circuit and trip circuit breakers when a fault is detected...
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.
Power line carrier communication (PLCC) is mainly used for telecommunication
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, tele-protection and tele-monitoring between electrical substation
Electrical substation
A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions...
s through power line
Power Line
Power Line is an American political blog, providing news and commentary from a conservative point-of-view. It was originally written by three lawyers who attended Dartmouth College together: John H. Hinderaker, Scott W. Johnson, and Paul Mirengoff...
s at high voltage
High voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...
s, such as 110 kV, 220 kV, 400 kV. The major benefit is the union of two applications in a single system, which is particularly useful for monitoring electric equipment and advanced energy management
Energy management
Energy Management is a degree offered by the University of Oklahoma's Michael F. Price College of Business. The OU degree program was the first of its kind, emerging in 1958 as the Petroleum Land Management program before becoming the Energy Management program in 1999.It is business-specific, with...
techniques (such asOpenADR and OpenHAN
OpenHAN
The openHAN suite of proposed standards for home area networks and home grids is promoted by the openAMI and UtilityAMI . Both efforts aim to standardize powerline networking interoperation from a utility point of view and ensure reliable communications co-extant with AC power outlets.Both...
).
The modulation generally used in these system is amplitude modulation
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
. 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
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
. 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 KHz to 500 KHz) and let power frequency current (50 Hz - 60 Hz) pass through. Wave traps are used in switchyard of most power stations to prevent carrier 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 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
Capacitor voltage transformer
A capacitor voltage transformer , or capacitance coupled voltage transformer is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay...
used for voltage measurement.
Power line carriers may change its transmission system from analog to digital to enable Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
devices. Digital power line carrier (DPLC) was developed for digital transmission via power lines. DPLC has the required quality of bit error rate characteristics and transmission ability such as transmitting information from monitored electric-supply stations and images.
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. Many technologies are capable of performing multiple applications. For example, a communication system bought initially for automatic meter reading
Automatic meter reading
Automatic meter reading, or AMR, is the technology of automatically collecting consumption, diagnostic, and status data from water meter or energy metering devices and transferring that data to a central database for billing, troubleshooting, and analyzing.This technology mainly saves utility...
can sometimes also be used for load control or for demand response
Demand response
In electricity grids, demand response is similar to dynamic demand mechanisms to manage customer consumption of electricity in response to supply conditions, for example, having electricity customers reduce their consumption at critical times or in response to market prices...
applications.
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.
Home control (narrowband)
Power line communications technology can use the electrical power wiring within a home for home automationHome automation
Home automation is the residential extension of "building automation". It is automation of the home, housework or household activity. Home automation may include centralized control of lighting, HVAC , appliances, and other systems, to provide improved convenience, comfort, energy efficiency and...
: 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
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
of between 20 and 200 kHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
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
X10 (industry standard)
X10 is an international and open industry standard for communication among electronic devices used for home automation, also known as domotics. It primarily uses power line wiring for signaling and control, where the signals involve brief radio frequency bursts representing digital information...
has been used since the 1970s.
The "universal powerline bus
Universal powerline bus
Universal powerline bus is a protocol for communication among devices used for home automation. It uses power line wiring for signaling and control....
", introduced in 1999, uses pulse-position modulation
Pulse-position modulation
Pulse-position modulation is a form of signal modulation in which M message bits are encoded by transmitting a single pulse in one of 2^M possible time-shifts. This is repeated every T seconds, such that the transmitted bit rate is M/T bits per second...
(PPM). The physical layer method is a very different scheme than the X10. LonTalk
LonTalk
LonTalk is a protocol optimized for control created by Echelon Corporation for networking devices over media such as twisted pair, powerlines, fiber optics, and RF...
, part of the LonWorks
LonWorks
LonWorks is a networking platform specifically created to address the needs of control applications. The platform is built on a protocol created by Echelon Corporation for networking devices over media such as twisted pair, powerlines, fiber optics, and RF...
home automation product line, was accepted as part of some automation standards.
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 kHz for telemetry purposes, and this continues. Consumer products such as baby alarms have been available at least since 1940.In the 1930s, ripple carrier signalling 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. For example, the Tokyo Electric Power Co ran experiments in the 1970s which reported successful bi-directional operation with several hundred units. Since the mid-1980s, there has been a surge of interest in using the potential of digital communications techniques and digital signal processing
Digital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
. The drive is to produce a reliable system which 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.
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
Telemetry
Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
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. 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 involves equipment belonging to the utility company (i.e. between the supply transformer substation up to the domestic meter), and 'consumer-side' applications which involves equipment in the consumer's premises. Possible utility-side applications include automatic meter reading
Automatic meter reading
Automatic meter reading, or AMR, is the technology of automatically collecting consumption, diagnostic, and status data from water meter or energy metering devices and transferring that data to a central database for billing, troubleshooting, and analyzing.This technology mainly saves utility...
(AMR), dynamic tariff control, load management, load profile recording, credit control, pre-payment, remote connection, fraud detection and network management, and could be extended to include gas and water.
A project of EDF, France includes demand management, street lighting control, remote metering and billing, customer specific tariff optimisation, contract management, expense estimation and gas applications safety.
There are also many specialised niche applications which 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 kHz with data rate up to 576 kbit/s.A project called Real-time Energy Management via Powerlines and Internet (REMPLI) was funded from 2003 to 2006 by the European Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
.
In 2009, a group of vendors formed the PoweRline Intelligent Metering Evolution (PRIME) alliance.
Transmitting radio programs
Sometimes PLC was used for transmitting radio programs over powerlines. When operated in the AM radio band, it is known as a carrier currentCarrier current
Carrier current is a method of low power AM radio transmission that uses the AC electrical system of a building to propagate a medium frequency, AM signal to a relatively small area, such as a building or a group of buildings...
system. Such devices were in use in Germany, where it was called Drahtfunk, and in Switzerland, where it was called Telefonrundspruch, and used telephone lines. In the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
, PLC was very common for broadcasting since the 1930s because of its low cost and accessibility. In Norway the radiation of PLC systems from powerlines was sometimes used for radio supply. These facilities were called Linjesender
Linjesender
A Linjesender was a low power longwave transmitter used for broadcasting in Norway. It consisted of a power line communication system, which fed the radio programme on a frequency in the longwave broadcasting range into an overhead electric power transmission line.Because Norway has many mountains,...
. In all cases the radio programme was fed by special transformers into the lines. To prevent uncontrolled propagation, filters for the carrier frequencies of the PLC systems were installed in substations and at line branches.
An example of the programs carried by "wire broadcasting" in Switzerland:
- 175 kHz Swiss Radio International
- 208 kHz RSR1 "la première" (French)
- 241 kHz "classical music"
- 274 kHz RSIRadiotelevisione svizzera di lingua italianaRadiotelevisione svizzera di lingua italiana is a Swiss public broadcasting organisation, part of SRG SSR. RSI handles production and broadcasting of radio and television programs in Italian for Switzerland...
1 "rete UNO" (Italian) - 307 kHz DRS 1DRS 1DRS 1 is a Swiss radio channel, one of six operated by SR DRS, with its headquarters in Zürich.Launched in 1931 it was the first German-language radio station for German-speaking Switzerland....
(German) - 340 kHz "easy music"
High-frequency (≥1 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 EthernetEthernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
port. Powerline adapter sets plug into power outlets and 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 video and data without the inconvenience of running dedicated network cables.
The most widely deployed powerline networking standard is from the HomePlug Powerline Alliance
HomePlug Powerline Alliance
The HomePlug Powerline Alliance is a trade association of electronics manufacturers, service providers, and retailers that establishes standards for, and tests members' devices for compliance to, the various power line communication technologies known as HomePlug.The alliance developed standards...
. HomePlug AV is the most current of the HomePlug specifications and was adopted by the IEEE P1901
IEEE P1901
The IEEE 1901 working group of the Institute of Electrical and Electronics Engineers develops standards for high speed power line communications....
group as a baseline technology 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
Universal Powerline Association
The Universal Powerline Association was a trade association that covered power line communication markets and applications. The UPA promoted and certified power line communication technology from 2004 to 2010.-History:...
, the HD-PLC Alliance and the ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
’s G.hn
G.hn
G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
specification.
Automotive uses
Power-line technology enables in-vehicle network communication of data, voice, music and video signals by digital means over direct currentDirect current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
(DC) battery power-line. Advanced digital communication techniques tailored to overcome hostile and noisy environment are implemented in a small size silicon device. One power line can be used for multiple independent networks. The benefits would be lower cost and weight (compared to separate power and control wiring), flexible modification, and ease of installation. Potential problems in vehicle applications would include the higher cost of end devices, which must be equipped with active controls and communication, and the possibility of intereference with other radio frequency devices in the vehicle or other places.
Prototypes are successfully operational in vehicles, using automotive compatible protocols such as CAN-bus, LIN-bus
Local Interconnect Network
The LIN-Bus is a vehicle bus standard or computer networking bus-system used within current automotive network architectures....
over power line (DC-LIN) and [DC-bus].
LonWorks power line based control has been used for an HVAC system in a production model bus.
The SAE J1772
SAE J1772
SAE J1772 is a North American standard for electrical connectors for electric vehicles maintained by the Society of Automotive Engineers and has the formal title "SAE Surface Vehicle Recommended Practice J1772, SAE Electric VehicleConductive Charge Coupler”...
committee developing standard connectors for plug-in electric vehicle
Plug-in electric vehicle
A plug-in electric vehicle is any motor vehicle that can be recharged from any external source of electricity, such as wall sockets, and the electricity stored in the rechargeable battery packs drives or contributes to drive the wheels...
s proposes to use power line communication between the vehicle, off-board charging station
Charging station
An electric vehicle charging station, also called EV charging station, electric recharging point, charging point and EVSE , is an element in an infrastructure that supplies electric energy for the recharging of electric vehicles, plug-in hybrid electric-gasoline vehicles) or semi-static and mobile...
, and the smart grid, without requiring an additional pin; SAE
SAE International
SAE International is an organization for engineering professionals in the aerospace, automotive, and commercial vehicle industries. The Society is a standards development organization for the engineering of powered vehicles of all kinds, including cars, trucks, boats, aircraft, and others.SAE...
and the IEEE Standards Association
IEEE Standards Association
The Institute of Electrical and Electronics Engineers Standards Association is an organization within IEEE that develops global standards in a broad range of industries, including: power and energy, biomedical and health care, information technology, telecommunication, transportation,...
are sharing their draft standards related to the smart grid and vehicle electrification.
Failure scenarios
There are many ways in which the communication signal may have error introduced into it. Interference, cross chatter, some active devices, and some passive devices all introduce noise or attenuation into the signal. When error becomes significant the devices controlled by the unreliable signal may fail, become inoperative, or operate in an undesirable fashion.- Interference: Interference from nearby systems can cause signal degradation as the modem may not be able to determine a specific frequency among many signals in the same bandwidth.
- Signal Attenuation by Active Devices: Devices such as relays, transistors, and rectifiers create noise in their respective systems, increasing the likelihood of signal degradation. Arc-fault circuit interrupterArc-fault circuit interrupterAn Arc Fault Circuit Interrupter is a circuit breaker designed to prevent fires by detecting a non-working electrical arc and disconnecting the power before the arc starts a fire...
(AFCI) devices, required by some recent electrical codes for living spaces, may also attenuate the signals. - Signal Attenuation by Passive Devices: Transformers and DC-DC converters attenuate the input frequency signal almost completely. "Bypass" devices become necessary for the signal to be passed on to the receiving node. A bypass device may consist of three stages, a filter in series with a protection stage and coupler, placed in parallel with the passive device.
Broadband over power line
Very different technologies are needed for higher-rate communication over wider distances, which also have their associated issues.While some have been in widespread use for a decade,
integrated circuits implementing one standard were introduced in May 2011.
Internet access
Internet accessInternet access
Many technologies and service plans for Internet access allow customers to connect to the Internet.Consumer use first became popular through dial-up connections in the 20th century....
service through existing power lines is often marketed as broadband over power lines (BPL), also known as power-line Internet or powerband. A computer (or any other device) would need only to plug a BPL modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
into any outlet in an equipped building to have high-speed Internet access. International Broadband Electric Communications or IBEC and other companies currently offer BPL service to several electric cooperatives.
BPL may offer benefits over regular cable modem
Cable modem
A cable modem is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a HFC and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high...
or digital subscriber line
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
(DSL) connections: the extensive infrastructure already available appears to allow people in remote locations to access the Internet with relatively little equipment investment by the utility. Cost of running wires such as Ethernet in many buildings can be prohibitive; Relying on wireless has a number of predictable problems including security, limited maximum throughput and inability to power devices efficiently.
But variations in the physical characteristics of the electricity network and the lack of standards mean that provisioning of the service is far from being a standard, repeatable process. And, the bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
a power line system can provide compared to cable and wireless is in question. The prospect of BPL was predicted to possibly motivate DSL and cable operators to more quickly serve rural communities.
PLC modems transmit in medium and high frequency (1.6 to 80 MHz electric carrier
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
). The asymmetric
Symmetry
Symmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection...
speed in the modem is generally from 256 kbit/s to 2.7 Mbit/s. In the repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
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
Gateway (telecommunications)
In telecommunications, the term gateway has the following meaning:*In a communications network, a network node equipped for interfacing with another network that uses different protocols....
s to the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
is up to 135 Mbit/s. To connect to the Internet, utilities
Public utility
A public utility is an organization that maintains the infrastructure for a public service . Public utilities are subject to forms of public control and regulation ranging from local community-based groups to state-wide government monopolies...
can use optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
backbone
Backbone network
A backbone network or network backbone is a part of computer network infrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, in different...
or wireless
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
link
Link (telecommunications)
In telecommunications a link is the communications channel that connects two or more communicating devices. This link may be an actual physical link or it may be a logical link that uses one or more actual physical links...
.
Deployment of BPL has illustrated a number of fundamental challenges, 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. Switching power supplies
Switched-mode power supply
A switched-mode power supply is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power...
often introduce noisy harmonic
Harmonic
A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency, i.e. if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. The harmonics have the property that they are all periodic at the fundamental...
s into the line. And unlike coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
or twisted-pair, the wiring has no inherent noise rejection. The system must be designed to deal with these natural signaling disruptions and work around them. For these reasons BPL can be thought of as a compromise between wireless transmission (where likewise there is little control of the medium through which signals propagate) and wired transmission (but not requiring any new cables).
Broadband over power lines has developed faster in Europe than in the United States due to a historical difference in power system design philosophies. Power distribution uses step-down transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s to reduce the voltage for use by customers. BPL signals cannot readily pass through transformers, as their high inductance
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
makes them act as low-pass filter
Low-pass filter
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
s, blocking high-frequency signals. So, repeaters must be attached to the transformers. In the U.S., it is common for a small transformer hung from a utility pole to service a single house or a small number of houses. In Europe, it is more common for a somewhat larger transformer to service 10 or 100 houses. This makes little difference for power distribution. But delivering BPL in a typical U.S. city requires an order of magnitude more repeaters than in a comparable European city. On the other hand, since bandwidth to the transformer is limited, this can increase the speed at which each household can connect, due to fewer people sharing the same line. One possible solution is to use BPL as the backhaul
Backhaul (telecommunications)
In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network, or backbone, of the network and the small subnetworks at the "edge" of the entire hierarchical network...
for wireless communications, for instance by hanging Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
access points or cellphone base stations on utility poles, thus allowing end-users within a certain range to connect with equipment they already have.
The second major issue is signal strength
Signal strength
In telecommunications, particularly in radio, signal strength refers to the magnitude of the electric field at a reference point that is a significant distance from the transmitting antenna. It may also be referred to as received signal level or field strength. Typically, it is expressed in...
and operating frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. The system was expected to use frequencies of 10 to 30 MHz, which has been used for many decades by amateur radio operator
Amateur radio operator
An amateur radio operator is an individual who typically uses equipment at an amateur radio station to engage in two-way personal communications with other similar individuals on radio frequencies assigned to the amateur radio service. Amateur radio operators have been granted an amateur radio...
s, as well as international shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
broadcasters and a variety of communications systems (military, aeronautical, etc.). Power lines are unshielded and will act as antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
s for the signals they carry, and they will interfere with shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
radio communications. Modern BPL systems use orthogonal frequency-division multiplexing
Orthogonal frequency-division multiplexing
Orthogonal frequency-division multiplexing is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio...
(|OFDM), which allows them to mitigate interference with radio services by removing specific frequencies used. A 2001 joint study by the American Radio Relay League
American Radio Relay League
The American Radio Relay League is the largest membership association of amateur radio enthusiasts in the USA. ARRL is a non-profit organization, and was founded in May 1914 by Hiram Percy Maxim of Hartford, Connecticut...
(ARRL) and HomePlug Powerline Alliance
HomePlug Powerline Alliance
The HomePlug Powerline Alliance is a trade association of electronics manufacturers, service providers, and retailers that establishes standards for, and tests members' devices for compliance to, the various power line communication technologies known as HomePlug.The alliance developed standards...
showed that for 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 at the notched frequencies" and interference only happened when the "antenna was physically close to the power lines" (however other frequencies still suffer from interference).
What the effects of large scale deployment on PLT modems in house will do to the notching has still to be defined, however in lab tests the notches appear to fill in due to intermodulation between modems.
Ultra-High-frequency (≥100 MHz)
Even higher information rate transmissions over power line use RF through microwave frequencies transmitted via a transverse modeTransverse mode
A transverse mode of a beam of electromagnetic radiation is a particular electromagnetic field pattern of radiation measured in a plane perpendicular to the propagation direction of the beam...
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
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
http://ntrg.cs.tcd.ie/undergrad/4ba2.05/group13/index.html#21 when used outdoors, the advantages of speeds competitive with fibre 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. Multiple Wi-Fi channels with simultaneous analog television in the 2.4 and 5.3 GHz unlicensed bands have been demonstrated operating over a single medium voltage line conductor. Because the underlying propagation mode is extremely broadband
Broadband
The term broadband refers to a telecommunications signal or device of greater bandwidth, in some sense, than another standard or usual signal or device . Different criteria for "broad" have been applied in different contexts and at different times...
(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.
US FCC
On 14 October 2004, the U.S. Federal Communications CommissionFederal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
adopted rules to facilitate the deployment of "Access BPL", the marketing term for Internet access
Internet access
Many technologies and service plans for Internet access allow customers to connect to the Internet.Consumer use first became popular through dial-up connections in the 20th century....
service over power lines. The technical rules are more liberal than those advanced by the US national amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
organization, the American Radio Relay League
American Radio Relay League
The American Radio Relay League is the largest membership association of amateur radio enthusiasts in the USA. ARRL is a non-profit organization, and was founded in May 1914 by Hiram Percy Maxim of Hartford, Connecticut...
(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.
One service was announced in 2004 for Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
, Kentucky
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...
, and Indiana
Indiana
Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...
.
On 3 August 2006 FCC adopted a memorandum opinion
Memorandum opinion
A memorandum opinion or memorandum decision is a judicial opinion that does not create precedent, persuasive or mandatory in some jurisdictions. A memorandum is often brief and written only to announce judgment in a particular case...
and an order on broadband over power lines, giving the go-ahead to promote broadband service to all Americans. The order rejected calls from aviation, business, commercial, amateur radio and other sectors of spectrum users to limit or prohibit deployment until further study was completed. FCC chief Kevin Martin said that BPL "holds great promise as a ubiquitous broadband solution that would offer a viable alternative to cable, digital subscriber line, fiber, and wireless broadband solutions".
'Notching out' and dynamic adaptation to contention
New FCC rules (and the IEEE standards) 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 were shut down, though whether it was in response to complaints is debatable. The need to deal with signals that inevitably will propagate through thick metal wires hanging above crowded areas was always an issue in BPL standardization and the technologies to resolve it are those already used for wireless, so the issue was primarily one of thresholds and agreement on who had priority for spectrum.In the US, simply ignoring wireless users was apparently not legal. The ARRL sued the FCC, claiming that the FCC violated the Administrative Procedure Act
Administrative Procedure Act
The Administrative Procedure Act , , is the United States federal law that governs the way in which administrative agencies of the federal government of the United States may propose and establish regulations. The APA also sets up a process for the United States federal courts to directly review...
in creating its rules. On 25 April 2008, a US Court of Appeals
United States Court of Appeals for the District of Columbia Circuit
The United States Court of Appeals for the District of Columbia Circuit known informally as the D.C. Circuit, is the federal appellate court for the U.S. District Court for the District of Columbia. Appeals from the D.C. Circuit, as with all the U.S. Courts of Appeals, are heard on a...
agreed with the ARRL that the FCC violated the APA, especially by redacting data from the public that could have shed doubt on the FCC's decision.
- "It is one thing for the Commission to give notice and make available for comment the studies on which it relied in formulating the rule while explaining its non-reliance on certain parts", D.C. Circuit Judge Judith Rogers wrote. "It is quite another thing to provide notice and an opportunity for comment on only those parts of the studies that the Commission likes best."
US power and telecommunications companies had meanwhile 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
American Radio Relay League
The American Radio Relay League is the largest membership association of amateur radio enthusiasts in the USA. ARRL is a non-profit organization, and was founded in May 1914 by Hiram Percy Maxim of Hartford, Connecticut...
and other groups claimed otherwise.
Some of the same providers conducting those trials later began commercial roll-outs in limited neighborhoods in selected cities, with some level of user acceptance but also many documented cases of interference reported to the FCC by amateur radio users. Some wireless users filed a petition for reconsideration with the FCC in February 2005.
In 2010, the AARL posposed a required 35 dB "notch depth".
United Kingdom and Europe
In the United KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and many other countries, high-voltage power lines are called "the mains" and power line communication is often called power line telecommunication (PLT).
Concern of radio users about the proliferation of PLT technology was acknowledged by the European Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
who, in August 2001 issued a Harmonised Standard. A Harmonised Standard can be used by manufacturers to demonstrate compliance with the Electromagnetic Compatibility (EMC) Directive (but is not mandatory) and will act as a benchmark for enforcement authorities across Europe.
The UK communications regulator Office of Communication
Ofcom
Ofcom is the government-approved regulatory authority for the broadcasting and telecommunications industries in the United Kingdom. Ofcom was initially established by the Office of Communications Act 2002. It received its full authority from the Communications Act 2003...
commissioned a study into PL, published in June 2010.
Ofcom also investigated alleged complaints of interference attributed to PLT apparatus. Complaints are from radio amateurs
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
, CB radio users and shortwave listeners
Shortwave listening
Shortwave listening is the hobby of listening to shortwave radio broadcasts located on frequencies between 1700 kHz and 30 MHz. Listeners range from casual users seeking international news and entertainment programming to hobbyists immersed in the technical aspects of radio reception and DXing...
and are normally httpresolved. No other radio service has been affected.
The independent study said it was "important that mitigating features are implemented in future
PLT devices." Newer PLT products adopted interference mitigation in their design.
An ‘adjournment debate’ on PLT took place on 18 May 2011, Mark Prisk (Minister for Business and Enterprise) responded on behalf of the government to a question tabled by Mark Lancaster) the adjournment debate can be viewed here, the transcript is here.
A draft European Standard (FprEN 50561-1) for PLT has been developed by CENELEC.
The Electromagnetic Compatibility Industry Association (EMCIA), formed in March 2002 for the benefit of companies involved in the supply, design, test or manufacture of EMC products, or the provision of EMC Services and is a UKTI Accredited Trade Organisation, submitted a stern report to the Parliamentary Committee overseeing broadband, stating that they "..very strongly recommend that the Committee specifically excludes the use of PowerLine Telecommunication (PLT*)..."
The Radio Society of Great Britain is extremely concerned over PLT and has established a Spectrum Defence Fund.
Other governments
Austria, Australia, New Zealand and other locations have also experienced early BPL's so-called "spectrum pollution" and raised concerns within their governing bodies. In the UK, the BBCBBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
has published the results of a number of tests (The effects of PLT on broadcast reception,PLT and Broadcasting, Co-existence of PLT and Radio Services) to detect interference from BPL installations. It has also made a video (Real Media format), showing broadcast of data and interference from in-home BPL devices.
In April 2009 the Wireless Institute of Australia reported that radio amateurs in Australia appear to be safe from the rollout of a nationwide Broadband over Powerline or BPL system. Australia's government announced that it will be building a system based on fibre optic technology for its backbone - though it would likely still rely on BPL on high-voltage lines in remote areas. This decision would appear to remove the possibility of widespread interference to radio communications from any network-wide adoption of BPL technology, but still leaves as a concern the possibility of interference from in-home use of G.hn over AC.
In June 2007, NATO Research and Technology Organisation
NATO Research and Technology Organisation
The NATO Research and Technology Organisation promotes and conducts co-operative scientific research and exchange of technical information amongst 26 NATO nations and 38 NATO partners...
released a report titled HF Interference, Procedures and Tools (RTO-TR-IST-050) which concluded that widespread deployment of BPL may have a "possible detrimental effect upon military HF radio communications and COMINT systems."
Standards
Two distinctly different sets of standards apply to powerline networking as of early 2010.Within homes, the HomePlug AV and IEEE 1901 standards specify how, globally, existing AC wires should be employed for data purposes. The IEEE 1901 includes HomePlug AV as a baseline technology, so any IEEE 1901 products are fully interoperable with HomePlug AV, HomePlug Green PHY or the forthcoming HomePlug AV2 specification (under development now and expected to be approved in Q1 2011).
Smart grids and use of BPL for telemetry and data provision by powercos
Power providers are also standardizing their internal and external communications including use of BPL technologies to provide direct links to power system components like transformers. In North America another IEEE standard group is supervising these activities.Unlike home users, power providers are more able to consider widespread deployment of fiber optic cables immune to electromagnetic interference (and which do not generate any) and for which mature devices (switches, repeaters) are available. Accordingly there is no one single compelling reason to carry data on the existing power lines themselves as there is in homes, except in remote regions where fibre optic networks would not normally be deployed at all. Power network architectures with many transformers are more likely to be served using fibre.
Even if a home is using BPL it may not necessarily connect to the Internet using a BPL-based gateway (typically a smart meter
Smart meter
A smart meter is usually an electrical meter that records consumption of electric energy in intervals of an hour or less and communicates that information at least daily back to the utility for monitoring and billing purposes. Smart meters enable two-way communication between the meter and the...
), although this would have major advantages to both the consumer and provider. NIST and IEEE have considered whether requiring smart meters to all be fully functioning BPL gateways would not accelerate demand side management and create a uniform market into which security, home control and other providers can sell.
Standards organizations
Several competing organizations have developed specifications, including the HomePlug Powerline AllianceHomePlug Powerline Alliance
The HomePlug Powerline Alliance is a trade association of electronics manufacturers, service providers, and retailers that establishes standards for, and tests members' devices for compliance to, the various power line communication technologies known as HomePlug.The alliance developed standards...
, Universal Powerline Association
Universal Powerline Association
The Universal Powerline Association was a trade association that covered power line communication markets and applications. The UPA promoted and certified power line communication technology from 2004 to 2010.-History:...
and HD-PLC Alliance. On December 2008, the ITU-T adopted Recommendation G.hn
G.hn
G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
/G.9960 as a standard for high-speed powerline, coax and phoneline communications. The National Energy Marketers Association
National Energy Marketers Association
National Energy Marketers Association is a trade association based in Washington, DC that represents wholesale and retail marketers of natural gas, electricity, as well as energy and financial related products....
was also involved in advocating for standards. IEEE P1901
IEEE P1901
The IEEE 1901 working group of the Institute of Electrical and Electronics Engineers develops standards for high speed power line communications....
is an IEEE working group developing the global standard for high speed powerline communications. In July 2009, the working group approved its "IEEE 1901 Draft Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications" as an IEEE draft standard for broadband over power lines defining medium access control
Media Access Control
The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...
and physical layer
Physical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
specifications. The IEEE 1901 Draft Standard was published by the IEEE in January 2010, the final standard approved on 30 September 2010 and published on 1 February 2011.
NIST
National Institute of Standards and Technology
The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
has included IEEE 1901, HomePlug
HomePlug
HomePlug is the family name for various power line communications specifications that support networking over existing home electrical wiring. Several specifications exist under the HomePlug moniker, with each offering unique performance capabilities and coexistence or compatibility with other...
AV and ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
G.hn
G.hn
G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
as "Additional Standards Identified by NIST Subject to Further Review" for the Smart grid in the United States
Smart grid in the United States
Support for the smart grid in the United States became federal policy with passage of the Energy Independence and Security Act of 2007. The law, Title13, sets out $100 million in funding per fiscal year from 2008–2012, establishes a matching program to states, utilities and consumers to build smart...
.
See also
- HomePlug Powerline AllianceHomePlug Powerline AllianceThe HomePlug Powerline Alliance is a trade association of electronics manufacturers, service providers, and retailers that establishes standards for, and tests members' devices for compliance to, the various power line communication technologies known as HomePlug.The alliance developed standards...
- HomePNAHomePNAThe HomePNA Alliance is an incorporated non-profit industry association of companies that develops and standardizes technology for home networking over the existing coaxial cables and telephone wiring within homes.-Overview:HomePNA does not manufacture products, although its members do...
- KNX (standard)KNX (standard)KNX is a standardized , OSI-based network communications protocol for intelligent buildings. KNX is the successor to, and convergence of, three previous standards: the European Home Systems Protocol , BatiBUS, and the European Installation Bus...
- List of broadband over power line deployments
- LonWorksLonWorksLonWorks is a networking platform specifically created to address the needs of control applications. The platform is built on a protocol created by Echelon Corporation for networking devices over media such as twisted pair, powerlines, fiber optics, and RF...
- Multimedia over Coax AllianceMultimedia over Coax AllianceMultimedia over Coax Alliance is a trade group promoting a standard that uses coaxial cables to connect consumer electronics and home networking devices in homes. It allows both data communication and the transfer of audio and video streams....
- PLC carrier repeating stationPLC Carrier Repeating StationA PLC carrier repeating station is a facility, at which a power line communication signal on a powerline is refreshed. Thereforethe signal is filtered out from the powerline, demodulated and modulated on a new carrier frequency, and then put over a LC network on the powerline again...
- Residential gatewayResidential gatewayA residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
- Universal Powerline AssociationUniversal Powerline AssociationThe Universal Powerline Association was a trade association that covered power line communication markets and applications. The UPA promoted and certified power line communication technology from 2004 to 2010.-History:...
- IEC 61334IEC 61334IEC 61334 is a standard for low-speed reliable power line communications by electricity meters, water meters and SCADA.It is also known as S-FSK, for "spread frequency shift keying" and was formerly known as IEC 1334 before IEC's most recent renumbering...