Power-line communication

Power line communication (PLC), also called power line carrier, mains communication, power line telecom (PLT), or power line networking (PLN), are terms describing several different systems for using electric power lines to carry radio signals for communication purposes.

Overview

Home control (Narrowband)

Power line communications technology can use the household electrical power wiring as a transmission medium. INSTEON and X10 are the two most popular, defacto standards utilizing power line communications for home control. This is a technique used in home automation for remote control of lighting and appliances without installation of additional control wiring.

Typically home-control power line communications 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 either be plugged into regular power outlets or else permanently wired in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same distribution system, these control schemes have a "house address" that designates the owner.

Home networking (Broadband)

Power line communications technology can also be used to interconnect (network) home computers, peripherals or other networked consumer peripherals, although at present there is no universal standard for this type of application. Standards for power line home networking have been developed by a number of different companies within the framework of the HomePlug Powerline Alliance and the Universal Powerline Association.

Internet access (Broadband over powerlines, BPL)

Broadband over power lines (BPL), also known as power-line internet or Powerband, is the use of PLC technology to provide broadband Internet access through ordinary power lines. A computer (or any other device) would need only to plug a BPL "modem" into any outlet in an equipped building to have high-speed Internet access.

BPL seems, at first glance, to offer benefits relative to regular cable or DSL connections: the extensive infrastructure already available would appear to allow people in remote locations to have access to the Internet with relatively little equipment investment by the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up.

However, variations in the physical characteristics of the electricity network and the current lack of IEEE standards mean that provisioning of the service is far from being a standardized, repeatable process, and the amount of bandwidth a BPL system can provide compared to cable and wireless is in question. Some industry observers believe the prospect of BPL will motivate DSL and cable operators to more quickly serve rural communities.

PLC modems transmit in medium and high frequency (1.6 to 30 MHz electric carrier). The asymmetric speed in the modem is generally from 256 kbit/s to 2.7 Mbit/s. In the repeater situated in the meter room the speed is up to 45 Mbit/s and can be connected to 256 PLC modems. In the medium voltage stations, the speed from the head ends to the Internet is up to 135 Mbit/s. To connect to the Internet, utilities can use optical fiber backbone or wireless link.

The system has a number of complex issues, the primary one being that power lines are inherently a very noisy environment. Every time a device turns on or off, it introduces a pop or click into the line. Energy-saving devices often introduce noisy harmonics into the line. The system must be designed to deal with these natural signaling disruptions and work around them.

Broadband over powerlines has developed faster in Europe than in the United States due to a historical difference in power system design philosophies. Nearly all large power grids transmit power at high voltages in order to reduce transmission losses, then near the customer use step-down transformers to reduce the voltage. Since BPL signals cannot readily pass through transformers — their high inductance makes them act as low-pass filters, blocking high-frequency signals — repeaters must be attached to the transformers. In the 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. For delivering power to customers, this difference in design makes little difference with power distribution, but it means delivering BPL over the power grid of a typical U.S. city will require an order of magnitude more repeaters than would be required in a comparable European city. However, 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 alternative is to use BPL as the backhaul for wireless communications, by for instance hanging Wi-Fi access points or cellphone base stations on utility poles, thus allowing end-users within a certain range to connect with equipment they already have. In the near future, BPL might also be used as a backhaul for WiMAX networks.

The second major issue is signal strength and operating frequency. The system is expected to use frequencies in the 10 to 30 MHz range, which has been used for decades by amateur radio operators, as well as international shortwave broadcasters and a variety of communications systems (military, aeronautical, etc.). Power lines are unshielded and will act as antennas for the signals they carry, and have the potential to completely wipe out the usefulness of the 10 to 30 MHz range for shortwave communications purposes.

Modern BPL systems use OFDM modulation which allows the mitigation of interference with radio services by removing specific frequencies used. A 2001 joint study by the ARRL and HomePlug powerline alliance showed that modems using this technique "in general that with moderate separation of the antenna from the structure containing the HomePlug signal that interference was barely perceptible" and interference only happened when the "antenna was physically close to the power lines".

Much higher speed transmissions using microwave frequencies transmitted via a newly discovered surface wave propagation mechanism called E-Line have been demonstrated using only a single power line conductor. These systems have shown the potential for symmetric and full duplex communication well in excess of 1 Gbit/s in each direction. Multiple WiFi channels with simultaneous analog television in the 2.4 and 5.3 GHz unlicensed bands have been demonstrated operating over a single medium voltage line. Furthermore, because it can operate anywhere in the 100 MHz - 10 GHz region, this technology can completely avoid the interference issues associated with utilizing shared spectrum while offering the greater flexibility for modulation and protocols found for any other type of microwave system.

Utility applications

Utility companies use special coupling capacitors to connect low-frequency 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 watts. These signals may be impressed on one conductor, on two conductors or on all three conductors of a high-voltage AC transmission line. Several different PLC channels may be coupled onto one HV line. Filtering devices are applied at substations to prevent the carrier frequency current from 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 protection relay can use a PLC channel to trip a line if a fault is detected between its two terminals, but to leave the line in operation if the fault is elsewhere on the system.

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

There are also some very low-bit rate power line communication systems used for automatic meter reading.

Technology

Technology is available from designs based on a number of different non compatible silicon vendor. These include Intellon's INT6000 silicon which meets the HomePlug AV specification (not interoperable with HomePlug 1.0 or Intellon's proprietary 85 Mbit/s Turbo mode) or DS2 DSS9 silicon which complies with Universal Powerline Association standards and other solutions from Panasonic and SiConnect. Some solutions are based on OFDM modulation with 1536 carriers and TDD or FDD channel access method. DS2 silicon may operate between 1 and 34 MHz. It provides a high dynamic range (90 dB) and offers frequency division and time division repeating capabilities. These characteristics allow the implementation of quality of service (QoS) and class of service (CoS) capabilities. Technologies deliver speeds of up to 200 Mbit/s at the physical layer and 130 Mbit/s at the application layer although actual throughput rates are much lower.

Standards

Several competing standards are evolving including the HomePlug Powerline Alliance, Universal Powerline Association, ETSI, and the IEEE. It is unclear which standard will come out ahead. X10 is a de facto standard also used by RadioShack's Plug'n'Power system.

CEPCA

Consumer Electronics Powerline Communications Alliance (CEPCA) (Sony, Mitsubishi and Panasonic) is developing a standard to realize coexistence between various Powerline technologies, available today. [3]

ETSI PLT

The following is from the ETSI PLT homepage [4].

The project will progress the necessary standards and specifications to cover the provision of voice and data services over the mains power transmission and distribution network and/or in-building electricity wiring.

The standards will be developed in sufficient detail to allow interoperability between equipment from different manufacturers and co-existence of multiple powerline systems within the same environment. Harmonized Standards will be developed to allow presumption of conformity with the relevant EU/EC Directives.

HomePlug Powerline Alliance

The HomePlug Powerline Alliance is a trade group consisting of over 65 member companies. It was founded in March 2000 by leading technology companies to provide a forum for the creation of specifications for home power line networking products and services. The Alliance's mission is to enable and promote rapid availability, adoption and implementation of cost-effective, interoperable and standards-based home power line networks and products. The Sponsors and members of the Board of Directors of the Alliance include: Comcast, Earthlink, GE, Intel, Linksys, Motorola, Radio Shack, Samsung, Sharp, and Sony. Because HomePlug technology is based on the contributions of multiple companies from around the world, the resulting standards offer best of class performance. The HomePlug Powerline Alliance has defined a number of standards:

• HomePlug 1.0 — specification for connecting devices via power lines in the home
• HomePlug AV — designed for transmitting HDTV and VoIP around the home
• HomePlug BPL — a working group to develop a specification for to-the-home connection
• Homeplug CC — Command and Control is a low-speed, very low-cost technology intended to complement the alliance's higher-speed powerline communications technologies. The specification will enable advanced, whole-house control of lighting, appliances, climate control, security and other devices.

IEEE

• IEEE P1675 "Standard for Broadband over Power Line Hardware" is a working group working on hardware installation and safety issues.

• IEEE P1775 "Powerline Communication Equipment - Electromagnetic Compatibility (EMC) Requirements - Testing and Measurement Methods" is a working group focused on PLC equipment, electromagnetic compatibility requirements, and testing and measurement methods.

• IEEE P1901 "IEEE P1901 Draft Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications" is a working group for delivering broadband over power lines. The aim is to define medium access control and physical layer specifications for all classes of BPL devices - from long distance connections to those within subscriber premises. Many comapines and standard bodies are participating in the developing IEEE P1901 standard including HomePlug Powerline Alliance, UPA, CEPCA and OPERA; this means a good chance for a unified power line communication standard in the future. Launch is expected in 2008.

• IEEE BPL Study Group — "Standardization of Broadband Over Power Line Technologies" drove the creation of the BPL related Pxxxx working groups. It still meets time-to-time looking to create new working groups if needed. website

LonWorks

LonWorks powerline communication is used world-wide, for example for Home Automation, Street Lighting, Energy Management and Utility Metering. Related standards can be found on [5]

OPERA

OPERA (Open PLC European Research Alliance) is a R&D Project with funding from the European Commission. It aims to improve the existing systems, develop PLC service, and standardise systems.

POWERNET

POWERNET is a R&D Project with funding from the European Commission. It aims to develop and validate a ‘plug and play’ Cognitive Broadband over Power Lines (CBPL) communications equipment that meet the regulatory requirements concerning electro-magnetic radiations and can deliver high data rates while using with low transmit power spectral density and working at low signal to noise ratio.

Universal Powerline Association (UPA)

The Universal Powerline Association (UPA) aligns industry leaders in the global Powerline Communications (PLC) market and covers all markets and both access and an in-home PLC technology to ensure a level playing field for the deployment of interoperable and coexisting PLC products to the benefit of consumers worldwide. UPA promotes products based on the UPA Digital Home Standard for home networking applications and on the Opera standard for BPL Power line access applications.

Potential for interference

Some groups oppose the proliferation of this technology, mostly due to its potential to interfere with radio transmissions. As power lines are typically untwisted and unshielded, they are essentially large antennas, and will broadcast large amounts of radio energy (see the American Radio Relay League's article). Because of their lack of shielding, the BPL systems are also at risk of being interfered with by outside radio signals.

Recently, power and telecommunications companies have started tests of the BPL technology, over the protests of the radio groups. After claims of interference by these groups, many of the trials were ended early and proclaimed successes, though the ARRL and other groups claimed otherwise. Some of the providers conducting those trials have now begun commercial roll-outs in limited neighborhoods in selected cities, with some level of user acceptance. There have been many documented cases of interference reported to the FCC by Amateur Radio users. Because of these continued problems, Amateur Radio operators and others filed a petition for reconsideration with the FCC in February 2005. Austria, Australia, New Zealand and other locations have also experienced BPL's spectrum pollution and raised concerns within their governing bodies. In the UK, the BBC has published the results of a number of tests to detect interference from BPL installations. They have also made a video (Real Media format), showing broadcast of data and interference from in-home BPL devices.

New FCC rules require BPL systems to be capable of remotely notching out frequencies on which interference occurs, and of shutting down remotely if necessary to resolve the interference. BPL systems operating within FCC Part 15 emissions limits may still interfere with wireless radio communications and are required to resolve interference problems. A few early trials have been shut down, though whether it was in response to complaints is debatable.

New Powerline modes are able to detect the existence of SW-Radio services at the location and time of operation by monitoring the ground noise at the socket where the modem is connected to. The frequencies allocated by radio broadcast will be omitted from Powerline communication. Such new technologies remove interferences from powerline modems to SW-Radio broadcast.

FCC

On October 14, 2004, the U.S. Federal Communications Commission adopted rules to facilitate the deployment of "Access BPL" -- i.e., use of BPL to deliver broadband service to homes and businesses. The technical rules are more liberal than those advanced by ARRL and other spectrum users, but include provisions that require BPL providers to investigate and correct any interference they cause. These rules may be subject to future litigation.

On August 8 2006 FCC Adopts Memorandum Opinion and Order on Broadband Over Power Lines giving the go-ahead to Promote Broadband Service to All Americans. The order rejects calls from aviation, business, commercial, amateur radio and other sectors of spectrum users to limit or prohibit deployment until further study is completed. FCC chief Kevin Martin said that "holds great promise as a ubiquitous broadband solution that would offer a viable alternative to cable, digital subscriber line, fiber, and wireless broadband solutions," and that BPL was one of the agency's "top priorities."

Deployment

• South Africa: Goal Technology Solutions has trialled the technology and is offering service in the suburbs of Pretoria with plans to extend coverage to other areas. Based on a Mitsubishi chipset, the company claims a maximum throughput of 90 Mbit/s although initially only "512ADSL equivalent speeds" are available.

• Portugal has recently ended BPL/PLC deployments in the country, reportedly for economic reasons. [6], [7], [8]

• Australia, Tasmania: In September 2005 electricity retailer Aurora Energy began a commercial trial of the technology, offering BPL services to 500 homes in the suburb of Tolmans Hill near Hobart. This followed a successful technological trial earlier that year.

• Canada, Quebec: 2005 PLC communication technology developed by Ariane Controlsis being installed inside and outside existing building to control lights and other energy hungry devices. ROI (return on investments) clearly shows that a lot of energy, thus costs, can be save by adding low cost devices that allows to better manage energy consumption.

• United States: The United Telecom Council publishes the FCC-mandated Interference Resolution Web site, which provides a list of all BPL deployments in the US.

• United States, Virginia: In October 2005 the city of Manassas began the first wide-scale deployment of BPL service in the nation, offering 10 Mbit/s service for under $30 USD per month to its 35,000 city residents, using MainNet BPL technology. On June 16, 2006 FCC directed the Manassas BPL System to resolve Amateurs' interference complaints. The FCC minced no words in detailing what it wants the city and BPL operator COMTek to do to ensure its system complies with Part 15 rules governing BPL systems and even hinted that it may shut down all or part of the system. [9]

• United States: As of April 2007, Motorola has shuttered its Powerline LV Access BPL and reportedly plans to re-purpose the technology to a new system called Powerline MU, which is for use within multiple-unit dwellings. Motorola's system uses only residential-side low-voltage power lines for transmission to reduce the antenna effect, and has successfully demonstrated frequency-notching for reduced potential for interference over the Amperion Inc. and Current Technologies LLC systems. The American Radio Relay League was invited by Motorola to participate with these tests, and even installed the Motorola system at their headquarters. Preliminary results were very positive with regard to interference because the Motorola system does not actually use BPL on the powerlines leading up to the neighborhood. The BPL carrier is only used for the last leg of the trip from the pole to the house and gets the signal to the pole via radio. This cuts down the extremely disruptive interference along nearly the entire length of the trip and instead limits the interference to the area surrounding the last leg to the house.

• BPL vendors such as Amperion Inc., Current Technologies LLC, Corinex, IBEC Inc., and InovaTech have deployed BPL systems in limited areas.

• California approved a plan on April 27, 2006 allowing high-speed internet providers to begin testing delivery of online access using power lines in the state.[10]

• InovaTech has been particularly active throughout Asia Pacific and Oceania regions with many successful trials in Australia, China, Indonesia, Hong Kong, Malaysia, Philippines and Taiwan. InovaTech has recently increased its focus to include Europe, the Middle East and Africa where it has undertaken several successful field trials and is believed to readying commercial operations in several locations. InovaTech is also understood to have a long term trial running in Russia. One of the most active solution providers, InovaTech is the first vendor to develop an integrated offering which integrates telecommunications and energy management capabilities.

• Romania: In January 2006, in the rural locality of Band, Mureş County, a PLC trial was introduced by the Ministry of Communications and Information Technology, offering phone and broadband internet access for €7 per month. The technology was introduced to 50 households. If successful, the technology will be extended to other rural areas throughout Romania.[11]

• Hungary: The first Powerline service in Hungary was realized at September 2003 in the Riverside apartmenthouse in Budapest by 23Vnet Ltd. The PLC equipments where supplied by ASCOM Powerline. After 4 months the service was counting 100 users from 450 apartment owners. The bandwidth is 4.5 Mbit/s. [12]

• Saudi Arabia: ElectroNet has been working with the Saudi Electric Company since 2005 on a Pilot Project using Broadband over Power Lines over Medium Voltage Cables and linking into a Low Voltage distribution within a shopping Mall. The Pilot Project also integrates Automatic Meter Readers. See http://www.electronetonline.com for more detail.

• SACMAC (Saudi Arabian Computer Management Consultants) has signed a deal to become an official system Integrator and Distributor for Mitsubishi PLC. It is expected to become a great successes considering that the existing broadband serviced, monopolized by the Saudi Telecom Company, is slow, expensive and has poor customer service (some clients report that company techs arrive months after ordering). SACMAC has declined to talk about specifics regarding availability and price but says it will start rolling out the service in a few months (as of May 2006) and its price will be lower than current broadband providers.

• Spain: Iberdrola and Endesa the main power companies in Spain, stop their projects to deploy PLC. [13]

• Ghana, West Africa: Cactel (Cactel Communications Ltd) successfully deployed an MV solution pilot in the Graphic Communications Group in Accra (June 2005), an REMS pilot for the Electricity company of Ghana (ECG) and is currently running a 40 user pilot at the University of Ghana in Legon. The current Pilot combines fibre, radio link, Wi-fi and PLC to provide Broadband internet access and telephony, It showcases the inter-operability of the PLC technology and the company's expertise in emerging market design and deployment. Cactel's national deployment aspirations are currently work in progress and the company is in deliberations with the national stakeholders in conjunction with the Ministry of Communications in Ghana (MoC). see http://www.cactel.com

• Philippines is deploying Broadband over Power Lines nationwide as well.

Narrowband power line communication

Narrowband power line communications started soon after the beginning of wide-spread electrical power supply. Around the year 1922 the first carrier frequency systems began to operate over high-tension lines in the frequency range 15 to 500 kHz for telemetry purposes, and this continues to the present time . 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 (240/415V) distribution systems. For many years the search has been going on for a cost effective bi-directional technology suitable for applications such as remote meter reading. For example, the Tokyo Electric Power Co was running experiments in the 1970’s which reported successful bi-directional operation with several hundred units . Since the mid-eighties 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. The narrowband powerline communications channel presents many technical challenges. A mathematical channel model and a survey of work can be found in reference no. 5.

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. There are a number of active developments that 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 (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, 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 side 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.

Transmitting radio programmes

Sometimes PLC was and is used for transmitting radio programmes over powerlines or over telephone lines. 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 USSR PLC was very common for broadcasting, because PLC listeners cannot receive foreign transmissions. 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. In order 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 programmes carried by "wire broadcasting" in Switzerland:

• 175 kHz Swiss Radio International
• 208 kHz RSR1 “la première” (French)
• 241 kHz “classical music”
• 274 kHz RSI1 “rete UN” (Italian)
• 307 kHz DRS1 (German)
• 340 kHz “easy music”

Automotive

Power-line technology enables in-vehicle network communication of Data, Voice, Music and Video signals by digital means over Direct Current (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.

Prototypes are successfully operational in vehicles, using automotive compatible protocols such as CAN-bus, LIN-bus over power line (DC-LIN) and DC-bus developed by Yamar.

Automotive Applications include Mechatronics (e.g. Climate control, Door module, Immobilizer, Obstacle detector), Telematics and Multimedia.

Benefits

• Reduction in cost and weight as compared to ordinary wiring.
• Flexible of modification.
• Simplicity of installation.
• Operation over 12V - 42V power networks.

See also

• Electric power transmission
• HomePlug Powerline Alliance
• HomePNA
• KNX (standard)
• List of PLC manufacturers
• LonWorks
• Multimedia over Coax Alliance
• Power over Ethernet
• Universal Powerline Association

References

• J. L. Blackburn (ed),Applied Protective Relaying, Westinghouse Electric Corporation (1976) Newark, New Jersey USA, no ISBN, Library of Congress Card No. 76-8060
• X.Carcelle Les reseaux CPL, Eyrolles (2006), ISBN : 2-212-11930-5

External links

• Plugtek Broadband Powerline Research eLibrary
• Broadband Over Power Line (BPL) and Amateur Radio
• BPL FAQ - Information on BPL and Radio Spectrum Interference Issues
• BPL Interference Issues in Tasmania - Information on BPL in Tasmania Australia including recordings and emission reports
• Tasmanian BPL Virtual Tours - Virtual Tours of the Mt Nelson and North Hobart BPL Trial areas
• PLT standard
• Conformity Review of FCC R&O on BPL
• BPL Interference Resolution Web site
• Cybertelecom :: Internet over Broadband over Powerlines and federal regulation
• [14]A Broadcast Engineer's Analysis of the Threat and Effect of BPL

Associations or alliances

• INSTEON Alliance
• Consumer Electronics Powerline Communications Alliance
• Universal Powerline Association
• PLC Utilities Alliance
• Homeplug Powerline Alliance
• PLC Forum
• Open PLC European Research Alliance (OPERA)
• Consumer Electronics Powerline Communication Alliance
• KONNEX Association - Home & Building Control (Narrowband PLC)
• [15] (POWERNET: An European Commission funded research project)
• Broadband over Power Lines - Truth in the news about Broadband over power lines
• PLC Solution Providers Alliance - Powerline Communications Alliance