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Power-line communication

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Power line communication (PLC), also called Broadband over Power Lines (BPL) or Power Line Telecoms (PLT), is a wireline technology that is able to use the current electricity networks for data and voice transmission. The carrier can communicate voice and data by superimposing an analog signal over the standard 50 or 60 Hz alternating current (AC). Traditionally electrical utilities used low-speed power-line carrier circuits for control of substations, voice communication, and protection of high-voltage transmission lines. One example of this technology is SCADA. More recently, high-speed data transmission has been developed using the lower voltage transmission lines used for power distribution. A short-range form of power-line carrier is used for home automation and intercoms.

Types of PLC technology

Indoors/Short Range

Indoors, the PLC equipment can use the household electrical power wiring as a transmission medium. This is a technique used in home automation for remote control of lighting and appliances without installation of additional control wiring. The HomePlug system is an example of this technology. The X10 home automation system uses power line communication at the zero crossing voltage point in the AC wave.

Typically these devices operate by injecting a carrier wave of between 20 and 200 kHz into the household wiring at the transmitter. The carrier is modulated by digital signals. Each receiver in the system has an address and can be individually commanded by the signals transmitted over the household wiring and decoded at the receiver. These devices may either be plugged into regular power outlets or else permanently wired in place. Since the carrier signal may propagate to nearby homes (or apartments) on the same distribution system, these control schemes have a "house address" that designates the owner.

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

Outdoors/Long Haul

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 30 to 300 kHz, with transmitter power levels up to hundreds of watts. These signals may be impressed on one conductor, on two conductors or on all three conductors of a high-voltage AC transmission line. Several different PLC channels may be coupled onto one HV line. Filtering devices are applied at substations to prevent the carrier frequency current from 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.


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[1], LIN sub-bus[2] DC-bus[3]. Automotive Applications include Mechatronics (e.g. Climate control, Door module, Immobilizer, Obstacle detector). Telematics and Multimedia.

  • Benefits
    • Saving the Cost and Weight of Ordinary Wiring,
    • Flexible Modifications
    • Simplicity of Installation.
    • Operation over 12V up to 42V power networks

Broadband over power lines

Broadband over Power Lines (BPL) aka 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 offers obvious benefits over regular cable or DSL connections: the extensive infrastructure already available would appear to allow more people in more locations to have access to the Internet. Also, such ubiquitous availability would make it much easier for other electronics, such as 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 standard, repeatable process and the amount of bandwidth a BPL system can provide compared to cable and wireless is in question.

High-speed data transmission, or Broadband over Power Line uses the electric circuit between the electric substations and home networks. A standard used for this is ETSI PLT.

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.

Differences in the electrical distribution systems in North America and Europe affect the implementation of BPL. In North America relatively few homes are connected to each distribution transformer, whereas European practice may have hundreds of homes connected to each substation. Since the BPL signals do not propagate through the distribution transformers, extra equipment is needed in the North American case.

Technology

Technology will deliver speeds of up to 200 Mbit/s at the physical layer and 130 Mbit/s at the application layer using HomePlug AV standard (interoperable with HomePlug 1.0 or Intellon proprietary 85 Mbit/s Turbo mode, already available) or proprietary DS2 technology which is based on OFDM modulation with 1536 carriers and TDD or FDD channel access method. DS2 technology may operate between 1 and 34MHz. It provides a high dynamic range (90 dB) and offers frequency division and time division repeating capabilities. These characteristics allow the implementation of quality of service (QoS) and class of service (CoS) capabilities.

Standards

Several competing standards are evolving including the HomePlug powerline alliance (which has defined the HomePlug 1.0 and the HomePlug AV high-speed networking technology), Universal Powerline Association, and the IEEE. It is unclear which standard will come out ahead. X10 is a de facto standard also used by RadioShack's Plug'n'Power system.


HomePlug Powerline Alliance

http://www.homeplug.com/


HomePlug 1.0

HomePlug 1.0 is the specification for a technology that connects devices to each other through the power lines in a home. HomePlug certified products connect PCs and other devices that use Ethernet, USB and 802.11 "Wi-Fi" technologies to the power line via a HomePlug "bridge" or "adapter" - some products even have HomePlug technology built-in. The HomePlug Alliance evaluated various powerline-networking technologies through an industry-wide, open evaluation process that incorporated theoretical analysis, lab testing and field trials. The criteria included 10 Mbit/s data rate, whole-house coverage, robustness and ease of implementation.


HomePlug AV

HomePlug AV was designed to support the high-bandwidth and low-latency demands of several simultaneous streams of HDTV and VoIP, made concurrently available in over 90% of power outlets in a home. The target applications are in-home distribution of audio-video in home-theater and data-networking environments. For this reason, in the given frequency range, HomePlug AV has pushed Shannon's Law to its limit and will provide a 200 Mbit/s class service at the PHY layer. After overhead considerations, the MAC layer will support over 100 Mbit/s.


HomePlug BPL

Broadband Power Line (BPL) refers to a to-the-home technology. Recently, the HomePlug Alliance announced the formation of the HomePlug Access BPL Working Group, whose first charter is to develop the Market Requirements Document (MRD) for a HomePlug BPL specification. Shortly after that announcement, the Alliance made an open invitation to utilities, ISPs, network operators and other interested parties from around the world, to participate in the development of or provide input for consideration in the MRD. In addition to being the roadmap for developing a BPL specification, the MRD will provide input into the "resource sharing" policy between In-home and BPL uses of powerline technology.


HomePlug Home Automation

Command-and-control applications.


IEEE

http://standards.ieee.org/ http://grouper.ieee.org/groups/ http://www.comsoc.org/


IEEE P1901 - Draft Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications http://grouper.ieee.org/groups/1901/index.html

The project will develop a standard for high speed (>100 Mbit/s at the physical layer) communication devices via alternating current electric power lines, so called Broadband over Power Line (BPL) devices. The standard will use trannsmission frequencies below 100 MHz. This standard will be usable by all classes of BPL devices, including BPL devices used for the first-mile/last-mile connection (<1500m to the premise) to broadband services as well as BPL devices used in buildings for LANs and other data distribution (<100 m between devices).

HomePlug Powerline Alliance and Universal Powerline Association are partecipating in IEEE P1901.


IEEE BPL - Standardization of Broadband Over Power Line Technologies http://grouper.ieee.org/groups/bpl/index.html

IEEE P1675 - Standard for Broadband over Power Line Hardware http://grouper.ieee.org/groups/bop/

IEEE P1775 - Another project approved by NesCom (IEEE Communications Society) on 12 May 2005 focuses on PLC equipment, electromagnetic compatibility requirements, and testing and measurement methods.


OPERA

http://ist-opera.org/

OPERA (Open PLC European Research Alliance)is a R&D Project with a budget of about 20 Million Euros, including a funding of 9 Million Euros from the European Commission (DG Information Society, IST Programme).

The stated scientific and technological objectives of the Project are:

  • Improve current Power Line Communication (PLC) systems - covering low voltage (LV) as well as medium voltage (MV) PLC system and looking at bandwidth, reach, ease of operation, EMC (electromagnetic compatibility), network management, channel modelling. Objectives relate to conditioning the power grid (using couplers and filters) and improving PLC equipment,
  • Develop optimal solutions for connection of the PLC access networks to the backbone networks. The objective in this area is to create well-adapted backbone solutions (LMDS, satellite, MV PLC, etc.). The main aim is to reach all end users independently of where they are,
  • Develop “ready to sell services” over PLC technology and design or improve low cost user terminals.

Furthermore the Project presents the following objectives:

  • Standardisation of PLC systems,
  • Definition of the business plan and procedures for network maintenance and service provisioning, along with market research to know the requirements of end users,
  • Dissemination of the Project results, respecting the intellectual property rights.


Universal Powerline Association (UPA)

http://www.upaplc.org/

The Universal Powerline Association (UPA) aligns industry leaders in the global Powerline Communications (PLC) market and covers all markets and both access and an in-home PLC technology to ensure a level playing field for the deployment of interoperable and coexisting PLC products to the benefit of consumer’s worldwide.

In May 2004, the UPA interest group was established by founding members. These founding members signed a Memorandum of Understanding in September 2004, and the UPA was officially announced in December 2004. The UPA members share a vision of openness and a federated PLC world to harmonize and share standards and regulations globally.

Members of the UPA are: Ambient Corporation, Ascom Powerline Communications, Corinex Communications, DS2, EDF (Electricite de France), Ilevo - Schneider Electric Powerline Communications AB (SEPC), Itochu, Sumitomo Electric Industries, Ltd. (SEI), and TOYOCOM.

Potential for Interference

Some groups oppose the proliferation of this technology, mostly due to its potential to interfere with radio transmissions. As power lines are typically untwisted and unshielded, they are essentially large antennas, and will broadcast large amounts of radio energy (see the American Radio Relay League's article).

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

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

Recently, Motorola has announced a new Low Voltage Access BPL system that has a reduced potential for interference over the Amperion Inc. and Current Technologies LLC systems.

FCC

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

Deployment

  • United States, Virginia: In October 2005 the city of Manassas began the first wide-scale deployment of BPL service in the nation, offering 10 Mbps service for under $30 USD per month to its 35,000 city residents.

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
  • {{|theaust}}

See also

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