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PROJECT REPORT

POWER LINE COMMUNICATION

INTRODUCTION

Power line communication (PLC), also called mains communication, powerline telecoms (PLT), powerband or power line networking (PLN) or powerarea networking (PAN) are terms describing several different systems forusing power distribution wires for simultaneous distribution of data. Thecarrier can communicate voice and data by superimposing an analog signalover the standard 50 or 60 Hz alternating current (AC). It includesBroadband over Power Lines (BPL) with data rates sometimes above 1Mbps and Narrowband over Power Lines with much lower data rates.Traditionally electrical utilities used low-speed power-line carrier circuits forcontrol of substations, voice communication, and protection of high-voltage

transmission lines. High-speed data transmission has been developed usingthe lower voltage transmission lines used for power distribution. A short-

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range form of power-line carrier is used for home automation and intercoms.

APPLICATIONS

1) HOME CONTROL::

Power line communications technology can use the household

electrical power wiring as a transmission medium. This is a technique usedin home automation for remote control of lighting and appliances withoutinstallation of additional control wiring.

Typically home-control power line communications devices operate bymodulating in a carrier wave of between 20 and 200 kHz into the householdwiring at the transmitter. The carrier is modulated by digital signals. Eachreceiver in the system has an address and can be individually commandedby the signals transmitted over the household wiring and decoded at thereceiver. These devices may either be plugged into regular power outlets or

else permanently wired in place. Since the carrier signal may propagate tonearby homes (or apartments) on the same distribution system, thesecontrol schemes have a "house address" that designates the owner.

2) HOME NETWORKING::

Another typical application of power line communications technologyto interconnect (network) home computers, peripherals or other networked

consumer peripherals. At present there is no universal standard forpowerline communication. Standards for power line home networking havebeen developed by a number of different companies within the framework of

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the HomePlug Powerline Alliance and the Universal Powerline Association.

3) INTERNET ACCESS (BROADBAND OVER POWERLINES,BPL)::

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

BPL offers obvious benefits relative to regular cable or DSLconnections: the extensive infrastructure already available would appear toallow 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 thephysical characteristics of the electricity network and the current lack ofIEEE standards mean that provisioning of the service is far from being astandardized, repeatable process, and the amount of bandwidth a BPLsystem can provide compared to cable and wireless is in question.

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

Differences in the electrical distribution systems in North America andEurope affect the implementation of BPL. In North America relatively few

homes are connected to each distribution transformer, whereas Europeanpractice may have hundreds of homes connected to each substation. Sincethe BPL signals do not propagate through the distribution transformers,extra equipment is needed in the North American case. However, sincebandwidth is limited this can increase the speed at which each householdcan connect, due to fewer people sharing the same line.

The system has a number of complex issues, the primary one beingthat power lines are inherently a very noisy environment. Every time adevice turns on or off, it introduces a pop or click into the line. Energy-savingdevices often introduce noisy harmonics into the line. The system must be

designed to deal with these natural signaling disruptions and work aroundthem.

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Broadband over powerlines has developed faster in Europe than inthe US due to a historical difference in power system design philosophies.Nearly all large power grids transmit power at high voltages in order toreduce transmission losses, then near the customer use step-downtransformers to reduce the voltage. Since BPL signals cannot readily passthrough transformers their high inductance makes them act as low-passfilters, blocking high-frequency signals repeaters must be attached to thetransformers. In the US, it is common for a small transformer hung from autility pole to service a single house. In Europe, it is more common for asomewhat larger transformer to service 10 or 100 houses. For deliveringpower to customers, this difference in design makes little difference, but itmeans delivering BPL over the power grid of a typical US city will require anorder of magnitude more repeaters than would be required in a comparableEuropean city. One possible alternative is to use BPL as the backhaul forwireless communications, by for instance hanging Wi-Fi access points or

cellphone base stations on utility poles, thus allowing end-users within acertain range to connect with equipment they already have. In the nearfuture, 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 asinternational shortwave broadcasters and a variety of communicationssystems (military, aeronautical, etc.). Power lines are unshielded and will actas transmitters for the signals they carry, and have the potential tocompletely wipe out the usefulness of the 10 to 30 MHz range for shortwave

communications purposes.

Modern BPL systems use OFDM modulation which allows themitigation of interference with radio services by removing specificfrequencies used. A 2001 joint study by the ARRL and HomePlug powerlinealliance showed that modems using this technique "in general that withmoderate separation of the antenna from the structure containing theHomePlug signal that interference was barely perceptible" and interferenceonly happened when the "antenna was physically close to the power lines".

Much higher speed transmissions using microwave frequenciestransmitted via a newly discovered surface wave propagation mechanismcalled E-Line have been demonstrated using only a single power lineconductor. These systems have shown the potential for symmetric and fullduplex communication well in excess of 1 Gbit/s in each direction. MultipleWiFi channels with simultaneous analog television in the 2.4 and 5.3 GHzunlicensed bands have been demonstrated operating over a single mediumvoltage line. Furthermore, because it can operate anywhere in the 100 MHz- 10 GHz region, this technology can completely avoid the interferenceissues associated with utilizing shared spectrum while offering the greater

flexibility for modulation and protocols found for any other type of microwavesystem.

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4) 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 30 to 300 kHz, with transmitter powerlevels up to hundreds of watts. These signals may be impressed on oneconductor, on two conductors or on all three conductors of a high-voltageAC transmission line. Several different PLC channels may be coupled ontoone HV line. Filtering devices are applied at substations to prevent thecarrier frequency current from being bypassed through the station apparatusand to ensure that distant faults do not affect the isolated segments of thePLC system. These circuits are used for control of switchgear, and forprotection of transmission lines. For example, a protection relay can use aPLC 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, fiberoptic cables for their primary system communication needs, the power-linecarrier apparatus may still be useful as a backup channel or for very simplelow-cost installations that do not warrant a fibre drop.

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

5) TRANSMITTING RADIO PROGRAMMES::

Sometimes PLC was and is used for transmitting radio programmesover powerlines or over telephone lines. Such devices were in use inGermany, where it was called "Drahtfunk" and in Switzerland, where it wascalled "Telefonrundspruch" and used telephone lines. In the USSR PLC wasvery common for broadcasting, because PLC listeners cannot receiveforeign transmissions. In Norway the radiation of PLC systems frompowerlines was sometimes used for radio supply. These facilities were

called Linjesender. In all cases the radio programme was fed by specialtransformers into the lines. In order to prevent uncontrolled propagation,filters for the carrier frequencies of the PLC systems were installed insubstations and at line branches.

An example of the programmes carried by "wire broadcasting" inSwitzerland:

175 kHz Swiss Radio International 208 kHz RSR1 la premire (French)

241 kHz classical music 274 kHz RSI1 rete UN (Italian)

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TECHNOLOGY

Technology is available from designs based on a number of different noncompatible silicon vendor. These include Intellons INT6000 silicon whichmeets the HomePlug AV specification (not interoperable with HomePlug 1.0or Intellons proprietary 85 Mbit/s Turbo mode) or DS2 DSS9 silicon whichcomplies with Universal Powerline Association standards and othersolutions from Panasonic and SiConnect. Some solutions are based onOFDM modulation with 1536 carriers and TDD or FDD channel accessmethod. DS2 silicon may operate between 1 and 34MHz. It provides a highdynamic range (90 dB) and offers frequency division and time divisionrepeating capabilities. These characteristics allow the implementation ofquality of service (QoS) and class of service (CoS) capabilities.Technologies deliver speeds of up to 200 Mbit/s at the physical layer and130 Mbit/s at the application layer although actual throughput rates aremuch lower.

STANDARDS

Several competing standards are evolving including the HomePlugPowerline Alliance, Universal Powerline Association, ETSI, and the IEEE. Itis unclear which standard will come out ahead. X10 is a de facto standardalso used by RadioShacks PlugnPower system.

ETSI PLT::

The project will progress the necessary standards and specificationsto cover the provision of voice and data services over the mains power

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transmission and distribution network and/or in-building electricity wiring.

The standards will be developed in sufficient detail to allowinteroperability 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 conformitywith the relevant EU/EC Directives.

HOMEPLUG POWERLINE ALLIANCE::

The HomePlug Powerline Alliance is a trade group consisting of over65 member companies. It was founded in March 2000 by leading technologycompanies to provide a forum for the creation of specifications for home

power line networking products and services. The Alliances mission is toenable and promote rapid availability, adoption and implementation of cost-effective, interoperable and standards-based home power line networks andproducts. The Sponsors and members of the Board of Directors of theAlliance include: Comcast, Earthlink, GE, Intel, Linksys, Motorola, RadioShack, Samsung, Sharp, and Sony. Because HomePlug technology isbased on the contributions of multiple companies from around the world, theresulting standards offer best of class performance. The HomePlugPowerline Alliance has defined a number of standards:

HomePlug 1.0 specification for connecting devices via power linesin the home

HomePlug AV designed for transmitting HDTV and VoIP around thehome

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 alliances higher-speedpowerline communications technologies. The specification will enableadvanced, whole-house control of lighting, appliances, climate control,security and other devices.

IEEE::

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

IEEE P1775 "Powerline Communication Equipment - Electromagnetic

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Compatibility (EMC) Requirements - Testing and MeasurementMethods" is a working group focused on PLC equipment,electromagnetic compatibility requirements, and testing andmeasurement methods.

IEEE P1901 "IEEE P1901 Draft Standard for Broadband over PowerLine Networks: Medium Access Control and Physical LayerSpecifications" is a working group for delivering broadband over powerlines. The aim is to define medium access control and physical layerspecifications for all classes of BPL devices - from long distanceconnections to those within subscriber premises.

Other related IEEE groups:

IEEE BPL Study Group "Standardization of Broadband Over Power

Line Technologies" drove the creation of the BPL related Pxxxx workinggroups. It still meets time-to-time looking to create new working groupsif needed.

OPERA::

OPERA (Open PLC European Research Alliance) is a R&D Projectwith 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 EuropeanCommission. It aims to develop and validate a plug and play CognitiveBroadband over Power Lines (CBPL) communications equipment that meetthe regulatory requirements concerning electro-magnetic radiations and candeliver high data rates while using with low transmit power spectral densityand working at low signal to noise ratio.

Universal Powerline Association (UPA)::

The Universal Powerline Association (UPA) aligns industry leaders inthe global Powerline Communications (PLC) market and covers all markets

and both access and an in-home PLC technology to ensure a level playingfield for the deployment of interoperable and coexisting PLC products to the

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benefit of consumers worldwide.

The Universal Powerline Association promotes products based on theUPA Digital Home Standard for home networking applications and on theOpera standard for BPL Power line access applications.

POTENTIAL FOR INTERFERENCE

Some groups oppose the proliferation of this technology, mostly due to itspotential to interfere with radio transmissions. As power lines are typicallyuntwisted and unshielded, they are essentially large antennas, and willbroadcast large amounts of radio energy. Because of their lack of shielding,the BPL systems are also at risk of being interfered with by outside radiosignals.

Recently, power and telecommunications companies have started tests ofthe BPL technology, over the protests of the radio groups. After claims ofinterference by these groups, many of the trials were ended early andproclaimed successes, though the ARRL and other groups claimedotherwise. Some of the providers conducting those trials have now beguncommercial roll-outs in limited neighborhoods in selected cities, with somelevel of user acceptance. There have been many documented cases of

interference reported to the FCC by Amateur Radio users. Because of thesecontinued problems, Amateur Radio operators and others filed a petition for

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reconsideration with the FCC in February 2005. Austria, Australia, NewZealand and other locations have also experienced BPLs spectrumpollution and raised concerns within their governing bodies. In the UK, theBBC has published the results of a number of tests to detect interferencefrom 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 outfrequencies on which interference occurs, and of shutting down remotely ifnecessary to resolve the interference. BPL systems operating within FCCPart 15 emissions limits may still interfere with wireless radiocommunications and are required to resolve interference problems. A fewearly trials have been shut down, though whether it was in response tocomplaints is debatable.

Recently, Motorola has announced a new Low Voltage Access BPL systemthat has a reduced potential for interference over the Amperion Inc. andCurrent Technologies LLC systems. The American Radio Relay League wasinvited by Motorola to participate with these tests, and even installed theMotorola system at their headquarters. Preliminary results were verypositive with regard to interference.

FCC::

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

On August 8, 2006 FCC Adopts Memorandum Opinion and Order onBroadband 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 orprohibit deployment until further study is completed. FCC chief Kevin Martinsaid that "holds great promise as a ubiquitous broadband solution that wouldoffer a viable alternative to cable, digital subscriber line, fiber, and wirelessbroadband solutions,"and that BPL was one of the agencys "top priorities."

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NARROWBAND POWER LINE

COMMUNICATION

Narrowband power line communications started soon after the beginning ofwide-spread electrical power supply. Around the year 1922 the first carrierfrequency systems began to operate over high-tension lines in thefrequency range 15 to 500 kHz for telemetry purposes, and this continues tothe present time. Consumer products such as baby alarms have beenavailable at least since 1940.

In the 1930s, ripple carrier signalling was introduced on the medium (10-20kV) and low voltage (240/415V) distribution systems. For many years the

search has been going on for a cost effective bi-directional technologysuitable for applications such as remote meter reading. For example, theTokyo Electric Power Co was running experiments in the 1970s whichreported successful bi-directional operation with several hundred units.Since the mid-eighties there has been a surge of interest in using thepotential of digital communications techniques and digital signal processing.The drive is to produce a reliable system which is cheap enough to bewidely installed and able to compete cost effectively with wireless solutions.The narrowband powerline communications channel presents manytechnical 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 beexpected of such a widely available medium. One natural application ofnarrow band power line communication is the control and telemetry ofelectrical equipment such as meters, switches, heaters and domesticappliances. There are a number of active developments that are consideringsuch applications from a systems point of view, such as Demand SideManagement. In this, domestic appliances would intelligently co-ordinatetheir 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 supplytransformer substation up to the domestic meter), and consumer-sideapplications which involves equipment in the consumers premises. Possibleutility-side applications include automatic meter reading, dynamic tariffcontrol, 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, streetlighting control, remote metering and billing, customer specific tariffoptimisation, contract management, expense estimation and gas

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applications safety.

There are also many specialised niche applications which use the mainssupply within the home as a convenient data link for telemetry. For example,in the UK and Europe a TV audience monitoring system uses powerlinecommunications as a convenient data path between devices that monitor TVviewing activity in different rooms in a home and a data concentrator whichis connected to a telephone modem.