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  • 7/29/2019 Lecture 1_Overview of PLC


    Lecture 1:Introduction and Historical Overview of

    Power Line Communications (PLC)Dr. Osama M. H. AminElectrical Engineering Department

    Assiut University

    Power Line Communications

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    What is this Lecture about?

    Course Objectives Course Information Introduction

    Historical Overview PLC Bands PLC Infrastructure PLC Characteristics (Noise and Channel) PLC Advantages and Disadvantages PLC Applications PLC Challenges PLC Studies and Standards

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    Course Objectives

    Present a wide-ranging introduction to PLC technology Identify the potential benefits of PLC for the future and existing

    communication systems

    Describe technical issues related to PLC Study the PLC channel characterization, communications on the

    physical layer and electromagnetic interference, through

    protocols, networks, standards, and up to systems andimplementations.

    Identify areas for further development of the technology thatwould enhance the communication services.

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    Course Information

    Instructor: Dr. Osama M. H. Aminu Email: [email protected]

    Course Syllabus: see the attached sheet References

    1. Power line communications: Theory and applications for narrowband and broadbandcommunications over power lines, H. C. Ferreira, L. Lampe, J. Newbury and T.G. Swart, 2011, Wiley publisher.

    2. Broadband Power Line Communication Systems: Theory and Applications, J.Anatory, and N. Theethayi, 2010.

    3. Broadband powerline communications: network design, H. Hrasnica, A. Haidineand R. Lehnert, 2004, John Wiley & Sons.

    Grading: To be discussed:u Exam(s), Project, Final, Attendance

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    PLC systems use the existing electrical power lines as a transmissionmedium to provide high-speed telecommunications capabilities bycoupling Radio Frequency (RF) energy onto the power line.

    The The Federal Communications Commission FCC in US hasidentified that broadband PLC has the potential to become an effectivemeans for last-mile delivery of broadband services and may offer acompetitive alternative to digital subscriber line (DSL), cable modem

    services, satellite, Wireless Fidelity (WiFi), fiber optic, and other highspeed internet access technologies. The FCC chose to use the term

    broadband over power line for consumer applications. Many peopleuse the terms PLC and BPL interchangeably.

    PLC is an interdisciplinary field that includes: antennas and propagation,power engineering, electromagnetic compatibility, telecommunications,and others.

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    The availability of much faster digital signal-processingcapabilities and the development of sophisticated modulation,

    encoding, and error correction schemes have allowed the

    introduction of new, low-power designs for carrier current

    devices. These new designs can overcome earlier technicalbandwidth limitations caused by the inherent noise andimpedance mismatches that are common on commercial power


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    Electric power line cables have been optimized for an averagetransmission of power of 50-60 hertz (Hz) and a maximum in

    the range of 400 Hz.

    Most BPL systems are designed to operate in the frequencyspectrum from 1.705 to 30 megahertz (MHz), but occasionallyup to 80 MHz, using MV and LV power distribution network


    HF has the rare ability to support long distance, point-to-pointcommunications with no infrastructure (e.g., repeaters) otherthan the transmission and reception equipment at each end

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    Historical Overview

    In the US, during the 1920s, AT&T was awarded several patents forthese technologies.

    During the 1930s, ripple carrier signaling (RCS) began to operate onpower lines. RCS used the frequency range 125 Hz - 3 KHz withamplitude shift keying (ASK) modulation. RCS provided data rates in

    the order of a few bits per second but this was sufficient for the loadmanagement and automatic reconfiguration of power distributionnetworks that were the most important tasks performed using RCS.

    In the 1950s, power utilities were using low frequencies (

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    PLC Bands

    l Low frequency: 0-1KHzl Utility use for control

    l Medium frequency: 1 Khz- 1 MHzl Residential and commercial control, radio

    l High frequency: 1 MHz 100 MHzl Broadband IH and AC

    l Ultra-high frequency: > 100 MHz

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    PLC Infrastructure

    BPL is designed to take advantage of the in-place electrical power grid,which varies among countries around the world. In the alternatingcurrent (A/C) electrical power grid is a three-tiered hierarchical systemthat is comprised of:

    High voltage (HV): (110380 kV) networks connect the powerstations with large supply regions or big customers. They usually span

    very long distances, allowing power exchange within a continent. High-voltage networks are usually realized with overhead supply cables.

    Medium voltage (MV): (1030 kV) networks supply larger areas,cities and big industrial or commercial customers. Spanned distancesare significantly shorter than in the high-voltage networks. Themedium-voltage networks are realized as both overhead andunderground networks.

    Low voltage (LV): (230/400 V, in the USA 110 V) networks supplythe end users either as individual customers or as single users of abigger customer. Their length is usually up to a few hundred meters. Inurban areas, low-voltage networks are realized with underground

    cables, whereas in rural areas they exist usually as overhead networks.

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    PLC Building blocks

    1. Concentrator/Injector is a device that aggregates the end-userdata onto the grid. Injectors are tied to the Internet backbone

    via fiber of T1 lines and interface to the power lines feeding theBPL service area.


    Repeater is a physical-layer hardware device used on a networkto extend the length, topology, or interconnectivity of thephysical medium beyond that imposed by a single segment.

    3. Extractors provide the interface between the power linescarrying BPL signals and the households within the service area.

    BPL extractors are usually located at each LV distributiontransformer feeding a group of homes.

    4. Router is a device that acts as an interface between twonetworks and provides network management functions.

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    BPL Equipment for Medium-Voltage Lines

    IBEC BPL Regenerator Units

    1st- Generation Unit2nd-Generation Unit

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    HomePlug-Modem Access

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    HomePlug-Compatible Modem ProvidingBroadband to the Power Outlet

    Typical BPLInternet Access Setup

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    5. Inductive couplers are used to connect BPL modems to themedium voltage power lines. An inductive coupler transfers the

    communications signal onto the power line by wrapping around

    the line, without directly connecting to the line. A major

    challenge is how to deliver the signal from the medium voltageline to the low voltage line that enters your house, because thetransformer that lowers the electric power from several

    thousands volts down to 220/110 is a potential barrier to the

    broadband signal.

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    BPL modems use silicon chips designed to send signals overelectric power lines, much like cable and DSL modems use

    silicon chips designed to send signals over cable and telephone

    lines. Advances in processing power have enabled new BPL

    modem chips to overcome difficulties in sendingcommunications signals over the electric power lines.

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    Power Line Characteristics

    The use of power line cables for HF data transmission presents a number oftechnically difficult challenges such as attenuation, random assemblednetwork, variable terminal impedance at different communication signalfrequencies and with the time of day as the networks electrical load pattern

    varies and atmospheric conditions (temperature, humidity, barometric

    pressure, lightning, sunspots, and the distance above ground all have aneffect).

    Despite the aforementioned transmission impediments, MV power lines areexcellent carriers of RF energy as they are comprised of open wireequipment. The number of MV line crossovers is much less than is found

    on LV lines. Thus, a low power transmission of only 10 watts can besufficient to overcome distances of 500 kilometers or more.

    HF signals can be injected onto a power line by using an appropriatelydesigned high pass filter. Received signal power will be maximized when theimpedance of the transmitter, power line and the receiver are matched.

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    PLC Noise Sources Periodic impulses as in switching power suppliesu Rich in harmonicsu Oscillator 20Kh to > 1MHzu Conduct oscillator noise onto power lineu Frequency often varies with loadu Switching power supply, halogen lamp, etc.u Severe noise power

    Universal series wound motorsu Vacuum cleaners, kitchen appliances, drillsu High repetition rate impulses

    Random Impulse noise as in Dimmersu

    Produce large impulses at 100Hz to 120 Hzu Large 20V to 50V impulses

    Power line intercomsu 3Vpp to 7Vpp from 150KHz to 400KHzu Large harmonicsu About 30KHz bandwidth

    Radio Interference

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    Drill Noise on Power Line

    0 50 100 150 200 250 300 350 400 450 5000.02





    Time (uS)


    0 5 10 15 20 25 30 35 40 45 50100





    Frequency (MHz)


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    Periodic Impulse Noise

    0 50 100 150 200 250 300 350 400 450 5000.006






    Time (uS)


    0 5 10 15 20 25 30 35 40 45 50100




    Frequency (MHz)


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    Random Impulse Noise

    0 50 100 150 200 250 300 350 400 450 5001





    Time (uS)


    0 5 10 15 20 25 30 35 40 45 50100





    Frequency (MHz)


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    Random Impulse Noise

    0 50 100 150 200 250 300 350 400 450 5002





    Time (uS)


    0 5 10 15 20 25 30 35 40 45 50






    Frequency (MHz)


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    Frequency Dependent Fading

    l Multiple reflection points in mediuml Wire gauge changesl Sharp turns in wiringl Junction box connections

    l Causes frequency dependent fadingl Longer impulse response => ISIl Load changes affect channell

    Every path is unique (even in each direction)

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    PLC Advantages

    Extensive coverage: power lines are installed almost everywhereand this provides broad coverage even for rural areas where

    other communication infrastructure may not be available.

    Cost: since existing power lines are used for the infrastructure ofPLC networks, communication can be established quickly andcost effectively (Gungor & Lambert 2006).

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    PLC disadvantages

    High noise resulting in high bit error rates: when it comes todata communications, power lines environments are considered

    noisy due to their surrounding by noise sources (e.g. electrical

    motors, power supplies, fluorescent lights and radio signal

    interference) (Pavlidou et al. 2003).Attenuation and distortion: signal attenuation and distortion

    can be significant for reasons such as power network physicaltopology and power lines impedance fluctuation. Furthermore,

    signal attenuation arises significantly at specific frequency bandsas a result of wave reflection at terminal points (Galli &Scaglione 2003).

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    Security: there is neither shielding nor twisting in power cablesand thus power lines produce a significant amount of Electro

    Magnetic Interference (EMI) which can be received via radioreceivers (Liu & Widmer 2003). Therefore, in order to guarantee

    security of data, appropriate encryption techniques must be usedto prevent interceptions by unauthorized persons.

    Open circuit problem: communication over the power lines islost with devices on the far side of an open circuit, which

    severely restricts the usefulness of power line carrier systems forapplications involving re-closers, switches, and outage detection.

    Interference: Usual PLC operating up to carrier frequencies of30 MHz will cause narrowband interference with several services

    in the corresponding bands like e.g. amateur radio.

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    PLC Applications

    Advanced Metering Infrastructure (AMI): electricity, water, or gasmeter readings can be transmitted over PLC, and collected at a centerpoint for billing, developing analytics, and controlling the power grid

    accordingly. The market for AMI is huge and it justifies continuous

    developments in PLC technologies. In order to move a step forwardtowards a smart grid, deploying AMI is a must.

    Home networks: electrical and electronic appliances within thehouse can be interconnected, and therefore monitored and controlledcentrally via end users. This is part of what is called a smart home.

    Last mile two-way data communication: as discussed earlier, PLCcan be used to connect customer premises with service providers;

    Internet broadband and control schemes are among the most well-known PLC access applications.

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    Distribution Automation and Supervisory Control and DataAcquisition (DA and SCADA): utility companies use such

    systems to monitor and control power distribution networks. It

    seems more viable to use PLC in such systems instead of PSTN

    or dedicated RF networks. Rural communication systems: in low density areas where

    installing capital intensive communication infrastructures is notpossible or non-profitable PLC is a good alternative.

    PLC is also under discussion for use on board an aircraft.Here, the challenge is a distribution of broadband services likeInternet access, video streams, and alike. Electromagneticcompatibility and the high required spectral efficiency suggest

    the use of a wired technology rather than wireless systems.

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    Smart grid: smart grid is an integrated application of information andcommunication technology (ICT) on electric power transmission anddistribution networks. A smart grid replaces analog electromechanical

    meters with digital meters that record real-time usage data. Smartmeters provide a communication path extending from generation

    plants to electrical outlets (smart sockets) by using robust two-waycommunications, advanced sensors and distributed computingtechniques to improve the efficiency, reliability and safety of power

    delivery and economy in electricity.

    Radio transmitting programs:PLC was and is used to transmit radioprograms over power-lines or over telephone lines, for example inGermany and Switzerland, the system were called as Drahtfunk and

    Telefonrundspruch respectively. In all cases the radio programs werefed by special transformers into the lines.

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    PLC Challenges1) Electromagnetic Interference

    This is a critical issue in PLC. The power line acts as a hugeantenna for transmitting and receiving signals, and the

    transmitted signal radiates in the air. It is very important that this

    radiated signal does not interfere with other communicationsystems, and distort them. The radiation of underground power

    lines is small, while the major contribution is generated fromhouseholds (unshielded wires around a household radiate

    heavily). A solution would be to use filters to block interferences.


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    2) Impedance Mismatches

    The power network is not matched with regards to impedance,unlike conventional communication systems. Input and output

    impedance varies with the addition and removal of loads at

    different locations on the power line. It can reach milli-ohms or

    kilo-ohms, and it is noteworthy to mention that impedance isvery low at the substation. In addition, there are impedancemismatches along the power line itself, such as mismatching

    between a power line cable and a cable box which results in

    signal attenuation. In order to avoid such impedance mismatches,filters need to be used depending on measured mismatches.

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    3) Signal-to-Noise Ratio

    One of the most important performance parameters whenevaluating a communication system is its Signal-to-Noise Ratio

    (SNR). The SNR value is the only parameter on which the

    achievable bit-error rate in a simple transmission model, namely

    the so-called additive white Gaussian noise (AWGN) channel,depends. It can be shown that the bit-error rate performanceimproves the increasing SNR values. The noise modeled as

    Gaussian wide-sense stationary process includes disturbances of

    many different sources in the receiver, i.e. thermal noise in thepower amplifiers, as well as on a power line, such as signal from

    vacuum cleaners, kitchen machines, TVs, computers, etc.

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    To avoid such distance restrictions, repeaters are added along thepower line. In order to improve the SNR, the use of filters is

    encouraged to block noise generated in households from

    disturbing the grid power lines. It is noteworthy to mention that

    although power lines are highly susceptible to disturbances andattenuation, other communication systems used today have thesame tendency.

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    4) RF Noise Issues

    Radiation from lightning discharges (atmospheric noise due tolightning)

    Unintended radiation from electrical machinery, electrical andelectronic equipment, power transmission lines, or from internal

    combustion engine ignition (man-made noise) Emissions from atmospheric gases and hydrometeorsThe ground, or other obstructions, within the antenna beam Radiation from celestial radio sources such as sunspots

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    PLC Studies

    NTIA Phase I Study

    In the United States, the National Telecommunications andInformation Administration (NTIA) has completed a study of

    the cumulative effects of BPL system deployments in major

    cities around the world on the users of HF spectrum.The NTIA concluded a Phase I study of BPL a Phase II study in

    January 2006.

    Phase I studied interference risks to radio reception in theimmediate vicinity of BPL and made mitigatingrecommendations to the FCC in the 1.7-80 MHz range.

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    Present at one measurement location where a large number ofBPL devices were deployed on multiple three-phase and single-

    phase MV power lines, appreciable BPL signal levels (i.e., at least

    5 dB higher than ambient noise) were observed beyond 500

    meters from the nearest BPL energized power lines. Finally, NTIAs measurements show that the radiated power

    from the BPL energized power lines was consistently higherwhen the measurement antenna was placed at a greater height

    (e.g., 10 meter vs. 2 meter).

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    NTIA recommendation :

    1. Use of the minimum output power needed from each BPLdevice

    2. Avoidance of locally used radio frequencies3. Differential-mode signal injection oriented to minimize


    4. Use of filters and terminations to extinguish BPL signals onpower lines where they are not needed

    5. Judicious choice of BPL signal frequencies to decreaseradiation.

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    BBC Studies

    The British Broadcasting Company (BBC) employs a staff ofResearch & Development engineers, scientists, andmathematicians for the purpose of keeping BBC at the forefrontof technology. During the period from 1999 to 2005, the BBCproduced a series of White Papers covering various aspects of

    BPL. The BBC was early to identify BPL as a technology thatcould support censorship by being employed to keep unwantedforeign shortwave signals from reaching citizens in various partsof the world.

    In October 1999, the BBC produced a study titled: Protectionof sensitive receiving sites which included aeronautical/marinesafety, monitoring, surveillance, and radio astronomy. The studyconcluded that the size of an exclusion zone (e.g., BPL-freearea)

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    In July 2000, a BBC study titled The Threat to New RadioSystems from Distributed Wired-Communication Installations

    concluded that many radio users stand to suffer serious

    disruption of their services if BPL communications systems

    were allowed to be widely deployed.A BBC research and development study published in June 2005,

    titled Co-existence of Power Line Telecommunications andRadio Services a possibility?

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    2.7.3 Manassas, Virginia Study

    In July 2006 an FCC accredited testing laboratory produced areport on the BPL system deployed by the city of Manassas,Virginia. The testing was conducted in response to a complaintfiled with the FCC by several local American Radio Relay League(ARRL) radio operators who asserted that the BPL system is

    generating unlawful interference. In addition to the laboratory testing activities, Main.Net (the

    manufacturer of the Manassas BPL system) set the power levelfor overhead equipment at 4; the equipment range being 1-7 with7 being the highest.

    Additionally, coupling adjustments and other alignments tooptimize signal propagation and minimize signal leakage weremade by Main.Net. The laboratory testing includedmeasurements at five overhead and five underground locations,

    which included both low and medium voltage lines.

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    ARRL Study

    The American Radio Relay League (ARRL) sponsored a study,published by MetaVox Incorporated in March of 2004, of BPL

    systems located in the vicinities of both Allentown, Pennsylvania

    and Manassas, Virginia.

    The FCC testing standards require that frequencies below 30MHz measurements should not be made in the near field. \

    In comments to the FCC dated July 7, 2003, the ARRL studyobserved that Making measurements at distances closer than 30

    meters and extrapolating at 40 dB/decade can easily result in anunderestimation of the actual maximum field at 30 meters

    distance, by over 20 dB in some cases.

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    IEEE Report on USA Broadband Networking

    In April 2005, the IEEE Committee on Communications andInformation Policy (CCIP) published a white paper titled,Providing Ubiquitous Gigabit Networks in The United States, which

    advocates that to remain competitive the US needs gigabit-per-

    second (Gb/s) networks instead of broadband networks. TheIEEE recommended the creation of a new generation ofbroadband wired and wireless networks as a national priority.

    For example, future access to a menu of 100 simultaneous videochannels at the high definition (HD) digital rate of 20 Mb/s per

    channel for a diverse audience of end users requires 2 Gb/scapacity.

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    Automatic Meter Reading in Egypt

    Initiate communication on specific time, Thursdays andSaturdays between 3:00 am to 9:00 am reported the best results.

    Avoid times which record high TV sets audience density. Using repeaters to reduce the runtime errors and one of the

    error correction methods to reduce the checksum errors.

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    Narrowband PLC Standards

    The ideal PLC low frequency narrowband standard would have scalablebitrates from 1bps to 10Kbps (up to 500Kbps). It would also support ruraland urban power grid data communications, and be available for AC as well

    as DC power lines.

    1. FCCThe FCC Standard is used in North America. It regulates the power andbandwidth of the transmitted data through power line networks. The

    frequency band allowed for this standard is between 0 and 530 kHz(Abdelhalim 2007). In the FCC rules, communication over power line is

    allowed outside the AM frequency band (outside 535 to 1705 kHz).2. CENELEC

    The CENELEC Standard is used in countries of the European Union,Iceland, Norway and Switzerland; the frequency band assigned to this

    standard is narrower than that of FCC: 3 kHz to 148.5 kHz.

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    BPL Systems

    Motorola Powerline LV Hybrid BPL delivery system that combines a wireless network

    infrastructure with customer delivery over LV power lines.

    A bridge is used to transfer the internet connection from thewireless distribution system onto LV power lines for delivery tocustomer homes, which use the existing in-home electrical wiringas a LAN.

    The Motorola system reduces HF band interference byrestricting the application of RF to LV power lines only. No MVlines are used. The system also makes use of notches.

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    Corridor Systems Motorola Powerline MV

    BPL system that operates entirely above the HF radio spectrumand is offered as an interference free BPL system. Corridor

    Systems BPL equipment operates in the range from 800 MHz

    10 GHz.

    Provide a low-cost solution with high-performance delivery ofinformation across MV power lines. Corridors system uses a

    transmission technique that transmits energy over a singleconductor of an existing MV power line at frequencies above the

    HF band, thus avoiding it interference issues.

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    This mode exhibits the three characteristics: (1) very low-lossover distance; (2) propagation speeds near the speed of light;

    and (3) low radiation

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    Home-Plug In-Home BPL 1.0

    The HomePlug Powerline Alliance was founded in March of2000 by 13 corporate members whose mission is to promote

    rapid availability, adoption, and implementation of interoperable

    home powerline networks and products. Among the

    participating members of this Alliance are: Intel, Motorola,Linksys, and Sony.

    The HomePlug Alliance thus far has produced two majorspecifications: (1) HomePlug 1.0 and (2) HomePlug AV.

    These specifications are not available in the public domain butare restricted to members of the Alliance although some high-

    level, technical overviews have been released.

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    However, in September 2002 the International Journal ofCommunications Systems published a paper titled: HomePlug1.0 Powerline Communication LANs Protocol Description andPerformance Results version 5.4..-- Limited Sepcs.

    HomePlug 1.0 offers the ability to create an in-home LAN usingthe power line infrastructure with data rates up to 14 Mb/s.

    The specification addresses the physical (PHY) and MediaAccess Control (MAC) layers but complete architecturalindependence is not maintained because both layers need packet

    length information and the MAC also needs information aboutthe priority of the packet and about contention control.

    Thus, the OSI architecture is compromised slightly in favor ofincreased efficiency.

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    HomePlug 1.0 technology uses a combination of adaptivetechniques on each link to optimize data throughput. For

    example, a different amplitude and phase response between any

    two links can be used. Channel adaptation is achieved by tone

    allocation, modulation, and the FEC rate chosen. The toneallocations are used to turn off heavily impaired carriers andthereby reduce the bit error rates (BER).

    The remaining adaptive techniques target the modulation andFEC rate selection to the remaining higher quality channels..

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    Wireless versus PLC

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    Home-Plug AV Specification

    The second generation of technology from the Home-Plug PowerlineAlliance. The purpose is to provide high-quality, multi-stream, entertainment-oriented

    networking over existing A/C wiring within the home.

    HPAV maintains backward compatibility and interoperability with HomePlug1.0 devices.

    HPAV employs PHY and MAC techniques that support up to a 200 M/bpspower line network for video, voice, and data.

    The PHY layer uses the 200 M/bps channel rate to provide a 150 M/bpsinformation rate with robust, near-capacity communications over noisy powerline channels.

    The MAC was designed to support both TDMA and Carrier Sense MultipleAccess (CSMA) based access with A/C line cycle synchronization.

    The TDMA access provides QoS guarantees including guaranteed bandwidthreservation, high reliability and tight control of latency and jitter.

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    IEEE P1675 Standard for BPL Hardware

    IEEE P1675 has been proposed as a comprehensive standard thataddresses

    Component standards Capacitive couplers Inductive couplers Cabinets and enclosures grounding and bonding. The hardware associated with the distribution lines for BPL

    signal injection.

    The equipment installation practices for the purpose of insuringsafety, considering that a very common distribution voltage is

    12,500 volts.

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    IEEE P1901 for PLC MAC and PHY Specification

    Goal: develop a standard for 100 M/bps or greater BPL PHYlayer speeds.

    Bandwidth: below 100 MHz. Purpose:u To be usable by all classes of BPL devices including BPL devices used for

    the first/last 1500 meters to the premise, for LANs and for use inbuildings.

    u This standard focus on the balanced and efficient use of the power linecommunications channel by all classes of Broadband PLC devices.

    u defining detailed mechanisms for coexistence and interoperability betweendifferent BPL devices, and ensuring that desired bandwidth and QoS aresupported

    It is limited to the PHY and MAC layers.

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    Thank you!

    Next Lecture will be onTransmission Line Theory