Broadband Communications over Power Lines

8/7/2019 Broadband Communications over Power Lines

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Broadband Communications

over Power Lines(PLC)

By Marc C. Tarplee, Ph.D. N4UFP

ARRL Technical CoordinatorSC Section


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What is PLC?


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PLC (also known as BPL) is a technique for

sending high speed data through the mediumvoltage power distribution network

The idea of sending data through the power

distribution network is not new

Utilities use LF for network control and telemetry(typically < 0.200 MHz)

Schools have used carrier current system for campus

radio systems that operate in the AM band (0.530

1.700 MHz) What makes BPL different is that it uses

frequencies between 2 and 80 MHz


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2. Types of PLC


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There are three major categories of PLC:

Access PLC uses electrical distribution lines,overhead or underground, to provide broadbandInternet access to homes and businesses.

This is currently in the developmental stage

In-building PLC uses the electrical wiring within a

building to network computers. Most systems use the HomePlug standard which provides

protection for amateur frequencies

Control PLC operates below 500 kHz, and is usedby electric-utility companies to control their

equipment using the power-lines as transmissionlines.

These systems are not a problem, although it is interesting tonote that utilities successfully lobbied against an amateur VLFallocation, claiming that amateur transmissions could disrupttheir communications.


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3. PLC Modulation Techniques


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Access PLC Access PLC systems are presently under

development. Current systems use OFDM

(orthogonal frequency division multiplexing) in

combination with some type of PSK .

Carrier frequencies can be between 2 and 30

MHz.

No filtering provisions are made to protect otherusers of the HF/VHF spectrum

Data throughput > 10 Mb/sec


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HomePlug HomePlug uses a combination of OFDM

(orthogonal frequency division multiplexing) and

DQPSK (differential quadrature phase shift

keying) to send data through power lines within

the home.

Carrier frequencies are between 4.5 and 21 MHz.

The modem output has notches at 3.5, 7.0, 10.1,14.0, and 18.1 MHz to reduce interference to

amateurs.

Data throughput > 10 Mb/sec


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HomePlug Software in the receiver continuously determines

the transfer function of the medium and carrier

frequencies are changed to use the best available

spectrum.

HomePlug signal power is spread over the entire

4.5 21 MHz bandwidth as the carrier frequencies

are changed.

HomePlug signals can pass through a residential

service entry panel with less than 10 dB loss.


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Control/Carrier Current PLC These use frequencies below 1.7 MHz.

Carrier current AM signals 0.53 1.70 MHz

LF telemetry/control signals used by utilities


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4. RFI from Access Line PLC


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Tests involving PLC systems in Japan and Europe

indicate that PLC can cause significantinterference to other users of the HF spectrum.

Medium voltage power distribution lines look verymuch like antennas at HF wavelengths.

The next slide shows the far-field pattern of a 328ft (100 m) segment of a typical MV distibutionline. The conductors are at a height of 10m (32 ft10 in) and they are spaced 1.5 m (4ft 5in) apart.

The load is assumed to be the primary of aneighborhood transformer, which is assumed tohave an impedance of 10 j25 ohms.


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Elevation patterns for radiation from MV Power Lines

Perpendicular to Lines Parallel to Lines

28 MHz

14 MHz

7 MHz

3.5 MHz

0.15 MHz

28 MHz

14 MHz

7 MHz

3.5 MHz

0.15 MHz

+9 dBi+5 dBi


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As might be expected, the power lines look like longwire antennas at HF, with some gain and a complexmulti-lobed radiation pattern

It is interesting to note that the signal transmitted fromthe power lines in the LF range (150 kHz) is less than 70 dbi in any direction.

Utilities RFI experience in the LF range is nopredictor of RFI problems in the HF range.

Because overhead power lines run in all directions, theresultant field produced by the entire powerdistribution system should be more or less isotropic inthe azimuthal plane.

ARRL simulations indicate that a fully-deployed accessline PLC system would raise the noise floor by 70 dB

(9 s-units + 16 dB)


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Japanese PLC RFI

Study

Noise Floor

These measurements were made at 7 MHz on a 96

km long path in Japan.

PLC signals raised the noise field strength by 25

dB


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Effect of PLC on HF Coverage

20 m Coverage under

normal conditions

20 m Coverage with access

PLC in neighborhood

> 75%

~ 50%

< 25%


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ARRL PLC Video


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5. RFI from HomePlug PLC


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HomePlug uses a spectral mask that provides 30dB of filtering in the amateur HF bands.

At current RF brightness levels of 80 dBm/Hz,

HomePlug signals can cause interference to

antennas (especially indoor) that run within 2 3

m of household power lines.

HomePlug signals can also leak into other

households with < 10 dB of attenuation, causingproblems for all homeowners sharing a common

transformer.


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6. What Can Be Done?


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The FCC recently closed off comment on the PLC

docket. Hundreds of amateurs did comment on theproblems with PLC during the comment period.

Measurements need to be made. If a utility isdeploying PLC in your area, please make

measurements of the noise. We need to show theFCC what the problems are.

It is very likely that some form of PLC will beimplemented the economic potential is to great.

It is important for amateurs to help steer theimplementation so that our frequencies areprotected

Documents

Broadband Communications over Power Lines