Download Broadband Communications over Power Lines (BPL)

Broadband Communications
over Power Lines
(PLC)
By Marc C. Tarplee, Ph.D. N4UFP
ARRL Technical Coordinator
SC Section
What is PLC?
• PLC (also known as BPL) is a technique for
sending high speed data through the medium
voltage 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
2. Types of PLC
• There are three major categories of PLC:
– Access PLC uses electrical distribution lines,
overhead or underground, to provide broadband
Internet 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 used
by electric-utility companies to control their
equipment using the power-lines as transmission
lines.
• These systems are not a problem, although it is interesting to
note that utilities successfully lobbied against an amateur VLF
allocation, claiming that amateur transmissions could disrupt
their communications.
3. PLC Modulation Techniques
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 other
users of the HF/VHF spectrum
• Data throughput > 10 Mb/sec
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
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.
HomePlug Spectral Mask
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 <0.2 MHz
• Signals have narrow bandwidth ( < 10 KHz) and
have carrier frequencies below all amateur bands.
• These signals do not generally present serious
interference problems to amateurs
• Data throughput << 1 Mb/sec
4. RFI from Access Line PLC
• Tests involving PLC systems in Japan and Europe
indicate that PLC can cause significant
interference to other users of the HF spectrum.
• Medium voltage power distribution lines look very
much like antennas at HF wavelengths.
• The next slide shows the far-field pattern of a 328
ft (100 m) segment of a typical MV distibution
line. The conductors are at a height of 10m (32 ft
10 in) and they are spaced 1.5 m (4ft 5in) apart.
The load is assumed to be the primary of a
neighborhood transformer, which is assumed to
have an impedance of 10 – j25 ohms.
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
+5 dBi
28 MHz
14 MHz
7 MHz
3.5 MHz
0.15 MHz
+9 dBi
• As might be expected, the power lines look like long
wire antennas at HF, with some gain and a complex
multi-lobed radiation pattern
• It is interesting to note that the signal transmitted from
the power lines in the LF range (150 kHz) is less than –
70 dbi in any direction.
• Utilities’ RFI experience in the LF range is no predictor
of RFI problems in the HF range.
• Because overhead power lines run in all directions, the
resultant field produced by the entire power
distribution system should be more or less isotropic in
the azimuthal plane.
• ARRL simulations indicate that a fully-deployed access
line PLC system would raise the noise floor by 70 dB
(9 s-units + 16 dB)
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
Effect of PLC on HF Coverage
> 75%
~ 50%
< 25%
20 m Coverage under
normal conditions
20 m Coverage with access
PLC in neighborhood
ARRL PLC Video
5. RFI from HomePlug PLC
• HomePlug uses a spectral mask that provides 30
dB 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, causing
problems for all homeowners sharing a common
transformer.
6. What Can Be Done?
• The FCC recently closed off comment on the PLC
docket. Hundreds of amateurs did comment on the
problems with PLC during the comment period.
• Measurements need to be made. If a utility is
deploying PLC in your area, please make
measurements of the noise. We need to show the
FCC what the problems are.
• It is very likely that some form of PLC will be
implemented – the economic potential is to great.
It is important for amateurs to help steer the
implementation so that our frequencies are
protected