Broadband Communications over Power Lines (PLC)

1. Broadband Communications over Power Lines(PLC) By Marc C. Tarplee, Ph.D. N4UFP ARRL Technical Coordinator SC Section

2. What is PLC?

3. 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

5. 2. Types of PLC

6. 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.

7. 3. PLC Modulation Techniques

8. 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

9. 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

10. 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.

11. HomePlug Spectral Mask

12. 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

13. 4. RFI from Access Line PLC

14. 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.

15. Elevation patterns for radiation from MV Power LinesPerpendicular to Lines Parallel to Lines +9 dBi 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

16. 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)

17. 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

18. > 75% ~ 50% < 25% Effect of PLC on HF Coverage 20 m Coverage with access PLC in neighborhood 20 m Coverage under normal conditions

19. ARRL PLC Video

20. 5. RFI from HomePlug PLC

21. 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.

22. 6. What Can Be Done?

23. 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