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From the CQ
Newsroom, 4/29/04:
NTIA
Report Finds Significant BPL Interference
The National Telecommunications and
Information Administration (NTIA) has issued its long-awaited report on
the interference potential of Broadband over Power Lines (BPL). Despite a
generally-glowing news release, the report itself identifies significant
interference risks from BPL and concludes that the methods currently used
for measuring BPL noise levels are inadequate and that more study is
needed on such areas as ionospheric propagation of BPL signals.
Our summary of the report's major findings follows:
NTIA concluded:
1) ...that the methods currently used to measure noise levels and
interference potential are inadequate: "(A)pplication of existing Part 15
measurement procedures for BPL systems results in a significant
underestimation of peak field strength. Underestimation of the actual peak
field strength is the leading contributor to high interference risks. As
applied in current practice to BPL systems, Part 15 measurement guidelines
to not address unique physical and electromagnetic characteristics of BPL
radiated emissions." (Executive Summary)
2) ... that noise levels must be measured from BPL-energized power lines
as well as the device coupling the signal to the power lines: "BPL
systems generate the highest electric field strength near the BPL device
for horizontal-parallel polarized signals. However, these systems generate
peak vertically-polarized field strength under and adjacent to the power
lines and at impedance discontinuities at substantial distances from the
BPL device." (Executive Summary)
3) ... that interference to weak-to-medium strength signals is likely out
to 460 meters (1500 feet; more than 1/4 mile) from a BPL noise source at
ground level and out to a 40-kilometer (25 mile) radius from the signal
source for an airplane at an altitude of up to 6 kilometers (approx.
20,000 feet): "Interference to land vehicle, boat, and fixed stations
receiving moderate-to-strong radio signals is likely in areas extending to
30 meters, 55 meters, and 230 meters, respectively, from one BPL device
and the power lines to which it is connected. With low-to-moderate desired
signal levels, interference is likely at these receivers within areas
extending to 75 meters, 100 meters and 460 meters from the power lines ...
(I)nterference to aircraft reception of moderate-to-strong radio signals
is likely to occur below 6 km altitude within 12 km center of the BPL
deployment. Interference likely would occur to aircraft reception of
weak-to-moderate radio signals within 40 miles of the center of the BPL
deployment area." (Executive Summary)
4) ... that results of BPL tests and implementations in other countries
have been mixed: "BPL apparently has been implemented with success in some
countries, while other countries have postponed implementation of BPL
systems until further interference studies are ... conducted. Still others
have withdrawn their approval for operation of BPL systems after
experiencing interference problems." (Section 9, Summary of Results).
One example cited was that "(d)uring an
emergency exercise of the Austrian Red Cross in May 2003, communication
was massively disturbed by (BPL), with interference levels exceeding the
limits by a factor of 10,000." (Appendix B)
5) ... that more study is needed in several important areas, including
skywave propagation of BPL signals, that it will conduct further studies
and issue a report later this year: "NTIA will complete a Phase 2 study
later this year that will assess the potential interference risks due to
aggregation and ionospheric propagation of interfering signals from BPL
systems; refine and apply BPL deployment models; and evaluate the
effectiveness of proposed Part 15 measurement techniques." (NTIA News
Release)
NTIA is recommending more stringent
measurement standards and procedures, along with several interference
mitigation techniques some not mentioned in the NPRM although it admitted
that the nature of power lines and of BPL would limit the effectiveness of
some of them. Additional recommendations are likely after the second phase
of the NTIA study is completed later this year. Acting NTIA Administrator
Michael Gallagher called the NTIA recommendations "the technical
foundation for the responsible deployment of broadband over power lines."
The full report may be downloaded,
either in full or chapter by chapter, from the NTIA website at:
http://www.ntia.doc.gov/new.html.
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