NTIA PROPOSES ‘RESPONSIBLE DEPLOYMENT’ OF BROADBAND OVER POWER LINE
NTIA proposed 41 frequencies in the 1.7-80 MHz range for special protection from unintentional radiation from broadband over power line (BPL) systems because of the critical or sensitive functions they support. In a report to the FCC released late Tues., the NTIA pointed out Commission rules and regulations, including Part 15, provide specific lists of protected frequencies in this range. They impose limitations on licensed services and unlicensed intentional radiation, the NTIA said, and the concept could be relevant for unintentional radiation by BPL systems as well because of interference risks. The report is titled Potential Interference from Broadband over Power Line (BPL) Systems to Federal Government Radio Communications at 1.7-80 MHz -- Phase I Study.
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In a letter to FCC Chmn. Powell that accompanied the report, NTIA Acting Dir. Michael Gallagher said protecting the 41 frequencies -- which represent less than 6% of the frequency capacity of BPL systems -- would “go a long way toward addressing potentially serious interference concerns.” There are 59,000 federal frequency assignments in the 1.7-80 MHz bands of spectrum, he said, including fixed mobile, radio astronomy, radar and broadcasting. The NTIA would work with the Commission to establish a “firm foundation for responsible deployment of BPL that will protect critical federal communications systems,” he said. While the commercial potential of BPL systems may be very high, he said, the “technical rules governing their deployment must address potential harmful interference to critical systems.” The report analyzed 10 million measurements of BPL systems, and it provides a “roadmap to that end,” Gallagher said.
“The good news is that the NTIA is allowing BPL to go forward; they just got conditions for going forward,” said Brett Kilbourne, regulatory dir.-United Power Line Council (UPLC). He said it was too early to determine what impact the proposal for special protection for 41 frequencies would have on the industry: “It’s not clear what they define as special protection.” While the agency wanted to protect those frequencies, the question was how many facilities were actually using those frequencies, he said: “The government isn’t going to disclose that to the entire public, so it’s something that we have to work out internally in discussions with the NTIA.”
The NTIA measurements and analysis of BPL signal radiation and propagation had shown that measurements intending to demonstrate compliance with Part 15 field strength limits (emissions) shouldn’t focus solely on BPL devices, the report said. BPL systems generate emissions under and adjacent to the power lines, and BPL systems generate peak emissions at small distances from both BPL devices and power lines. Analysis also showed that application of existing Part 15 compliance measurement procedures for BPL systems results in significant underestimation of peak emissions, the report said: “Underestimation of the peak field strength is the leading contributor to high interference risks.” Refining compliance measurement procedures for BPL systems wouldn’t impede BPL technology, it said, because BPL networks could be implemented with existing field strength limits. Therefore, it wasn’t recommending the FCC relax Part 15 field strength limits for BPL systems, the NTIA said.
The NTIA recommended measures to prevent or eliminate BPL interference: (1) Mandatory registration of planned and deployed BPL systems would enable radio operators to advise BPL operators of anticipated interference problems and suspected actual interference, substantially helping prevent and mitigate interference. (2) BPL developers should routinely use the minimum output power needed from each BPL device (3) Locally used radio frequencies should be avoided and differential-mode signal injection oriented to minimize radiation. (4) Filters and terminators should be used to extinguish BPL signals on power lines where they aren’t needed. (5) Judicious choice of BPL signal frequencies would decrease radiation. The NTIA said the 2nd phase of its study will assess the interference risks due to “aggregation and ionospheric propagation” of interfering signals from BPL systems, refine and apply BPL models and evaluate the effectiveness of its recommendations to the FCC.
Kilbourne said the main issue for NTIA was the emission measuring guidelines. “I don’t see they have an issue so much with the [emission] limits themselves.” The NTIA had made recommendations based on some of their measurements, he said, and “the question then is are those measurements accurate and are those recommendations appropriate. That’s something we need to continue to study.” Another positive development, he said, was that the NTIA had made clear its report wasn’t the final word and it was willing to work with the industry and the FCC. Alan Shark, pres. of the Power Line Communications Assn. (PLCA) said the industry believed some of the measurements made by the NTIA weren’t “necessarily the best way to do it.” The good news, he said, was that the report wouldn’t cause the FCC to take any stronger action that it has already proposed.