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ARRL Strengthens the Case for Mandatory BPL Notching


On November 30, the ARRL filed an ex parte submission with the FCC, providing additional support for its position that the FCC should require mandatory notching of the amateur bands by Broadband over Power Line (BPL). The ARRL’s filing stated such devices can cause harmful interference to Amateur Radio operators, and requested that the FCC “establish rules that are appropriate for unlicensed BPL systems and which minimize the interference potential.”

After the FCC released its Request for Further Comment and Further Notice of Proposed Rule Making (Further Notice) in July 2009, the ARRL filed comments and reply comments and made oral and written ex parte filings, urging the adoption of Part 15 Rules which reflect both the capabilities and practices of the bulk of the BPL industry, and which are sufficient to protect licensed radio services in the HF and VHF bands.

“It has been painfully apparent that the present rules permit the deployment of BPL in configurations which cause severe, ongoing harmful interference if operated on radio spectrum that is in use locally,” the ARRL asserted in its filing. The ARRL, in its numerous filings on this issue has “strenuously urged” the FCC to require full time, mandatory notching of all amateur allocations to at least 35 dB notch depths. “This level of notching is both achievable by present BPL systems and is typically, but not universally, implemented by the BPL industry.”

The ARRL maintains that mandatory, full time 35 dB notch depth requirements can be implemented in the FCC’s BPL rules without adverse impact on the BPL industry. Most BPL systems are already notched at this level: “Although that conclusion is unrebutted in the record in this proceeding, it may be useful to provide documentation of this de facto industry standard. This ex parte filing contains that documentation.”

Even though there are tens of millions of broadband lines available in the US, BPL has only captured 0.011 percent of that market; each time the FCC releases an updated broadband report, the numbers get even smaller. The ARRL pointed out that BPL is only mentioned in the National Broadband Plan on page 337 as “an information service,” and that the interference potential of BPL is an issue that “most assuredly is and has been one of the major handicaps to the deployment of the technology.”

The ARRL noted that “reduction of the interference potential of BPL to licensed radio services to manageable levels cannot but help salvage whatever potential BPL may have in the future for broadband access, or for Smart Grid applications.” If there are Smart Grid applications for BPL, the ARRL insisted that the interference potential must be addressed soon, “so as to avoid the fundamental incompatibility between BPL and the Amateur Radio Service that exists as the result of the present BPL rules.”

The ARRL pointed out that it has been 18 months since the FCC released its Further Notice, more than two and a half years since the Court of Appeals remanded the case to the Commission for further proceedings, and more than six years since the Commission first adopted the inadequate and insufficient Part 15 Rules governing BPL systems: “There is no reason why the BPL rules should not be amended immediately to impose a mandatory, full-time, 35 dB notching requirement for all BPL equipment in all Amateur allocations. If that is done, the fundamental incompatibility is effectively eliminated, and BPL can, going forward, avoid the stigma of the Amateur Radio spectrum polluter that it has been shown to be in deployments throughout the United States and elsewhere in the world.” In May 2008, the US Court of Appeals for the District of Columbia Circuit found that the FCC violated the Administrative Procedure Act and failed to provide a reasoned explanation for its choice of the extrapolation factor.

Full-Time, 35 dB Notching of Amateur Allocations Is the De Facto Industry Standard for BPL Systems and the Rules Should Incorporate that Standard

The ARRL attached seven documents (Exhibits A-G) to its ex parte submission. Exhibit A, written by ARRL Laboratory Manager and BPL expert Ed Hare, W1RFI, thoroughly reviewed cooperative industry efforts to design broadband systems in such a way as to, where necessary, utilize notching or spectral masks in order to avoid fundamental incompatibility in the use of the radio spectrum allocated to the Amateur Service. Hare points out that in some, but not all, cases, these efforts are not adhered to on a voluntary basis and the regulations must therefore mandate the industry “best practices.” Hare cites experiences with Home Phone Networking Alliance (HPNA) standards, Very High Speed Digital Subscriber Lines (VDSL) systems, and Home Plug in-Premise BPL (Exhibit B) as evidence that full time notching of Amateur Radio allocations is a standard procedure that has worked well on a cooperative basis.

“Spectral masking to protect specific radio services is a mature and proven technology that, if made part of regulations for broadband emitters,” Hare maintained, “would serve to ensure that the rules that govern unlicensed devices have a strong foundation written into the rules on which other industries can build a similar success.” Cooperative efforts in 2006 between the ARRL and DS2 -- a major manufacturer of BPL-protocol chipsets -- resulted in documentation of improvements that DS2 had made to its BPL technology. The changes DS2 made to its products significantly improved the notching capability of the generation-2 DS2 chipsets which are capable of notch depths of 40 dB (Exhibit C).

Exhibit A cites the IEEE standard on BPL protocols and specifications (IEEE P1901, Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications). This standard establishes the need for BPL systems to completely avoid the use of spectrum allocated to the Amateur Radio Service. Using Orthogonal Frequency Division Multiplexing (OFDM) emissions with notches for amateur spectrum, the standard reveals maximum transmission rates of 220 Mb/s, with 440 Mb/s optional, demonstrating that notching the amateur bands does not have a major deleterious effect on BPL-system performance. Notch depth under this standard is equivalent to minus 35 dB; however, in practice, the notch depth achievable is on the order of minus 45 dB.

Exhibit A also cites a June 2010 report (Exhibit G) by the United Kingdom’s Office of Communications (OFCOM) that concluded “that BPL systems will result in widespread harmful interference to amateur, international broadcast, FM narrowband and FM broadcast operations unless existing practices of notching and adaptive power control are incorporated in formal regulations. Specifically, the report concludes that “Our results show that users of sensitive radio systems may increasingly suffer interference from PLT devices.” OFCOM recommends that notching of amateur allocations be “formalized” in regulations “to ensure that their introduction can be relied upon.” The Report specifies the notch depth of the UPA specification -- the BPL technology most common in the UK -- as 40 dB (pages 17-24 of Exhibit A).

Exhibit D is a report on the errors in the United Power Line Council BPL database. According to Hare, there are numerous errors and several omissions in the United Power Line Council (UPLC) BPL database: “Some of these omissions are very self-evident, so there is no valid reason for these errors other than the lack of oversight and/or cross checking that is not being performed by the database administrator. The errors, omissions and an ever-growing number of BPL systems that have shut down but are still continued to be listed in the database seriously lessen the usefulness of the database.”

ITU Supports Notching

Hare also cites multiple reports in Exhibit A from the International Telecommunication Union (ITU) that support the ARRL’s position. Report ITU-R SM-2158 -- Impact of Power Line Telecommunication Systems on Radiocommunication Systems Operating in the LF, MH, HF and VHF bands Below 80 MHz -- from September 2009, concludes that because electrical power lines are not designed for the transmission of high data rate signals, BPL (commonly called PLT outside the US) signals on electrical power lines have the potential of causing interference to radiocommunication services. It also said that a noise level increase (BPL plus ambient noise) of no more than 0.5 dB is necessary for stations in the Amateur Service, because amateurs frequently operate at or near the minimum signal-to-noise ratio for effective communication. Amateurs, the report states, communicate effectively with a signal-to-noise ratio of 6 dB for voice communications in a nominal 2.4 kHz bandwidth, and as low as minus 6 dB (relative to the same bandwidth) for Morse code or spectrum-efficient data modes.

ITU Recommendation P.372 specifies median levels of man-made noise in different environments, including “quiet rural areas.” This category describes the noise levels in residential areas where Amateur Radio operators typically operate fixed stations. Hare said in Exhibit A that the levels of man-made noise described in ITU Recommendation P.372-10 “provide a reasonable estimate of the current levels of man-made noise and a reasonable basis to use in setting limits and protection levels,” which have not changed substantially during the past 30 years.

The ARRL maintains that the ITU-R SM-2158 report provides a good basis on which to set BPL limits: “BPL emits at a relatively uniform level across a wide frequency range. Some BPL systems operate on a near-continuous basis. For access BPL deployed on overhead power lines, BPL emits at or near the emissions limits for long distances down lines on which it is deployed. Therefore, it is clear that the ubiquitous deployment of BPL, especially access BPL on medium-voltage distribution lines, would result in interference levels that exceed the protection criteria anywhere that BPL is deployed.”

As amateur stations can be fixed or mobile, the ARRL asserts “that the only practical way to implement required interference protection is to have spectral masks applied to BPL for the spectrum allocated to the Amateur Radio Service.

Hare also cited ITU-T document G.9960 -- Unified High-Speed Wire-Line Based Home Networking Transceivers – Foundation” that addresses notch depth. That report recommends for BPL systems a notch depth of 30 dB (pages 29 and 30 of Exhibit A).

Notched vs Un-notched

Exhibit E and Exhibit F discuss testing of BPL systems already in place and the success of notched systems versus those that attempted to notch amateur bands based on interference complaints. “While anecdotal, these studies clearly illustrate both the adequacy of full-time notching of amateur allocations (with notch depths of 35 dB) and the inadequacy of post hoc interference mitigation through partial notching. They also reveal that there are current interference problems where BPL is deployed unless the industry standard full-time 35 dB notching of all amateur allocations is utilized.”

Hare concluded that testing with the BPL industry and by independent entities, statements by the BPL industry, BPL-industry specifications such as HomePlug, the Commission’s own staff measurements and findings, and international and BPL industry consensus standards “uniformly result in the same inescapable conclusion: It is both practical and necessary to avoid the use of the amateur bands in the design and specification of BPL systems. Those systems that have followed the industry’s standards have from an EMC perspective been successful. The Commission’s Rules should be modified to incorporate this necessary regulatory restriction, in order to protect licensed services.”

It is the ARRL’s position that “notch depth at or near 35 dB is easily achievable, with 40 dB or more being typical in the most robust designs. Most of the present Access BPL deployments in the United States, though not all, are using the improved technology of 40 dB notching developed by DS2 or are using HomePlug technology, with fixed notches in the Amateur bands. Studies of measured field strength and notch depth of BPL devices conducted by a number of authoritative sources show that a combination of a correct extrapolation factor based on 20 dB/decade in the region beyond wavelength/2pi from radiating BPL systems and a mandated notch depth of 35 to 40 dB provide the required protection criteria shown to be necessary in the ITU-R in its SM-2158 report.”

The ARRL contends that “because adherence to industry norms is not uniformly adhered to; because BPL interference, once it arises, has proven difficult or impossible to remedy; because limited Commission enforcement resources are typically not deployed to Amateur Radio interference cases; and because the Commission’s rules should reflect sufficient technical limits available from current technology to avoid interference to licensed radio services from unlicensed BPL systems ex ante, the BPL rules should be modified without further delay.”



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