What is Broadband over Power Lines?
Broadband over power lines (BPL) is a general term that covers any technology that uses electric-utility distribution lines or in-premise power lines to conduct broadband signals for computer networking or utility smart-grid applications. Under Part 15 of the FCC rules, the use of power-company wiring to deliver Internet access or smart-grid communication to homes and businesses is called "access BPL." The use of premise wiring to network computers within a building is called "in-premise BPL." Access BPL that operates between 1.7 and 80 MHz has special provisions in Part 15 of the FCC's rules to control its interference potential. The present FCC rules, however, are insufficient to effectively control the interference that results when BPL uses any radio spectrum that is in use near the BPL system or device.
ARRL had taken the FCC to federal court over the content of its BPL rules. In April 2008 the court remanded the BPL rules back to the FCC. In November 2011, in response to the court's order, the FCC issued a 2nd Report and Order that essentially affirmed the rules it had originally written, with only minor change. ARRL has filed a Petition for Reconsideration of this new Report and Order as its next step to try to get the FCC to write good rules that address the serious interference potential that comes from putting broadband HF and VHF signals onto power lines.
Radio-Frequency Interference from BPL
Radio amateurs are not opposed to broadband services. On the contrary, they tend to be early adopters of new technology. However, BPL represents a potential for interference that is almost without precedent. The interference potential of other forms of broadband, such as fiber-to-the-home, DSL and various forms of wireless broadband is much lower than it is with BPL.
BPL operates under Part 15 of the FCC’s rules for unlicensed devices, as an unintentional, carrier-current emitter. (A carrier-current device is any device that intentionally conducts signals onto the ac-mains or distribution electrical wiring.) Although carrier-current devices meet radiated emissions limits, not conducted limits like other broadband technologies, the power levels typically used by BPL systems are approximately 30 to 40 dB greater than the FCC limits for other unintentional emitters. To put this into layman's terms, one BPL device generates as much noise as 1000 to 10,000 other devices regulated by different Part 15 rules. It is not surprising that BPL poses a much higher interference threat than almost all other types of unlicensed emitters of RF noise.
Because power lines are not designed to prevent radiation of RF energy, BPL represents a significant potential interference source for all radio services using this frequency range, including the Amateur Radio Service. Overhead electrical power lines and residential wiring act as antennas and overhead power lines radiate the broadband signals as radio signals throughout entire neighborhoods and along roadsides. Interference has been observed nearly one mile from the nearest access BPL source.
With an interference potential that is as much as 10,000 times greater than other devices, for BPL to operate successfully, extraordinary attention must be paid to the electromagnetic-compatibility (EMC) aspects of BPL. To avoid causing interference, BPL must not use spectrum that is in use near a BPL system or device. In residential neighborhoods, this includes the Amateur Radio Service, the Citizens Band Radio Service (CB), the reception of international shortwave broadcast and other radio use such as government time signals (WWV), etc. For BPL devices that operate above 54 MHz, there is also the potential for interference to broadcast television to occur.
Despite its significant interference potential, BPL can be successfully implemented in ways that can avoid widespread RFI problems. From the perspective of Amateur Radio, this means that BPL systems and devices must not use the amateur bands, with sufficient filtering to reduce BPL noise in the amateur bands to a level comparable to other devices.
This has sometimes been done successfully within the BPL industry. Some access BPL providers have installed systems that applied spectral masks (notching) on all HF and VHF amateur bands. This was a successful model (before the utilities involved shut down the BPL systems for other financial and technical reasons). ARRL staff has evaluated several of these notched access BPL systems and has determined that state-of-the-art spectral notching for the amateur bands provides a good general solution that prevents most interference problems.
Industry groups, such as HomePlug and the HomeGrid Forum have implemented industry specifications that also have spectral notches for the amateur bands. This is a successful model, because with millions of in-premise modems deployed, ARRL has not received reports of harmful interference involving HomePlug or HomeGrid Forum products. These groups realize that for BPL to achieve its potential, its proponents and regulators must proactively address interference problems through good rules and industry standards and practices.
Technical Uncertainty
This protection for Amateur Radio is good news, because it shows that BPL can be implemented without interference. However, this successful model was not adopted into the FCC’s rules, so those who may want to use BPL for utility or in-premise applications have no assurance that the technology they may buy can avoid interference problems. Until all BPL is implemented with spectral notches for the amateur bands, with additional protection for other users of spectrum, it is very much “buyer beware” when it comes to making technology choices.
What is the status of BPL?
From a regulatory standpoint, BPL is an unlicensed, unintentional emitter of RF energy and is subject to FCC rules that require that BPL systems may only operate subject to the express condition that harmful interference is not caused to licensed radio services. BPL is not entitled to protection from interference. So far, access BPL has been deployed in numerous temporary test sites but in few commercial installations. The vast majority of these trials were abandoned by the electric utilities or BPL manufacturers involved, for various reasons, and most commercial installations have been shut down because they proved to be not economically viable. It must be noted that a number of these installations were documented as causing harmful interference to Amateur Radio stations that were not resolved prior to their being shut down.
Despite the very limited deployment, considerable interference has been documented in all access BPL systems that did not notch the amateur bands. In October 2004, November 2006 and November 2011, the Federal Communications Commission (FCC) adopted new rules for BPL systems. These rules place new restrictions on BPL systems in recognition of the fact that they pose a greater threat of radio interference than most Part 15 devices, such as garage door openers. However, the new rules are not sufficient to reduce the probability of harmful interference to reasonable levels. Administrative appeals of the rules are underway and further court challenges are possible.
Why are the regulations inadequate?
The Communications Act of 1934 and the FCC Rules have long required that unlicensed emitters such as BPL systems must protect licensed radio services from interference, and that they must accept any interference to their operation that is the result of normal activity by licensed radio services. However, in practice it is often difficult to resolve such interference problems in the field. In one case in Cedar Rapids, Iowa, access BPL engineers spent 12 weeks trying to solve an interference problem without success. The interference did not cease until the BPL trial was terminated prematurely. This pattern has been repeated again and again in other access BPL systems.
Studies by the National Telecommunications and Information Administration (NTIA) show that the probability of interference from a BPL system operating at the FCC radiated emission limit on the same frequency as a typical two-way radio station is essentially 100% for distances of 200 to 400 meters from the power line, depending on the frequency. Despite this clear evidence that the limit is too permissive, the FCC declined to impose a tighter limit except in frequency bands used for critical federal communications. This means that unless BPL manufacturers voluntarily design their systems for reduced emissions, BPL system operators will have to take expensive steps to correct interference on a case-by-case basis. That may not be possible under some circumstances unless they turn off their systems. Of course, they will strongly resist having to do so. This is why radio operators are so concerned, and why BPL customers cannot be assured of receiving reliable broadband service until notching of the amateur bands is adopted by all implementers of BPL and made part of successful regulations.
Has the interference potential been proven?
The ARRL Laboratory has made measurements of strong BPL radiation and interference in a number of trial areas. The Lab's findings of interference and related information, including video and audio recordings of actual interference, have been well documented in ARRL’s filings with the FCC on the BPL rulemaking proceeding. These and other observations of radio-frequency interference at BPL test sites in the US are a matter of public record in FCC files.
An April 27, 2004 report released by the NTIA acknowledges that BPL signals "unintentionally radiate" from power lines. The NTIA also said that the then-current FCC Part 15 measurement techniques may "significantly underestimate" peak BPL field strength and that "interference risks are high under existing FCC Part 15 rules." The FCC rulemaking only partially addressed these concerns.
Although some BPL proponents dispute these claims of interference to licensed services, they have provided little in the way of calculations or measurements of BPL radiation levels -- and what they have provided into the record in the BPL rulemaking proceeding has been flawed by technical errors.
Others at risk
- The "short waves" -- the only part of the radio spectrum that supports long-distance, intercontinental radio communication. The short waves are used for international broadcasting, aeronautical, maritime, disaster relief, and other services including the military.
- The "low-band VHF" frequency range that is heavily used by volunteer fire departments, police, and other first responders.
- Depending on their distance from a BPL system, some public safety and federal government radio systems could receive harmful interference.
Solutions
Although the present FCC BPL rules have not adequately protected licensed radio services from interference, if BPL systems and their designs avoid the use of locally used spectrum, interference can be avoided. For the Amateur Radio Service, because amateur stations use sensitive receivers and efficient antennas and with few exceptions are located in residential or rural areas, this requires that permanent notches in the amateur bands be used. Many in the BPL industry recognize this important EMC principle. ARRL calls on these industry leaders to join it in persuading the FCC to include these successful practices in equally successful rules that all stakeholders should support.
ARRL -- The National Association for Amateur Radio
www.arrl.org · Newington, CT 06111
January 2012
