FCC gives Broadband Over Power Line a second chance

It's once more into the breach for the Federal Communications Commission's efforts to authorize Broadband Over Power Line technology. On Friday, the agency issued a new Notice of Proposed Rulemaking, asking for feedback on the power levels Access BPL systems should operate at so that they don't interfere with other services. The American Radio Relay League (ARRL) stopped this process dead in its tracks last year, having raised concerns about the transparency of the proceeding and BPL's potential for messing with ham radio signals and other bands. But the Commission is sticking to its guns, arguing that the technical standards it has already set may still be sufficient—at least, with a modification or two. BPL's critics "do not provide convincing information" that the FCC should change course, the NOPR says.

Third pipe dreams

Access BPL boosters say that transmitting broadband along electric power lines represents a potential "third pipe" alternative to cable and DSL. But the market for it has been slow to develop, and the ARRL took the FCC to court over its BPL plans in 2007, warning that the service could muck up neighboring transmissions (the League has a video demonstrating interference with a licensed ham radio signal from a demonstration roadside line along which BPL was active).

In April 2008, the DC Circuit Court of Appeals for the District of Columbia agreed with two of ARRL's complaints. First, the agency had heavily redacted its studies of potential BPL interference, to the point where there was "little doubt that the Commission deliberately attempted to 'exclude from the record evidence adverse to its position'," the appeals court declared. On top of that, the FCC had not sufficiently explained its rationale for the power/interference standards it established.

The redaction that ARRL protested was, well, a bit disturbing (our story about it here). The FCC says it touched up various documents "on the basis that they represented preliminary or partial results or staff opinions that were part of the internal deliberative process." 

But that rationale didn't impress the court. For example, somebody at the agency whited out from a Powerpoint slide a sentence asserting that a tested BPL system was "not a point source." Why is that significant? Because BPLs are line sources, and critics charge that interference from line sources attenuates (or decays) more slowly than from point sources, such as local transmitters.

Power struggles

But now the FCC has dutifully released all its non-redacted BPL-related testing materials. And the Commission's NOPR is asking for feedback on the power levels it should authorize for Access BPL so that it doesn't radiate into other licensed services. Basically the issue here is that "extrapolation factor"—how quickly do BPL emissions decay at various levels of power strength, and thus pose less of an interference threat. A lower level of dB extrapolation per "decade" (distances measured via a factor of ten) means a slower rate of decay, meaning that the FCC should generally recommend tighter standards of emissions control for the service.

In the past,  the Commission suggested using 40 dB per decade as the factor for frequencies under 30 MHz. ARRL has recommended cutting that number in half (20 dB), backing its arguments with three studies produced by the United Kingdom's OFCOM and one by the Comite International Special des Perturbations Radioelectriques (CISPER). 

But the FCC says it questions the relevance of these studies, suggesting that they provide only "anecdotal information," insufficient to support "a statistically valid and comprehensive description of how BPL emissions attenuate over the short distances at which measurements are made." And the agency says more recent experiments validate its recommendations.

On the other hand, the Commission says it is willing to meet the public halfway and possibly go with 30 dB per decade, even though this could "increase the compliance burden for BPL equipment." The question is now open for public response. "We request comment on the suitability of an extrapolation factor lower than 40 dB per decade" as well as recommendations for how to test the technology, the FCC says. "Interested parties are invited to suggest alternative values for the extrapolation factor that would account for the variability of attenuation rates without unfairly burdening manufacturers of users of BPL equipment and systems."

It has taken a while for the FCC to return to this issue. The ARRL, in fact, filed yet another petition with the DC Court of Appeals in June, asking the Commission to get on the dime. Now the ball is back in ARRL's court to respond to the Commission's latest proposals. The comment cycle starts when the FCC publishes this notice in the Federal Register.