Broadband over Power Lines -- how bad an idea can you get?

Fred Goldstein,  July 2004


it kind of works.  Sort of.  But then, so does dumping one's raw sewage into the nearest river ...


...BPL is a gift of the entire HF radio spectrum to a handful of electric utilities...

reason that Powell is supporting BPL seems to be in order to provide some cover for his ferociously anti-competitive telecom policies...

some countries still do go to great lengths to cut off their residents from uncontrolled access to foreign ideas.  BPL might be a "perfect" match...

It no doubt sounds reasonably attractive at first.  An additional competitive source of broadband Internet access to the home, courtesy of the power lines.  Broadband Power Line carrier (BPL) has attracted the attention of investors and regulators.  Several companies have introduced products, and trials are under way in several places.  So what's the problem?

But a better way to frame the question is to ask, what's not a problem?  BPL is a truly wacky idea, but in the bad sense, one of those half-baked concepts that would never get off the ground if regulators and investors understood what they were talking about!  The idea is to take digital information and modulate it, using wideband spreading techniques, across the shortwave radio spectrum (3-30 MHz, also known as High Frequency, or HF) and feed it onto high-voltage power transmission lines, and put similar transmitters in the neighborhoods for the return path.  The sad part is that it kind of works.  Sort of.  But then, so does dumping one's raw sewage into the nearest river.  Both move the goods, but both cause pollution in the process.

Transmission lines are not all transmission lines

BPL's main problem is that it attemtps to use power transmission lines, designed to carry 60 Hz high-power electricity, as radio transmission lines.  Those are two very different tasks!  As frequencies rise, alternating current waves become more and more prone to radiate away from their transmission lines.  At 60 Hz, this is not a sereious problem.  But once frequencies get up into the Megahertz range, it's mighty serious indeed.  Power lines, which are untwisted pairs usually separated by some matter of feet, are not shielded, or in any way designed to confine radio waves that they might happen to be carrying.  They act as big antennas.  This effect can be used advantageously:  Many "carrier-current" radio transmitters depend on the inevitable leakage of power wiring to distribute unlicensed broadcasting, legally, around college campuses, tunnels, and other defined spaces. 

This is in marked contrast with, say, coaxial cable, whose outer layer is usually a grounded shield designed specifically to isolate the signal being carried from its environment.  Coaxial cable is designed to be a radio frequency transmission line.  Telephone cable is tightly twisted (hence the moniker "twisted pair") which delivers similar shielding at lower frequencies. That's how DSL, which actually goes into the AM broadcast spectrum, works.  Ironically, power lines probably have less attenuation than coax, and thus can carry radio waves a longer distance without regeneration, because they are so big. But for the most part they're too big to shield.  The low attenuation theoretically
makes BPL potentially attractive in suburban areas, though it is unlikely to be useful in rural areas that currently lack any broadband access. 

So as a result of this lack of shielding, BPL emits radio frequency interference.  Lots of it, and -- being "broadband" -- across lots of frequencies.  Americans aren't the world's most avid shortwave radio listeners, to be sure, but if they were, then they'd rapidly notice that BPL systems put out noise all across the shortwave broadcasting bands. They put noise across the HF amateur radio bands.  Early tests of BPL have confirmed the worst, too:  The noise isn't just a tiny increase in the background noise floor.  It's often loud enough to basically obliterate almost everything else!  It's within legal limits for unintentional radiation, but those rules were written with the expectation that the unintentional radiator would be a narrowband signal in a single location, not broadband along the entire power line. And it is not currently permissible to cause serious interference to a licensed user of the spectrum, even within those limits.  But the BPL industry has asked the FCC to raise the current limits on permitted interference by several orders of magnitude.

Politicians who support BPL are taking advantage of the fact that almost everyone nowadays makes some use of the Internet, while the HF radio spectrum's users are relatively few. 
Government and military agencies are major users of that part of the radio spectrum, and they're not happy about BPL's interference potential!  The National Telecommunications and Information Agency (NTIA), the Department of Commerce office that coordinates government spectrum usage (essentially on a peer-to-peer basis with the FCC, which nominally only regulates how non-government spectrum is used), has expressed its opposition. So did the Federal Emergency Managment Agency (FEMA), though, curiously, they later backed off of their strong opposition, raising some suspicions of political intervention.  But the FCC is pressing ahead with rule revisions to permit BPL, under its nominal authority to regulated unintended emissions.

Amateur radio and shortwave listening are seen as the province of a small number of aging geeks, and will be most severely impacted, since already-legal BPL interference levels are above "S9" across their frequency bands.  The lack of shielding works both ways, too:  BPL is quite prone to interference from nearby radio transmitters.  Legally, a licensed transmitter takes absolute precedence over an unlicensed emitter.  But what would be the political fallout of a ham radio operator whose station, operating legally, degraded his neighbors' BPL Internet connectivity?  Presuming, of course, that the ham operator could remain on the HF bands at all, given all of the noise.  BPL companies have tried to notch out ham radio bands from their systems, to reduce interference, albeit not very successfully; they are likely to still be susceptible to interference.  Likewise, power companies testing BPL have sometimes tried to clean up their power lines in order to reduce the effects of interference that occurs from other sources, be it lightning or other transmitters.  But they have not been very successful.

In the late 1970s, personal computers began to catch on, and many of the early ones had similar problems with unintentional radiation.  The FCC of that era stepped in and imposed strict emissions limits on computing devices, the now well-established "Class A" and "Class B" certifications.  This was costly to the computer industry; Radio Shack, for one, had to redesign its popular but extremely noisy TRS-80 computers and use metallic shielding, not just a cheap plastic case.  The current FCC, on the other hand, seems to be going to the opposite extreme, encouraging the widespread deployment of devices that may generate far more interference than any ordinary PC.

The FCC holds regular auctions of radio spectrum in order licenses services like wireless telephony, video distribution, and radio paging.  Yet BPL is a gift of the entire HF radio spectrum to a handful of electric utilities.  Are we seeing yet another power play by the energy sector, which seems to be so dominant in the Bush-Cheney administration?

Not a good alternative to common carriage

The other main reason that FCC Chairman Michael Powell is supporting BPL seems to be in order to provide some cover for his ferociously anti-competitive telecom policies.  The Telecom Act was supposed to open up access to the networks.  Earlier rules, such as 1980's Computer II ruling, required telephone companies to offer nondiscriminatory access to their networks to information service providers.  In other words, they could not reserve their monopoly lines for their own competive affiliates.  Without that ruling, the public Internet might not have been possible.  Powell is not only trying to roll back the Telecom Act with the cutoff of many unbundled network elements to CLECs, but (in CC Docket 02-33) he's trying to remove the entire common carrier obligation from ILEC-provided "broadband" services.  Thus independent ISPs won't even be able to buy raw DSL service any more.  The only provider of information over the twisted-pair network will be the ILEC or its chosen affilliates. The cable network will be one alternative, but it has never been common carriage, and usually only offers one ISP.  Absent the competitive pressures of common-carriage DSL, can all cable operators be expected to avoid taking advantage of the reduced level of competition?

Powell's favorite type of competition is intermodal.  It assumes that there are mulitple physical pipes -- cable, telephone, power line, satellite, radio -- and that this is sufficient competition to allow the owners of the most-regulated pipe -- telephone wire -- to be deregulated in a manner never before even seriously contemplated.  The only CLECs, in this model, are those who hang their own wire on the poles; ISPs can either strike a private deal with the owner of a physical pipe or hang up their servers.  Radio spectrum bandwidth is quite finite -- wireless Internet access is almost certainly going to be too costly for widespread fixed use in urban areas, and spectrum policies would need to be drastically rewritten in order to find the bandwidth needed.  (To their credit, some people inside the FCC organization are trying to do just that, but it's an uphill struggle and at best years away from fruition.)  Satellites suffer from speed-of-light delays (300 kilometers per millisecond: It's not just a good idea, it's the law!)  So BPL is a theoretical way to break the duopoly just enough to permit more deregulation. The FCC has made clear that BPL will not be common carriage.  It will be entirely the private matter of the power company, not available to any old ISP.

But even if that were acceptable, BPL's techical issues remain serious.  Security, for one thing -- unless it's encrypted, everyone's signals will be detectable all over the neighborhood.  (Cable modems always include encryption capabilities, though it is not always turned on by the network operators.)  Also, the signal has to be injected into the high-voltage neighborhood power mains.  These are stepped down to household level (117/234 volt) by transformers, which block BPL.  Typically, one transformer serves no more than eight houses.  For BPL to reach the house, a lineman would have to install a high-voltage bypass capacity across the transformer.  This has been seen as fairly practical in Europe, where 240-volt transformers are typically shared among 200 or so homes, but is a serious problem in North America.  So some BPL systems simply put WiFi access points on the poles, and hope for the best.  (The 2.4 GHz WiFi band is getting very crowded.) 

But come to think of it, can't power companies simply string fiber optics (which don't conduct electricity, so don't need much distance from the power lines) along their poles?  That would be a better solution, offering more bandwidth with no interference problems, and they have to roll the trucks anyway to put up BPL access points.  Indeed, haven't they pulled a lot of fiber anyway, using it for metering and control purposes?  Power companies often sell fiber-optic bandwidth at competitive prices, operating as CLECs or carriers' carriers.  BPL may be a bit cheaper,  but fiber is pretty plentiful nowadays. 

At the risk of seeming paranoid, here's another explanation.  BPL isn't really intended for widespread use in the United States.  It's being talked about for show, to give the ILECs plausible cover.  But it is intended for export.  Remember the cold war?  Remember how the Russians used to jam Voice of America and other western shortwave stations, which were fairly popular in their otherwise-closed countries?  Had BPL been available then, they would have loved it!  Russia doesn't care any more, but some countries still do go to great lengths to cut off their residents from uncontrolled access to foreign ideas.  BPL might be a "perfect" match for the Great Firewall of China!  Bring carefully filtered Internet services to the masses while cutting off access to foreign broadcasts.  And don't forget Saudi Arabia, that other paragon of enforced virtue, whose ties to this year's White House are extremely close.  You can expect BPL to be big there.  And never mind the notch filters.