Now that same idea, transmitting information over power lines, is the center of a major controversy. The technology is called BPL for Broadband over Power Line. It's regulated by the very same FCC Part-15 rules, updated to account for the quirks of sending broadband Internet service over the public power grid.
It's a compelling idea. Not everyone can get broadband via DSL on a telephone line, cable modem service or wireless transmissions. It's expensive to string new fiber optic or copper cables on poles or bury them in the ground. But just look up and you'll see plenty of power lines available.
Electric utility service is about the most universal service you can find. The power lines run underground in cities and subdivisions, then overhead around town and on giant towers as far to the horizon as you can see. If all that existing transmission line can be pressed into service for carrying data as well as power, the broadband infrastructure problem is solved. Even better, every house and office is wired for electrical service. You wouldn't even need to run Cat-5 networking cable. The wires in the wall are your network. No computer, printer or VoIP telephone would need anything more than a power cord to connect it.
As you may suspect, there are some flies in this ointment. The biggest one is that the medium and short wave frequencies used for BPL don't like to confine themselves to the power wiring. They escape by radiating just like radio waves from an antenna. The question is who do they bother and is there a way to avoid it?
The group having the most anxiety over this is the Amateur Radio Operators or Hams. Their hobby involves listening for very weak voice and coded signals from around the world. Even the low power requirements of Part-15 may not be enough to prevent the broadband data signals form BPL from creating static that can drown out faint signals in very sensitive receivers. Actually, any radio service operating in the bands from 1.7 to 80 MHz, including shortwave broadcasts and marine & public service two-way radio, could potentially be affected.
The government has protected certain interests by prohibiting BPL transmission on key channels used by aircraft and excluding operation near coast guard facilities and radio telescopes. Otherwise, BPL is allowed to share channels with commercial and amateur stations, but not to interfere.
The compromise solution to the interference problem is to deal with it on a case by case basis. The expectation is that a relatively few people located close to overhead power lines will actually experience a conflict. When a complaint occurs, the BPL operator will "notch out" or remove a narrow slice of BPL signal on the particular channel being contested. That works because the BPL signal is actually a wide spectrum consisting of hundreds and even thousands of individual carrier signals, each responsible for just a part of the entire bandwidth. Remove a few and you decrease the speed of your BPL service, but not by much. This scheme is called Multi-Carrier Modulation (MCM) or Orthogonal Frequency Division Multiplexing (OFDM) and is widely used in digital signal transmission, including DSL Internet and digital radio broadcasting.
The other fly in the ointment is cost. Power lines were designed to efficiently carry 60 Hz, not 60 Megahertz. Special couplers have to be installed to get the BPL signal around transformers that tend to filter out high frequencies. Repeaters are needed on long stretches of open wire because the low power digital signals fade as they go down the line. At this point, it looks like the population density is too low in rural areas to support the cost of providing broadband over power lines without special public funding.
It's important to remember that the FCC only authorized BPL with updates to its Part-15 rules on October 14, 2004. There have been only a handful of pilot programs with varying degrees of success up to this point. My best guess is that BPL is very unlikely to unseat DSL, Cable and Dedicated Internet services and achieve the dream of the nation's power grid also becoming the nation's data grid. Instead, it will find niches where it works well and is profitable and others where it doesn't. Further technology developments may surprise us the way broadband over telephone lines keeps increasing in speed to where it can now rival fiber optic cables.
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