Electronic Design

Broadband Over Powerline: Beyond The Interference

I wonder if any of you readers will march on Washington to protest FCC chairman Michael Powell's recent statements promoting the future of broadband over powerline (BPL). I know BPL is an incendiary issue with many of you, not because you're working on developing the technology, but because you're ham radio operators aware of potential BPL interference issues.

Powell made his pro-BPL comments at a technology demonstration sponsored by PG&E and AT&T last month in Menlo Park, Calif. "Powerline technology holds great promise to bring high-speed Internet access to every power outlet in America," he said. Such comments from high-level government officials don't resonate well with many hams. The ARRL (American Radio Relay League) said the FCC is "turning a blind eye" to the realities of interference issues.

Electronic Design received a torrent of e-mail from readers after Lou Frenzel, our Communications/Networking Editor, wrote an op-ed saying the ARRL was overreacting (see ED Online 7961). Many of you said that BPL's significant interference problems extend beyond hams, as it also jams local emergency transmissions.

Rather than jumping into the heat of the FCC/ARRL debate, I'm more interested in how technological innovation can extinguish this controversy. You readers have solved many greater engineering challenges than this one!

At the BPL event where Powell spoke, AT&T's Irwin Gerszberg, director of local network access technology, cited developing technology that will enable BPL to avoid interference with radio signals. I interviewed Gerszberg to get his take on how these interference issues will be solved. He is optimistic interference can be overcome by controlling the transmission power, radiation pattern, and modulation techniques and by using new technology to "get around interference problems" when they are detected.

Next-generation BPL, he said, will transmit at the higher end (the 30- to 50-MHz range) of the BPL spectrum, where previous-generation systems used spread-spectrum and caused more interference problems with ham reception (in the HF spectrum). Another piece of the solution, he said, is to use a "triple play" broadband architecture combining fiber, power lines, and Wi-Fi. Interference is minimized by using BPL to transmit over short distances, rather than trying to send the signal miles and miles.

"We use fiber to bring high speed into neighborhoods, then take it off a node and inject it into the high-voltage line. Then we use a repeater every 500 feet on utility poles, so we only need to have enough power to go 500 feet," he explained.

In a rural setting, the signal might be transmitted further between repeaters—but not more than a couple miles. "You have to have some backbone connectivity. BPL modems can do 200 Mbits/s. You don't want to go 200 miles with that," he said.

While Powell's comments about "high speed to every power outlet" imply a combination of HomePlug (in-house powerline distribution) with BPL (long-distance powerline data transmission), Gerszberg sees the advantage of using Wi-Fi technology to bring the signal the last 200 feet into the home. With repeaters on phone poles at 500-foot intervals, "we won't have more than 250 feet to any customer," he said.

HOT CITIES
This scenario brings the additional benefits of wireless connectivity to whole neighborhoods, creating "hot cities," said Gerszberg, where people could "pull out laptops and pick up a detection point, just like you would with a cell phone." Thank the recent cost reductions in wireless modems for making such a vision possible and for changing the strategy for how BPL can be implemented, Gerszberg said.

The other key interference-busting advance, said Gerszberg, are chips with 500 orthogonal frequency-division multiplexing (OFDM) tones that can easily identify and "notch out" specific problematic areas. The adaptive systems, he said, can detect where hams are operating. By using OFDM and digital filters, the systems then can shut down those tones and operate around them. Also, AT&T is working with partners on coupling technology to put signals on high-voltage line with much less leakage on the line itself, he said.

Most BPL trials conducted to date in the U.S., said Gerszberg, have been based on soon-to-be outdated technology. Gerszberg, who holds 70 patents on local-access technology, believes the current focus on BPL will lead to fast development and payback because of some strong market advantages. "Underground-wired neighborhoods can pose nasty challenges," he said. "You have to dig up streets to put in new cable. But BPL works underground very nicely. In fact, there's much less interference underground because you're shielded by all that dirt."

Also driving the advance of BPL, he said, are the electric utilities' goals to have bidirectional communications for access and equipment monitoring, advanced metering, pricing incentives, and load management. Gerszberg said it's the first time in communication history that there is technology out there that services two totally different industries: communications and the power industry. "Check the history books. I can't think of another example," he said.

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