Broadband Power Line Tutorial

by James Stenger

Broadband power line (BPL) is the term coined by the FCC for new modems (BPL modems) used to deliver IP-based broadband services on electric power lines. On April 23, 2003, the FCC adopted a Notice of Inquiry (NOI), expressing enthusiasm about the potential of the BPL technology to enable electric power lines to function as a third wire into the home, and create competition with the copper telephone line and cable television coaxial cable line. The FCC said that BPL service can be offered now using BPL modems that comply with existing FCC Rules. However, the FCC also asked whether changes to its rules are needed, either to remove unnecessary barriers to BPL service or to protect other devices from interference from BPL modems.

BPL modems use silicon chips designed to send signals over electric power lines, much like cable and DSL modems use silicon chips designed to send signals over cable and telephone lines. Advances in processing power enable new BPL modem chips to overcome difficulties in sending communications signals over the electric power lines that could not be overcome with less computing power. BPL modem speed, like cable and DSL modem speeds, is changing rapidly with each advance in new technology, so it would be difficult to make any generalization here that would be accurate or timely.

The FCC NOI discusses two types of BPL, In-house BPL and Access BPL.

In-house BPL is a home networking technology that uses the transmission standards developed by the HomePlug Alliance. Products for in-home networking using the electric outlets in your home (or office) are available in stores now. In-house BPL products can comply relatively easily with the radiated emissions limits in Part 15 of the FCC’s Rules, because the products connect directly with the low voltage electric lines inside your home or office. In-home networking, while exciting and innovative, is not a major policy concern for the FCC. What the FCC is really wrestling with is how to get broadband Internet access over “the last mile” to the home.

Access BPL is a new technology to carry broadband Internet traffic over medium voltage power lines. BPL modems that electric utilities and their service partners can install on the electric distribution network also are available now. Medium voltage power lines are the electric lines that you see at the top of electric utility poles beside the roadways in areas that do not have underground electric service. Typically there are three electric lines (called phases A, B and C), each carrying several thousand volts. One phase is usually enough to power the houses on a residential street, two or even three phases can be joined together to power the big electric motors in an industrial or commercial area. (You also may see a fourth wire that is the ground wire.)

Inductive couplers are used to connect BPL modems to the medium voltage power lines. An inductive coupler transfers the communications signal onto the power line by wrapping around the line, without directly connecting to the line. A major challenge is how to deliver the signal from the medium voltage line to the low voltage line that enters your house, because the transformer that lowers the electric power from several thousands volts down to 220/110 is a potential road block to the broadband signal. Several methods are now available that successfully solve this problem.

Interference issues between unlicensed devices, including BPL modems, and other electronic devices are governed by Part 15 of the FCC’s Rules. All electronic devices sold in the U.S. have to meet FCC radio frequency (RF) emissions limits. When BPL modems are installed on underground electric lines, the communications signal is shielded by the conduit and the earth and as a result is unlikely to cause interference to other communications services. The FCC is more concerned about the interference potential of BPL signals transmitted on exposed, overhead medium voltage power lines.

Public comment responding to the NOI on BPL is invited by the FCC, both from the proponents of the new BPL service, i.e., electric utilities and BPL vendors, as well as those who might be impacted by the BPL signals. For example, on most electric utility poles you will notice that below the four electric utility lines there is a lower segment of the pole where telephone and cable television wires are attached (referred to as the communications space). One of the questions the FCC asks is whether radiated signals from access BPL systems on the electric power lines would interfere with signals on the cable and telephone lines, and vice versa. We can expect a lively debate in the comments filed in response to the NOI on this issue, since the parties involved are competing for the same customers.

A more intelligent electric power grid. Speaking of competitors, why should we care about any of this when 3G wireless cellular telephone networks, wireless in-home networking and Wi-Fi hotspots claim to have the answer to delivering broadband to everyone? Electric utilities are not just looking at BPL as a way of entering the communications business. In fact, they may want to leave that part of BPL to a partner, perhaps an ISP, a CLEC or a long distance company looking for an alternative last mile path to their customers. Electric utilities are interested in BPL because it can give them an intelligent electric distribution grid. This could result in lower electric power costs, less pollution and greater reliability and security.

A better connected appliance. What’s interesting about BPL is that every electric device is connected to the electric distribution network. Potentially then, BPL could let chips in every electric device talk to each other. Could we put a Wi-Fi, Blue Tooth or other wireless chip in every appliance? Yes – but BPL may be a better solution. Those who had PC’s before the Internet exploded remember the difference in functionality between a standalone PC and a networked PC. Networking every electric device together over the power lines might result in a similar growth in productivity and convenience for your home and office.

More Information

The text of the FCC NOI can be found here (PDF).
Website of the HomePlug Alliance: www.homeplug.org

About the Author

The author of this tutorial on BPL, James A. Stenger, is a telecom lawyer in Washington, D.C. He worked on BPL for two years leading up to the FCC NOI adopted in April, 2003.

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