Broadband over power lines (BPL)

Last updated: August 20, 2008.

High-speed Internet access anywhere, anytime—that's what we've increasingly come to expect in the 21st-century information age. But what if you live in a rural area where it's too expensive for a telecoms company to provide broadband? Or what if your house has old telephone wiring or the room you want to work in doesn't have a telephone access point? Worry not! The solution could be BPL (broadband over power lines)—a way of piping broadband to your home and channelling it from one room to another using the standard electricity supply. BPL is also known as HomePlug (the name of an alliance of manufacturers who make the equipment) and, in the UK, as "networking over the mains." Let's take a closer look at how it works!

Photo: Ordinary, medium-voltage electric power lines like these can be used to bring broadband Internet to your home.

Sending two signals down one line

If you know something about broadband Internet already, you're probably aware that it works by splitting your ordinary telephone line into a number of separate channels. Some of them carry your phone calls, as usual, some carry downloads (information coming from the Internet to your home), and some handle uploads (information going the opposite way). Broadband uses low-frequency electric signals to carry ordinary phone calls and higher-frequency signals to carry Internet data. Electronic filters separate the two kinds of signal, with the low frequencies going to your telephone and the higher frequencies to your Internet modem.

Does that sound so strange? It's really not so hard to use a single medium to carry more than one thing. People work this way all the time. If you've ever stood quietly in a corner of a cocktail party tuning in on different conversations, you'll know how easy it is to do. The air in the room is like a giant pipe carrying many different sounds to your ears. But, using something called selective attention, your brain can tune into one conversation or another depending on whom you find most interesting. Broadband Internet works a bit like this too. A single piece of telephone cable carries both phone calls and Internet data. Your telephone listens just to the calls; your modem lists only to the data.

Access BPL: bringing broadband to your home

If you can send computer data down a phone line, there's no reason why you can't channel it down a power line as well. Some Internet service providers (ISPs) are already using overhead and underground power lines to carry broadband data long distances to and from their customers in what's called access BPL. It's exactly the same principle as sending broadband over a phone line: a high-frequency signal carrying the broadband data is superimposed on the lower-frequency, alternating current that carries your ordinary electric power. In your home, you need to have slightly modified power outlets with an extra computer socket. Plug in a special BPL modem, plug that into your computer, and your broadband is up and running in no time.

Photo: With BPL, your modem takes its signal from your domestic electricity socket rather than your telephone socket.

In-house BPL: carrying broadband within your home

You can also use BPL with traditional telephone or cable broadband to bring Internet access to all the different rooms in your home. You simply plug the Ethernet lead from your normal modem into a special adapter that fits into one of the power outlets. Your home electricity circuit then takes the broadband to and from every room in your house as a high-frequency signal superimposed on top of the power supply. If you want to use broadband in a bedroom, you simply plug another Ethernet adapter into one of the ordinary power outlets in that room and plug your computer into it. In-house BPL, as this system is known, is a great way of getting broadband in any part of your home. It's particularly useful if you have a big house with thick walls that make wireless Internet impossible.

Smart homes of the future?

BPL opens up an even more exciting possibility for the future. If we can connect computers using the ordinary power lines in our home, there's nothing to stop us connecting up domestic appliances both to one another and to the Internet. Smart homes (in which appliances are switched on and off automatically by electronic controllers or computers) have used this basic idea for years—but BPL could take it much further and make it far more widespread. Imagine a future where you can use a Web browser on your computer at work to switch on the electric cooker in the kitchen at home, ready for when you arrive. Or how about using a Web browser to turn your home lights on and off when you're staying in a hotel, to give added protection against intruders? Just imagine the possibilities: BPL could take remote control to an amazing new level!

Further reading

Websites produced by companies who make BPL equipment are worth a look for further information. Here are a few for starters. Look in the products section of each website under "powerline" or "Ethernet adapters":

• HomePlug Powerline Alliance: Industry group promoting powerline technology.
• Belkin: Make a system called Powerline.
• Devolo: German manufacturer of a popular powerline system called dLAN.
• Netgear: Make powerline Ethernet adapters and wireless access points.
• Zyxel: Offer a range of powerline Ethernet adapters.