High-speed data transfer over home power lines clears the way for a true plug-and-play home network
Thanks to the emergence of faster powerline communications (PLC) standards, anything from Internet to high-definition television signals can be sent to every room of the house — as long as it's equipped with an electrical receptacle.
In 2001, a group of companies formed the HomePlug Alliance, which created the HomePlug 1.0 standard to transmit data at speeds of 14 megabits per second over electrical wires. To date, more than 4 million devices based on this standard have been sold worldwide.
Until recently, HomePlug was primarily used for networking computers. However, this summer the HomePlug Alliance released its newest PLC standard, HomePlug AV, which stands for audio and video. This new standard allows a data transfer rate of up to 200 megabits per second — plenty fast enough to handle multiple high-definition video streams at once. It uses 128-bit AES Encryption to ensure privacy of the data exchanged over the network and is designed for backward compatibility with HomePlug 1.0 products. Products containing this technology are expected to hit the consumer market early this year.
While the data transfer speed of HomePlug appears promising, even more telling may be the high-profile companies this technology has attracted. Since the new technology was announced, Intel, Motorola, Cisco, General Electric, Sharp, and Samsung have all joined the HomePlug Alliance. In fact, Intel powerline initiative manager Matt Theall even took over as president.
A new standard. “What makes HomePlug so compelling is the fact that there's a power outlet every 8 feet by building code,” says Andy Melder, senior vice president of Intellon, a founding member of the HomePlug Alliance and a major manufacturer of HomePlug silicon chips. “So what electrical contractors do is simply lay out the electrical wiring per code without consideration whatsoever that HomePlug will be using that wire for other purposes.”
In fact, he says the technology requires no real installation. Just by plugging in a HomePlug-enabled adapter into a wall receptacle and connecting it to an Ethernet cable, every receptacle in the house can have data transmitted to it over the home's existing electrical wiring system. Then adapters can be used in other parts of the house for access to Internet, HDTV, VoIP, etc. The broadband signal can enter the home using a variety of methods — including broadband over powerlines (BPL), if the user's utility provider offers this service — before it is dispersed throughout the home.
The idea is technology manufacturers will eventually include silicon chips in their devices to read the signal coming through the electrical receptacle. Therefore, in many cases, purchasing a converter won't even be necessary. The user will simply plug in an electronic device, and it can receive both communication signals and power simultaneously through its power cord.
“Just like five years ago, for example, if you bought a laptop computer, chances are it didn't have a WiFi chip in it, so you had to go out and buy a PC adapter card,” Melder says. “The same thing will happen with HomePlug.”
Sending data over home powerlines is not a new concept. As early as the mid-'80s, a technology called X10 allowed end-users to control the lighting throughout the home from one central control console using adapters that plugged into the wall. But simple command and control doesn't require the signal processing that data, video, and audio streams demand. Because electrical lines are inherently noisy, especially when hairdryers, dishwashers, and vacuums are in use, HomePlug had to develop a method of moving the data around the noise.
HomePlug AV sends data over the electric wires in the home using the frequency spectrum from 2 MHz to 30 MHz. That spectrum is broken up into 1,000 different carriers — each of which has the ability to be phase shifted with modulation densities from 1 bit per carrier symbol to 10 bits per carrier symbol. If one of these carriers contains too much noise, the data will shift to another carrier through the use of windowed orthogonal frequency division multiplexing (OFDM).
“The sophistication of the algorithms and the performance of silicon have advanced to the point where we can do these things in real time,” Melder says.
Real time is especially important for audio and video. “If I type in a URL and hit enter on my keyboard, it doesn't matter if it takes 1 second or 1.2 seconds for that Web site to come up,” he maintains. “But if I want to move video or audio around, I can no longer tolerate a delay in the arrival of any packet that's tied to a video stream or an audio stream, because immediately my usage experience goes down the tubes.”
Filling in the gaps. With PLC technology supporting data, audio, and video, a “smart home” for the masses seems closer than ever. People could record their favorite show using the digital video recorder (DVR) in their bedroom and then stream the video to their large flat panel display in the family room later to watch it. Digital pictures downloaded to a PC could instantly be displayed on a TV in the basement. A printer could be shared with every computer in the house just by plugging it in. Every electrical device in the home could be interconnected via the home's electrical network. But PLC technology is unlikely to completely replace other data transmission technologies any time soon. That's because HomePlug adapters can also be used to enhance other networking systems.
“HomePlug technology is just an alternative for expanding or completing coverage, filling up gaps in your coverage,” says analyst Joyce Putscher of market research firm In-Stat in Scottsdale, Ariz., explaining how wireless LAN service providers can reap the benefits of HomePlug technology. “If a customer is having trouble getting reception in a room or two, they want to make their customer happy, so some of the service operators are starting to just send them a [wireless LAN] adapter,” Putscher says.
Homebuilders may also find themselves benefiting from PLC technology. Homebuilder Benjamin Johnson, president of Martineck-Johnson Custom Homes, says that just knowing this technology is available makes him comfortable enough to install less Cat. 5 cable in his new homes. In fact, he only installs about one-third as much cable as he did before learning of HomePlug AV, primarily for traditional phone lines.
“We still generally run one Cat. 5 to every room, but I don't have to worry about my homeowner calling me up and saying, ‘Gee, I wanted to put my computer over here instead of over there,’ because I know that by using the [HomePlug] technology they can do it themselves,” he says.
Johnson also notes that the way his new homes are wired electrically will not need to change in any way to accommodate HomePlug equipment. Melder agrees, adding, “There's been quite a bit of testing done in the early days of various homes of different sizes, of different construction, and different wiring material being used, whether it was aluminum or whether it was copper — none of that matters.”
Overcoming obstacles. Though builders and service providers may be excited about HomePlug, not everyone is thrilled. The frequency spectrum used by HomePlug is also the same spectrum used by ham radio operators, who are concerned about the signal in the wires radiating and causing interference in their communications. For this reason, Melder says, HomePlug has “notched out” certain frequencies used by ham operators. In other words, these frequencies are assigned a null value and are not utilized by HomePlug.
“The American Relay Radio League (ARRL) has products that they've tested where they are used right next to a ham radio, and they cannot see the HomePlug products operating, because notching is done so deeply in terms of attenuation and so precisely, that the ham frequencies aren't touched at all,” Melder says.
A study of the HomePlug 1.0 standard conducted by broadband consulting firm Systems Dynamic in 2003 notes some of the drawbacks of the original standard, most of which have been remedied with HomePlug AV. It warns that HomePlug adapters should not be plugged into traditional surge protectors. Through this research, the consulting firm found that the better the surge protector, the worse the HomePlug performance. In fact, analysts say a UPS will block HomePlug completely. To address this issue, some manufacturers now sell surge protectors and UPSs specifically designed to work with HomePlug networks.
HomePlug is not the only standard for transmitting data across home electrical wires, but it is certainly the most predominant standard in the United States. However, another standard by a company in Spain, DS2, also offers 200 megabits per second performance, and claims to have provided chips for 100,000 powerline networking devices distributed by Telefonica, a Spanish phone company. But analyst Putscher doesn't feel that there is any kind of a standards war developing between DS2 and HomePlug.
“Some operators may deploy and offer DS2-based units to their customers and some may offer HomePlug, so at this moment I don't see one going totally away,” she says.
Future plans call for HomePlug to make its technology available for use over cable and phone lines to provide even further home coverage. “So not only are we focused on powerline, which is the most ubiquitous medium in the home, but we can also apply it to any other already in-place wiring.” Melder says. “I can't help but be very bullish on where this is going over the course of the next 18 to 24 months.”