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LEDs to transmit data, too?

Posted: 10 Jun 2010 ?? ?Print Version ?Bookmark and Share

Keywords:LED? solid-state lighting? wireless communications? Wi-Fi?

With preparations under way for a shift to solid-state lighting based on high-output LEDs, a proverbial light bulb has appeared above the heads of some forward-looking engineers. Their proposal: Why not switch the LEDs on and off so fast the eye cannot tell, in order to use them to transmit data too?

With enough advance work, every new LED light fixture could also be wired into the network backbone, accomplishing ubiquitous wireless communications to any device in a room without burdening the already crowded RF bands. Visible light communications (VLC) is being refined by industry, standards groups and well-funded government initiatives. And the stakes are enormous, since the traditional lighting market is measured in trillions of dollars and the transition to solid-state has already begun. This year, LED lighting will account for more than a $1 billion market, with projected growth to about $7.3 billion by 2014, according to Strategies Unlimited.

Of course, solid-state lighting's priorities are to lower greenhouse gas emissions and users' utility bills, since LED lamps use less power than today's standard lighting products. But the enormous size of the market has already prompted nearly every major electronics research organization to begin developing VLC applications.

Most of those apps will not attempt to replace other wireless technologies, such as Bluetooth, Wi-Fi, WiMAX and LTE, but will aim for niches that are not well served by RF wireless today-from hospitals and aircraft, where RF can interfere with signals in life-critical equipment, to robots that could navigate halls for mail delivery using virtual signposts in overhead lighting, or signage that could supply additional information when a phone camera is pointed it.

Japan's Visible Light Communications Consortium, with members Casio, NEC, Panasonic Electric Works, Samsung, Sharp and Toshiba as well as telecom carriers like NTT Docomo, was instrumental in stimulating the IEEE 802.15 Wireless Personal Area Network standards committee to add a ".7" effort to elevate visible light communications to the same wireless status as RF and infrared. The 802.15.7 committee just approved the current draft of the wireless VLC standard at the working group level, "but we still have a lot of comments to resolve," said Rick Roberts, a scientist at Intel Labs (Portland, Ore.) who acts as technical editor for the IEEE 802.15.7 committee.

"The stimulus for getting IEEE involved is the ubiquitous deployment of LEDs. The technology is there for illumination, but if a wireless market is going to be there too, we know from past experience that there needs to be standardization for interoperability," said Roberts. "Our standardization efforts started in 2008, and we are hoping to have the ink dry on the standard next year."

Just as brake lights "tell" drivers to stop, VLC could send the same message to engine-control units for collision avoidance.
Graphics provided by Boston University applications. Source: Boston University

Dual use of LED lighting for illumination and communication would enable ubiquitous computing, with separate data streams for each device in the room.

According to Roberts, the primary objective for the 802.15.7 committee is to enforce a standard that puts illumination first and communications second. "Visible light communications is the only [wireless comms] signal you can see with the human eye, so it cannot be obtrusive," he said. "For instance, it would not be good for remote controls, because people watch TV in darkened rooms; you don't want flashes of light being emitted by the remote. . . Using [LEDs] for communications cannot cause flicker, and [VLC] has to accommodate anything that people normally do with illumination sources, like dimming them."

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