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'Smart lighting' efforts ease congestion in RF bands

Posted: 13 Oct 2008 ?? ?Print Version ?Bookmark and Share

Keywords:lighting LED? wireless? broadband?

A "smart lighting" initiative being funded by the government seeks to piggyback wireless communications capabilities into future LED lighting installations to provide more broadband access points.

The $18.5 million, 10-year National Science Foundation program includes more than 30 university researchers from Boston University, Rensselaer Polytechnic Institute in New York and the University of New Mexico.

The initiative enables to employ visible light beams for communications between wireless devices and LED-based lighting fixtures. The LED-based scheme can also be used to communicate between automobiles that are increasingly using LEDs. The general goal is to establish new communication capacities into all LED lights, while loosening congestion in current RF bands.

"There is a long history of communications of this type with IR, and there is the IR Data Association that has protocols for many years for PDAs, printers and laptops," said Thomas Little, professor, Boston University. "What we are doing is seizing this opportunity to embed networking in the LED lighting revolution. As incandescent and fluorescent bulbs are modified, we look forward to embed a networking technology into LED lighting," he added.

Light-based communications capacities that now employ IR LEDs like remote controls will be adapted by using visible light so that transceivers in digital devices can communicate with lighting fixtures. The fixtures would be hard-wired to the Internet. Unlike RF-based Wi-Fi access nodes, which must share spectrum will all users, line-of-sight communications via visible light could help separate data streams to be fed to each device.

The researchers have worked with several modulation schemes, involving encoders that use standard binary codes, non-return-to-zero encoders, pulse-code modulation and pulse-density modulation. They claim that each of these schemes can be made to work without flickering lights, so long as data rates are above 900KHz.

Initial prototypes, which will be shown next year at speeds from 1Mbit/s to 10Mbit/s, will use off-the-shelf LEDs and photodiodes to handle transmission and reception functions. The researchers also plan to develop novel semiconductor technologies that could eventually allow visible light transceivers to be established.

"We, as part of the system, need a receiver usually done with a photodiode. One idea is to use the same LED with a reverse bias. In effect, as a part of the manufacturing process, we make some of the LEDs as receivers and some as senders," said Little.

The group will also experiment using multiple light wavelengths to encode multiple data steams on the different colors of light that when combined create white LEDs. Light polarization will also be the focus of multiplex communication strategies employing visible light.

Boston University will discuss system-level issues, including computer networking application development. IC device development will be conducted by Rensselaer Polytechnic Institute and University of New Mexico researchers.

Boston University has set up a Website to disseminate information about the smart lighting initiatives.

- R. Colin Johnson
EE Times

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