Visible Light Communication in the Dark

Prototype for DarkLight visible light communication. (Source: R. Gill, Dartmouth Col.)

Prototype for DarkLight visible light communication. (Source: R. Gill, Dartmouth Col.)

With the rise in wearables such as smart­watches and fitness trackers that rely on smart sensors, and the continued popu­larity of smart­phones, smart devices are taking our country by storm. Wireless data for such devices is typi­cally beamed through Wi-Fi or Bluetooth, yet, the new wireless communi­cation techno­logy of “visible light communi­cation (VLC),” has emerged as a new option albeit with limi­tations due to the challenges it faces in practice, such as being easily blocked or not being able to sustain trans­mission when light is off. Through a new Dartmouth project called “DarkLight,” researchers have developed and demon­strated for the first-time, how visible light can be used to transmit data even when the light appears dark or off. DarkLight provides a new communi­cation primitive similar to infrared communi­cation, however, it exploits the LED lights already around us rather than needing addi­tional infrared emitters.

Through DarkLight, light-based communi­cation is sustained even when LEDs emit extremely low luminance, by encoding data into ultra-short, imperceptible light pulses by using off-the-shelf, low-cost LEDs  and photo­diodes, semi­conductor devices that convert light into a current. In order for the DarkLight proto­type to efficiently generate and reliably detect ultra-short light pulses, Dartmouth researchers developed a holistic solution to meet challenges regarding circuit designs, data encoding/decoding schemes, and DarkLight networking. The current DarkLight proto­type supports 1.6-Kbps data rate at 1.8-m distance.

DarkLight defies the long-standing assump­tion that visible light communi­cation requires a visible light beam to shine. For end users/consumers, this means that visible light can be reused in many scenarios that were never considered possible until now. DarkLight offers new capa­bilities in the areas of visible light communi­cation and sensing:

  • For visible light communi­cation, if you don’t want your lights on, such as during a sunny day or when you go out or leave your home, DarkLight could serve as a special mode that your ceiling LED lights switch to, so that the light bulbs can still beam data to smart devices (e.g., smart sensors, smart­phones) in the environ­ment.
  • LEDs and light sensors are common on smart­phones. With DarkLight, data could be transmitted by using your phone’s flashlight to another phone in proximity, without shining a light beam. The techno­logy offers one more alternative for secure communi­cation, since visible light is direc­tional and degrades fast over distance.

“With DarkLight, we can poten­tially enable light sensing so that it is always on, 24/7, regardless of the light’s illumination status,” says the project’s principal inves­tigator Xia Zhou, assistant professor of computer science and co-director of the DartNets (Dartmouth Networking and Ubi­quitous Systems Lab), which helped conduct the study. DartNets’ research focuses on broad appli­cations, systems, and networking per­spectives of smar­tphones and smart device systems. “DarkLight shows new possi­bilities on what visible light alone can do. We believe there are a lot more interes­ting appli­cations yet to come,” added Zhou. (Source: Dartmouth Col.)

Reference: The DarkLight Rises: Visible Light Communication in the Dark, MobiCom 2016: The 22nd Annual International Conference on Mobile Computing and Networking, New York, USA

Link: DarkLight project, Dept of Computer Science, Dartmouth College, Hanover, New Hampshire, USA

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