Visible light communication system LED LAN : Nakagawa Group

The Nakagawa Laboratory is researching communication using visible light, an everyday phenomenon all around us.

The Nakagawa Lab is a world pioneer in visible light communication. Professor Nakagawa and Professor Haruyama serve as Honorary Chairman and Chairman of the Visible Light Communication Consortium. Along with many businesses, the Consortium is working to standardize visible light communication.

At Keio Techno-Mall in December 2009, there were demos of visible light communication, and the latest research results were presented.



Q. Regarding the specifics of our research, the idea is to use the light you can see from LED lighting, traffic signals, and signs to send information. If that becomes possible, then because LED lighting is used in lots of places, people would be able to use a ubiquitous network.

In one of the demos at Keio Techno-Mall, a robot was controlled using visible light communication. Position data is sent using visible light to control the robot, which has an image sensor as well as a light sensor. The robot can determine its own position, based on data about the position of the light source.

Q. In this demo, the scenario is that these sensors are attached to a wheelchair, and position data is received from the LED lighting in a hospital, to guide the patient to a doctor. 

In the Nakagawa Lab, another example of visible light communication is a demo wireless LAN system that uses visible light to achieve a speed of 100 Mbps. If such systems can be implemented, theyll enable data communication in places where radio signals cant be used, such as trains, airplanes, and hospitals.

Q. A feature of this demo is that it uses a new technology: theres a mirror in front of the receiver on the device side, and the mirror is accurately pointed at the light source. If you block the light with your hand, the mirror searches for a light source. If you take your hand away, the mirror finds the light source, and it stabilizes.

Q. Regarding these three demos, in the first one, weve tried to improve the image sensor so the signal can be transmitted at a higher data rate. By improving the signal processing circuit of an image sensor which are widely used in digital cameras, its possible to receive at 1 Mbps, and to receive not only position data from visible light, but video and audio content as well. In other words, a single device can be used to receive both video and audio content, and position data to show where the content is coming from.

Q. We think the killer app for visible light communication will be positioning services, to tell the user where they are. Current positioning services like car navigators utilize GPS, but GPS cant be used indoors, where reception is poor. So, the idea is to use indoor LED lighting to enable navigation indoors. As I mentioned earlier, I think this system could be used to help patients find their way around hospitals and to control robots.