Visible Light Communications

Indoor

 

 

 Solid state lighting is predicted to replace fluorescent and other lighting sources for general illumination, due to its reliability and the potential for highly efficient sources.  Compared with other sources of illumination these devices can be modulated at high data rates, offering the opportunity for communications as well as illumination from these sources. Such Visible Light Communications (VLC) has been investigated in Japan by the Visible Light Communications Consortium (VLCC). There is now growing interest in Europe, with work in an EC funded FP7 project on Home Access Networks (OMEGA), and also standardisation effort within IEEE 802.15.7

Work at Oxford has focused on using white LEDs for illumination and communications with several demonstration links and publications.

 

Projects and investigations

Music transmission using a desk lamp

A desk lamp was modified to use four white LEDs to provide illumination and also to transmit data. The LED is modulated using a ~6Mbit/s data signal from a CD player and the optical signal is detected using a small receiver unit. The data is recovered and an A/D converter then creates audio signals for a pair of loudspeakers. The lamp transmits data over a range of up to a few metres.
 
 

High speed transmission using an LED array

White LEDs have a significant amount of series inductance and a series capacitor can be used to peak their optical response at a particular electrical driving frequency. Using an array of LEDs with a different set of peak frequencies allows an overall wide channel bandwidth. A link that operates at 40Mbit/s (NRZ-OOK) over several metres was fabricated.


High speed transmission using equalisation

Equalisation can be used to tailor the transmission response of a single LED, and also to alter the frequency response of the optical receiver in a data link. We have undertaken a number of different simulations and experiments to investigate this technique, and showed a 100Mbit/s (NRZ-OOK) short range data link using receiver equalisation and blue filtering of the LED response.