Wirelessly transmitting a grayscale image using visible light

We present the use of visible light as an alternative to wireless radio communication. We use common data encryption techniques followed by modulation of the signal using Orthogonal Frequency Division Multiplexing. The modulated signal is used to drive common Light Emitting Diodes which transmit a binary bit-stream in the form of light, through air as the medium. A photo detector, used at the receiver, along with a driver circuit and the appropriate decryption block is used to get back the original data. In this paper we show how a regular grayscale image can be transmitted with this method and faithful reproduction is achievable at the receiver. LED bulbs are used as transmitters and the intensity of the LEDs is varied at very high rate, using OFDM modulation technique to encode the image data, such that the intensity appears constant to the human eye. Thus, apart from providing illumination, the LED bulb transmits data at high rates. The sensitive receiver circuit is designed to detect these small instantaneous changes in the LED intensity and hence decode the received data, thereby reproducing the image in its original quality. The integration of high response Silicon PIN Photodiodes with signal processing tools makes this possible. Specific design measures prevent ambient light from interfering with the demodulation process at the receiver. Although this method can be currently used for short range, future developments can really expand its scope.