Visible light communication system

Abstract

There are two categories of current Visible Light Communication (VLC) systems according to their data modulation. One is to modulate the information by the frequency of LED visible light. The other one is embed information into the images displayed on screen [2].There are many factors, such as the position of capturing, trembling, ambient light, the performance of the display (e.g. display rate, display resolution and colorspace or color mode) and the performance of the camera (e.g. capture rate, lens distortion and image resolution), affect the quality of Visible light communication’s link. A recent work, RDCode is proposed to solve the issue. We evaluated performance RDCode on different mobile devices, under different environments, using different block size, among multiple users and Bit Error Rate (BER) variation in time and space. However, RDCode is not performing well in an unstable environment. This report presents SoftReTransmission (SoftRT) a light weight bit-level data retransmission scheme that enables adaptive and robust VLC transmission over screen-camera links on top of the RDCode. We develop a system that use color distance as the soft hint to provide the confidence level of how likely the bit is correctly decoded for each bit to the upper layers. We design a bit level soft hint based partial package combining schema that combines previously demodulated bits with current received bits to achieve a higher decoding rate.