CGH for Indoor Visible Light Communication System

In this paper, we propose, design, and evaluate two indoor visible light communication (VLC) systems based on computer generated holograms (CGHs); a simple static CGH-VLC system and an adaptive CGH-VLC system. Each transmitter is followed by the CGH, and this CGH is utilized to direct part of the total power from the best transmitter and focus it to a specific area on the communication floor. This leads to reduction in inter-symbol interference and increasing in the received optical power, which leads to higher data rates with a reliable connection. In the static CG11H-VLC system, the CGH generates 100 beams (all these beams carry same data) from the best transmitter and directs these beams to an area of 2 m x 2 m on the communication floor. In the adaptive CGH-VLC system, the CGH is used to generate eight beams from the best transmitter and steer these beams to the receiver's location. In addition, each one of these eight beams carries a different data stream. Whereas in the first system, a single photodetector is used (added simplicity), an imaging receiver is used in the second one to obtain spatial multiplexing. We consider the lighting constraints where illumination should be at acceptable level and consider diffusing reflections (up to second order) to find the maximum data rate that can be offered by each system. Moreover, due to the fact that each beam in the adaptive CGH-VLC system conveys a different data stream, co-channel interference between beams is taken into account. We evaluate our proposed systems in two different indoor environments: an empty room and a realistic room using simple on off-keying modulation. The results show that the static CGH-VLC system offers a data rate of 8 Gb/s while the adaptive CGH-VLC system can achieve a data rate of 40 Gb/s.