Visible Light Communication System Based On White LEDs

The trends that LEDs replacing of incandescent and fluorescent lamps for lighting are very clear. The feature that white LEDs can be used for both illumination and communications makes visible-light communication (VLC) has become a hot point in recent years. With the rapid popularization of computers, smart devices, the bandwidth and coverage of access networks need further improvement. VLC technology is a promising communication technology for high speed data transmission to solve the bottlenecks.Based on the VLC system architecture, the simulation analysis of key device and key technologies of the system are presented in this paper. The optical field distribution of white LEDs was simulated, the channel frequency response was measured, and transmission characteristics of various modulation formats were analyzed in simulation. Simulation results show that the OFDM signal is more suitable for the white channel, due to its better tolerance to frequency fading. Based on the frequency response of white channel, the software pre-equalization technology based on OFDM was proposed to compensate for channel attenuation and improve system performance. Besides, this paper also proposed the use of Nyquist windowing to improve the performance of OFDM receiver, and software post-equalization technology to compensate for frequency offset and phase noise.Based on simulation analysis, we experimentally demonstrated 2x1 and 3x1 multiple-inputs single-output (MISO) OFDM-VLC system based on subcarrier multiplexing. By adopting frequency pre/post-equalization technology to improve the syster BER performance,90 Mb/s signals have been successfully transmitted over 1 m visible channel. This paper also proposed a configuration of wavelength division multiplexing (WDM)-VLC system adopting pre/post-equalization and an adaptive Nyquist windowing of the OFDM signal in the receiver. Based on this configuration, we demonstrated a 750 Mb/s WDM-VLC transmission system based on RGB-LED.