Visible Light Full-Duplex Communication System Design

Visible light communication(VLC)is a new communication technology with lighting function and communication function.Most of the existing researches about visible light communication focus on the one-way downlink transmission,but the realization of indoor visible light uplink transmission is still in the course of exploration.On the analysis of full-duplex communication under one-way light source,the visible light reverse transmission scheme based on defocused "cat-eye" effect is designed on the theoretical analysis of modemmethod.Furthermore,the indoor visible light single-source full-duplex communication system is developed on the scheme.The main work is as follows:1.The channel model is analyzed in the visible light full-dulpex communication system.With the full-duplex communication principle under one-way light source,a modem and demodem scheme suitable for uplink and downlink is chosen.Peripheral high-power white LED drive circuit,modulator.drive circuit,signal processing circuit and high-speed light receiving circuit are designed.2.Modulator and demodulator for the digital DQPSK(Differential Quadrature Reference Phase Shift Keying)is designed in the FPGA(Field Programmable Gate Array).The real-time demodulation for the downlink DQPSK signal is actualized by polarity costas loop and lead-lag phase-locked loop.3.Uplink modulator is designed based on defocused "cat-eye" reverse modulation principle,by which the visible light full-duplex communication link with single LED is achieved by remodulating the downlink light signal and signal processing circuit.4.The FPGA design for the modulator and demodulator of 4FSK(quaternary frequency shift keying)modulator in the uplink is actualized.And the 4FSK demodulator is designed to improve the anti-noise performance for the uplink based on cross-correlation algorithm.According to the overall scheme,the visible light full-duplex communication system has been designed and tested.The experiment results have shown that the system achieves full-duplex communication link without interference between uplink and downlink with the only light source of downlink,and the system works well.