Research And Implementation Of High-Speed Visible Light Communication System

With the advancement of wireless communication technology and the popularization of various terminal equipments, the data transmission rate and the service quality of wireless communication are put forward higher requirements. In the face of higher speed and more reliable data transmission requirements as well as scarce radio spectrum resources, visible light communication (VLC), which utilizes free visible light band and holds a huge potential for communication capacity, has attracted great attention from domestic and international academic and industrial area. This thesis will study VLC technology which uses visible light to transfer data, and focus on the design and hardware realization of a high-speed VLC system based on RGB light emitting diode (LED) as light sources.Firstly, this paper investigates the physical layer technology of VLC system and proposes a novel optimization algorithm by making use of the anti-periodic property of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) time domain signal to recover the clipping signal at the ACO-OFDM receiver. With the beginning of illustrating the VLC system model, we analyze the characteristics of signal in ACO-OFDM system and provide theoretical analysis of the proposed optimization algorithm. And then the optimal receiver model is deduced and the effectiveness of the proposed optimization algorithm is verified via simulation.Secondly, the circuit of VLC transceiver end driver is designed and implemented. At the transmitter, by introducing the operating characteristics of RGBA LED and analyzing the circuit theory of using field effect transistor (FET) to drive LED, this paper finishes the key parameters design of LED driver circuit. At the receiver, after studying the performance parameters of photodiode (PD) and analyzing the principle of PD two-stage amplifier driving circuit, including trans-impedance amplifier (TIA) and voltage amplifier, the detailed key parameters of PD driver circuit are provided.Thirdly, this thesis studies the hardware design and implementation of the VLC system digital baseband. Based on the DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) system model and the overall system block diagram, the system baseband scheme, including basic parameters, physical layer data frame structure and baseband implementation structure and so on, are designed. And then this paper demonstrates the method of the field programmable gate array (FPGA) hardware realization of the designed VLC system digital baseband, especially the implementation details of the transceiver’s key modules.Finally, detailed analysis and tests of the DCO-OFDM VLC system are performed, including channel frequency response, time-domain waveform signal, signal spectrum, transfer rate and bit error rate (BER). The test results indicate that without convolution encoder, the average rate of application layer is about 508Mbps and BER is less than 10-4, and when adding 1/2 convolution encoder and setting 3m transmission distance, the system can achieve high-definition video in real-time and reliable transmission, the high-speed VLC system constructed in this paper successfully realize the system requirements.