Research Of Key Technologies In High-Speed Visible Light Communication

Visible light communication (VLC) is a wireless communication technology which uses visible light to transfer data. This thesis focuses on the key technologies of high-speed VLC system using light emitting diode (LED). A 200Mbps demonstration system based on DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) is designed and implemented, whose transmission distance is up to 3 meters.Firstly, the intensity modulation, direct detection (IM/DD) and DCO-OFDM system is introduced. Due to the orthogonal frequency division multiplexing (OFDM) system’s high peak to average power ratio, the DCO-OFDM signal is proposed to be double-sided symmetrically clipped. The optimal DC bias value is deduced at given transmitter power and the algorithm is verified by simulation.Secondly, analog front ends of the VLC transmitter and receiver are designed and implemented. The transmitter uses the field effect transistor (FET) to drive LED. The circuit theory and the design of key parameters are analyzed, and the nonlinearity factors in the LED driving circuit are simulated. The receiver is constructed by photodiode (PD), trans-impedance amplifier (TIA) and voltage amplifier. The circuit theory and the design of key parameters are analyzed, and the receiver’s performance is simulated.Thirdly, the baseband system design based on DCO-OFDM is given. The system’s basic parameters, the way of carrier loading and the frame structure are introduced. Main attention is paid to system’s synchronization algorithms. The frame detection algorithm is given and the detection threshold is determined by simulation. The effects of symbol timing offset are analyzed and the symbol timing synchronization algorithm is given. Based on DCO-OFDM, sampling frequency offset effects are analyzed and compensation algorithm is proposed.Then, the designed baseband system is implemented by field programmable gate array (PFGA) programming. The detail describtions and the simulation results of the transmitter and receiver’s main modules are given.At last, analysis and tests of the demonstration system are carried out.