Design Of The White LED Communication System On FPGA

Indoor optical wireless communication system provides an attractive alternative for realizing next generation wireless local area network.Attaching communication by illumination LEDs provide additional valuable functionality to LED lighting fixtures as optical communication transmitters at little cost.Therefore,a white LED-based VLC system is designed and a joint coding and modulation scheme is proposed,afterwards the system performance is verified through the video transmission experiment.Firstly,for the hardware implementation of VLC system,a platform including FPGA,transmitter and receiver is designed for an indoor VLC system using FPGA and white LED.The FPGA device uses its parallel processing and reprogrammable features to complete the encoding and modulation of digital signals,while completing the network interface communication between FPGA and PC.For the transmitter,the circuit is designed with the comprehensive analysis of the electrical characteristics of the two white LEDs?blue-white LED,RGB-LED?.For the receiver,a PIN-PD based receiver circuit is designed with the analysis of the photodiode conversion efficiency,dark current,noise and other parameters.Secondly,for the realization of communication and dimming control function in VLC system,a scheme of dimming control using joint coding modulation is proposed,which is mainly designed from two parts of data intra-frame and data inter-frame.In the data intra-frame,in order to solve the light source flicker caused by the mismatch of the duty cycle between intra-frame and inter-frame,the precise dimming control scheme using PWM is adopted.In the data inter-frame,the RLL coding?Manchester?4B/6B?is designed to avoid long run-length,conducive clock recovery and ensure DC balance,and two schemes?MPPM.OPPM?for dimming control by changing the modulation order are proposed,to meet the system power and spectral efficiency requirements respectively.Finally,for VLC system application functions,this paper set up a VLC-based video transmission system,which includes full-duplex communication mode based on air separation technology and streaming media push and play program based on HTTP protocol.Then,the performance of the system was tested experimentally,the result shows that the system can transmit video signals stably at the optical clock rate of 2MHz,the system optimal BER is less than 10_-9 at the transmission distance of 65cm.