The Design Of Visible Light Communication System Based On FPGA

With the continuous improvement of LED lamp performance and the continuous expansion of LED lamp application,the use of LED as a light source of visible light communication technology is maturing.White LED not only provides lighting,but also achieve data transmission when in the lighting.Visible light communication technology with rich spectrum resources,LED light has high response sensitivity,energy saving,communication security and other advantages.Visible light communication technology alleviates the problem of spectrum resources tension that existing in wireless communications.Based on the above research value,study and designs the visible light communication system based on FPGA.This paper mainly research and design the white LED communication between the two computers.First,the background and significance of the visible light communication system and the research status at home and abroad are analyzed.Secondly,this paper analyzes the principle and characteristics of light source white LED and photodetector PIN.The characteristics of LED include volt-ampere characteristics,modulation characteristics,spectral characteristics,and radiation characteristics.By analyzing the links and channels of visible light communication,the system determines the use of directional line of sight link and intensity modulation direct detection(IM / DD).This paper analyzes the communication protocol,2FSK modulation and demodulation method and development tool FPGA in the overall design of the system as the theoretical basis for the subsequent modulation and demodulation design.Then do the specific design of the system software and hardware,the system software design using FPGA to do 2fsk modulation and demodulation of the asynchronous serial data send by PC side.The modem includes a frequency module,a data receiving module,a modulation module,a demodulation module,a data sending module and a display module.Which including a total of six modules.In which the divides module divides the system clock to get fs,f0,f1,f2,ftb five kinds of frequency.Where fs as receive and transmit clock for the data receiving module and the data sending module.F0 is the fundamental frequency of the modulation module,f1,f2 is the carrier frequency of modulation module.Ftb is the clock frequency of display module.The function of the data receiving module is to complete the accurate reception of asynchronous serial data.The function of the modulation module is to encode the binary data to 2FSK.The function of the demodulation module is to demodulate the 2FSK signal into binary data.The display module displays the data of the receiving module,thus intuitively verifying that the receiving module has correctly received the asynchronous serial data.The data of the demodulation module is also displayed through the display module to verify that the demodulation module has implemented the function of demodulating the 2FSK signal.The function of the sending module is to send the demodulated data to the PC receiving terminal.The hardware design includes the transmitter and receiver circuit design.The LED driver circuit of the transmitter performs the function of DC driving LED to work normally and load the AC signal into the DC bias current.The function of the receiving circuit is to convert the detected optical signal into an electrical signal.At this time,the electric signal is a very weak(?A order)current signal,which needs to be converted into a voltage signal and amplified to reach the TTL level.The receiver circuit includes a preamplifier circuit,a low-pass filter circuit and a main amplifier circuit.The system uses ISE software to write and debug the program,through the professional EDA simulation tool ModelSim to do the waveform simulation of the six functional modules,through the analysis of signal waveform verify that each module has achieved the desired function.Using the oscilloscope to observe the signal in all aspects of the waveform,analysis and verify the function of hardware and software side.First observe the modulation signal waveform of the FPGA development board,verify that it completes the 2FSK modulation function,then observe the waveform after photoelectric conversion,analyze the change of the waveform parameters and the distortion,take the corresponding compensation measures and observe whether the processed waveforms eliminate the distortion.Finally,observe the waveform of FPGA demodulation path,verify its completion demodulation function.After the test of the hardware and software functions is completed,the PC side of the serial assistant as a source and sink on the visible optical communication system to verify the overall.The FPGA-based visible-light communication system designed in this paper can achieve the expected transmission of data between two PCs.In summary,the idea of using 2FSK for signal modulation and demodulation is proposed for the first time.The characteristics of the channel when the data are transmitted by visible light,the principle and characteristics of the white LED and the PIN photodetector,and the signal sampling method of the asynchronous communication are studied in depth.Analysis,the traditional optical fiber communication directly use 0,1 code control light source to carry the data,when the continuous transmission of 0 will seriously affect the light intensity,proposed a new VLC signal 2FSK modulation ideas,that is through dual-frequency signals to carried 0 and 1 to achieve the function of illumination and data transmission.Put forward that through using 16 times the rate of data sampling to solve the problem of asynchronous sampling phase mismatch.The overall scheme of the system is designed,and the solution measure that when the clock of both side of data receive and send is not synchronized is proposed.Make use of FPGA technology for signal modulation and demodulation circuit design,At the same time designed the photoelectric conversion and receiving circuit.The VHDL program of VLC signal 2FSK modulation is programmed.The system is programmed in Xilinx's ISE development environment.The model is simulated by ModelSim software.Finally,the generated bit stream file is downloaded to the Spartan XC3S100 E chip for data modulation and demodulation test.The system achieves a predetermined design effect.