Research On LWT-OFDM Visible Light Communication System Based On RS

Orthogonal Frequency Division Multiplexing(OFDM)is a multi-carrier modulation technology with orthogonal transform as the core,Applying it to visible light communication(VLC)can effectively improve the communication performance,However,the traditional OFDM signals based on Fast Fourier Transform(FFT)are greatly affected by LED nonlinearity,Sensitive to frequency offset,The peak-to-average power ratio is also higher.Based on this,this thesis applies the Lifting Wavelet Transform(LWT)and OFDM to visible light communication,which can not only improve the reliability of communication,but also have a high frequency spectrum utilization rate.The specific research contents include the following points:1.Based on the Lambert radiation model,the indoor direct line of sight link and non line of sight link models are established.The two channels are mathematically modeled in the experimental model,and the influence of indoor multipath effect on the reliability of optical communication is verified by simulation.According to the characteristics of optical channel,DC-biased Optical-OFDM(DCO-OFDM)and Asymmetrically Clipped Optical-OFDM(ACO-OFDM)systems are analyzed.The signal characteristics in time domain and frequency domain are compared,and the efficiency,reliability and peak to average ratio are studied.2.Based on the DCO-OFDM system,a visible light OFDM system scheme based on lifting wavelet transform is proposed,and the LWT-OFDM system model is built.The wavelet base function is selected for the sub-carrier,and the high and low frequency separation of the signal is realized by predicting and updating the signal.Using the good scale and translational orthogonal characteristics of the boosted wavelet,the system communication reliability is improved.Since there is no need to add a cyclic prefix,the peak-to-average ratio can be reduced while improving the spectral efficiency.The system is optimized and analyzed from the aspects of improving the wavelet basis and the number of wavelet decomposition layers,and the Haar wavelet basis and the number of wavelet decomposition layers suitable for the system are selected.The simulation results show that when the front-end modulation is BPSK,the number of carriers is 64,the bit error rate is 10^-4,the performance of the LWT-OFDM system is improved by 5d B compared with the FFT-OFDM system.3.The introduction of LWT-OFDM into the visible light communication system can not only effectively reduce the peak-to-average ratio,but also provide a coding space margin for the cascaded channel coding modules.In order to increase the automatic detection and error correction function of the system,this thesis designs a visible light LWT-OFDM system based on RS coding.The coding operation is performed in the Galois field,and the BM iteration algorithm with higher decoding efficiency is selected.In this thesis,RS(255,239)is selected.when the bit error rate is 10^-4,the system performance is improved by 4d B compared with the unconcatenated RS code.4.On the basis of theoretical analysis and simulation experiments,this thesis designs the data frame structure,algorithm program and visible light transceiver hardware circuit of the system are designed,and an experimental test platform is built using signal generators,oscilloscopes and other equipment to verify the system.Perform point-to-point data transmission and reception on the optical track,the transmission distance is 20cm,the power of the LED is1W,the Haar wavelet base is selected,the number of carriers is 64,and the"quality factor"of the received data is analyzed by the modulation error ratio.The result shows that the front-end modulation When it is BPSK and QPSK,the modulation error rate of the system is 11.4d B and10.2d B respectively,which can ensure that 99.97%and 99.88%of the data are accurately demodulated and ensure the effective transmission of the signal.