Research On Channel Equalization And Modulation And Demodulation Technology Of Indoor Visible Light Communication System

Visible Light Communication transmits signals through visible light,enabling both lighting and communication functions without the need for other hardware devices.Indoor visible light communication technology provides a new solution for wireless communication due to the advantages of no electromagnetic radiation,ultra-wide use frequency band and popularity of LED lighting equipment.Therefore,it has important practical value for its research.At present,indoor visible light communication systems still have some shortcomings.For example,indoor optical signals are affected by inter-symbol interference(ISI)and external optical noise at the receiving end.These factors can significantly reduce the decision accuracy of the received signal,and thus seriously affect the performance of the visible light communication system.Aiming at the problem of inter-symbol interference and optical noise in indoor visible light system,this paper studies the adaptive equalization technology and modulation and demodulation technology suitable for visible light communication systems.The main research contents include:1.The model of indoor visible light communication system is established,and the communication link and communication channel are analyzed.The influence of inter-symbol interference and optical noise in communication is theoretically analyzed,which provides a theoretical basis for studying adaptive equalization technology and modulation and demodulation technology.2.Through the research of fixed-step LMS algorithm and its various variable-step LMS algorithms,the existing deficiencies are analyzed.According to the variable step size principle,a variable-step LMS algorithm based on sinusoidal function is proposed.The simulation results show that The algorithm can speed up the convergence and obtain a small steady-state error,and the steady-state error in the convergence phase changes within a small range.According to the distribution law of indoor VLC channel,an initialization method based on the difference ratio of received signals is proposed.The simulation results show that the method can accelerate the convergence speed of the algorithm to a greater extent and the convergence speed is increased by 2.5 times.3.Based on pulse position modulation(PPM),a double-interval pulse position modulation(DIPPM)method is proposed,which is theoretically analyzed and simulated with PPM modulation and MPPM modulation.The simulation results show that the bandwidth utilization of DIPPM modulation is higher than that of PPM modulation,and the anti-interference is better than MPPM modulation.4.Based on the above research results,an indoor visible light communication system was built.First,the modulation and demodulation scheme is implemented on the FPGA,and then the indoor visible light communication system is built by using the BER tester and the channel model established by MATLAB.Among them,the channel equalization adopts a variable step size LMS algorithm based on a sine function and an initialization method based on a difference ratio of received signals.The experimental results show that the main performance improvement of DIPPM modulation is basically consistent with the theoretical analysis,and as the m value of the original data bit increases,the anti-interference of DIPPM modulation is stronger.The modulation and demodulation scheme and channel equalization technique proposed in this paper can effectively reduce the influence of optical noise and inter-symbol interference,and it is expected to improve the overall performance of the visible light communication system.