Design And FPGA Implementation Of Adaptive Filter In Visible Light Communication System

With the rapid development of visible light communication,engineers are continually pursuing higher communication rates and communication distances.This puts higher requirements on the design of the visible light communication system,especially for the outdoor visible light communication system,which faces more complicated communication environment and background light noise,this undoubtedly makes the design of the visible light communication system more difficult.The complex background light noise faced by outdoor visible light communication systems greatly limits the performance of optical communication systems.The background light noise mainly includes solar noise,various artificial light source noises(incandescent lamps,fluorescent lamps,light-emitting diodes(LEDs),etc.)and the noise formed by once reflection or even twice reflections.The background light noise can seriously interfere with the transmission of signal light and even cause signal light to be annihilated in noise.As a result,the output signal-to-noise ratio of the communication system is reduced,and the reliability of the communication system is lowered too.Therefore,the de-drying algorithm in the visible light communication system has very high practicability and research value.Based on the actual visible light communication system,this paper uses the adaptive filtering algorithm to filter the background light noise in the optical communication system,and completes the design and FPGA implementation of the adaptive filter in the visible light communication system.The main work of the thesis is as follows:1.Study the relevant theory of adaptive filter,including the basic structure of adaptive filter,the realization of Wiener filter and the solution process of its optimal solution,the theoretical derivation of adaptive filtering algorithm and the comparison of its advantages and disadvantages with related algorithms.Among them,the adaptive filtering algorithms mainly include least mean square error(LMS)algorithm and least squares(RLS)algorithm.2.An adaptive filtering system based on PSK modulation is designed for the actual visible light communication system.The input and output signals and desired signals of the optical communication system are designed.At the same time,the cost function of maximizing the interval between demodulated constellations is proposed.We also construct the Expected signals by demodulating constellation points,which taking into account the computational efficiency and design simplicity of the system simultaneously.3.Based on the above system design,this paper uses the real PSK signal which polluted by noise as the input signal of the adaptive filtering system,simulates the performance of various adaptive filtering algorithms under the system,and finally chooses the least mean square error(LMS)algorithm as the adaptive filtering algorithm of the system through comparison,and obtains the optimal parameter set under the LMS algorithm finally.4.In view of the above scheme,this paper gives the overall design block diagram and modular design scheme based on FPGA.Finally,all functions are realized through Verilog.Finally,the board-level verification of the system is realized by using the development board of FPGA.The input signal-to-noise ratio of the system is 2 dB,the demodulation output signal-to-noise ratio is 9.86 dB,and the signal-to-noise ratio enhancement is 7.86 dB.