| Visible light communication(VLC)technology is considered as one of the development directions of the next generation wireless communication because it does not occupy the radio frequency band,fast data transmission,high confidentiality and environmental protection.Asymmetric limit-optical orthogonal frequency division multiplexing(ACO-OFDM)modulation is often used in indoor VLC communication systems because of its high optical power efficiency.However,this technology has the problem that the peak-to-average ratio(PAPR)is too high,so that when the signal with high PAPR passes through the LED,it will cause serious limiting distortion,resulting in deterioration of system performance.Therefore,PAPR suppression has become an urgent problem to be solved in visible ACO-OFDM system.Partial transmission sequence(PTS)technology can effectively reduce signal PAPR,but this technology has the high computational complexity and disadvantages of low speed after transmitting sideband information,so it is necessary to study and solve.This thesis mainly aims at the problem of excessively high PAPR after the introduction of orthogonal frequency division multiplexing(OFDM)into VLC technology,and explores the use of intelligent algorithms to improve PTS technology to ensure better decoding performance of the receiver.This thesis improved and optimized the PTS strategy based on genetic algorithm(GA)and particle swarm optimization(PSO)respectively,mainly aiming at reducing the search times of PTS algorithm to reduce the PAPR of ACO-OFDM system.At the same time,this thesis studies the transmission of sideband information by ACO-OFDM even carrier,aiming to realize the transmission of sideband information while maintaining the signal transmission rate.The main research contents of this thesis are as follows:(1)PTS(GA-PTS)technology based on genetic algorithm is improved,and phase factor pairs are proposed to replace the selection operation in GA,which reduces the PAPR of signal and reduces the computational complexity.The experimental results show that the proposed scheme can effectively reduce PAPR by 0.3dB and reduce the computation amount by 37.5%.(2)For PTS(PSO-PTS)technology based on particle swarm optimization algorithm,three improved algorithms are designed.First,PSO algorithm with variable particle number can further reduce the computational complexity by reducing the number of particles involved in each generation;Second,the PSO algorithm with variable inertia weight can improve the PAPR suppression performance by dynamically adjusting the inertia weight value in the iterative process.Third,PSO algorithm based on cross operation is introduced to improve the global convergence performance of genetic algorithm.Simulation results show that the proposed three improved algorithms can further reduce PAPR,and finally achieve 0.2-0.3dB reduction.(3)Aiming at the problem of transmission rate reduction caused by sideband information inserted into signals optimized by traditional PTS technology,explore the use of idle ACO-OFDM even carrier to transmit sideband information,realize sideband information transmission while maintaining the original information transmission rate.Simulation results show that the system does not introduce additional distortion.Moreover,in the visible ACO-OFDM system with twice-order reflections,when the signal-to-noise ratio is greater than 6dB,GA-PTS scheme and PSO-PTS scheme have better error performance compared with the PTS technology. |
