Research On The Denoising Of Laser Phase Ranging Signal Based On Wavelet Transform

The field with the greatest application value and the best development prospect of laser is the ranging field.The effective ranging method and accuracy determine the practical value of the ranging system.However,in the actual data acquisition process,there is inevitably the impact of noise,which will make the ranging system lose its due role in serious cases.Therefore,before the calculation of the collected data,it is necessary to complete the denoising of the received data.This paper describes the characteristics of phase method laser ranging.Aiming at the problem that the measurement range and measurement accuracy cannot be met simultaneously when using single frequency laser for phase method laser ranging,a dual-frequency measuring ruler is proposed to complete the ranging.The derivation of the splicing of the dual-frequency ruler is completed,and the calculation formula of the distance using the dual-frequency ruler is obtained.The mathematical model of the phase laser ranging system is built.In the establishment of the model,the low-frequency ruler is determined according to the measurement range of the phase-method laser ranging system,and the high-frequency ruler is determined according to the accuracy requirements;Then the mathematical model of noise-free signal is established,which mainly includes transmitting signal and receiving signal;Then it is concluded that the noise type in the system is Gaussian white noise;Finally,the relationship between the phase error and the signal-to-noise ratio is determined according to the lower limit of the Cramerol,and the lowest allowable signal-to-noise ratio within the range of measurement accuracy is obtained,and the mathematical model of the noisy echo signal is established.Aiming at the noise problem,the paper uses wavelet threshold denoising algorithm to complete the denoising process.The design of the echo signal denoising simulation experiment is completed,and the optimal parameters of the wavelet threshold denoising algorithm are obtained.By comparing the signal to noise ratio and root mean square error of the signal before and after denoising,it is proved that the wavelet threshold denoising algorithm has a good ability to remove the noise in the echo signal.Aiming at the problem that the selection of threshold in wavelet threshold denoising algorithm is a reflection of logical thinking and is not target-oriented,this paper proposes to use particle swarm optimization(PSO)algorithm to optimize the wavelet threshold,and take the signal-to-noise ratio of echo signal as the fitness function to optimize the parameters of wavelet threshold algorithm.The results show that the PSO+wavelet threshold denoising algorithm can complete the signal-to-noise separation of the echo signal containing Gaussian white noise,After denoising,the signal-to-noise ratio increases by 13.4105 d B,and the signal-to-noise ratio increases by 54.31%;The root-mean-square error is reduced by 78.64%.At the same time,compared with the existing denoising algorithm,the new algorithm can obtain higher signal-to-noise ratio and smaller root-mean-square error,which shows the superiority of PSO+wavelet threshold denoising algorithm.In order to meet the accuracy requirements,it is required that the echo signal can reach the minimum allowable signal-to-noise ratio under the condition of different algorithm processing.The use of sliding mean filtering algorithm,median filtering algorithm,wavelet threshold algorithm and PSO+wavelet threshold denoising algorithm can improve the processing of echo signals with the minimum signal-to-noise ratio of 15 d B,16 d B,16 d B and 12 d B respectively to meet the design requirements.The use of sliding mean filtering algorithm,median filtering algorithm,wavelet threshold algorithm and PSO+wavelet threshold algorithm reduces the allowable minimum signal-to-noise ratio by 39.25% and 35.20% respectively compared with the unused algorithm 35.20% and 51.40%.After using PSO+wavelet threshold algorithm to denoise the echo,the lower quality signal can be processed to meet the design requirements,and the design difficulty of the ranging system can be reduced to a greater extent.