Design Of Undersampling Frequency Estimation System For Frequency Modulated Laser Ranging Beat Signal

Linear frequency modulated continuous wave laser ranging technology is widely used in aerospace,precision machining and other important fields due to its high measurement accuracy and strong anti-interference ability.With the advancement of FM nonlinear calibration technology and the application of wideband laser in ranging system,the frequency of the beat signal generated in the ranging process is getting higher and higher,which brings great challenges to sampling.Therefore,a new method for estimating the frequency of beat signals under undersampling conditions is proposed in this paper,and a new solution to the problems of low accuracy of frequency estimation with undersampling,complex aliasing frequency screening and poor anti-noise performance is proposed.so as to accurately estimate the frequency of the beat signal.The main research work of this paper is as follows:1.The principle of linear frequency modulation continuous wave laser ranging is deeply investigated,the advantage of triangular wave modulation is explained.The distance formula of stationary and vibrating objects are deducted,and the factors which affecting the accuracy of LFMCW laser ranging are analyzed.The results show that the accuracy of the beat signal frequency estimation is the key factor affecting the accuracy of ranging.2.Aiming at the problems of high sampling rate and large frequency estimation error of the existing beat signal frequency estimation method,a new method of double-rate frequency estimation with undersampling is proposed.Under the undersampling condition,the FFT processing is performed on the beat signals of different sampling rates,then the energy center of gravity is combined with the CZT algorithm to improve the estimation accuracy of the aliasing frequency,and the frequency offset value is used for phase correction,the aliasing frequency which corrected by the phase is combined to the sampling rate to realize the beat signal frequency estimate.The simulation results show that the proposed method can accurately estimate the frequency of the beat signal at low SNR.3.The hardware implementation of the dual-rate undersampling beat signal frequency estimation method is studied.A single-channel dual-rate undersampling frequency estimation system consisting of upper computer and lower computer is developed.A trigger circuit,an ADC sampling circuit,an FPGA-based read/write control logic circuit,and an ARM-based data transmission circuit are designed.At the same time,the MATLAB software is used to realize the energy center of gravity combined with the CZT algorithm,and the upper computer software is programed.4.Complete the functional test of each module and the overall test of the system,and verify the effectiveness of the proposed algorithm.The experimental results show that under the condition of undersampling,the proposed method can achieve accurate frequency estimation of the beat signal,and the estimation error is within 5ppm.