Research On Laser Ranging Technology Based On Pulse Position Modulation

With the development of lidar technology,the application scenarios of lidar are increasing.In the face of complex application environment,it is an important research direction of lidar technology to further improve the detection performance of detection system by improving the anti-jamming ability of the system.Pulse position modulation,as a type of pulse modulation,has a constant pulse width and pulse amplitude,and the time interval value between adjacent pulses changes with the modulation signal.When the modulation signal has a random-like characteristic,the generated pulse position modulation sequence not only shows good auto-correlation and cross-correlation,but also the duty cycle between pulses can be adjusted during the modulation process,and the receiving system can still have a high signal-to-noise ratio under the condition of limited average power.Compared with pseudo-random continuous signal,its code density is lower and its application scope is wider.Therefore,if pulse position modulation is applied to a lidar system,it should have unique technical advantages.This article hopes to carry out a beneficial discussion from the theory and technology.The main research contents are as follows:(1)The structure and realization principle of analog and digital pulse position modulation modes are analyzed,and the advantages and disadvantages of the two generation modes are compared.On this basis,using the fuzzy function as an evaluation tool,the fuzzy function diagrams of pulse position modulation under different modulation signal excitations are compared,which provides theoretical basis for the selection of modulation signal and the subsequent adoption of chaotic pulse position modulation signal as the transmitting waveform of lidar ranging system.(2)Several common chaotic maps are discussed.Chaotic sequences generated by logistic chaotic maps are used as modulation signals of pulse position modulation.The power spectrum,autocorrelation and mutual correlation of chaotic pulse position modulation signals are analyzed by numerical simulation.In order to obtain the signal waveform with better correlation,the influence of the parameters of the chaotic pulse position modulation signal on its correlation is studied by combining with the generating formula of the chaotic pulse position modulation signal,which lays a foundation for the optimization of the pulse train.(3)In order to make the pulse position modulation sequence have better correlation characteristics and lower noise floor,this paper uses a differential evolution algorithm to optimize the signal sequence.An optimization process for chaotic pulse position modulation sequence is given.The correlation signal-to-noise ratio and sidelobe level are used as the objective function of sequence optimization at the same time,and the pulse sequence waveform with better signal-to-noise ratio and sidelobe level is obtained.(4)Combining with the characteristics of chaotic pulse position modulation signal,the ranging principle and detection performance of the laser ranging system based on chaotic pulse position modulation are analyzed.The feasibility of the system was verified by setting up the ranging experimental system,and the signal noise ratio of the system was analyzed under different noise levels.Finally,the detection performance of the system,the influence of sequence autocorrelation and sequence optimization on system ranging,and the anti-interference ability of the system under different signal interference are analyzed.