Signal Detection And Processing Of Precision Parallel Laser Ranging System

With the progress of social science and the extensive application of ranging technology, Laser Ranging increasingly applied to large, real-time, dynamic scanning measurement, such as construction of three-dimensional map, measurement of large-size building, real-time surfaces information collection and so on, this proposed the dual requirements of high precision and high efficiency to laser ranging system. Currently widely used laser ranging methods are phase laser range measurement and pulse flight time laser range measurement. The former has high precision, but the measurement is slow and scanning point-by-point lead to low efficiency. The latter measure distance, but the measurement accuracy is low, both of them are difficult to simultaneously satisfy the dual requirements of high accuracy and high efficiency.The paper researched a parallel laser ranging system based on the principle of frequency division multiplex, which is on the basis of phase shift laser ranging. The system selected multipath modulation signal with different frequency to drive a plurality of laser device emission ranging optical wave, and the illumination intensity changes in accordance with the modulation signal. Single modulated signal using synthesized wave includes both high-frequency and low-frequency, by combining the results of two distance measuring tape, we can eliminate the uncertainties caused by the entire wavelength. The multi-channel echo signal reflected by the target mixed together and received by the same photo detector, converted the optical signal into an electrical signal. The electrical signal after photoelectric conversion carried preamplifier, clutter filter pretreatment, then send it to mixer unit with the reference signal, selected the valid signal by low pass filter. Use multi-channel AD collected the parallel signal and converted the analog electrical signal to a digital signal, then detected the phase of the signal by digital signal processor. We can find the corresponding spectral lines to solve the phase of multi-channel signals at the same time according to the frequency difference of each channel. Through calculated the phase difference between the echo signal and reference signal of each channel, could obtain the distance of multiple measurement points simultaneously, realized parallel ranging and improved the measurement efficiency. The paper made a detailed analysis of its modulation and demodulation principle and signal detection and processing methods, analyzed the composition of each module and the factors affecting to accuracy. It made a model for each module and conducted a systematic integration, then made a detailed analysis of the impact of the source phase noise and frequency error, the different type of modulation waveform and the phase detection method to the range accuracy by systems modeling and simulation. The simulation result shows that:the modulation waveform use the superposition of high-frequency sine wave and low-frequency sine wave, and the phase detection method use all-phase FFT algorithm can improve the precision of the system significantly. Finally, this paper designed and implemented the parallel laser ranging system related hardware circuit, and laid a solid foundation for the future debugging and applications.