Research On Multiple Pulse Laser Rangingtechnology Based On FPGA

Pulsed laser ranging is the most widely used technique in the distance measurement, traditional laser ranging machine adopts analog circuit, has the advantages of simple structure, but the anti-interference ability is poor, when probing in bad weather and complex background environment, prone to the phenomenon of "false alarm" or "Miss", and ranging accuracy lower.The basic principle of laser ranging is studied, and the pulse laser ranging performance equation and signal-to-noise ratio equation, according to the statistical detection theory to calculate the false alarm probability and detection probability to meet the required minimum signal-to-noise ratio and threshold noise ratio. And in order to meet the requirement, this paper designs two models, short-range mode and remote mode. Remote measurement mode, for laser weak echo signal to noise ratio is low echo signal is difficult to detect the problem, this paper studies the theory and implementation of weak signal detection technology, the multi pulse detection, based on field programmable gate array(FPGA), a method of multi pulse weak signal processing is proposed, focus on the cumulative average algorithm, through theoretical derivation and Matlab environment simulation of multi pulse ranging experiments. The results show that multi pulse cumulative average utilization signal correlation and noise is not related to the characteristics, the cumulative N times, can improve the SNR by the square root of N times, thus reconstruct echo pulse waveform. Experimental platform is built, in order to determine the exact location of the pulse echo. The echo pulse window for 5 median filter processing and experimental data show that the algorithm can improve the measurement range, measurement range 1400 m and repeated measurement error is better than 1m.Short range measurement mode, as long as can detect the echo pulse, the time difference between the transmitted pulse and the echo pulse can be measured directly, time interval measurement accuracy determines the ranging accuracy. A high precision time interval measurement method based on clock interpolation is proposed, 5 with frequency 400 MHz with FPGA internal phase-locked loop, phase uniform distribution of clock signals as in clock. Experimental results show that the measurement resolution 250 ps and measurement error is less than 10 cm.