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Design and Performance Analysis of the Fractional Domain Adaptive Filtering Algorithm for Coherent Imaging Laser Radar
L-J. Li, W. Lu and W. Qi

The bandpass filtering output signal of a coherent imaging laser radar system is a mixed signal including target return signal, noise and co-frequency interference caused by imperfect shielding. Their characteristics in the time domain and the frequency domain are very similar and it is difficult to separate them. In order to solve this problem we introduced the fractional domain adaptive filtering algorithm. The analytic expression of fractional Fourier transform (FRFT) of laser radar’s return signal in theory was deduced and proved that the return signal has the characteristic of energy aggregation in fractional domain, but the co-frequency interference and noise do not have this characteristic. On this basis we constructed fractional domain adaptive filter and did filtering experiment on the return signal of coherent imaging laser radar developed by our team. By comparing the spectrum information before filtering and that after filtering it was obvious that the co-frequency interference had been mostly filtered and the complete signal was reserved without distortion. Signal noise ratio (SNR) was enhanced from 1.06 dB to 4.67 dB simultaneously; moreover, there was not any other involved noise added to the return signal of laser radar. In this work the fractional domain adaptive filtering algorithm was proved to provide a novel method for coherent imaging laser radar signal processing.

Keywords: Laser radar, fractional Fourier transform (FRFT), adaptive filtering, signal noise ratio (SNR)

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