High-precision frequency estimation for frequency modulated continuous wave laser ranging using the multiple signal classification method.

Abstract

The long fiber frequency sampling method is used to eliminate the nonlinearity of laser tuning in the frequency-modulated continuous-wave laser detection and ranging (FMCW ladar) technique. However, although it has high precision, it is affected by the picket fence effect and spectrum leakage. In this paper, we propose a novel frequency estimation method, multiple signal classification (MUSIC), to be used instead of the conventional fast Fourier transform (FFT)-based algorithm in order to obtain better range precision. The proposed method was verified by experiments. In the experiments, when the distance was up to 3.814m and chirped bandwidth was equal to 20nm (2.5THz), the full width at half-maximum of the range peak, which represented the estimated precision of frequency obtained by MUSIC, was 20μm, and it was improved by 7 times compared to the FFT-based method. Meanwhile, to evaluate the performance of the proposed method, the frequency estimation according to the Cramer-Rao lower bound (CRLB) was also performed. The experimental results have shown that the mean square error of distance estimation based on the MUSIC algorithm is 0.56μm, which is much closer to the CRLB of 0.18μm than the mean square error of the conventional FFT-based method. Furthermore, we demonstrated that the MUSIC estimator has an unparalleled advantage over other estimators in the high-precision ranging fields.