Multi-Target Simultaneous Measurement of Distance and Velocity With Arbitrary Waveform FMCW LiDAR System

Capable of high-precision simultaneous measurement of target distance and velocity, frequency modulated continuous wave (FMCW) LiDAR has shown promising prospects in many applications, including autonomous driving, military and aerospace. However, conventional FMCW LiDAR systems suffer from two inherent limitations: frequency waveform nonlinearity and incapability for effective multi-target detection. The nonlinearity of frequency waveform will destroy the monophonic nature of coherent signal and leads to a significant degradation of target detection. Meanwhile, the frequency mismatch problem that arises in multi-target scenarios will lead to ambiguous target detection. This article proposes and demonstrate a novel FMCW LiDAR system utilizing arbitrary frequency waveforms, which is capable of multi-target simultaneous measurement of distance and velocity. The coherent light model under multi-target scenarios is rigorously established and an auxiliary interferometer is utilized to recover the light frequency information. The quadrature coherent detection is utilized to generate the complex beat signal. The distances and velocities of multiple targets are precisely extracted from the complex signal based on maximum likelihood estimation. The Cramér-Rao bound of proposed algorithm is rigorously derived and is verified through Monte-Carlo simulations in complex scenarios. In experiments, we realize a multi-target simultaneous distance and speed measurement scenario by measuring multiple positions of a rotating disk. Meanwhile, three different frequency waveforms are utilized for measurements to verify the applicability of our method to arbitrary frequency waveforms. The results show that our method can accurately extract the distances and velocities of multiple targets under low SNR conditions.