Joint Multiple FMCW Chirp Sequence Processing for Velocity Estimation and Ambiguity Resolving

In FMCW automotive radar applications, it is often a challenge to design a chirp sequence that satisfies the requirements set by practical driving scenarios and simultaneously enables high range resolution, large maximum range, and unambiguous velocity estimation. To support long-range scenarios the chirps should have a sufficiently long duration compared to their bandwidth. At the same time, the long chirps result in ambiguous velocity estimation for targets with high velocity. The problem of velocity ambiguity is often solved by using multiple chirp sequences with co-prime delay shifts between them. However, coherent processing of multiple chirp sequences is not possible using classical spectral estimation techniques based on Fast Fourier Transform (FFT). This results in statistically not efficient velocity estimation and loss of processing gain. In this work, we propose an algorithm that can jointly process multiple chirp sequences and resolve possible ambiguities present in the velocities estimates. The resulting algorithm is statistically efficient, and gridless. Furthermore, it increases the resolution of velocity estimation beyond the natural resolution due to its super-resolution properties. These results are confirmed by both numerical simulations and experiments with automotive radar IC.