Doppler Ambiguity Resolution for Binary-Phase-Modulated MIMO FMCW Radars

State-of-the-art FMCW automotive radar sensors contain Multiple-Input Multiple-Output (MIMO) arrays to obtain a good angular resolution. Binary phase modulation (BPM) is a technique used on these systems to achieve a high Signal-to-noise ratio (SNR), compared to the commonly used Time-division multiplexing (TDM). As several chirps are combined to transmit a binary code, the approach suffers from a reduced maximum unambiguous velocity. In this paper, we implement three approaches for the velocity disambiguation in a MIMO radar with four transmitters using Hadamard coding. The first two approaches require three heterogeneous frames and are based on an exact method (Chinese Remainder Theorem), and an unsupervised learning technique (Density Based Spatial Clustering of Applications with Noise) respectively. The third approach determines the true velocity by searching for the strongest response in the angular spectrum of a single frame, which suffers from a negative bias caused by the phase codes. The approaches are validated and compared in MATLAB simulations.