Solving Doppler Ambiguity Using Folded Array in Uniform Phase DDM Method

Due to the availability of maintaining the orthogonality between transmit signals and effectively leveraging time resources, the Doppler division multiplexing (DDM) method has been widely investigated for operating multiple-input multiple-output (MIMO) radar systems. However, the number of peaks equal to the number of transmitting (Tx) antenna elements appear along the velocity axis for every target, and it leads to the Doppler ambiguity problem. As a solution, we propose a novel approach to resolve the Doppler ambiguity using the phase information of the folded array, which overlaps certain antenna array elements when forming the entire MIMO antenna array. The proposed method consists of two main steps. First, we apply the uniform phase DDM (UP-DDM) to simultaneously transmit signals for each Tx antenna element. This method results in multiple peaks for the same target occurring at constant intervals along the velocity axis. By using the similarity of phase values between overlapping MIMO array elements, our proposed method can accurately determine the precise order of the Tx antenna elements. Since the proposed method resolves Doppler ambiguity and enables the use of noncoherent integration on both the receiving (Rx) and Tx antenna channels, it significantly improves the signal-to-noise ratio and increases the detection probability. Simulation and experimental results based on automotive radar sensors demonstrate the effectiveness of the proposed method and we expect that this method enables reliable perception tasks for autonomous driving.