A Novel Low-Complexity Angle-Assisted Delay and Doppler Estimation for MIMO-OTFS

Multiple-input multiple-output orthogonal time frequency space (MIMO-OTFS) is considered one of the potential technologies for high-speed mobile scenarios. However, in such systems, fractional delay and Doppler estimation is a major challenge due to the limitation of delay-Doppler (DD) grid resolution. In this paper, we propose a low-complexity angle-assisted delay and Doppler estimation (AADDE) algorithm for MIMO-OTFS systems. AADDE reduces computational complexity by estimating delay and Doppler parameters separately, and the angle information is used to improve estimation performance. In addition, we propose a two-dimensional (2D) grid segmentation scheme to estimate fractional DD with AADDE. Specifically, an iterative approach is developed to identify the true fractional DD index using a variable search step size, achieving lower complexity than existing off-grid search methods. Complexity analysis and simulation results demonstrate the effectiveness of the proposed AADDE algorithm, which also approaches the Cramér-Rao lower Bound.