Multi-Target DoA Estimation With mmWave MIMO Radar Using Limited Number of Sensors

This paper addresses the problem of estimating incoming signals' direction of arrival (DoA) in multiple-input multiple-output (MIMO) radar systems when the number of reflectors exceeds that of the sensors. Existing methods, such as co-prime and nested arrays, address this limitation by increasing the degree of freedom (DoF) using expanded antenna array geometries. However, these methods introduce practical challenges, including increased array size and added system complexity and cost due to the additional receiver (Rx) front-end modules and analog-to-digital converter (ADC) units required for each antenna element. The proposed method overcomes these limitations and enables the detection of more targets than sensors without necessitating hardware modifications by using a standard uniform linear array (ULA) and enhancing the DoF entirely at the signal processing stage. The proposed method integrates the capabilities of the 2D multiple signal classification (MUSIC) algorithm with the 2D forward-backward spatial smoothing (FBSS) technique to surpass the theoretical limit of the minimum angular resolution. The effectiveness of the proposed method is validated through extensive simulations and real-world measurements. Comparative evaluations against popular DoA estimation techniques further underscore its practical advantages and robustness.