“…According to the classical literature review on this topic, these approaches can be broadly divided into three categories [ 26 , 27 ]: time delay based, beamforming based, and high-resolution spectral estimation based methods. This taxonomy relies on the fact that ASL has traditionally been considered a signal processing problem based on the definition of a signal propagation model [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ], but, more recently, the range of proposals in the literature has also considered strategies based on exploiting the optimization techniques and mathematical properties of related measurements [ 35 , 36 , 37 , 38 , 39 ], and also the use of machine learning strategies [ 40 , 41 , 42 ], aimed at obtaining direct mapping from specific features to source locations [ 43 ], an area in which deep learning approaches are starting to be applied and that will be further described later in this section.…”