  This paper proposes the Newtonized fully corrective forward greedy
selection-cross validation-based (NFCFGS-CV-based) channel estimator for
millimeter (mmWave) hybrid massive multiple-input multiple-output (MIMO)
systems with low-resolution analog-to-digital converters (ADCs). The proposed
NFCFGS algorithm is a gridless compressed sensing (CS) technique that combines
the FCFGS and Newtonized orthogonal matching pursuit (NOMP) algorithms. In
particular, NFCFGS performs single path estimation over the continuum at each
iteration based on the previously estimated paths. The CV technique is adopted
as an indicator of termination in the absence of the prior knowledge on the
number of paths, which is a model validation technique that prevents
overfitting.
