  In this paper, we study the effects of the variations of the propagation
delay over large-scale antenna-arrays used in massive multiple-input
multiple-output (MIMO) wideband communication systems on the statistical
properties of the channel. Due to its simplicity and popularity, the Elliptical
geometry-based stochastic channel model (GBSM) is employed to demonstrate new
non-stationary properties of the channel in the frequency and spatial domains
caused by the drift of delays. In addition, we show that the time of travel of
multi-path components (MPCs) over large-scale arrays may result in overlooked
frequency and spatial decorrelation effects. These are theoretically
demonstrated by deriving the space-time-frequency correlation functions
(STFCFs) of both narrowband and wideband Elliptical models. Closed-form
expressions of the array-variant frequency correlation function (FCF), power
delay profile (PDP), mean delay, and delay spread of single- and multi-confocal
Elliptical models are derived when the angles of arrival (AOAs) are von Mises
distributed. In such conditions, we find that the large dimensions of the
antenna array may limit the narrowband characteristic of the single-ellipse
model and alter the wideband characteristics (PDP and FCF) of the
multi-confocal Elliptical channel model. Although we present and analyze
numerical and simulation results for a particular GBSM, similar conclusions can
be extended to other GBSMs.
