A Study of Delay Drifts on Massive MIMO Wideband Channel Models

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-timefrequency
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.