  In this paper, a three-dimensional (3D) geometry based stochastic model
(GBSM) for a massive multiple-input multiple-output (MIMO) communication system
employing practical discrete intelligent reflecting surface (IRS) is proposed.
The proposed channel model supports the scenario where both transceivers and
environments move. The evolution of clusters in the space domain and the
practical discrete phase shifts are considered in the channel model. The
steering vector is set at the base station for the cooperation with IRS.
Through studying statistical properties, the non-stationary properties are
verified. We find that IRS plays a role in separating the whole channel and
make the absolute value of time autocorrelation function (ACF) larger than the
situation without employing IRS. Time ACF of the case using discrete phase
shifts is also compared with the continuous case.
