  As one of the key technologies for the sixth generation (6G) mobile
communications, intelligent reflecting surface IRS) has the advantages of low
power consumption, low cost, and simple design methods. But channel modeling is
still an open issue in this field currently. In this paper, we propose a
three-dimensional (3D) geometry based stochastic model (GBSM) for a massive
multiple-input multiple-output (MIMO) communication system employing IRS. The
model supports the movements of the transmitter, the receiver, and clusters.
The evolution of clusters on the linear array and planar array is also
considered in the proposed model. In addition, the generation of reflecting
coefficient is incorporated into the model and the path loss of the sub-channel
assisted by IRS is also proposed. The steering vector is set up at the base
station for the cooperation with IRS. Through studying statistical properties
such as the temporal autocorrelation function and space correlation function,
the nonstationary properties are verified. The good agreement between the
simulation results and the analytical results illustrates the correctness of
the proposed channel model.
