  Cell-free massive multiple-input multiple-output (MIMO) and intelligent
reflecting surface (IRS) are considered as the prospective multiple antenna
technologies for beyond the fifth-generation (5G) networks. Cell-free MIMO
systems powered by IRSs, combining both technologies, can further improve the
performance of cell-free MIMO systems at low cost and energy consumption. Prior
works focused on instantaneous performance metrics and relied on alternating
optimization algorithms, which impose huge computational complexity and
signaling overhead. To address these challenges, we propose a novel two-step
algorithm that provides the long-term passive beamformers at the IRSs using
statistical channel state information (S-CSI) and short-term active precoders
and long-term power allocation at the access points (APs) to maximize the
minimum achievable rate. Simulation results verify that the proposed scheme
outperforms benchmark schemes and brings a significant performance gain to the
cell-free MIMO systems powered by IRSs.
