  Cell-free (CF) massive multiple-input multiple-output (MIMO) and
reconfigurable intelligent surface (RIS) are two promising technologies for
realizing future beyond-fifth generation (B5G) networks. In this paper, we
consider a practical spatially correlated RIS-aided CF massive MIMO system with
multi-antenna access points (APs) over spatially correlated fading channels.
Different from previous work, the electromagnetic interference (EMI) at RIS is
considered to further characterize the system performance of the actual
environment. Then, we derive the closed-form expression for the system spectral
efficiency (SE) with the maximum ratio (MR) combining at the APs and the
large-scale fading decoding (LSFD) at the central processing unit (CPU).
Moreover, to counteract the near-far effect and EMI, we propose practical
fractional power control (FPC) and max-min power control algorithms to further
improve the system performance. We unveil the impact of EMI, channel
correlations, and different signal processing methods on the uplink SE of user
equipments (UEs). The accuracy of our derived analytical results is verified by
extensive Monte-Carlo simulations. Our results show that the EMI can
substantially degrade the SE, especially for those UEs with unsatisfactory
channel conditions. Besides, increasing the number of RIS elements is always
beneficial in terms of the SE, but with diminishing returns when the number of
RIS elements is sufficiently large. Furthermore, the existence of spatial
correlations among RIS elements can deteriorate the system performance when RIS
is impaired by EMI.
