  We consider a practical spatially correlated reconfigurable intelligent
surface (RIS)-aided cell-free (CF) massive multiple-input-multiple-output
(mMIMO) system with multi-antenna access points (APs) over spatially correlated
Rician fading channels. The minimum mean square error (MMSE) channel estimator
is adopted to estimate the aggregated RIS channels. Then, we investigate the
uplink spectral efficiency (SE) with the maximum ratio (MR) and the local
minimum mean squared error (L-MMSE) combining at the APs and obtain the
closed-form expression for characterizing the performance of the former. The
accuracy of our derived analytical results has been verified by extensive
Monte-Carlo simulations. Our results show that increasing the number of RIS
elements is always beneficial, but with diminishing returns when the number of
RIS elements is sufficiently large. Furthermore, the effect of the number of AP
antennas on system performance is more pronounced under a small number of RIS
elements, while the spatial correlation of RIS elements imposes a more severe
negative impact on the system performance than that of the AP antennas.
