Spatially Correlated RIS-Aided CF Massive MIMO Systems With Generalized MR Combining

In this correspondence, we study the uplink ergodic net throughput of a spatially correlated reconfigurable intelligent surface (RIS)-aided cell-free (CF) massive multiple-input multiple-output (MIMO) system over Rayleigh fading channels. We investigate the impact of the generalized maximum ratio (GMR) combining and obtain the closed-form expression for characterizing the uplink net throughput revealing that the GMR can double the system performance compared with the maximum ratio (MR) in our system. Then, we compare the performance and complexity of the MR, GMR, and large-scale fading decoding (LSFD). Moreover, we consider a practical fractional power control to mitigate the inter-user interference. The obtained interesting results show that the system performance decreases with the increasing number of RIS elements. It reveals that efficient interference cancellation processing is needed to cope with severer pilot contamination brought by the large number of RIS elements to improve the system performance. Finally, the accuracy of our derived analytical results has been verified by Monte-Carlo simulations.