Analyzing Energy Efficiency Trade-Offs in RIS Aided Cell-Free Massive MIMO Networks

Cell-free massive multiple-input multiple-output (CF-mMIMO) network allows multiple access points (APs) to serve users with no cell boundaries. This helps in serving a large number of users with a uniform quality of service (QoS). However, the large-scale deployment of such a network results in poor energy efficiency (EE) and higher deployment cost. Recently, reconfigurable intelligent surfaces (RISs) are being considered to improve the energy efficiency of the CF-mMIMO network. In this work, we investigate the extent to which the EE can be improved by varying the proportions of APs and RISs in the network. We analyze the trade-offs for the centralized and distributed processing schemes under a generic power consumption model and quantify the optimal number of APs and RISs required. Results unveil that the RIS aided CF-mMIMO can significantly enhance the EE gains if the APs and RISs are employed in an optimal proportion.