Energy Efficiency Fairness of Active Reconfigurable Intelligent Surfaces-Aided Cell-Free Network

Reconfigurable intelligent surface (RIS) has been widely recognized as a promising technique for future wireless communications. Benefiting from its ability to improve channel capacity with low cost and power consumption, the concept of RIS-aided cell-free network is proposed to break the bottleneck of current network architecture. However, the multiplicative fading effect (MFE) introduced by RIS prevents RIS-aided cell-free network from higher network capacity. To further increase the capacity of the RIS-aided cell-free network, in this paper, we propose the concept of active RIS-aided cell-free network, where the RIS is replaced by active RIS in traditional RIS-aided cell-free network. Moreover, we analyze the proposed network by investigating its energy-efficiency fairness (EEF). To elaborate, we formulate the EEF maximization problem in the active RIS-aided cell-free network, and propose a joint beamforming and resource allocation (JBRA) algorithm by exploiting alternating optimization (AO) and fractional programming (FP). Simulations results verify the proposed active RIS-aided cell-free network as well as the JBRA algorithm as an energy-efficient design for cell-free network with large network capacity.