Comparative Analysis of Reconfigurable Intelligent Surfaces and Relay Nodes for Energy Saving

Different technologies are currently being investigated to reduce the energy consumption of beyond 5 G systems. Two of the most preeminent ones are the Reconfigurable Intelligent Surfaces (RISs) and the relays, as both of them allow reducing the overall transmitted power levels at the base stations. However, due to the different nature of the two approaches, RISs being mostly passive while relays being active devices, it is unclear in which conditions one or the other leads to higher energy savings. This paper intends to shed light on this question by presenting a thorough analytical study of both approaches. Compared to the current literature, this study goes a step further by considering a more accurate RIS modeling based on actual RIS equipment, a thorough comparison of different energy consumption models, and a comprehensive study in a realistic environment of a university campus including indoor and outdoor propagation.