Operator Perspective: How to Choose between the RIS and Full/Half-Duplex Relay

A potential 6G technology called Reconfigurable Intelligent Surface (RIS) uses meta-surface to reflect the signal to the user. The usage of RIS as a passive full-duplex relay to support wireless communication is a strong one because of its distinctive qualities of low cost, low energy consumption, excellent reliability, and big capacity. At the same time, the related technology active full-duplex relay which evolves from traditional half-duplex relay is also a candidate 6G technology. Both RIS and full/half-duplex relay is a node between source and destination to improve the performance of system, so how to choose between them? In this study, we examine the two technologies' performance from the viewpoint of the operators. In order to make the comparison fair, an evaluated model is proposed, and we get the closed expression of achieved rates for RIS and active relay to provide a deterministic calculation for the comparison. The results show that both RIS and full-duplex active relay are effective for the performance improvement, which of the two has the higher achieved rates is determined by the element number of RIS and the self-interference suppression of full-duplex relay.