Outage Probability Analysis of RIS-Assisted Relay Transmission Systems.

This paper investigates the outage performance of a reconfigurable intelligent surface (RIS)-assisted relay transmission network consisting of a source, a destination, multiple decode-and-forward (DF) relays, and a RIS, where the RIS assists in the source-to-relay and relay-to-destination transmissions. We propose two RIS-assisted relay selection schemes, namely the RIS-assisted round-robin scheduling (RIS-RRS) scheme and the RIS-assisted opportunistic relay selection (RIS-ORS) scheme. We analyze closed-form expressions of outage probabilities (OPs) for the RIS-RRS and RIS-ORS schemes and also carry out the minimization of the OPs to enhance outage performance through the optimization of RIS deployment location. It is shown that the proposed RIS-assisted relay selection achieves better outage performance than the conventional relay selection without RIS and RIS-aided source transmission without relays. Moreover, the RIS-ORS scheme generally outperforms the RIS-RRS scheme in terms of the outage probability. Additionally, numerical results show that the OPs of RIS-RRS and RIS-ORS schemes can be further reduced by adjusting the RIS deployment location.