Reconfigurable Intelligent Surfaces-aided Transmissions in a SIMO Network: A Secrecy Analysis

In this work, we investigate the secrecy performance of reconfigurable intelligent surfaces (RIS)-aided network consisting of two legitimate nodes (i.e., transmitter and receiver) and several passive eavesdroppers. A RIS is installed between the legitimate transmitter and receiver to enhance the received signal quality and, consequently, increase the achievable secrecy rates. Furthermore, we consider a multi-antenna legitimate receiver combining the received signal copies, reaching via the RIS, using the maximal-ratio combining technique. In addition, we assume the presence of a friendly jammer that aims at degrading the eavesdroppers' links quality. We propose two RIS phase shift configuration strategies, where the RIS is either aligned to the channel of the antenna with the best cascaded channel quality or to a randomly-selected one's channel. An approximate expression for the system's secrecy outage probability (SOP) is provided for the second strategy, while extensive numerical simulation results are provided for both proposed schemes, showing the superiority of the former strategy in terms of SOP performance for different values of the number of reflective elements, legitimate receiver antennas, and eavesdroppers.