Enhancing physical layer security with reconfigurable intelligent surfaces and friendly jamming: A secrecy analysis

Abstract

Despite its numerous advantages in enhancing wireless systems’ reliability and secrecy performance, the implementation of reconfigurable intelligent surfaces (RIS) is faced with several challenges, such as optimizing RIS phase-shift configuration to maximize the secrecy performance, particularly in multi-antenna and jamming-aided communication systems, and with the presence of phase quantization errors (PQEs) impairment due to the finite precision. Furthermore, it is crucial to provide an analytical evaluation for RIS-and-jamming-aided multi-antenna schemes. In this paper, the secrecy of a dual-hop wireless communication system, assisted by an RIS in each hop, is quantified. In particular, a multi-antenna relay assists the source node’s communication with a multi-antenna destination. Under the presence of PQEs and several eavesdroppers in the second hop, an RIS splitting technique into equal-size areas, along with friendly jamming, is used to maximize the received legitimate signal power at the relay and destination nodes and disrupt the eavesdroppers. The scheme’s secrecy level is evaluated by deriving novel approximate and asymptotic expressions of the secrecy outage probability (SOP) metric in terms of the main network parameters. Results show that the secrecy is significantly enhanced by increasing the jamming power, the number of reflective elements (REs), or the number of antennas at the relay. In particular, an SOP of 10−6 is reached with 2 receive antennas at the relay and destination, 25 REs per each RIS zone, and −30 dB of normalized jamming power-to-noise ratio even when the legitimate links’ average normalized signal-to-noise ratios are less than the eavesdropper’s one (i.e., strong eavesdropping). It is also shown that the number of quantization bits does not influence the secrecy when exceeding 3 bits. Lastly, the increase in the number of eavesdroppers does not yield a significant secrecy loss.