Security-Reliability Trade-Off Analysis of RIS-Aided Multiuser Communications

In this paper, we examine the physical layer security of a reconfigurable intelligent surface (RIS)-aided wireless network consisting of multiple users, a RIS, and a multi-antenna base station (BS) in the presence of an eavesdropper, where a particular user is selected to send messages in the uplink. To secure the RIS-aided multiuser communications, we adopt friendly jamming techniques with the help of a RIS, and propose the random jammer selection and RIS aided user scheduling (RJSR-US), optimal jammer selection and RIS aided user scheduling (OJSR-US), as well as multiple jammers and RIS aided user scheduling (MJR-US) schemes. The non-jamming RIS-aided user scheduling (NJR-US) scheme is considered as a baseline. We conduct security-reliability trade-off (SRT) performance analysis of RJSR-US, OJSR-US, and MJR-US as well as NJR-US schemes in terms of deriving their closed-form outage probability (OP) and intercept probability (IP) expressions over spatially-correlated channels. Secrecy gain analysis further demonstrates that the RJSR-US, OJSR-US, and MJR-US schemes outperform the NJR-US scheme in terms of SRT. Additionally, we present a definition for the normalized intercept and outage probabilities (IOPs), based on which an optimization analysis of proposed jamming schemes is carried out for minimizing the IOP through an iterative search of power allocation between the scheduled user and jammers. Finally, simulations unveil the SRT benefit of the RJSR-US, OJSR-US, and MJR-US schemes compared with the conventional NJR-US scheme. Furthermore, the SRT performance can be improved by adjusting jamming power allocation for the RJSR-US, OJSR-US, and MJR-US schemes, especially in the high SNR region.