Security-Reliability Trade-off in Cyber-Physical Cooperative Systems with Non-Ideal Untrusted Relaying

In this paper, we examine the security-reliability trade-off (SRT) in a cyber-physical cooperative system where a source transmits to a destination assisted by a non-ideal untrusted amplify-and-forward (AF) relay with hardware impairments. We analyze the SRT under the following two transmission protocols: 1) Destination-based cooperative jamming (DBCJ) where the untrusted relay retransmits a combination of information signals from the source and jamming signals from the destination, and 2) conventional direct transmission (DT) where the relay is not used for information transmission but is treated as an eavesdropper. We accurately characterize the SRT of the two protocols based on novel closed-form expressions derived for the connection outage probability (COP) and the intercept probability (IP). Our theoretical results reveal that non-ideal AF relaying can improve the system security such that for transmission rates above a given threshold the IP is equal to zero. Numerical results highlight that non-ideal relaying improves the SRT of DT and degrades the SRT of DBCJ.