Characterization of untrusted relaying networks in the presence of an adversary jammer

By considering an adversary jammer in a communication network, we investigate the secrecy performance of a cooperative wireless network comprised of a source, a destination and an untrusted amplify-and-forward relay. We assume that either the source or the destination, as well as the jammer are equipped with large-scale multiple antennas systems, while the rest are equipped with a single-antenna. To prevent the untrusted relay from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as destination-assisted cooperative jamming. On the other hand, the role of the jammer is to disturb the communication by transmitting jamming signals toward the untrusted relay. Given this system model, novel closed-form expressions are extracted for the ergodic secrecy rate (ESR) with Rayleigh fading channels. We further evaluate the ESR at high signal-to-noise ratio (SNR) and then determine the high SNR slope and power offset of the ESR to get some insights into the network. Next, with the aim of maximizing the instantaneous secrecy rate, we derive new closed-form solutions for the optimal power allocation (OPA). Numerical examples depict that the presented OPA considerably improves the system secrecy rate compared to the equal power allocation (EPA) which reveals the priority of our optimized network. We also illustrate that by increasing the number of jammer antennas, the ESR performance of both the OPA and EPA is reduced. The results state that unlike the EPA technique, increasing the number of source antennas enhances the ESR of the proposed OPA technique which reveals the priority of our OPA.