Secure communication with a multiple-antennas untrusted relay in presence of randomly distributed adversary jammers

In this article, we examine the achievable secrecy rate of a cooperative network including one source, one destination, and one untrusted amplify-and-forward relay, where randomly located adversary jammers attempt to disrupt the wireless communications. The relay has multiple antennas, while the other nodes have a single antenna. The adversary jammers are placed following a Poisson Point Process (PPP) and aim to interfere with the untrusted relay's channel. The relay employs maximal-ratio combining (MRC) to mitigate the jammers' impact and retransmits the signal to the destination using maximum ratio transmission (MRT). To prevent the relay from capturing the message, the destination injects pre-known artificial noise, known as destination-assisted cooperative jamming. We present a closed-form solution for the Ergodic secrecy rate (ESR) of the system with Rayleigh fading channels. An optimization problem for maximizing the secrecy rate is also designed, resulting in a closed-form formula for optimal power allocation (OPA) between the source and destination.