Covert Communication and Secure Transmission in the Presence of Multiple Antenna Untrusted Relay

In this study, we investigate information-theoretical security and covert communication. In covert communication, our aim is communication via the source-relay-destination link, without noticing the existence of communication by the multiple antenna warden. For secure transmission, our aim is to prevent possible eavesdropping by multiple antenna untrusted relay. To satisfy these requirements, we proposed a cooperative jamming strategy in two phases of transmission. In the proposed scheme, the source has multiple antenna and the efficiency of the maximum-ratio transmission/maximum-ratio combining (MRT/MRC) method for sending data to the relay has been evaluated. Due to the total transmit power restriction in each phase, a constrained optimization problem is formulated. Then, it is solved by converting to a multi-objective optimization problem. Finally, we employ the non-dominated sorting genetic algorithm II (NSGAII) to solve it.