Secrecy capacity enhancement in two-hop DF relaying systems in the presence of eavesdropper

In this paper, we propose a random phase shifting scheme applied to modulated data symbols of a dual-hop decode-and-forward (DF) relaying system to enhance its secrecy capacity in the presence of an eavesdropper, which can wiretap the communication signals of both hops. The random phase shift used in the proposed scheme is generated using a shared secret between transmitter and receiver of each hop, such as the reciprocal channel between the communicating devices, which is not accessible to the eavesdropper. Through theoretical analysis of the secrecy capacity, we have proven that the proposed scheme improves the ergodic secrecy capacity of the system. Notably, the proposed scheme is energy efficient so it can be applied to the systems with limited power resources at source and relay nodes.