A Collaboration Incentive Exploiting the Primary-Secondary Systems’ Cross Interference for PHY Security Enhancement

We investigate the spectrum sharing possibility as an incentive to enhance the physical layer security. The concept behind is that a legitimate source-destination pair, communicating in the presence of a passive eavesdropper, stimulates the help of another source-destination nodes looking for transmission opportunities, referred to as secondary network (SN). We thus propose a cooperative scheme, whereby the secondary transmitter (ST) will act as a friendly jammer to confound the eavesdropper and be granted to share the spectrum of the legitimate pair, referred to as primary network (PN), as a reward. Meanwhile, the ST has to secure its own secrecy communication and thus exploit the impact of the induced interference by the PN. To evaluate the performance of our cooperative scheme, we derive the closed-form expressions of the secrecy outage probability (SOP) for both cooperative networks. However, to assess its usefulness, we introduce the mutual outage probability (MOP) and we carry out analysis to derive its expression. We show that a satisfactory SOP is a necessary condition for triggering the cooperation, whereas a satisfactory MOP is a sufficient condition to guarantee that the PN-SN collaboration leads to a win-win situation. Furthermore, an asymptotic analysis is also carried out to derive the generalized secrecy diversity for the scheme under investigation, where it has been shown that the primary system achieves its full secrecy diversity order, equal to the number of antenna at the primary transmitter. Such results present useful insights for practical design and setups.