Destination-assisted jamming for physical-layer security in SWIPT cognitive radio systems

In this paper, we investigate the security for cognitive radio networks with simultaneous wireless information and power transfer (SWIPT). In such a system, an energy-limited secondary user (SU) helps relay the traffic from a primary user (PU) to the primary receiver (PR) and assists PU secure communication using beamforming technology, in return to serve its own secondary receiver in the same spectrum. In order to further enhance the security of PU traffic performance and increase the energy harvested by SU, we propose a destination-assisted scheme in which the PR transmits jamming signal to confuse the eavesdropper, while jamming signal can also be used to power SU. The beamforming vectors and power split ratio are jointly designed to maximize the secrecy rate of PU while satisfying the rate demand of SU. It boils down to a challenging non-convex problem. We resolve this issue by a general two-stage procedure. First, by fixing the power split ratio, we obtain the optimal beamforming vectors by applying the semi-definite relaxation (SDR) technique and the Charnes Cooper transformation. Then, the problem is solved by a one-dimension search to obtain the optimal power split ratio. Extensive simulations are provided and the results demonstrate that our proposed scheme has good performance.