Clean relaying in cognitive radio networks with variational distance secrecy constraint

In this paper we investigate the cooperative secure communication in a four-node cognitive channel where the secondary receiver is treated as a potential eavesdropper with respect to the primary transmission with variational distance constraint. And the primary user´s secrecy rate is required to be unchanged. We propose the clean relaying with the cooperative jamming scheme to achieve this goal, where the secondary transmitter splits its transmitting phase into two non-overlapped intervals after successfully decoding the primary message. Due to the considered secrecy metric, we resort to the information spectrum method, to derive the achievable secrecy rates for the primary user. Then we formulate the secondary user´s rate maximization problem over the power allocation and time splitting at the cognitive transmitter under the constraint that primary user´s secrecy rate is unchanged. Numerical results show that the secondary transmitter can choose clean relaying or pure cooperative jamming according to the relative positions of the nodes to achieve better performance than the one without any clean phase.