Resource Allocation for Cognitive Radio With Primary User Secrecy Outage Constraint

We consider a cognitive radio network where multiple secondary users (SUs) coexist with a primary user (PU). There exist multiple eavesdroppers (EAVs) who attempt to overhear the PU confidential messages. We propose to let the SUs interfere with the EAVs to protect the PU and gain transmission opportunities at the same time. A new type of PU protection criterion, namely PU secrecy outage constraint, is proposed to guarantee that the PU secrecy outage probability does not increase due to the SU transmission. Our aim is to maximize the SU ergodic transmission rate subject to the PU secrecy outage constraint and the SU transmit power constraint. For the special single EAV and single SU with perfect channel state information (CSI) scenario, we drive the optimal power allocation strategy as well as a low-complexity closed-form suboptimal strategy. Then, using the insights gained from the special scenario, we propose heuristic joint SU scheduling and power allocation strategies for the complex scenario of multiple EAVs and SUs with perfect or imperfect CSI. Extensive simulations are conducted to verify our proposed strategies. It is shown that the proposed strategies can well protect the PU in terms of secrecy outage probability even with imperfect CSI and simultaneously provide transmission opportunities for the SUs.