Secure Degrees of Freedom in K-Helper MIMO Cognitive Radio Systems with No Eavesdropper CSI

Secure degrees of freedom (DoF) in MIMO cognitive radio system is studied in this paper. We consider a cognitive radio system with one primary source-destination pair, multiple secondary source-destination pairs and an eavesdropper against whom the primary user intends to secure its data. In this system, multiple secondary user pairs help to secure primary user's data against eavesdropping. In return, these secondary users are allowed to access primary user's spectrum. All users, including primary user pair, K >= 2 secondary user pairs and the eavesdropper are equipped with M antennas. We investigate the secure DoF without the knowledge of eavesdropper's channel state information (CSI). A beamforming design is proposed to achieve secure DoF d for primary user and DoF d for all secondary users if Kd <= M. Simulation examples corroborating the theoretical results are presented.