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.