Physical Layer Security in Cognitive Radio Based Self-Organization Network

This paper focuses on a cognitive radio network (CRN), where both the primary and the secondary users (PUs and SUs) communicate with confidential messages. The secondary network is a distributed wireless self-organization network transmitting messages with collaborative beamforming. A multi-antenna target unknown eavesdropper (TUE), whose wiretap target is not assumed, appears in the CRN. A specific application of spectrum leasing is designed to ensure the secrecy performance of the whole network, in which the SUs access the spectrum in reward of helping improve the secrecy performance of the entire CRN. The transmit signals of the secondary network are designed to ensure the secrecy rate performance of both the primary and the secondary networks. To make it solvable with a method based on parameterizing the power gain region, the secrecy rate balancing problem is relaxed. The relaxation is further proved to be tight and the relaxed problem is equivalent to the original problem. Finally, we use a two-dimensional search to achieve the optimal transmit beamformer. According to the simulation, the proposed beamforming strategy enjoys an obvious performance gain comparing to the traditional zero-forcing beamforming.