Interference Improves PHY Security for Cognitive Radio Networks

In a cognitive radio (CR) network, the transmitting signal of a secondary user (SU) is traditionally considered to be harmful for the primary user (PU), since it decreases the capacity of the PU's channel. However, for PU's secrecy capacity, the SUs' interference can be beneficial if it decreases the capacity of the source-eavesdropper channel more than that of the source-destination channel. In this paper, we consider using the SUs' interference to improve the PU's secrecy capacity and providing the SUs the opportunity to access the spectrum as a reward. But, there exists a tradeoff between the SUs' channel capacity and the PU's secrecy capacity. To decide which SUs can share the spectrum with the PU, we present a coalition formation game model with nontransferable utility, and propose a merge and split algorithm. The simulation results verify the efficiency of the proposed algorithm in terms of both the SUs' channel capacity and the PU's secrecy capacity in various scenarios.