Secrecy Capacity and Energy Efficiency of Spectrum Sharing Networks Incorporating Physical Layer Security

Underutilized wireless channel is a waste of spectral resource. Eavesdropping compromises data secrecy. How to overcome the two problems with one solution? In this paper, we propose a spectrum sharing model that defends against eavesdropping. Consider a source-destination channel that is being eavesdropped. Cognitive radio can help jamming the eavesdropper. Friendly jamming is a physical layer security method of protecting data secrecy based on radio propagation characteristic. In return, the helper is allowed to access the unused channel of the source. The desirable characteristic of cognitive radio is its capability of sensing the occupancy or vacancy of the channel. This work investigates the secrecy capacity $C_S$ and energy efficiency $\mu$ of such a spectrum sharing network that deploys physical layer security method. The main factors that affect $C_S$ and $\mu$ are the transmit powers of the source and cognitive radio. We present a novel expression that permits finding the sensing duration $t$ that optimizes $\mu$.