Secrecy Rate and Energy Harvesting Trade-off in Cognitive Wireless Energy Transfer Systems

This paper considers a novel secure cognitive wireless energy transfer system, where a wireless energy transfer (WET) system coexists with a wireless information transmission (WIT) system in the presence of an illegal eavesdropper. For the considered coexisting scenario, the energy transmitter of WET helps the WIT system to achieve secure communication in reward for being allowed to used the WIT's spectrum band. According to the condition of whether the energy transmitter is truthful or not, we propose two types of cooperative jamming scheme, namely noise jamming and information jamming, for the energy transmitter. For each proposed scheme, we characterize the achievable secrecy rate-harvested energy region by optimizing the energy transmitter's beamforming vectors. We also provide the semi-definite relaxation-based approach to solve the resulting non-convex optimization problems optimally. The numerical results are finally provided to show the effectiveness of the proposed scheme.