Optimal Energy Harvesting Time and Power Allocation Policy in CRN Under Security Constraints from Eavesdroppers

In this paper, we study energy harvesting cognitive radio networks (CRNs) in the presence of multiple eavesdroppers (EAVs) and multiple primary users (PUs). In particular, the secondary user (SU) harvests energy from multiple primary user transmitters (P-Tx), and then uses this harvested energy to deliver packets to the secondary access point (SAP). The SU communication faces multiple EAVs intending to steal its confidential information. In order to protect itself against multiple EAVs and also to protect the PUs communication from interference generated by the SU signals, the SU should be equipped with a suitable power allocation strategy which is derived from channel state information, harvested energy, security constraints given by the SU, and interference constraint given by the PU. Accordingly, an energy harvesting and communication protocol is proposed. Further, the optimal energy harvesting time, a power allocation policy, and a channel selection strategy for the SU are derived and analyzed. To this end, closed-form expressions for the packet error probability and the average packet delay including retransmissions are obtained. Interestingly, the numerical results obtained in this paper show that the proposed power allocation and channel selection strategy does not only improve the spectrum and energy utilization, but also protect the confidential information of the SU from the EAVs.