Secrecy Outage Analysis of CR-SWIPT Networks With Artificial Noise and Spatially Random Secondary Terminals

In this paper, the secrecy outage performance of cognitive radio (CR) systems with simultaneous wireless information and power transfer (SWIPT) is investigated, in which non-colluding eavesdroppers (Eves) are randomly located in a 2-dimensional disk and artificial noise is added to safeguard the secrecy performance of the targeted information delivery in the secondary network. The secondary users coexist with primary users in the same bands while the secondary user transmitter (SU-TX) transmits confidential messages to a legitimate receiver (Bob) and energy to multiple energy-receivers (ERs) via the same radio frequency signals. Apart from harvesting energy, these ERs may act as Eves to overhear the confidential information only for Bob. SU-TX equipped with multiple antennas performs beamforming to Bob, which is equipped with multiple antennas and adopts selection combining (SC) scheme. To enhance the secure performance of the considered CR-SWIPT system, SU-TX adds artificial noise (AN) to the original signal designed for Bob according to the instantaneous channel state information (CSI) between SU-TX and Bob, where the artificial noise and original signals for Bob are orthogonal so that Bob can cancel this noise. On ERs' side, the total received energy for harvesting is not degraded, and a lower signal-to-interference-plus-noise ratio for eavesdropping on the information between SU-TX and Bob is introduced. The approximated closed-form expression for the secrecy outage probability (SOP) is derived by using Gauss-Laguerre quadrature, as well as the asymptotic results are valid in the high signal to noise ratio region. Finally, Monte-Carlo simulations are presented to validate the correctness of the derived analytical results.