Energy Efficiency in Secure IRS-Aided SWIPT

This letter studies the energy efficiency (EE) in a secure intelligent reflecting surface (IRS)-aided simultaneous wireless information and power transfer (SWIPT) network, where an access point (AP) serves information decoding receivers (IDRs) and energy harvesting receivers (EHRs) assisted by an IRS. An optimization problem is formulated to maximize the system EE by jointly optimizing the transmit beamforming vectors at the AP, the artificial noise (AN) covariance matrix at the AP, and the phase shifts at the IRS. To handle the non-convex problem, semi-definite relaxation (SDR) is adopted and then an efficient algorithm based on alternating optimization (AO) is proposed to obtain the suboptimal solution. Simulation results show that the system EE is significantly enhanced by employing IRS and optimizing AN. Moreover, EE firstly increases and then decreases with the increment of the number of reflecting elements. Additionally, the system EE decreases with the increment of the circuit power consumed by both the AP and the IRS.