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.

中文翻译：

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安全 IRS 辅助 SWIPT 中的能源效率

这封信研究了安全智能反射面 (IRS) 辅助的同步无线信息和电力传输 (SWIPT) 网络中的能效 (EE)，其中接入点 (AP) 为信息解码接收器 (IDR) 和能量收集接收器提供服务（ EHR）由 IRS 协助。通过联合优化 AP 处的发射波束成形矢量、AP 处的人工噪声 (AN) 协方差矩阵和 IRS 处的相移，制定了优化问题以最大化系统 EE。为了处理非凸问题，采用半定松弛（SDR），然后提出一种基于交替优化（AO）的有效算法来获得次优解。仿真结果表明，通过采用IRS和优化AN，系统EE显着增强。而且，EE随着反射元件个数的增加先增大后减小。另外，系统EE随着AP和IRS消耗的电路功率的增加而减小。