Reconfigurable intelligent surfaces (RISs) achieve high passive beamforming gains for signal enhancement or interference nulling by dynamically adjusting their reflection coefficients. Their employment is particularly appealing for improving both the wireless security and the efficiency of radio frequency (RF)-based wireless power transfer. Motivated by this, we conceive and investigate a RIS-assisted secure simultaneous wireless information and power transfer (SWIPT) system designed for information and power transfer from a base station (BS) to an information user (IU) and to multiple energy users (EUs), respectively. Moreover, the EUs are also potential eavesdroppers that may overhear the communication between the BS and IU. We adopt two-timescale transmission for reducing the signal processing complexity as well as channel training overhead, and aim for maximizing the average worst-case secrecy rate achieved by the IU. This is achieved by jointly optimizing the short-term transmit beamforming vectors at the BS as well as the long-term phase shifts at the RIS, under the energy harvesting constraints considered at the EUs and the power constraint at the BS. The stochastic optimization problem formulated is non-convex with intricately coupled variables, and is non-smooth due to the existence of multiple EUs/eavesdroppers. No standard optimization approach is available for this challenging scenario. To tackle this challenge, we propose a smooth approximation aided stochastic successive convex approximation (SA-SSCA) algorithm. Furthermore, a low-complexity heuristic algorithm is proposed for reducing the computational complexity without unduly eroding the performance. Simulation results show the efficiency of the RIS in securing SWIPT systems. The significant performance gains achieved by our proposed algorithms over the relevant benchmark schemes are also demonstrated.
翻译:重新配置的智能表面(RIS)能取得高被动波束增益,通过动态调整其反射系数,提高信号增强或干扰,从而消除信号增强或干扰。他们的就业特别有利于改善无线频率(RF)的无线电传输的无线安全和效率。为此,我们设想并调查一个由RIS辅助的安全的同步无线信息和电力传输系统(SWIPT),该系统旨在从基站(BS)向信息用户(IU)和多个能源用户(EU)分别提供信息和电力传输。此外,欧盟还有可能透视BS和IU之间的通信。我们采用了两次级传输,以降低信号处理的复杂程度以及频道培训管理费的效率。这是通过联合优化从BS公司向信息用户(IU)和多个能源用户(ERS)的信息和电力用户(RIS)的低级变异能变换,在欧盟考虑的能源回收限制和BS公司(BS)的电流变法约束之下,我们采用了双向流流的变压变现,这种变压的变现性变现性变现为SBSBSBSB。