标题： 基于RIS的绿色安全通信：主动RIS还是被动RIS？ 显示英文标题

标题： RIS-Assisted Green Secure Communications: Active RIS or Passive RIS?

摘要： 可重构智能表面（RIS）是6G无线通信的有前途的技术，最近也显示出能够提高安全通信。 然而，在基站和用户之间的反射链路中存在“双重衰落”效应，因此被动RIS在典型通信场景中只能实现微不足道的安全增益。在本文中，我们提出了一种主动RIS辅助的多天线物理层安全传输方案，其中主动RIS可以主动放大信号。 我们的目标是在保密速率约束下最小化发射功率。 为了解决非凸优化问题，提出了一种基于惩罚的交替最小化（AltMin）算法，以优化发射端的波束成形器和RIS上的反射矩阵。 仿真结果表明，主动RIS可以有效抵抗“双重衰落”效应的影响，并且比被动RIS更节能。 显示英文摘要

摘要： Reconfigurable Intelligent Surface (RIS) is one of the promising techniques for 6G wireless communications, and recently has also been shown to be able to improve secure communications. However, there is a "double fading" effect in the reflection link between base station and user, thus passive RIS only achieves a negligible secrecy gain in typical communications scenarios.In this letter, we propose an active RIS-aided multi-antenna physical layer secrecy transmission scheme, where the active RIS can amplify the signal actively. Our aim is to minimize the transmit power subject to the constraint of secrecy rate. To solve the non-convex optimization problem, a penalty-based alternating minimization (AltMin) algorithm is proposed to optimize both the beamformer at the transmitter and the reflection matrix at RIS. Simulation results show that active RIS can resist the impact of "double fading" effect effectively, and is more energy efficient than passive RIS.