Reconfigurable intelligent surface (RIS), a recently introduced technology for future wireless communication systems, enhances the spectral and energy efficiency by intelligently adjusting the propagation conditions between base stations (BSs) and mobile equipments (MEs). An RIS consists of many low-cost passive reflecting elements that are optimized to improve the quality of the received signal. In this paper, we study the problem of power control at the BS and RIS optimization for application to physical-layer broadcasting. Our goal is to minimize the transmit power at the BS by jointly designing the transmit beamforming at the BS and the phase shifts of the passive elements at the RIS. Furthermore, to help validate the proposed optimization methods, we derive lower bounds to quantify the average transmit power at the BS as a function of the number of MEs, the number of RIS elements, and the number of antennas at the BS. The simulation results demonstrate that the average transmit power at the BS is close to the lower bound in an RIS-aided system, and is significantly lower than the average transmit power in conventional schemes without an RIS.

中文翻译：

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用于物理层广播的可重构智能表面辅助功率控制

可重构智能表面 (RIS) 是最近为未来无线通信系统引入的一项技术，它通过智能调整基站 (BS) 和移动设备 (ME) 之间的传播条件来提高频谱和能源效率。RIS 由许多低成本的无源反射元件组成，这些元件经过优化以提高接收信号的质量。在本文中，我们研究了 BS 的功率控制问题和 RIS 优化以应用于物理层广播。我们的目标是通过联合设计 BS 的发射波束成形和 RIS 的无源元件的相移来最小化 BS 的发射功率。此外，为了帮助验证所提出的优化方法，我们推导出下界来量化作为 ME 数量、RIS 元素数量和 BS 天线数量的函数的 BS 的平均发射功率。仿真结果表明，基站的平均发射功率接近RIS辅助系统的下限，明显低于没有RIS的传统方案的平均发射功率。