Reconfigurable intelligent surfaces (RISs) are an emerging technology for enhancing the performance of wireless networks at a low and affordable cost, complexity, and power consumption. We introduce an algorithm for optimizing a single-input single-output RIS-assisted system in which the RIS is modeled by using an electromagnetic-compliant framework based on mutual impedances. More precisely, we provide the following new contributions: (i) in the absence of mutual coupling among the scattering elements of the RIS, we derive a closed-form expression for the optimal tunable impedances, which inherently accounts for the interplay between the amplitude and phase of the lumped loads of the RIS; and (ii) in the presence of mutual coupling, we introduce an iterative algorithm for optimizing the tunable impedances of the RIS. The algorithm is proved to be convergent by showing that the objective function is non-decreasing and upper bounded. Numerical results reveal that the mutual coupling among the scattering elements of the RIS significantly affects the end-to-end signal-to-noise ratio (SNR) if the inter-distance is less than half of the wavelength. If the RIS is optimized by explicitly taking into account the impact of mutual coupling, a better end-to-end SNR is obtained.
翻译:重新配置的智能表面(RIS)是一种新兴技术,用低廉和负担得起的成本、复杂性和电力消耗来提高无线网络的性能。我们采用了一种优化单一投入单输出单输出的RIS辅助系统的算法,在这个系统中,通过使用基于相互阻碍的符合电磁框架来模拟RIS。更确切地说,我们提供了以下新的贡献:(一)在RIS的散射元素之间没有相互连接的情况下,我们为最佳的金枪鱼阻力产生了一种封闭式表达方式,这种障碍必然地说明RIS包装负荷的膨胀和阶段之间的相互作用;(二)在相互连接的情况下,我们采用了一种迭代算法,以优化RIS的金枪鱼阻力。更确切地说,我们提供这种新的贡献是为了表明,目标功能是非下降和上层绑定的。 数值结果显示,RIIS的散射元素之间的相互联动,对最终到端的信号到端的比值(SNRR)的相互作用程度要小一些,如果通过相互最短的里程考虑,则相互的里程到最短的里程对双波的影响要小。