Reconfigurable Intelligent Surfaces (RISs) are recently attracting a wide interest due to their capability of tuning wireless propagation environments in order to increase the system performance of wireless networks. In this paper, a multiuser wireless network assisted by a RIS is studied and resource allocation algorithms are presented for several scenarios. First of all, the problem of channel estimation is considered, and an algorithm that permits separate estimation of the mobile user-to-RIS and RIS-to-base stations components is proposed. Then, for the special case of a single-user system, three possible approaches are shown in order to optimize the Signal-to-Noise Ratio with respect to the beamformer used at the base station and of the RIS phase shifts. Then, for a multiuser system with two cells, assuming channel-matched beamforming, the geometric mean of the downlink Signal-to-Interference plus Noise Ratios across users is maximized with respect to the base stations transmit powers and RIS phase shifts configurations. In this scenario, the RIS is placed at the cell-edge and some users are jointly served by two base stations to increase the system performance. Numerical results show that the proposed procedures are effective and that the RIS brings substantial performance improvements to wireless system.

中文翻译：

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单小区和多小区无线网络中的 RIS 配置、波束成形器设计和功率控制

可重构智能表面 (RIS) 最近吸引了广泛的兴趣，因为它们能够调整无线传播环境以提高无线网络的系统性能。在本文中，研究了由 RIS 辅助的多用户无线网络，并针对多种场景提出了资源分配算法。首先，考虑了信道估计问题，并提出了一种允许对移动用户到RIS和RIS到基站分量进行单独估计的算法。然后，对于单用户系统的特殊情况，展示了三种可能的方法，以便针对基站使用的波束成形器和 RIS 相移优化信噪比。然后，对于具有两个小区的多用户系统，假设信道匹配波束成形，相对于基站发射功率和 RIS 相移配置，用户间下行链路信号干扰加噪声比的几何平均值最大化。在这种场景下，RIS放置在小区边缘，部分用户由两个基站共同服务，以提高系统性能。数值结果表明，所提出的程序是有效的，RIS 为无线系统带来了实质性的性能改进。