This paper investigates the passive beamforming and information transfer (PBIT) technique for multiuser multiple-input multiple-output (Mu-MIMO) systems with the aid of reconfigurable intelligent surfaces (RISs), where the RISs enhance the primary communication via passive beamforming (P-BF) and at the same time deliver additional information by the on-off reflecting modulation (in which the RIS information is carried by the on/off state of each reflecting element). For the P-BF design, we propose to maximize the achievable user sum rate of the RIS-aided Mu-MIMO channel and formulate the problem as a two-step stochastic program. A sample average approximation (SAA) based iterative algorithm is developed for the efficient P-BF design of the considered scheme. To strike a balance between complexity and performance, we further propose a simplified P-BF algorithm by approximating the stochastic program as a deterministic alternating optimization problem. For the receiver design, the signal detection at the receiver is a bilinear estimation problem since the RIS information is multiplicatively modulated onto the reflected signals of the reflecting elements. To solve this bilinear estimation problem, we develop a turbo message passing (TMP) algorithm in which the factor graph associated with the problem is divided into two modules: one for the estimation of the user signals and the other for the estimation of the on-off state of each RIS element. The two modules are executed iteratively to yield a near-optimal low-complexity solution. Furthermore, we extend the design of the Mu-MIMO PBIT scheme from single-RIS to multi-RIS, by leveraging the similarity between the single-RIS and multi-RIS system models. Extensive simulation results are provided to demonstrate the advantages of our P-BF and receiver designs.

中文翻译：

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可重构智能表面辅助多用户 MIMO 系统的无源波束成形和信息传输设计

本文研究了借助可重构智能表面 (RIS) 的多用户多输入多输出 (Mu-MIMO) 系统的无源波束成形和信息传输 (PBIT) 技术，其中 RIS 通过无源波束成形 (P -BF)，同时通过开-关反射调制传递附加信息（其中RIS信息由每个反射元件的开/关状态携带）。对于 P-BF 设计，我们建议最大化 RIS 辅助 Mu-MIMO 信道的可实现用户总和率，并将问题表述为两步随机程序。一种基于样本平均近似 (SAA) 的迭代算法被开发用于所考虑方案的高效 P-BF 设计。为了在复杂性和性能之间取得平衡，我们通过将随机程序近似为确定性交替优化问题，进一步提出了一种简化的 P-BF 算法。对于接收器设计，接收器处的信号检测是一个双线性估计问题，因为 RIS 信息被乘法调制到反射元件的反射信号上。为了解决这个双线性估计问题，我们开发了一种涡轮消息传递 (TMP) 算法，其中与问题相关的因子图分为两个模块：一个用于估计用户信号，另一个用于估计 on-每个 RIS 元件的关闭状态。这两个模块迭代执行以产生近乎最优的低复杂度解决方案。此外，我们将 Mu-MIMO PBIT 方案的设计从单 RIS 扩展到多 RIS，通过利用单 RIS 和多 RIS 系统模型之间的相似性。提供了广泛的仿真结果来证明我们的 P-BF 和接收器设计的优势。