Reconfigurable surface (RS) has been shown to be an effective solution for improving wireless communication links in general multi-user multiple-input multiple-output (MU-MIMO) setting. Current research efforts have been largely directed towards the study of reconfigurable intelligent surface (RIS), which corresponds to an RS made of passive reconfigurable elements with only phase shifting capabilities. RIS constitutes a cost- and energy- efficient solution for increased beamforming gain since it allows to generate constructive interference towards desired directions, e.g., towards a base station (BS). However, in many situations, multiplexing gain may have greater impact on the achievable transmission rates and number of simultaneously connected devices, while RIS has only been able to achieve minor improvements in this aspect. Recent work has proposed the use of alternative RS technologies, namely amplitude-reconfigurable intelligent surface (ARIS) and fully-reconfigurable intelligent surface (FRIS), to achieve perfect orthogonalization of MU-MIMO channels, thus allowing for maximum multiplexing gain at reduced complexity. In this work we consider the use of ARIS and FRIS for simultaneously orthogonalizing a MU-MIMO channel, while embedding extra information in the orthogonalized channel. We show that the resulting achievable rates allow for full exploitation of the degrees of freedom in a MU-MIMO system with excess of BS antennas.

翻译：可重构表面(RS)已被证明是在通用多用户多输入多输出(MU-MIMO)环境下改善无线通信链路的有效解决方案。当前研究主要集中于可重构智能表面(RIS)，其由仅具备移相能力的无源可重构元件构成。RIS通过向期望方向（如基站BS方向）产生相干干涉，可提升波束赋形增益，是一种高性价比且节能的方案。然而在许多场景中，复用增益对可达传输速率和同时连接设备数量的影响更为显著，而RIS在此方面仅能实现微小改进。最新研究提出采用替代性RS技术，即幅度可重构智能表面(ARIS)与全可重构智能表面(FRIS)，以实现MU-MIMO信道的完美正交化，从而在降低复杂度的同时获得最大复用增益。本文考虑利用ARIS和FRIS实现MU-MIMO信道正交化，同时在正交化信道中嵌入额外信息。研究表明，所得可达速率能够充分利用超量基站天线配置下MU-MIMO系统的自由度。