Although the emerging reconfigurable intelligent surface (RIS) paves a new way for next-generation wireless communications, it suffers from inherent flaws, i.e., double-fading attenuation effects and half-space coverage limitations. The state-of-the-art double-face active (DFA)-RIS architecture is proposed for significantly amplifying and transmitting incident signals in full-space. Despite the efficacy of DFA-RIS in mitigating the aforementioned flaws, its potential drawback is that the complex active hardware also incurs intolerable energy consumption. To overcome this drawback, in this paper we propose a novel dynamic energy-saving design for the DFA-RIS, called the sub-array based DFA-RIS architecture. This architecture divides the DFA-RIS into multiple sub-arrays, where the signal amplification function in each sub-array can be activated/deactivated dynamically and flexibly. Utilizing the above architecture, we develop the joint optimization scheme based on transmit beamforming, DFA-RIS configuration, and reflection amplifier (RA) operating pattern to maximize the energy efficiency (EE) of the DFA-RIS assisted multiuser MISO system considering the perfect/imperfect channel state information (CSI) case. Then, the penalty dual decomposition (PDD) based alternating optimization (AO) algorithm and the constrained stochastic majorization-minimization (CSMM) based AO algorithm address non-convex problems in the perfect/imperfect CSI case, respectively. Simulation results verified that our proposed sub-array based DFA-RIS architecture can benefit the EE of the system more than other RIS architectures.

翻译：尽管新兴的可重构智能表面为下一代无线通信开辟了新途径，但其存在固有缺陷，即双衰落衰减效应和半空间覆盖限制。业界提出的先进双面有源智能反射面架构能够实现全空间信号的显著放大与传输。虽然双面有源智能反射面有效缓解了上述缺陷，但其复杂的硬件结构也带来了难以承受的能耗问题。为克服这一不足，本文提出一种基于子阵列的双面有源智能反射面创新动态节能架构。该架构将双面有源智能反射面划分为多个子阵列，每个子阵列的信号放大功能均可实现动态灵活的激活与休眠控制。基于此架构，我们针对完美与非完美信道状态信息场景，开发了融合发射波束成形、双面有源智能反射面配置及反射放大器工作模式的联合优化方案，以最大化双面有源智能反射面辅助多用户MISO系统的能量效率。随后，分别采用基于惩罚对偶分解的交替优化算法与基于约束随机最大最小化的交替优化算法，解决完美与非完美信道状态信息场景下的非凸优化问题。仿真结果表明，相较于其他智能反射面架构，本文提出的基于子阵列的双面有源智能反射面架构能更有效地提升系统能量效率。