Active RISs: Signal Modeling, Asymptotic Analysis, and Beamforming Design
Active RISs: Signal Modeling, Asymptotic Analysis, and Beamforming Design
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有源 RIS：信号建模、渐近分析和波束成形设计
DOI：
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发表时间：
2022
期刊：
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通讯作者：
H. Poor
中科院分区：
文献类型：
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作者：
Zijian Zhang;L. Dai;Xibi Chen;Chang;Fan Yang;R. Schober;H. Poor
可重构智能表面（RISs）已成为未来6 G网络的候选技术。然而，由于“乘性衰落”效应，现有的无源RISs在具有强直接链路的环境中仅实现可忽略的容量增益。在本文中，积极的RISs的概念进行了研究，以克服这一根本性的限制。与现有的无源RISs反射信号而不放大不同，有源RISs可以通过集成到其元件中的放大器放大反射信号。为了表征信号放大并纳入有源元件引入的噪声，我们通过对制造的有源RIS元件的实验测量来验证有源RIS的信号模型。基于已验证的信号模型，提出了有源RIS辅助的多用户多输入单输出（MU-MISO）系统的和速率最大化问题，并提出了一种联合发射预编码和反射波束形成算法来解决该问题。仿真结果表明，在一个典型的无线系统中，现有的无源RISs只能实现3%的和速率增益，而有源RISs可以实现62%的和速率增益，从而克服了“乘性衰落”效应。最后，研制了一台64单元有源RIS辅助无线通信样机，并通过外场试验验证了有源RIS的显著增益。
Reconfigurable intelligent surfaces (RISs) have emerged as a candidate technology for future 6G networks. However, due to the “multiplicative fading” effect, the existing passive RISs only achieve a negligible capacity gain in environments with strong direct links. In this paper, the concept of active RISs is studied to overcome this fundamental limitation. Unlike the existing passive RISs that reflect signals without amplification, active RISs can amplify the reflected signals via amplifiers integrated into their elements. To characterize the signal amplification and incorporate the noise introduced by the active components, we verify the signal model of active RISs through the experimental measurements on a fabricated active RIS element. Based on the verified signal model, we formulate the sum-rate maximization problem for an active RIS aided multi-user multiple-input single-output (MU-MISO) system and a joint transmit precoding and reflect beamforming algorithm is proposed to solve this problem. Simulation results show that, in a typical wireless system, the existing passive RISs can realize only a negligible sum-rate gain of 3%, while the active RISs can achieve a significant sum-rate gain of 62%, thus over coming the “multiplicative fading” effect. Finally, we develop a 64-element active RIS aided wireless communication prototype, and the significant gain of active RISs is validated by field test.