As a revolutionary paradigm for controlling wireless channels, reconfigurable intelligent surfaces (RISs) have emerged as a candidate technology for future 6G networks. However, due to the multiplicative fading effect, RISs only achieve a negligible capacity gain in many scenarios with strong direct links. In this paper, the concept of active RISs is proposed to overcome this fundamental limitation. Unlike the existing passive RISs that reflect signals without amplification, active RISs can amplify the reflected signals. We develop a signal model for active RISs, which is validated through experimental measurements. Based on this model, we formulate the sum-rate maximization problem for active RIS aided multiple-input multiple-output (MIMO) systems and a precoding algorithm is proposed to solve this problem. Results show that, in a typical wireless system, the existing passive RISs can realize only a negligible sum-rate gain of 3\%, while the proposed active RISs can achieve a significant sum-rate gain of 108\%, thus overcoming the multiplicative fading effect.
翻译:作为控制无线信道的革命范式,可重新配置的智能表面(RIS)已成为未来6G网络的候选技术,然而,由于倍增式衰减效应,RIS在许多情况中只能取得微不足道的能力,而且具有很强的直接联系。在本文件中,主动的RIS概念是为了克服这一基本限制而提出的。与现有反映信号而没有放大的被动的RIS概念不同,主动的RIS可以扩大反射信号。我们为主动的RIS开发了一个信号模型,通过实验测量加以验证。基于这一模型,我们为主动的RIS辅助的多产出(MIMO)系统制定了总和率最大化问题,并提出了解决这一问题的预编码算法。结果显示,在典型的无线系统中,现有被动的RIS只能实现微小的总和率3 ⁇ 的收益,而拟议的主动的RIS则能够取得108 ⁇ 的重大总和收益,从而克服了多法化效应。