We analyze and compare different methods for handling the mutual coupling in RIS-aided communication systems. A new mutual coupling aware algorithm is derived where the reactance of each element is updated successively with a closed-form solution. In comparison to existing element-wise methods, this approach leads to a considerably reduced computational complexity. Furthermore, we introduce decoupling networks for the RIS array as a potential solution for handling mutual coupling. With these networks, the system model reduces to the same structure as when no mutual coupling were present. Including decoupling networks, we can optimize the channel gain of a RIS-aided SISO system in closed-form which allows to analyze the scenario under mutual coupling analytically and to draw connections to the conventional transmit array gain. In particular, a super-quadratic channel gain can be achieved which scales as N^4 where N is the number of RIS elements.

翻译：我们分析并比较了RIS辅助通信系统中处理互耦的不同方法。提出了一种新的互耦感知算法，其中每个元件的电抗通过闭式解依次更新。与现有的逐元素方法相比，该方法显著降低了计算复杂度。此外，我们引入RIS阵列的去耦网络作为处理互耦的潜在解决方案。通过引入这些网络，系统模型简化为无互耦时的相同结构。在包含去耦网络的情况下，我们可以通过闭式解优化RIS辅助SISO系统的信道增益，从而能够从解析角度分析互耦场景，并与传统发射阵列增益建立联系。特别地，可实现超二次信道增益，其缩放比例为N^4，其中N为RIS元件数量。