We analyze the influence of a reconfigurable intelligent surface (RIS) on the Gram channel eigenvalues in a high signal-to-noise ratio (SNR) scenario. This allows to connect specific channel properties with the rank improvement capabilities of the RIS. In particular, fundamental limits due to a possible line of sight (LOS) setup between the base station (BS) and the RIS are derived. Furthermore, dirty paper coding (DPC) based schemes are compared to linear precoding in such a scenario and it is shown that under certain channel conditions, the performance gap between DPC and linear precoding vanishes.

翻译：我们分析了在高峰值信噪比（SNR）场景下，可重构智能表面（RIS）对格拉姆信道特征值的影响。这使我们能够将特定信道特性与RIS的秩提升能力相关联。特别地，推导了基站（BS）与RIS之间可能存在视距（LOS）传播时的基本极限。此外，比较了该场景下基于脏纸编码（DPC）的方案与线性预编码的性能，并证明在特定信道条件下，DPC与线性预编码之间的性能差距将消失。