Communicating with Large Intelligent Surfaces: Fundamental Limits and Models
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This paper analyzes the fundamental communication problem involving large intelligent surfaces (LIS) starting from electromagnetic (e.m.) arguments. Since the numerical solution of the corresponding optimal eigenfunction problem is in general computationally prohibitive, simple but accurate analytical expressions for the link gain and available degrees-of-freedom (DoF) are derived. It is shown that the achievable DoF and gain offered by the wireless link are determined only by geometric factors, and that the classic Friis' formula is no longer valid in this scenario where transmitter and receiver could operate in the near-field regime. Furthermore, results indicate that, contrarily to classic MIMO systems, when using LIS one can exploit all the potentially available DoF even in LOS conditions, which corresponds to a drastic increase of spatial capacity density.
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