Beyond Massive-MIMO : The Potential of Data-Transmission with Large Intelligent Surfaces

Abstract

In this paper, we consider the potential of data-transmission in a system with a massive number of radiating and sensing elements, thought of as a contiguous surface of electromagnetically active material. We refer to this as a Large Intelligent Surface (LIS). The "LIS" is a newly proposed concept, which conceptually goes beyond contemporary massive MIMO technology, and arises from our vision of a future where man-made structures are electronically active with integrated electronics and wireless communication making the entire environment "intelligent". Firstly, we consider capacities of single-antenna autonomous terminals communicating to the LIS where the entire surface is used as a receiving antenna-array in a perfect line-of-sight (LOS) propagation environment. Under the condition that the surface-area is sufficiently large, the received signal after a matched-filtering (MF) operation can be closely approximated by a sinc-function-like intersymbol interference (ISI) channel. Secondly, we analyze a normalized capacity measured per unit-surface, for a fixed transmit power per volume-unit with different terminal-deployments. As terminal-density increases, the limit of the normalized capacity [nats/s/Hz/volume-unit] achieved when wavelength $\lambda$ approaches zero is equal to half of the transmit power per volume-unit divided by noise spatial power spectral density (PSD). Thirdly, we show that the number of independent signal dimensions that can be harvested per meter deployed surface is $2/\lambda$ for one-dimensional terminal-deployment, and $\pi/\lambda^{2}$ per square meter for two and three dimensional terminal-deployments. Lastly, we consider implementations of the LIS in the form of a grid of conventional antenna-elements, and show that the sampling lattice that minimizes the surface-area and simultaneously obtains one independent signal dimension for every spent antenna is the hexagonal lattice