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

TLDR

Large intelligent surfaces (LIS) extend massive MIMO by turning man‑made structures into electronically active, environment‑wide antenna arrays, and when sufficiently large, their matched‑filter output behaves like a sinc‑function ISI channel. The paper investigates the data‑transmission potential of a massive, contiguous electromagnetic surface by analyzing the achievable capacity per square meter for a given transmit power per volume unit. The authors model single‑antenna terminals communicating to the LIS as a large receiving array, analyze per‑square‑meter capacity for a fixed transmit power density, and design a low‑complexity channel‑shortening demodulator. The study finds that a large LIS supports 2/λ independent dimensions per meter for linear deployments and π/λ^2 per square meter for planar or volumetric deployments, and that a hexagonal antenna lattice minimizes surface area while providing one dimension per antenna.

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, that 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". We consider capacities of single-antenna autonomous terminals communicating to the LIS where the entire surface is used as a receiving antenna array. 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. We analyze the capacity per square meter (m^2) deployed surface, \hat{C}, that is achievable for a fixed transmit power per volume-unit, \hat{P}. Moreover, we also show that the number of independent signal dimensions per m deployed surface is 2/\lambda for one-dimensional terminal-deployment, and \pi/\lambda^2 per m^2 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 of the LIS and simultaneously obtains one signal space dimension for every spent antenna is the hexagonal lattice. We extensively discuss the design of the state-of-the-art low-complexity channel shortening (CS) demodulator for data-transmission with the LIS.