Multiuser MIMO with Large Intelligent Surfaces: Communication Model and Transmit Design

TL;DR

This paper develops a comprehensive communication model for multiuser MIMO systems utilizing large intelligent surfaces, capturing complex effects like superdirectivity and mutual coupling, and proposes optimized transmit designs under practical constraints.

Contribution

It introduces a circuital and channel model for LIS-based MIMO systems that includes superdirectivity and mutual coupling, and derives transmit strategies considering realistic power and loss constraints.

Findings

Model accounts for superdirectivity and mutual coupling effects.

Derived transmit strategies include matched filter and MMSE precoding.

Provides analytical expressions for radiated and received powers.

Abstract

This paper proposes a communication model for multiuser multiple-input multiple-output (MIMO) systems based on large intelligent surfaces (LIS), where the LIS is modeled as a collection of tightly packed antenna elements. The LIS system is first represented in a circuital way, obtaining expressions for the radiated and received powers, as well as for the coupling between the distinct elements. Then, this circuital model is used to characterize the channel in a line-of-sight propagation scenario, rendering the basis for the analysis and design of MIMO systems. Due to the particular properties of LIS, the model accounts for superdirectivity and mutual coupling effects along with near field propagation, necessary in those situations where the array dimension becomes very large. Finally, with the proposed model, the matched filter transmitter and the weighted minimum mean square error precoding are derived under both realistic constraints: limited radiated power and maximum ohmic losses.